~?Ang, W. S. Elimelech, M.2008XFatty acid fouling of reverse osmosis membranes: Implications for wastewater reclamation 4393-4403Water Research4216OctEffluent organic matter (EfOM) contributes significantly to organic fouling of reverse osmosis (RO) membranes in advanced wastewater reclamation. In this study, the effect of feed solution chemistry (solution pH and Ca2+ concentration) on the fouling of RO membranes by octanoic acid-selected to represent fatty acids in EfOM-is investigated. Crossflow fouling experiments demonstrate that RO membrane fouling is much more significant at solution pH below the pK, of the octanoic acid (pK(a) = 4.9) than at ail elevated pH. Octanoic acid permeates across the membranes more readily at solution pH below its pK, than at elevated pH At pH below the octanoic acid pK, fouling behavior is not affected by calcium ions, whereas at elevated pH, the rate of flux decline decreases with higher calcium ion concentration. The effect of calcium on the fouling behavior was further verified from foulant-foulant adhesion forces, determined by atomic force microscopy (AFM) force measurements under solution chemistries identical to those of the crossflow fouling experiments. To investigate the implications of octanoic acid fouling for wastewater reclamation, the effect of octanoic acid on membrane fouling by a combination of organic foulants in the presence of calcium ions is studied. At a solution chemistry simulating that of typical wastewater effluents, the addition of octanoic acid to a feed solution containing alginate, bovine serum albumin, and Suwannee River natural organic matter, does not enhance membrane fouling behavior. This observation could be attributed to the significant contribution of the alginate-calcium complexes within the fouling layer to the total membrane resistance. (C) 2008 Elsevier Ltd. All rights reserved.://000260757300020 0043-1354ISI:000260757300020~?+Saleh, N. B. Pfefferle, L. D. Elimelech, M.2008tAggregation Kinetics of Multiwalled Carbon Nanotubes in Aquatic Systems: Measurements and Environmental Implications 7963-7969"Environmental Science & Technology4221Nov 1~The initial aggregation kinetics of multiwalled carbon nanotubes (MWNTs) were examined through time-resolved dynamic light scattering. Aggregation of MWNTs was evaluated by varying solution pH and the concentration of monovalent (NaCl) and divalent (CaCl2 and MgCl2) salts. Suwannee River humic acid (SRHA) was used to study the effect of background natural organic matter on MWNT aggregation kinetics. Increasing saltconcentration and addition of divalent calcium and magnesium ions induced MWNT aggregation by suppressing electrostatic repulsion, similar to observations with aquatic colloidal particles. The critical coagulation concentration (CCC) values for MWNTs were estimated as 25 mM NaCl, 2.6 mM CaCl2, and 1.5 mM MgCl2, An increase in solution pH from acidic (pH 3) to basic (pH 11) conditions resulted in a substantial (over 2 orders of magnitude) decrease in MWNT aggregation kinetics, suggesting the presence of ionizable functional groups on the MWNT carbon scaffold. The presence of humic acid in solution markedly enhanced the colloidal stability of MWNTs, reducing the aggregation rate by nearly 2 orders of magnitude. The enhanced MWNT stability in the presence of humic acid is attributable to steric repulsion imparted by adsorbed humic acid macromolecules. Our results suggest that MWNTs are relatively stable at solution pH and electrolyte conditions typical of aquatic environments.://000260561200041 0013-936XISI:000260561200041~?Chen, K. L. Elimelech, M.2008Interaction of Fullerene (C-60) Manoparticles with Humic Acid and Alginate Coated Silica Surfaces: Measurements, Mechanisms, and Environmental Implications 7607-7614"Environmental Science & Technology4220Oct 15The deposition kinetics of fullerene (C-60) nanoparticles onto bare silica surfaces and surfaces precoated with humic acid and alginate are investigated over a range of monovalent (NaCl) and divalent (CaCl2) salt concentrations using a quartz crystal microbalance. Because simultaneous aggregation of the fullerene nanoparticles occurs, especially at higher electrolyte concentrations, we normalize the observed deposition rates by the corresponding favorable (transport-limited) deposition rates to obtain the attachment efficiencies, alpha. The deposition kinetics of fullerene nanoparticles onto bare silica surfaces are shown to be controlled by electrostatic interactions and van der Waals attraction, consistent with the classical particle deposition behavior where both favorable and unfavorable deposition regimes are observed. The presence of dissolved humic acid and alginate in solution leads to significantly slower deposition kinetics due to steric repulsion. Precoating the silica surfaces with humic acid and alginate exerts similar steric stabilization in the presence of NaCl. In the presence of CaCl2, the deposition kinetics of fullerene nanoparticles onto both humic acid- and alginate-coated surfaces are relatively high, even at relatively low (0.3 mM) calcium concentration. This behavior is attributed to the macromolecules undergoing complex formation with calcium ions, which reduces the charge and steric influences of the adsorbed macromolecular layers.://000259988400013 0013-936XISI:000259988400013~?$Kang, S. Mauter, M. S. Elimelech, M.2008RPhysicochemical determinants of multiwalled carbon nanotube bacterial cytotoxicity 7528-7534"Environmental Science & Technology4219Oct 1Rational modification of carbon nanotubes (CNTs) to isolate their specific physical and chemical properties will inform a mechanistic understanding of observed CNT toxicity in bacterial systems. The present study compares the toxicity of commercially obtained multiwalled carbon nanotubes (MWNTs) before and after physicochemical modification via common purification and functionalization routes, including dry oxidation, acid treatment, functionalization, and annealing. Experimental results support a correlation between bacterial cytotoxicity and physicochemical properties that enhance MWNT-cell contact opportunities. For example, we observe higher toxicity when the nanotubes are uncapped, debundled, short, and dispersed in solution. These conclusions demonstrate that physicochemical modifications of MWNTs alter their cytotoxicity in bacterial systems and underline the need for careful documentation of physical and chemical characteristics when reporting the toxicity of carbon-based nanomaterials.://000259603700080 0013-936XISI:000259603700080~?Mauter, M. S. Elimelech, M.20088Environmental applications of carbon-based nanomaterials 5843-5859"Environmental Science & Technology4216Aug 15://000258439600006 0013-936XISI:000258439600006~?Mi, B. Elimelech, M.2008MChemical and physical aspects of organic fouling of forward osmosis membranes292-302Journal Of Membrane Science3201-2Jul 15The growing attention to forward osmosis (FO) membrane processes from various disciplines raises the demand for systematic research on FO membrane fouling. This study investigates the role of various physical and chemical interactions, such as intermolecular adhesion forces, calcium binding, initial permeate flux, and membrane orientation, in organic fouling of forward osmosis membranes. Alginate, bovine serum albumin (BSA), and Aldrich humic acid (AHA) were chosen as model organic foulants. Atomic force microscopy (AFM) was used to quantify the intermolecular adhesion forces between the foulant and the clean or fouled membrane in order to better understand the fouling mechanisms. A strong correlation between organic fouling and intermolecular adhesion was observed, indicating that foulant-foulant interaction plays an important role in determining the rate and extent of organic fouling. The fouling data showed that FO fouling is governed by the coupled influence of chemical and hydrodynamic interactions. Calcium binding, permeation drag, and hydrodynamic shear force are the major factors governing the development of a fouling layer on the membrane surface. However, the dominating factors controlling membrane fouling vary from foulant to foulant. With stronger intermolecular adhesion forces, hydrodynamic conditions for favorable foulant deposition leading to cake formation are more readily attained. Before a compact cake layer is formed, the fouling rate is affected by both the intermolecular adhesion forces and hydrodynamic conditions. However, once the cake layer forms, all three foulants have very similar flux decline rates, and further changes in hydrodynamic conditions do not influence fouling behavior. (C) 2008 Elsevier B.V. All rights reserved.://000257834700033 0376-7388ISI:000257834700033~?1Tiraferri, A. Chen, K. L. Sethi, R. Elimelech, M.2008cReduced aggregation and sedimentation of zero-valent iron nanoparticles in the presence of guar gum71-79(Journal Of Colloid And Interface Science3241-2AugInjection of nanoscale zero-valent iron (NZVI) is potentially a promising technology for remediation of contaminated groundwaters. However, the efficiency of this process is significantly hindered by the rapid aggregation of the iron nanoparticles. The aim of this study was to enhance the colloidal stability of the nanoparticles through the addition of the "green" polymer guar gum. We evaluated the properties of guar gum and its influence on the surface properties, particle size, aggregation, and sedimentation of iron nanoparticles. Commercial iron nanoparticles were dispersed in guar gum solutions, and their aggregation and sedimentation behaviors were compared to those of bare iron nanoparticles and commercial nanoparticles modified with a biodegradable polymer (polyaspartate). High performance size exclusion chromatography, charge titration, and viscosity assessment showed that guar gum is a high molecular weight polymer which is nearly neutrally charged, rendering it suitable for steric stabilization of the iron nanoparticles. Electrophoretic mobility measurements demonstrated the ability of guar gum to adsorb on the nanoparticles, forming a slightly negatively charged layer. Dynamic light scattering experiments were conducted to estimate the particle size of the different nanoparticle suspensions and to determine the aggregation behavior at different ionic strengths. Guar gum effectively reduced the hydrodynamic radius of the bare nanoparticles from 500 nm to less than 200 nm and prevented aggregation of the nanoparticles even at very high salt concentrations (0.5 M NaCl and 3 MM CaCl2). Sedimentation profiles of the different nanoparticle suspensions confirmed the improved stability of the iron nanoparticles in the presence of guar gum. The results strongly suggest that guar gum can be used to effectively deliver stabilized zero-valent iron nanoparticles for remediation of contaminated groundwater aquifers. (c) 2008 Elsevier Inc. All rights reserved.://000257232100010 0021-9797ISI:000257232100010~?4Kang, S. Herzberg, M. Rodrigues, D. F. Elimelech, M.2008;Antibacterial effects of carbon nanotubes: Size does matter 6409-6413Langmuir2413Jul 1We provide the first evidence that the size (diameter) of carbon nanotubes (CNTs) is a key factor governing their antibacterial effects and that the likely main CNT-cytotoxicity mechanism is cell membrane damage by direct contact with CNTs. Experiments with well-characterized single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) demonstrate that SWNTs are much more toxic to bacteria than MWNTs. Gene expression data show that in the presence of both MWNTs and SWNTs, Escherichia coli expresses high levels of stress-related gene products, with the quantity and magnitude of expression being much higher in the presence of SWNTs.://000257101100005 0743-7463ISI:000257101100005~? /Huertas, E. Herzberg, M. Oron, G. Elimelech, M.2008XInfluence of biofouling on boron removal by nanofiltration and reverse osmosis membranes264-270Journal Of Membrane Science3181-2Jun 20Excess of boron in water poses a problem due to adverse effects on crop production as well as human health and aquatic life. This study examined the influence of biofouling of NF and RO membrane on the performance of the membranes in removing boron from a synthetic wastewater effluent. Accelerated laboratory-scale biofouling experiments were carried out with commercial thin film composite NF and RO membranes under controlled conditions. Permeate flux decline, down to less than 25% of its initial value, and substantial decrease in boron rejection were attributed to extensive biofilm growth on the membranes. For the RO membrane, boron rejections declined by 45 and 34% of the initial values for influent boron concentrations of 5.5 and 1.1 mg B/L, respectively, whereas the corresponding declines in boron rejection for the NF membrane were 44 and 13% of the initial values. These adverse effects of biofilm growth on permeate water flux and boron rejection are attributed to both an increase in hydraulic resistance to permeate flow due to bacterial extracellular polymeric substances (EPS) and a biofilm-enhanced concentration polarization near the membrane surface. (c) 2008 Elsevier B.V. All rights reserved.://000257005300029 0376-7388ISI:000257005300029~? McCutcheon, J. R. Elimelech, M.2008iInfluence of membrane support layer hydrophobicity on water flux in osmotically driven membrane processes458-466Journal Of Membrane Science3181-2Jun 20Osmotically driven membrane processes, such as forward osmosis (FO) and pressure-retarded osmosis (PRO), rely on the utilization of large osmotic pressure differentials across semi-permeable membranes to generate water flux. Previous investigations on these two processes have demonstrated how asymmetric membrane structural characteristics, primarily of the support layers, impact water flux performance. In this investigation we demonstrate that support layer hydrophilicity or wetting plays a crucial role in water flux across asymmetric semi-permeable membranes. The results show that the polyester(PET) non-woven and polysulfone supports typically present in thin-film composite (TFC) reverse osmosis (RO) membranes do not wet fully when exposed to water, thereby resulting in a marked decrease in water flux. A cellulosic RO membrane exhibited modestly higher water fluxes due to its more hydrophilic support layer. Removal of the PET layers from the cellulosic and TFC RO membranes resulted in an increased water flux for the cellulosic membrane and very little change in flux for the TFC membrane. Pretreatment with hydraulic pressure (RO mode), feed solution degassing, and use of surfactants were used to further elucidate the wetting mechanisms of the different support layers within each membrane. The importance of considering membrane support layer chemistry in further development of membranes tailored specifically for osmotically driven membrane processes is discussed. (C) 2008 Elsevier B.V. All rights reserved.://000257005300054 0376-7388ISI:000257005300054~? De Kerchove, A. J. Elimelech, M.2008IBacterial swimming motility enhances cell deposition and surface coverage 4371-4377"Environmental Science & Technology4212Jun 15The influence of bacterial motility on cell transport and deposition was investigated in a well-characterized radial stagnation point flow (RSPF) chamber. Deposition experiments were conducted with nonmotile (PAO1 Delta fliC Delta pilA) and motile (PAO1 Delta pilA) strains of Pseudomonas aeruginosa, and oppositely (positively) charged modified quartz surfaces. Deposition dynamics of the two bacterial strains were determined over a wide range of solution ionic strengths and at two flow velocities. The observed deposition dynamics were modeled using a modified expression of the random sequential adsorption (RSA) blocking function accounting for the impacts of hydrodynamic and electrostatic interactions on cell deposition. Results for the nonmotile bacteria indicated that the changes in blocking rate and surface coverage with ionic strength and flow rate were similar to those expected for nonbiological, "soft" particles, for which the coupling of hydrodynamic interactions and electrostatic repulsion governs the deposition dynamics. In contrast, deposition dynamics of the motile bacterial cells reduced blocking rates and enhanced maximum coverages, approaching the jamming limit predicted for "hard" ellipsoids of 0.583. We hypothesized that cell motility allows the upstream swimming of bacteria and subsequent cell deposition on regions which are otherwise inaccessible to nonmotile cell deposition due to the "shadow effect".://000256705600024 0013-936XISI:000256705600024~? +Brady-Estevez, A. S. Kang, S. Elimelech, M.2008SA single-walled-carbon-nanotube filter for removal of viral and bacterial pathogens481-484Small44Apr://000255620400019 1613-6810ISI:000255620400019J~? De Kerchove, A. J. Elimelech, M.2008sCalcium and magnesium cations enhance the adhesion of motile and nonmotile Pseadomonas aeruginosa on alginate films 3392-3399Langmuir247Apr 11We investigated the impact of calcium and magnesium ions on the deposition kinetics of flagellated and nonflagellated Pseudomonas aeruginosa onto an alginate conditioning film in a radial stagnation point flow system. The bacterial deposition/adhesion behavior was related to structural changes of the alginate film in the presence of the divalent cations. Our results showed that adhesion of nonmotile bacteria was governed by cation bridging interactions between high-affinity sites at the bacterial surface and either clean or alginate-conditioned substrate surfaces. For motile bacteria, the adhesion onto clean quartz was governed by electrostatic interactions while adhesion onto alginate-conditioned quartz was dependent on the structure and viscoelastic properties of the alginate film in the presence of calcium or magnesium. We demonstrate that bacterial adhesion behavior is governed both by the effects of divalent cations on the surface properties of the bacteria and the substrate and by the type of specific interactions occurring between these two surfaces.://000254480500060 0743-7463ISI:000254480500060K~?VShannon, M. A. Bohn, P. W. Elimelech, M. Georgiadis, J. G. Marinas, B. J. Mayes, A. M.2008CScience and technology for water purification in the coming decades301-310Nature4527185Mar 20+One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water- rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re- use of wastewater and efficient desalination of sea and brackish water.://000254117400037 0028-0836ISI:000254117400037U~?Herzberg, M. Elimelech, M.2008lPhysiology and genetic traits of reverse osmosis membrane biofilms: a case study with Pseudomonas aeruginosa180-194 Isme Journal22FebJBiofilm formation of Pseudomonas aeruginosa on the surface of a reverse osmosis (RO) membrane was studied using a synthetic wastewater medium to simulate conditions relevant to reclamation of secondary wastewater effluent. P. aeruginosa biofilm physiology and spatial activity were analyzed following growth on the membrane using a short-life green fluorescent protein derivative expressed in a growth-dependent manner. As a consequence of the limiting carbon source prevailing in the suspended culture of the RO unit, a higher distribution of active cells was observed in the biofilm close to the membrane surface, likely due to the higher nutrient levels induced by concentration polarization effects. The faster growth of the RO-sessile cells compared to the planktonic cells in the RO unit was reflected by the transcriptome of the two cultures analyzed with DNA microarrays. In contrast to the findings recently reported in gene expression studies of A aeruginosa biofilms, in the RO system, genes related to stress, adaptation, chemotaxis and resistance to antibacterial agents were induced in the planktonic cells. In agreement with the findings of previous P. aeruginosa biofilm studies, motility- and attachment-related genes were repressed in the RO A aeruginosa biofilm. Supported by the microarray data, an increase in both motility and chemotaxis phenotypes was observed in the suspended cells. The increase in nutrient concentration in close proximity to the membrane is suggested to enhance biofouling by chemotaxis response of the suspended cells and their swimming toward the membrane surface.://000253492900006 1751-7362ISI:000253492900006I~?Weronski, P. Elimelech, M.2008lNovel numerical method for calculating initial flux of colloid particle adsorption through an energy barrier406-415(Journal Of Colloid And Interface Science3192Mar 15Using variable substitution, we present a general method for the numerical solution of stiff, ordinary, linear, homogeneous differential equations characteristic of colloid particle adsorption/deposition over an energy barrier. For the example of the radial impinging jet system, we demonstrate the application of this method of calculating the colloid concentration profile and initial particle flux in the presence of repulsive electrostatic interactions between the particle and adsorption surface. We show that our method works well in systems with energy barriers up to the order of hundreds of U, at which point the adsorption flux vanishes. The numerical results obtained with our method are in good agreement with the known limiting analytical approximations for the particle flux through an energy barrier and for a low Peclet number. The developed numerical code is very stable over a wide range of physical parameters, and its accuracy for the most challenging parameter sets is on the order of 10(-4). To achieve this stability, we have derived and employed a single formula for the van der Waals dispersion interaction, working at both a small and a large separation distance. We show that this formula converges to the known available analytical expressions for dispersion forces in the limit of small and large separation distance. We also demonstrate that the maximum deviations between our formula and the other equations appear in the intermediate range of the separation distance and do not exceed 10%. (C) 2007 Elsevier Inc. All rights reserved.://000253259100004 0021-9797ISI:000253259100004~?Zda Silva, A. K. Le Saux, J. C. Parnaudeau, S. Pommepuy, M. Elimelech, M. Le Guyader, F. S.2007Evaluation of removal of noroviruses during wastewater treatment, using real-time reverse transcription-PCR: Different behaviors of genogroups I and II 7891-7897&Applied And Environmental Microbiology7324Dec%Noroviruses, an important cause of gastroenteritis, are excreted by infected individuals and are therefore present in wastewater. We quantified norovirus genogroup I (GI) and GII in wastewater at different locations in France and evaluated removal by a range of treatment types, including basic (waste stabilization pond), current industry standard (activated sludge), and state-of-the-art (submerged membrane bioreactor) treatments. Noroviruses were quantified using real-time reverse transcription-PCR (rRT-PCR). Mengovirus was used as a virus extraction control, and internal controls were used to verify the level of GI and GII rRT-PCR inhibition. A total of 161 (81 influent and 79 effluent) samples were examined; GI and GII were detected in 43 and 88% of the influent samples, respectively, and in 24 and 14% of the effluent samples, respectively. Physicians in France report far more cases of GII than GI during outbreaks; thus, the frequent presence of GI was unexpected. The GI influent concentrations were more variable, the peak GI influent concentrations were higher than the peak GII influent concentrations at all four sites (up to 1 x 10(9) and 6 x 10(7) genome copies/liter, respectively), and the average positive influent concentrations of GI were higher than the average positive influent concentrations of GII The maximum effluent breakthrough concentrations were 6 x 10(6) and 3 x 10(6) genome copies/liter for GI and GII, respectively, indicating that the four treatment systems studied decreased the norovirus contamination load in receiving waters.://000251902300012 0099-2240ISI:000251902300012~?-de Kerchove, A. J. Weronski, P. Elimelech, M.2007Adhesion of nonmotile Pseudomonas aeruginosa on "soft" polyelectrolyte layer in a radial stagnation point flow system: Measurements and model predictions 12301-12308Langmuir2324Nov 20Prediction of bacterial deposition rates onto substrates in natural aquatic systems is quite challenging because of the inherent complexity of such systems. In this study we compare experimental deposition kinetics of nonmotile bacteria (Pseudomonas aeruginosa) on an alginate-coated substrate in a radial stagnation point flow (RSPF) system to predictions based on DLVO theory. The "softness" of the surface layer of the bacteria and alginate-coated substrate was considered in the calculations of their electrokinetic surface properties, and the relevance of both the classical zeta potential and the outer surface potential as surrogates for surface potential was investigated. Independent of the used electrical potentials, we showed that significant discrepancies exist between theory and experiments. Analysis of microscopic images in the RSPF system has demonstrated, for the first time, that irreversible deposition of particles or cells entrapped in the secondary energy minimum can occur on the alginate layer, despite the hydrodynamic forces resulting from the radial flow in the RSPF system. It is suggested that polymeric structures associated with the surface of the particle/cell and the alginate-coated substrate are responsible for the transition between the secondary minimum and primary energy well. This mode of deposition is likely to be important in the deposition of microorganisms in complex aquatic systems.://000250976700059 0743-7463ISI:000250976700059*~?/McGinnis, R. L. McCutcheon, J. R. Elimelech, M.2007GA novel ammonia-carbon dioxide osmotic heat engine for power generation13-19Journal Of Membrane Science3051-2Nov 15A novel method of converting thermal energy into mechanical work is presented, using semi-permeable membranes to convert osmotic pressure into electrical power. This method, a closed cycle pressure-retarded osmosis (PRO) process known as an osmotic heat engine (OHE), uses a concentrated ammonia-carbon dioxide draw solution to create high osmotic pressures which generate water flux through a semi-permeable membrane against a hydraulic pressure gradient. The depressurization of the increased draw solution volume in a turbine produces electrical power. The process is maintained in steady state operation through the separation of the diluted draw solution into a re-concentrated draw solution and (nearly) deionized water working fluid, both for reuse in the engine. The use of deionized water working fluid has been shown to allow for high membrane water flux and efficient mass transport, as internal concentration polarization effects are eliminated. Modeling of the engine indicates that membrane power density may exceed 200 W/m(2), given appropriate operating conditions. The thermal efficiency of the engine is predicted to approach a maximum of 16% of Carnot efficiency (maximum theoretical engine efficiency), with practical efficiencies most likely in the range of 5-10% of Carnot efficiency. The temperature of heat used for the engine may be very low (40 degrees C with a 20 degrees C ambient temperature), allowing for the production of potentially low cost, carbon neutral power from waste heat, low temperature geothermal reservoirs, or other non-combustion thermal energy sources. This combination of a highly concentrated NH3/CO2 draw solution and a deionized working fluid may allow for highly effective power generation from osmotic pressure gradients. (c) 2007 Elsevier B.V. All rights reserved.://000250890600003 0376-7388ISI:000250890600003~?$Hill, J. E. Kysela, D. Elimelech, M.2007TIsolation and assessment of phytate-hydrolysing bacteria from the DelMarVa Peninsula 3100-3107Environmental Microbiology912Dec}The Delaware-Maryland-Virginia (DelMarVa) Peninsula, flanking one side of the Chesapeake Bay, is home to a substantial broiler chicken industry. As such, it produces a significant amount of manure that is typically composted and spread onto local croplands as a fertilizer. Phytate (myo inositol hexakisphosphate), the major form of organic phosphorus in the manure, can be hydrolysed by microorganisms to produce orthophosphate. Orthophosphate is a eutrophication agent which can lead to algal blooms, hypoxia and fish kills in the Chesapeake Bay and its tributaries. This transect study reveals a subpopulation of heterotrophic, thiosulfate-utilizing bacteria that can degrade phytate within the watershed as well as its receiving water sediment. Aerobic isolates were typical soil bacteria, e.g. Pseudomonad, Bacillus and Arthrobacter species, as well as a less common Staphylococcus inhabitant. Bacillus pumilus, Staphyloccocus equorum, Arthrobacter bergei and Pseudomonas marginalis strains have not been previously described as phytate-degrading. Each site along the transect - from manure pile to receiving sediment - was host to a population of bacteria that can degrade phytate and hence, each is a possible non-point source of orthophosphate pollution. Each new isolate could provide an enzyme additive for monogastric feed, thus reducing the impact of excessive phytate load on the environment.://000250761300017 1462-2912ISI:000250761300017~?3Kang, S. Pinault, M. Pfefferle, L. D. Elimelech, M.2007DSingle-walled carbon nanotubes exhibit strong antimicrobial activity 8670-8673Langmuir2317Aug 14We provide the first direct evidence that highly purified single-walled carbon nanotubes (SWNTs) exhibit strong antimicrobial activity. By using a pristine SWNT with a narrow diameter distribution, we demonstrate that cell membrane damage resulting from direct contact with SWNT aggregates is the likely mechanism leading to bacterial cell death. This finding may be useful in the application of SWNTs as building blocks for antimicrobial materials.://000248730500006 0743-7463ISI:000248730500006~? de Kerchove, A. J. Elimelech, M.2007rImpact of alginate conditioning film on deposition kinetics of motile and nonmotile Pseudomonas aeruginosa strains 5227-5234&Applied And Environmental Microbiology7316AugThe initial deposition of bacteria in most aquatic systems is affected by the presence of a conditioning film adsorbed at the liquid-solid interface. Due to the inherent complexity of such films, their impact on bacterial deposition remains poorly defined. The aim of this study was to gain a better understanding of the effect of a conditioning film on the deposition of motile and nonmotile Pseudomonas aeruginosa cells in a radial stagnation point How system. A well-defined alginate film was used as a model conditioning film because of its polysaccharide and polyelectrolyte nature. Deposition experiments under favorable (nonrepulsive) conditions demonstrated the importance of swimming motility for cell transport towards the substrate. The impact of the flagella of motile cells on deposition is dependent on the presence of the conditioning film. We showed that on a clean substrate surface, electrostatic repulsion governs bacterial deposition and the presence of flagella increases cell deposition. However, our results suggest that steric interactions between flagella and extended polyelectrolytes of the conditioning film hinder cell deposition. At a high ionic strength (100 mM), active swimming motility and changes in alginate film structure suppressed the steric barrier and allowed conditions favorable for deposition. We demonstrated that bacterial deposition is highly influenced by cell motility and the structure of the conditioning film, which are both dependent on ionic strength.://000248825900020 0099-2240ISI:000248825900020~?0Asatekin, A. Kang, S. Elimelech, M. Mayes, A. M.2007xAnti-fouling ultrafiltration membranes containing polyacrylonitrile-graft-poly (ethylene oxide) comb copolymer additives136-146Journal Of Membrane Science2981-2Jul 20_Membrane fouling is one of the most important challenges faced in membrane ultrafiltration (UF) operations. In this study, polyacrylonitrile-graftpoly(ethylene oxide) (PAN-g-PEO), an amphiphilic comb copolymer with a water-insoluble polyacrylonitrile (PAN) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains, was used as an additive in the manufacture of novel PAN UF membranes. During casting, the PAN-g-PEO additive segregates to form a PEO brush layer on all membrane surfaces, including internal pores. Wettability, pure water permeability, and resistance to irreversible fouling increased when either the amount of PAN-g-PEO added to the membrane or the PEO content of the comb copolymer was increased. These trends were consistent with measured adhesion forces between the membranes and a carboxylated latex particle probe in an atomic force microscopy (AFM) analysis, and with the near-surface PEO coverage as determined by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) revealed further effects of additive incorporation on membrane morphology. In 24-h dead-end filtration studies, blend membranes prepared with 20 wt% PAN-g-PEO (comb PEO content: 39 wt%) were found to resist irreversible fouling by 1000 ppm solutions of bovine serum albumin (BSA), sodium alginate, and humic acid, recovering the initial pure water flux completely by a pure water rinse, or a backwash in the case of humic acid. This exceptional anti-fouling performance holds promise for extending UF membrane lifetimes without need for aggressive cleaning procedures. (c) 2007 Elsevier B.V. All rights reserved.://000247703900015 0376-7388ISI:000247703900015~?McCutcheon, J. R. Elimelech, M.2007QModeling water flux in forward osmosis: Implications for improved membrane design 1736-1744 Aiche Journal537JulOsmotically-driven membrane processes, such as forward osmosis and pressure retarded osmosis, operate on the principle of osmotic transport of water across a semipermeable membrane from a dilute feed solution into a concentrated draw solution. The major hindrance to permeate water flux performance is the prevalence of concentration polarization on both sides of the membrane. This article evaluates the external and internal boundary layers, which decrease the effective osmotic driving force. By modeling permeate flux performance, the role that feed and draw concentrations, membrane orientation, and membrane structural properties play in overall permeate flux performance are elucidated and linked to prevalence of external and internal concentration polarization. External concentration polarization is found to play a significant role in the reduction of driving force, though internal concentration polarization has a far more pronounced effect for the chosen system conditions. Reduction of internal concentration polarization by way of membrane modification was found to improve the predicted flux performance significantly, suggesting that alteration of membrane design will lead to improved performance of osmotically driven membrane processes. (c) 2007 American Institute of Chemical Engineers.://000247713200010 0001-1541ISI:000247713200010U~?0Kang, S. Asatekin, A. Mayes, A. M. Elimelech, M.2007SProtein antifouling mechanisms of PAN UF membranes incorporating PAN-g-PEO additive42-50Journal Of Membrane Science2961-2Jun 159The antifouling mechanism of a novel polyacrylonitrile (PAN) ultrafiltration (UF) membrane incorporating the amphiphilic comb copolymer additive, polyacrylonitrile-graft-polyethylene oxide (PAN-g-PEO), has been investigated using a laboratory-scale cross-flow test unit and atomic force microscopy (AFM). In fouling tests with a bovine serum albumin (BSA) solution, PAN UF membranes incorporating 20% PAN-g-PEO possessed excellent antifouling characteristics, whereas a commercial PAN UF membrane showed severe pore blocking that followed with surface cake formation. The PAN-g-PEO/PAN blend membranes also exhibited fouling reversibility and constant BSA retention, which indicate their ability to separate macromolecules without altering the molecular weight cut-off. An AFM analysis with a model carboxylated colloid-probe measured no adhesion force with the blend membrane, while the commercial PAN membrane exhibited strong adhesion to the probe, consistent with the fouling properties of the membranes. The antifouling character of the blend membrane is attributed to the surface segregation and local orientation of PAN-g-PEO molecules at the membrane surface and pore walls during membrane casting, creating a dense PEO brush layer that provides a steric barrier to protein adsorption. (C) 2007 Elsevier B.V. All rights reserved.://000246988800006 0376-7388ISI:000246988800006;~?Ang, W. S. Elimelech, M.2007[Protein (BSA) fouling of reverse osmosis membranes: Implications for wastewater reclamation83-92Journal Of Membrane Science2961-2Jun 15/Effluent organic matter (EfOM) has been known to contribute significantly to organic fouling of reverse osmosis (RO) membranes in advanced wastewater reclamation. In this study, the effects of feed solution chemistry (calcium concentration, ionic strength, and solution pH) and feed foulant composition on fouling of RO membranes by bovine serum albumin (BSA) - selected to represent proteins in EfOM - are investigated. Crossflow fouling experiments show that RO membrane fouling by BSA is enhanced at higher calcium concentration and at a solution pH at the BSA isoelectric point (pH 4.7). It is further demonstrated that BSA fouling of RO membranes is significantly enhanced in the presence of alginate (a model polysaccharide) as co-foulant. There appears to be an initial synergistic fouling effect when RO membranes are fouled by both BSA and alginate, as compared to fouling by BSA or alginate alone. Foulant-foulant adhesion forces, determined by AFM force measurements under solution chemistries identical to those of the crossflow fouling experiments, further confirm the trends of the fouling profiles. It is consistently shown that solution chemistries and foulant compositions that induce higher fouling rates are associated with greater foulant-foulant adhesion forces. (C) 2007 Elsevier B.V. All rights reserved.://000246988800011 0376-7388ISI:000246988800011W~?Lee, S. Elimelech, M.20079Salt cleaning of organic-fouled reverse osmosis membranes 1134-1142Water Research415MarCleaning of organic-fouled reverse osmosis membranes with concentrated salt solutions has been investigated. Polysaccharides (alginate and pectin) and Suwannee River natural organic matter were used as model organic foulants. By systematically varying the chemical and physical factors affecting salt cleaning efficiency, we were able to elucidate the processes and mechanisms involved during salt cleaning. Chemical factors investigated included salt dose, salt type, and organic foulant composition, while physical factors included cleaning contact time, crossflow velocity, cleaning solution temperature, and permeation rate. Atomic force microscopy (AFM) was utilized to quantify the reduction in intermolecular foulant-foulant adhesion upon salt cleaning. Our results showed that salt cleaning was quite effective in cleaning reverse osmosis membranes fouled by gel-forming hydrophilic organic foulants, such as alginate and pectin. The proposed mechanism for salt cleaning involves structural changes of the cross-linked gel layer on the membrane surface upon exposure to the salt solution followed by an ion exchange reaction that induces the breakup of calcium-foulant bonds as well as calcium bridging (cross-linking) between foulant molecules. The results obtained from AFM force measurements as well as foulant release experiments confirmed that these chemical reactions were the major mechanisms of salt cleaning. Salt cleaning appears to be an effective cleaning method, and may prove useful for membrane-based advanced wastewater reclamation, where a large fraction of the organic foulants is hydrophilic. (C) 2006 Elsevier Ltd. All rights reserved.://000246465400021 0043-1354ISI:000246465400021~?&Chen, K. L. Mylon, S. E. Elimelech, M.2007Enhanced aggregation of alginate-coated iron oxide (hematite) nanoparticles in the presence of calcium, strontium, and barium cations 5920-5928Langmuir2311May 22{Early-stage aggregation kinetics studies of alginate-coated hematite nanoparticles in solutions containing alkaline-earth metal cations revealed enhanced aggregation rates in the presence of Ca2+, Sr2+, and Ba2+, but not with Mg2+. Transmission electron microscopy (TEM) imaging of the aggregates provided evidence that alginate gel formation was essential for enhanced aggregation to occur. Dynamic light scattering (DLS) aggregation results clearly indicated that a much lower concentration of Ba2+ compared to Ca2+ and Sr2+ was required to achieve a similar degree of enhanced aggregation in each system. To elucidate the relationship between the alginate's affinities for divalent cations and the enhanced aggregation of the alginate-coated hematite nanoparticles, atomic force microscopy (AFM) was employed to probe the interaction forces between alginate-coated hematite surfaces under the solution chemistries used for the aggregation study. Maximum adhesion forces, maximum pull-off distances, and the work of adhesion were used as indicators to gauge the alginate's affinity for the divalent cations and the resulting attractive interactions between alginate-coated hematite nanoparticles. The results showed that alginate had higher affinity for Ba2+ than either Sr2+ or Ca2+. This same trend was consistent with the cation concentrations required for comparable enhanced aggregation kinetics, suggesting that the rate of alginate gel formation controls the enhanced aggregation kinetics. An aggregation mechanism incorporating the gelation of alginate is proposed to explain the accelerated aggregate growth in the presence of Ca2+, Sr2+, and Ba2+.://000246456700016 0743-7463ISI:000246456700016 :~?Herzberg, M. Elimelech, M.2007RBiofouling of reverse osmosis membranes: Role of biofilm-enhanced osmotic pressure11-20Journal Of Membrane Science2951-2May 315A bench-scale investigation of RO biofouling with Pseudomonas aeruginosa PAO I was conducted in order to elucidate the mechanisms governing the decline in RO membrane performance caused by cell deposition and biofilm growth. A sharp decline in permeate water flux and a concomitant increase in salt passage were observed following the inoculation of the RO test unit with a late exponential culture of P. aeruginosa PA01 under enhanced biofouling conditions. The decrease in permeate flux and salt rejection is attributed to the growth of a biofilm comprised of bacterial cells and their self-produced extracellular polymeric substances (EPS). Biofilm growth dynamics on the RO membrane surface are observed using confocal microscopy, where active cells, dead cells, and EPS are monitored. We propose that the biofilm deteriorates membrane performance by increasing both the trans-membrane osmotic pressure and hydraulic resistance. By comparing the decrease in permeate flux and salt rejection upon fouling with dead cells of P aeruginosa PA01 and upon biofilm growth on the membrane surface, we can distinguish between these two fouling mechanisms. Bacterial cells on the membrane hinder the back diffusion of salt, which results in elevated osmotic pressure on the membrane surface, and therefore a decrease in permeate flux and salt rejection. On the other hand, EPS contributes to the decline in membrane water flux by increasing the hydraulic resistance to permeate flow. Scanning electron microscope (SEM) images of dead cells and biofilm further support these proposed mechanisms. Biofilm imaging reveals an opaque EPS matrix surrounding P. aeruginosa PA01 cells that could provide hydraulic resistance to permeate flux. In contrast, SEM images taken after fouling runs with dead cells reveal a porous cake layer comprised of EPS-free individual cells that is likely to provide negligible resistance to permeate flow compared to the RO membrane resistance. We conclude that "biofilm-enhanced osmotic pressure" plays a dominant role in RO biofouling. (C) 2007 Elsevier B.V. All rights reserved.://000246534500003 0376-7388ISI:000246534500003P~?McGinnis, R. L. Elimelech, M.2007JEnergy requirements of ammonia-carbon dioxide forward osmosis desalination370-382 Desalination2071-3Mar 10]The energy requirements of ammonia-carbon dioxide forward osmosis (FO)desalination are predicted by the use of chemical process modeling software (HYSYS). The FO process is modeled using single or multiple distillation columns to separate draw solution solutes from the product water for solute recycling within the FO system. Thermal and electrical energy requirements of the process are calculated, as well as a combined term for equivalent electrical work. The results of the simulations are compared to the energy requirements of current desalination technologies. Energy savings of FO compared to current technologies, on an equivalent work basis, are projected to range from 72% to 85%. Forward osmosis desalination is in an early stage of its development, and several areas of future work promise opportunities to improve its energy utilization and cost.://000245885100033 0011-9164ISI:000245885100033~?Chen, K. L. Elimelech, M.2007Influence of humic acid on the aggregation kinetics of fullerene (C-60) nanoparticles in monovalent and divalent electrolyte solutions126-134(Journal Of Colloid And Interface Science3091May 1cThe early stage aggregation kinetics of fullerene C-60 nanoparticles were investigated in the presence of Suwannee River humic acid and common monovalent and divalent electrolytes through time-resolved dynamic light scattering (DLS). In the absence of humic acid, the aggregation behavior of the fullerene nanoparticles in the presence of NaCl, MgCl2, and CaCl2 was found to be consistent with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. In the presence of humic acid and NaCl or MgCl2 electrolytes, the adsorbed humic acid on the fullerene nanoparticles led to steric repulsion, which effectively stabilized the nanoparticle suspension. This behavior manifested in a dramatic drop in the rate of aggregation, an increase in the critical coagulation concentration (CCC), and an attained value of less than unity for the inverse stability ratio (or attachment efficiency) at high MgCl2 concentrations. While the increase in the nanoparticle stability was similarly observed in the presence of humic acid at low CaCl2 concentrations, enhanced aggregation occurred at higher CaCl2 concentrations. Measurement of scattered light intensities over time indicated significant aggregation of the humic acid macromolecules in solutions of high CaCl2 concentrations. Transmission electron microscopy (TEM) imaging of the fullerene aggregate structures in the presence of humic acid revealed that bridging of the fullerene nanoparticles and aggregates by the humic acid aggregates is the likely mechanism for the enhanced aggregation at high CaCl2 concentrations. (c) 2007 Elsevier Inc. All rights reserved.://000245561200018 0021-9797ISI:000245561200018~? Nguyen, T. H. Elimelech, M.2007vAdsorption of plasmid DNA to a natural organic matter-coated silica surface: Kinetics, conformation, and reversibility 3273-3279Langmuir236Mar 13A quartz crystal microbalance with dissipation (QCM-D) has been used to determine the adsorption rate of ampicillin-resistant linear and supercoiled plasmid DNA onto a silica surface coated with natural organic matter (NOM). The structure of the resulting adsorbed DNA layer was determined by analyzing the viscoelastic properties of the adsorbed DNA layers as they formed and were then exposed to solutions of different ionic composition. The QCM-D data were complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. The obtained results suggest that electrostatic interactions control the adsorption and structural changes of the adsorbed plasmid DNA on the NOM-coated silica surface. The adsorption of DNA molecules to the NOM layer took place at moderately high monovalent (sodium) electrolyte concentrations. A sharp decrease in solution ionic strength did not result in the release of the adsorbed DNA, indicating that DNA adsorption on the NOM-coated silica surface is irreversible under the studied solution conditions. However, the decrease in electrolyte concentration influenced the structure of the adsorbed layer, causing the adsorbed DNA to adopt a less compact conformation. The linear and supercoiled DNA had similar adsorption rates, but the linear DNA formed a thicker and less compact adsorbed layer than the supercoiled DNA.://000244650000050 0743-7463ISI:000244650000050~?!Kuznar, Z. A. Elimelech, M.2007kDirect microscopic observation of particle deposition in porous media: Role of the secondary energy minimum156-162?Colloids And Surfaces A-Physicochemical And Engineering Aspects2941-3Feb 15A flow-cell has been constructed where micrometer-sized particles flow horizontally through a single layer of packed glass beads. Deposition is viewed through a fluorescent microscope with phase contrast capabilities. This allows the visualization of particle deposition in porous media in real time and provides insight into phenomena such as secondary minimum deposition of particles and microbial pathogens during physicochemical filtration. At low ionic strengths (1-3 mM), no deposition was observed on the collector beads. As the monovalent salt concentration was raised to moderate ionic strengths (10-30 nnM), the particles became trapped in the secondary minimum and translated along the glass bead surface, accumulating near the rear of the spherical collectors. At high ionic strength (100 mM), no calculated electrostatic energy barrier to deposition exists and particles deposited over the entire surface of the spherical collector. It is concluded that deposition in the secondary energy minimum is an important removal mechanism for micrometer-sized particles in flow through granular porous media. (c) 2006 Elsevier B.V. All rights reserved.://000244617500021 0927-7757ISI:0002446175000213~?"Nguyen, T. H. Elimelech, M.2007fPlasmid DNA adsorption on silica: Kinetics and conformational changes in monovalent and divalent salts24-32Biomacromolecules81Jan*A quartz crystal microbalance with dissipation (QCM-D) is used to determine the adsorption rate of a supercoiled plasmid DNA onto a quartz surface and the structure of the resulting adsorbed DNA layer. To better understand the DNA adsorption mechanisms and the adsorbed layer physicochemical properties, the QCM-D data are complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. The data from simultaneous monitoring of variations in frequency and dissipation energy with the QCM-D suggest that the adsorbed DNA layer is more rigid in the presence of divalent (calcium) cations compared to monovalent (sodium) cations. Adsorption rates are significantly higher in the presence of calcium, attaining a transport-limited rate at about 1 mM Ca2+. Results further suggest that in low ionic strength solutions containing 1 mM Ca2+ and in moderately high ionic strength solutions containing 300 mM NaCl, plasmid DNA adsorption to negatively charged mineral surfaces is irreversible.://000243337600004 1525-7797ISI:000243337600004E~?# de Kerchove, A. J. Elimelech, M.2007gFormation of polysaccharide gel layers in the presence of Ca2+ and K+ ions: Measurements and mechanisms113-121Biomacromolecules81Jan4Understanding the adsorption properties of polysaccharides in terms of substrate affinity, kinetics, and layer structure is of paramount importance in numerous industrial and natural systems. The structural growth of the layers of two model polysaccharidessodium alginate and polygalacturonic acid (PGA)was characterized by quartz crystal microbalance with dissipation and atomic force microscopy. Monitoring the variations in frequency and dissipation energy provides insights into both the average adsorbed mass and the viscoelastic properties of the adsorbed layer of polyelectrolytes along with the associated ions and water molecules. Both polysaccharides had similar adsorption patterns with increasing ionic strengths and showed significant complexation of calcium ions. In the presence of calcium, the alginate gel layer exhibited significant swelling with an increasing concentration of monovalent salt that the PGA gel layer did not manifest. Basing our discussion on the "egg-box model", we interpreted these different swelling behaviors as resulting from differences in the complexation modes of the two polysaccharides. The dimerization of the polymers by cross-linking and the weaker dimer-dimer associations play major roles in the sensitivity of the polysaccharide gel matrix to high salt concentration environments.://000243337600016 1525-7797ISI:000243337600016~?$Montgomery, M. A. Elimelech, M.2007NWater and sanitation in developing countries: Including health in the equation17-24"Environmental Science & Technology411Jan 1://000243124600010 0013-936XISI:000243124600010~?%*Nghiem, L. D. Schafer, A. I. Elimelech, M.2006~Role of electrostatic interactions in the retention of pharmaceutically active contaminants by a loose nanofiltration membrane52-59Journal Of Membrane Science2861-2Dec 15The role of electrostatic interactions in the separation of pharmaceuticals by a loose nanofiltration (NF) membrane was examined. While retention of the non-ionizable pharmaceutical carbamazepine was relatively independent of the solution chemistry, retention of the ionizable pharmaceuticals, sulfamethoxazole and ibuprofen, was strongly influenced by the solution pH and ionic strength. This finding is consistent with previous results investigating the effects Of Solution pH and ionic strength on the retention of proteins and organic acids. Pharmaceutical retention increases dramatically as the compound transforms from a neutral to a negatively charged species when the solution pH increases above its pK(a) value. In contrast, solution ionic strength suppresses the double layer or the Debye screening length and therefore reduces the effectiveness of electrostatic interaction as a major retention mechanism by the loose NF membranes. However, because of the formation of a hydrated layer around the charged functional groups of the pharmaceuticals and the fact that at a sufficiently high ionic strength the Debye length approaches a relatively constant value, this reduction in retention is relatively small. As a result, even at comparatively elevated ionic strengths, retention of the negatively charged sulfamethoxazole and ibuprofen by the loose NF membrane is considerably high. (c) 2006 Elsevier B.V. All rights reserved.://000242988100011 0376-7388ISI:000242988100011_~?&Chen, K. L. Elimelech, M.2006EAggregation and deposition kinetics of fullerene (C-60) nanoparticles 10994-11001Langmuir2226Dec 19wThe aggregation and deposition kinetics of fullerene C-60 nanoparticles have been investigated over a wide range of monovalent and divalent electrolyte concentrations by employing time-resolved dynamic light scattering (DLS) and quartz crystal microbalance (QCM), respectively. Aggregation kinetics of the fullerene nanoparticles exhibited reaction-limited (slow) and diffusion- limited (fast) regimes in the presence of both electrolytes, having critical coagulation concentrations (CCC) of 120 and 4.8 mM for the monovalent (NaCl) and divalent (CaCl2) salts, respectively. The measured stability ratios of the aggregating fullerene nanoparticles were in very good agreement with Derjaguin-Landau- Verwey-Overbeek (DLVO) theory, with a derived Hamaker constant of 6.7 x 10(-21) J for the fullerene nanoparticles in aqueous medium. For the deposition kinetics studies, the rate of fullerene nanoparticle deposition increased with increasing electrolyte concentrations, as was indicated in the aggregation kinetics results. However, at electrolyte concentrations approaching or exceeding the CCC, the rate of deposition dropped sharply due to significant concurrent aggregation of the fullerene nanoparticles. The deposition of the fullerene nanoparticles was further shown to be mostly irreversible, with immediate detachment of the nanoparticles observed only when exposed to a solution of high pH.://000242771200026 0743-7463ISI:000242771200026~?'NAsatekin, A. Menniti, A. Kang, S. T. Elimelech, M. Morgenroth, E. Mayes, A. M.2006cAntifouling nanofiltration membranes for membrane bioreactors from self-assembling graft copolymers81-89Journal Of Membrane Science2851-2Nov 15cUltrafiltration (UF) membranes, often employed in membrane bioreactors (MBRs), exhibit high susceptibility to fouling by extracellular polymeric substances (EPS). As potential alternatives, commercial polyvinylidene fluoride (PVDF) OF membranes were coated with the amphiphilic graft copolymer poly(vinylidene fluoride)-graft-poly(oxyethylene) methacrylate, PVDF-g-POEM, to create thin film composite (TFC) nanofiltration membranes. Pure water permeabilities up to 56 L/m(2) h MPa were obtained at pressures of 0.21 MPa (30 psi). The new TFC NF membranes exhibited no irreversible fouling in 10-day dead-end filtration studies of model organic foulants bovine serum albumin, sodium alginate and humic acid at concentrations of 1000 mg/L and above. Dead-end filtration of activated sludge from an MBR (1750 mg/L volatile suspended solids, VSS) resulted in constant flux throughout the 16 h filtration period. Fouling performance of the TFC NF membrane and effluent water quality were substantially improved in all cases over that for the base PVDF OF membrane. Utilizing the atomic force microscope (AFM) colloid probe technique, the measured interaction force profiles indicated the presence of repulsive steric interactions, which likely prevent the attachment of foulants to the TFC NF membrane. Similarly, the adhesion (pull-off) curves reveal the absence of foulant adhesion to the TFC NF membrane surface, even in the presence of divalent calcium ions. In contrast, when such force measurements are carried out with the base PVDF OF membrane, substantial adhesion forces are registered. (c) 2006 Elsevier B.V. All rights reserved.://000242209000007 0376-7388ISI:000242209000007|~?(+Gray, G. T. McCutcheon, J. R. Elimelech, M.2006TInternal concentration polarization in forward osmosis: role of membrane orientation1-8 Desalination1971-3Oct 2vThe mechanisms governing internal concentration polarization (ICP) were studied using well-controlled forward osmosis experiments. The relationship between osmotic pressure and water flux was observed across a range of solute concentrations and molecular weights. The effect of membrane orientation on ICP was also studied. Two regimes of ICP-dilutive and concentrative-were described and characterized, and their governing equations were tested. Resistances to solute diffusion within the membrane porous support layer were calculated under each regime and found to be consistent across a wide variety of experimental parameters.://000241913000001 0011-9164ISI:000241913000001~?)McCutcheon, J. R. Elimelech, M.2006oInfluence of concentrative and dilutive internal concentration polarization on flux behavior in forward osmosis237-247Journal Of Membrane Science2841-2Nov 1Osmosis through asymmetric membranes has been studied as a means of desalination via forward osmosis and power generation through a process known as pressure retarded osmosis. The primary obstacle to using asymmetric membranes for osmotic processes is the presence of internal concentration polarization, which significantly reduces the available osmotic driving force. This study explores the impact of both concentrative and dilutive internal concentration polarization on permeate water flux through a commercially available forward osmosis membrane. The coupling of internal and external concentration polarization is also investigated. A flux model that accounts for the presence of both internal and external concentration polarization for the two possible membrane orientations involving the feed and draw solutions is presented. The model is verified by data obtained from laboratory-scale experiments under well controlled conditions in both membrane orientations. Furthermore, the model is used to predict flux performance after hypothetical improvements to the membrane or changes in system conditions. (c) 2006 Elsevier B.V. All rights reserved.://000241431400025 0376-7388ISI:000241431400025~?* de Kerchove, A. J. Elimelech, M.2006jStructural growth and viscoelastic properties of adsorbed alginate layers in monovalent and divalent salts 6558-6564Macromolecules3919Sep 19The growth and evolution of the viscoelastic properties of an alginate layer as a function of ionic strength and the presence of divalent calcium ions are monitored by quartz crystal microbalance with dissipation and atomic force microscopy. The properties of the alginate layer are investigated by combining results of incremental layer thickness or adsorbed areal mass, viscoelastic properties of the film, adhesion forces between adsorbing polysaccharides, and pull- off distances of the adsorbed molecules. In the absence of calcium, alginate adsorption behavior is strongly influenced by charge screening of the negatively charged carboxyl moieties of the alginate molecules. Reduction in alginate layer swelling is observed as ionic strength is increased, most likely due to Donnan equilibrium effects. The presence of calcium ions induces the formation of a thick and fluid gel layer via the complexation of alginate molecules. As the monovalent salt concentration is increased, a displacement of the ion- exchange equilibrium takes place in response to the competition between monovalent ( potassium) and divalent ( calcium) cations. The resulting impact of this phenomenon on the structure and viscoelastic properties of the alginate layer is discussed.://000240437200036 0024-9297ISI:0002404372000361~?+*Cath, T. Y. Childress, A. E. Elimelech, M.2006BForward osmosis: Principles, applications, and recent developments70-87Journal Of Membrane Science2811-2Sep 15,Osmosis is a physical phenomenon that has been extensively studied by scientists in various disciplines of science and engineering. Early researchers studied the mechanism of osmosis through natural materials, and from the 1960s, special attention has been given to osmosis through synthetic materials. Following the progress in membrane science in the last few decades, especially for reverse osmosis applications, the interests in engineered applications of osmosis has been spurred. Osmosis, or as it is currently referred to as forward osmosis, has new applications in separation processes for wastewater treatment, food processing, and seawater/brackish water desalination. Other unique areas of forward osmosis research include pressure-retarded osmosis for generation of electricity from saline and fresh water and implantable osmotic pumps for controlled drug release. This paper provides the state-of-the-art of the physical principles and applications of forward osmosis as well as their strengths and limitations. (c) 2006 Elsevier B.V. All rights reserved.://000240207800004 0376-7388ISI:000240207800004~?,*Costa, A. R. de Pinho, M. N. Elimelech, M.2006IMechanisms of colloidal natural organic matter fouling in ultrafiltration716-725Journal Of Membrane Science2811-2Sep 15The role of membrane pore size and solution chemistry in ultrafiltration (UF) membrane fouling by colloidal natural organic matter (NOM) has been investigated. Fouling experiments were conducted with two laboratory-made cellulose acetate UF membranes, with estimated pore sizes of 2 and 10 urn, under identical hydrodynamic conditions. Flux decline with colloidal NOM was independent of pH and increased in the presence of calcium. The membrane pore size has been found to influence membrane flux decline. Permeate flux for the more permeable membrane (10 nm pore size) decreased faster than the flux of the tightest, less permeable membrane (2 nm pore size). The adhesion forces between the foulant (colloidal NOM) and the clean membrane, and between the foulant in bulk solution and foulant in the fouling layer, were determined by atomic force microscopy (AFM). Force measurements confirmed the fouling trends with calcium ions. For a given solution chemistry, foulant-foulant adhesion was identical for both membranes, indicating that the more pronounced flux decline observed for the largest pore-size membrane was not related to differences in intermolecular chemical interactions among NOM molecules. At the earlier stage of filtration, the dominant fouling mechanism was pore blocking for both membranes. For longer filtration times, there was a transition in the fouling mechanism from pore blocking to cake formation. This transition occurred first for the more permeable membrane, indicating that colloidal NOM penetrates more readily into the pores of this membrane and that the relative size of colloidal NOM and the membrane pore influences the rate of pore blocking. The results further suggest that the structure of the fouling layer is dependent on the operating pressure. At high pressure, the compactness and specific resistance of the colloidal NOM layer substantially increase, and thus, significantly affect the extent of flux decline. (c) 2006 Elsevier B.V. All rights reserved.://000240207800077 0376-7388ISI:000240207800077~?-Li, Q. L. Elimelech, M.2006|Synergistic effects in combined fouling of a loose nanofiltration membrane by colloidal materials and natural organic matter72-82Journal Of Membrane Science2781-2Jul 5Fouling of nanofiltration (NF) membranes in water treatment and wastewater reuse applications is often caused by both colloidal materials and dissolved organic matter. However, most past mechanistic studies on NF membrane fouling have focused on either colloidal fouling or organic fouling. In this study, the performance of a 'loose', low salt rejection NF membrane during combined fouling by both colloidal materials and dissolved natural organic matter (NOM) was compared with that during colloidal fouling and organic fouling alone. A significant synergistic effect was observed during combined fouling, manifested as considerably higher flux decline rate than what expected based on the sum of colloidal and organic fouling alone. Microscopic analysis of the colloid/organic foulant layer structure confirmed faster foulant accumulation on the membrane surface, indicating a mechanism of hindered back diffusion of colloidal and organic foulants. The membrane flux decline during combined fouling was also found to depend on solution chemistry and colloidal particle size. Notably, the effects of these factors are different from those during fouling by colloidal materials or dissolved organic matter alone. (c) 2005 Elsevier B.V. All rights reserved.://000238409300009 0376-7388ISI:000238409300009~?./McCutcheon, J. R. McGinnis, R. L. Elimelech, M.2006Desalination by ammonia-carbon dioxide forward osmosis: Influence of draw and feed solution concentrations on process performance114-123Journal Of Membrane Science2781-2Jul 5Forward (direct) osmosis (FO) using semi-permeable polymeric membranes may be a viable alternative to reverse osmosis as a lower cost and more environmentally friendly desalination technology. The driving force in the described FO process is provided by a draw solution comprising highly soluble gases-ammonia and carbon dioxide. Using a commercially available FO membrane, experiments conducted in a crossflow, flat-sheet membrane filtration cell yielded water fluxes ranging from 1 to 10 mu m/s (2.1 to 21.2 gal ft(-2) d(-1) or 3.6 to 36.0 1 m(-2) h(-1)) for a wide range of draw and feed solution concentrations. It was found, however, that the experimental water fluxes were far lower than those anticipated based on available bulk osmotic pressure difference and membrane pure water permeability data. Internal concentration polarization was determined to be the major cause for the lower than expected water flux by analysis of the available water flux data and SEM images of the membrane displaying a porous support layer. Draw solution concentration was found to play a key role in this phenomenon. Sodium chloride rejection was determined to be 95-99% for most tests, with higher rejections occurring under higher water flux conditions. Desalination of very high sodium chloride feed solutions (simulating 75% recovery of seawater) was also deemed possible, leading to the possibility of brine discharge minimization. (c) 2005 Elsevier B.V. All rights reserved.://000238409300013 0376-7388ISI:000238409300013$~?/ Elimelech, M.20060The global challenge for adequate and safe water3-104Journal Of Water Supply Research And Technology-Aqua551Feb<This paper was presented as a lecture for the 2005 Clarke Prize. it addresses the global challenge for adequate and safe water through several cases involving water scarcity and quality. The first case, in Namibia, exemplifies water scarcity and the harnessing of water science and technology to extract water for potable use from a nontraditional source - domestic wastewater. The second case focuses on water scarcity and the implications for national stability and regional peace, illustrated by Israel and its neighboring countries. The third discussion is related to water quality, specifically the lack of safe drinking water in the developing world. Drawing from these cases, it is shown that global water scarcity and quality problems involve complex technological, societal, cultural, economical, and political aspects.://000236569100002 0003-7214ISI:000236569100002~?0Kuznar, Z. A. Elimelech, M.2006TCryptosporidium oocyst surface macromolecules significantly hinder oocyst attachment 1837-1842"Environmental Science & Technology406Mar 15xThe role Cryptosporidium parvum oocyst surface macromolecules play in controlling oocyst adhesion (deposition) kinetics to quartz surfaces has been investigated utilizing a radial stagnation point flow system. Deposition kinetics and corresponding attachment efficiencies of viable oocysts were compared with those after treatment with a digestive enzyme (proteinase K) to cleave these surface macromolecules. Low deposition rates were observed with viable oocysts over the entire range of ionic strengths (0) investigated, even at ionic strengths as high as 100 mM where the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability predicts the absence of an electrostatic energy barrier. "Electrosteric" repulsion between the oocyst surface macromolecules and the quartz surface is surmised to cause these low deposition rates and attachment efficiencies. However, after removal of these surface macromolecules by the digestive enzyme, increased attachment efficiencies were observed over the entire range of ionic strengths. This significant increase in the deposition kinetics was seen despite the oocysts having a more negative zeta potential following the removal of the surface macromolecules. After treatment with proteinase K, the oocysts no longer experienced electrosteric repulsive forces, and their deposition kinetics followed the general behavior predicted by DLVO theory.://000236213900019 0013-936XISI:000236213900019~?1&Chen, K. L. Mylon, S. E. Elimelech, M.2006fAggregation kinetics of alginate-coated hematite nanoparticles in monovalent and divalent electrolytes 1516-1523"Environmental Science & Technology405Mar 1The early stage aggregation kinetics of bare and alginate-coated hematite nanoparticles are acquired through time-resolved dynamic light scattering (DILS). Varying concentrations of monovalent (NaCl) and divalent (MgCl2 and CaCl2) electrolytes are employed to induce aggregation. In the presence of NaCl and MgCl2,the alginate-coated hematite nanoparticles undergo aggregation through electrostatic destabilization as described by the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This is ascertained through examination of the favorable and unfavorable regimes of the stability curves depicting the attachment efficiency as a function of salt concentration. Additional evidence may be found in the aggregation kinetics of alginate-coated particles, which under favorable aggregation conditions, are reasonably close to that of bare hematite nanoparticles. However, in the presence of CaCl2,the aggregate growth rate of alginate-coated hematite nanoparticles is much higher than that which conventional diffusive aggregation predicts. Dispersed hematite primary particles and lower-order aggregates enmeshed within extended alginate gel networks were observed under transmission electron microscope (TEM). The proposed mechanism for enhanced aggregation suggests an apparent increase in the collision radii of alginate coated hematite nanoparticles through alginate gel network formation from the particle surface. Additionally, cross-linking between unadsorbed (suspended) alginate macromolecules may form bridges between hematite-alginate gel clusters. It is further established that the presence of background electrolyte NaCl in solution is detrimental to the calcium-induced enhanced aggregation.://000235796100028 0013-936XISI:000235796100028~?2 Lee, S. Ang, W. S. Elimelech, M.2006`Fouling of reverse osmosis membranes by hydrophilic organic matter: implications for water reuse313-321 Desalination1871-3Feb 5Effluent organic matter (EfOM) is suspected as a major cause of fouling of reverse osmosis (RO) membranes in advanced wastewater reclamation. Among the main constituents in EfOM, polysaccharides are the most ubiquitous. The influence of solution chemistry and hydrodynamics on RO membrane fouling with alginate - a model for polysaccharides in secondary wastewater effluent - was systematically investigated. Results of fouling runs with alginate demonstrate that RO membrane fouling increases with decreasing pH, increasing ionic strength, and addition of calcium ions. At fixed solution ionic strength and pH, the presence of divalent calcium ions, at concentrations typical of those found in secondary wastewater effluent, had a dramatic effect on membrane fouling. However, for similar concentrations of divalent magnesium ions, fouling was negligible. The severe fouling in the presence of calcium is attributed to the formation of a thick, dense alginate gel layer on the membrane surface via calciumalginate complexation and crosslinking (bridging) of alginate macromolecules by calcium. In addition to solution chemistry, hydrodynamic operating conditions - initial permeate flux and crossflow velocity - were also shown to influence RO membrane fouling with alginate.://000235585000030 0011-9164ISI:000235585000030~?3#Ang, W. S. Lee, S. Y. Elimelech, M.2006UChemical and physical aspects of cleaning of organic-fouled reverse osmosis membranes198-210Journal Of Membrane Science2721-2Mar 15The role of chemical and physical interactions in cleaning of organic-fouled reverse osmosis (RO) membranes is systematically investigated. Fouling and cleaning experiments were performed with organic foulants (alginate and natural organic matter) that simulate effluent organic matter (EfOM) and selected cleaning agents using a laboratory-scale crossflow test unit. Following accelerated organic fouling runs with divalent calcium ions, cleaning experiments were performed at various chemical and physical conditions. The results showed that a metal chelating agent (EDTA) and an anionic surfactant (SDS) were able to clean the fouled RO membrane effectively by optimizing chemical (dose and pH) and physical (time, crossflow velocity, and temperature) conditions during cleaning. The permeate flux was, however, poorly recovered when cleaning was performed with NaOH (pH 11). Interfacial force measurements (by AFM) further confirmed the cleaning results, demonstrating the influence of cleaning agents on reducing the foulant-foulant adhesion force. The results showed that the adhesion force caused by calcium-induced foulant-foulant interaction was reduced significantly with EDTA and SDS cleaning, while substantial adhesion force still remained following NaOH cleaning. It is proposed that an efficient cleaning agent and favorable cleaning conditions could be selected by considering two important mechanisms: chemical reaction between cleaning agents and foulants in the fouling layer, and mass transfer of chemical agents (from the bulk phase to the fouling layer) and foulants (from the fouling layer to the bulk phase). (c) 2005 Elsevier B.V. All rights reserved.://000235413000022 0376-7388ISI:000235413000022~?4Lee, S. Elimelech, M.2006WRelating organic fouling of reverse osmosis membranes to intermolecular adhesion forces980-987"Environmental Science & Technology403Feb 1Organic fouling of reverse osmosis (RO) membranes and its relation to foulant-foulant intermolecular adhesion forces has been investigated. Alginate and Suwannee River natural organic matter were used as model organic foulants. Atomic force microscopy was utilized to determine the adhesion force between bulk organic foulants and foulants deposited on the membrane surface under various solution chemistries. The measured adhesion force was related to the RO fouling rate determined from fouling experiments under solution chemistries similar to those used in the AFM measurements. A remarkable correlation was obtained between the measured adhesion force and the fouling rate under the solution chemistries investigated. Fouling was more severe at solution chemistries that resulted in larger adhesion forces, namely, lower pH, higher ionic strength, presence of calcium ions (but not magnesium ions), and higher mass ratio of alginate to Suwannee River natural organic matter. The significant adhesion force measured with alginate in the presence of calcium ions indicated the formation of a crossed-linked alginate gel layer during fouling through intermolecular bridging among alginate molecules.://000235227600059 0013-936XISI:000235227600059z~?5Li, Q. Elimelech, M.2004PNatural organic matter fouling and chemical cleaning of nanofiltration membranes245-251@4th World Water Congress: Innovation In Drinking Water Treatment45-66Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water quality control applications. Because fouling strongly depends on the feed water quality, especially the ionic composition, chemical cleaning solutions should be chosen to target the solution chemistry that is most responsible for the formation of a compact, high resistance fouling layer. In this study, the effect of solution chemistry on natural organic matter (NOM) fouling of two NF membranes with different surface properties was investigated. Compared to monovalent cations, divalent cations were found to greatly enhance NOM fouling by complexation. Moreover, calcium ions caused a much greater fouling rate than magnesium ions, presumably due to the intermolecular bridging formed among NOM molecules through the calcium ions. Various chemical cleaning solutions were evaluated for water flux recovery efficiency. Although both deionized water and dilute NaOH solution were found effective in cleaning membranes fouled in the absence of calcium ions, efficient chemical cleaning in presence of calcium was achieved only when the calcium ion bridging was eliminated. The cleaning efficiency was shown to be highly dependent on solution pH and the concentration of the chemical cleaning agent.://000227429400029 4WATER SCIENCE AND TECHNOLOGY: WATER SUPPLY 1606-9749ISI:000227429400029t~?6+Nghiem, L. D. Schaffer, A. I. Elimelech, M.2005>Nanofiltration of hormone mimicking trace organic contaminants 2633-2649!Separation Science And Technology4013sThe removal mechanisms of three hormone mimicking organic compounds by nanofiltration (NF) membranes have been examined. Two NF membranes having different pore sizes were used in laboratory-scale nanofiltration experiments with feed solutions spiked with a hormone mimicking compound-nonylphenol, tert-butylphenol, or bisphenol A. Retention of the compounds was determined at various solution chemistries, namely aqueous solution pH, ionic strength, and presence of natural organic matter. The nanofiltration behavior of the selected hormone mimicking compounds appears similar to that of natural hormones as reported in our previous work. While the solution pH can dramatically influence the retention of hormone mimicking compounds by a loose NF membrane, ionic strength does not affect the nanofiltration of such contaminants. However, in the presence of natural organic matter in the feed solution, ionic strength appears to play a significant role in solute-solute and solute-membrane interactions, resulting in increased retention due to partitioning of the hormone mimicking compounds onto organic matter at a higher ionic strength.://000233305000004 0149-6395ISI:000233305000004#~?7Tufenkji, N. Elimelech, M.2005Reply to comment on breakdown of colloid filtration theory: Role of the secondary energy minimum and surface charge heterogeneities 10896-10897Langmuir2123Nov 8://000233129500101 0743-7463ISI:0002331295001011~?8*Nghiem, L. D. Schafer, A. I. Elimelech, M.2005?Pharmaceutical retention mechanisms by nanofiltration membranes 7698-7705"Environmental Science & Technology3919Oct 1'This study investigates the retention mechanisms of three pharmaceuticals-sulfamethoxazole, carbamazepine, and ibuprofen-by nanofiltration (NF) membranes. Laboratory-scale experiments were carried out with two wellcharacterized NF membranes, with the goal of relating pharmaceutical retention behavior to membrane characteristics, physicochernical properties of the pharmaceutical molecules, and solution chemistry. Results show that retention of pharmaceuticals by a tight NF membrane is dominated by steric (size) exclusion, whereas both electrostatic repulsion and steric exclusion govern the retention of ionizable pharmaceuticals by a loose NF membrane. In the latter case, speciation of pharmaceuticals may lead to a dramatic change in retention as a function of pH, with much greater retention observed for ionized, negatively charged pharmaceuticals. For uncharged pharmaceutical species, intrinsic physicochemical properties of the pharmaceutical molecules can substantially affect their retention. In its neutral form, ibuprofen adsorbs considerably to the membrane because of its relatively high hydrophobicity. Similarly, polarity (represented by the dipole moment) can influence the separation of molecules that are cylindrical in shape because they can be directed to approach the membrane pores head-on due to attractive interaction between the molecule polar centers and fixed charged groups on the membrane surface. This phenomenon is probably inherent for high dipole moment organic compounds, and the governing retention mechanism remains steric in nature.://000232410000057 0013-936XISI:000232410000057~?9 Lee, S. Cho, J. W. Elimelech, M.2005mCombined influence of natural organic matter (NOM) and colloidal particles on nanofiltration membrane fouling27-41Journal Of Membrane Science2621-2Oct 1\The combined influence of natural organic matter (NOM) and colloidal particles on the fouling of thin-film composite nanofiltration (NF) membranes is systematically investigated. Combined fouling is compared to the individual fouling behaviors (i.e., colloid or NOM alone) with respect to fouling mechanisms and the effect of concentration factor (or recovery). Results demonstrate that (1) "cake-enhanced osmotic pressure" (CEOP) is a key fouling mechanism for individual colloidal fouling, (2) NOM-calcium complexation is the dominant factor governing individual NOM fouling, and (3) combined fouling is affected by both CEOP and NOM-calcium complexation. The extent of flux decline for combined fouling, however, is less than what inferred from additivity of the individual contributions of colloidal and NOM fouling to flux decline. This observation implies that the contributions of the fouling mechanisms appear to be relatively less significant for combined fouling compared to their separate influences on individual colloidal and NOM fouling. An increase in colloidal stability in presence of NOM and the competition between colloids and NOM for calcium are likely explanations for this behavior. It is further shown that NF membrane salt rejection increases noticeably in case of combined fouling compared to individual colloidal fouling due to the formation of an active rejecting layer by the accumulated NOM on the membrane surface. Results from combined fouling runs involving EDTA treatment confirm that both CEOP and NOM-calcium complexation take place simultaneously. (c) 2005 Elsevier B.V. All rights reserved.://000232188000005 0376-7388ISI:000232188000005~?:)Ball, W. P. Elimelech, M. Tobiason, J. E.2005KIn honor of Charles R. O'Melia: Researcher, scholar, engineer, and educator 352A-353A"Environmental Science & Technology3917Sep 1://000231723800001 0013-936XISI:000231723800001~?;)Walker, S. L. Redman, J. A. Elimelech, M.2005Influence of growth phase on bacterial deposition: Interaction mechanisms in packed-bed column and radial stagnation point flow systems 6405-6411"Environmental Science & Technology3917Sep 1The influence of bacterial growth stage on cell deposition kinetics has been examined using a mutant of Escherichia coliK12. Two experimental techniques-a packed-bed column and a radial stagnation point flow (RSPF) system-were employed to determine bacterial deposition rates onto quartz surfaces over a wide range of solution ionic strengths. Stationary-phase cells were found to be more adhesive than mid-exponential phase cells in both experimental systems. The divergence in deposition behavior was notably more pronounced in the RSPF than in the packed-bed system. For instance, in the RSPF system, the deposition rate of the stationary-phase cells at 0.03 M ionic strength was 14 times greater than that of the mid-exponential cells. The divergence in the packed-bed system was most significant at 0.01 M, where the deposition rate for the stationary-phase cells was nearly 4 times greater than for the mid-exponential cells. To explain the observed adhesion behavior, the stationary and mid-exponential bacterial cells were characterized for their size, surface charge density, electrophoretic mobility, viability, and hydrophobicity. On the basis of this analysis, it is suggested that the stationary cells have a more heterogeneous distribution of charged functional groups on the bacterial surface than the mid-exponential cells, which results in higher deposition kinetics. Furthermore, because the RSPF system enumerates only bacterial cells retained in primary minima, whereas the packed column captures mostly cells deposited in secondary minima, the difference in the stationary and mid-exponential cell deposition kinetics is much more pronounced in the RSPF system.://000231723800021 0013-936XISI:000231723800021u~?<RAbudalo, R. A. Bogatsu, Y. G. Ryan, J. N. Harvey, R. W. Metge, D. W. Elimelech, M.2005Effect of ferric oxyhydroxide grain coatings on the transport of bacteriophage PRD1 and Cryptosporidium parvum oocysts in saturated porous media 6412-6419"Environmental Science & Technology3917Sep 1To test the effect of geochemical heterogeneity on microorganism transport in saturated porous media, we measured the removal of two microorganisms, the bacteriophage PRDI and oocysts of the protozoan parasite Cryptosporidium parvum, in flow-through columns of quartz sand coated by different amounts of a ferric oxyhydroxide. The,experiments were conducted over ranges of ferric oxyhydroxide coating fraction of lambda = 0-0.12 for PRD1 and from lambda = 0-0.32 for the oocysts at pH 5.6-5.8 and 10(-4) M ionic strength. To determine the effect of pH on the transport of the oocysts, experiments were also conducted over a pH range of 5.7-10.0 at a coating fraction of lambda = 0.04. Collision (attachment) efficiencies increased as the fraction of ferric oxyhydroxide coated quartz sand increased, from alpha = 0.0071 to 0.13 over lambda = 0-0.12 for PRD1 and from alpha = 0.059 to 0.75 over lambda = 0-0.32 for the oocysts. Increasing the pH from 5.7 to 10.0 resulted in a decrease in the oocyst collision efficiency as the pH exceeded the expected point of zero charge of the ferric oxyhydroxide coatings. The collision efficiencies correlated very well with the fraction,of quartz sand coated by the ferric oxyhydroxide for PRD1 but not as well for the oocysts.://000231723800022 0013-936XISI:000231723800022"~?= de Kerchove, A. J. Elimelech, M.2005oRelevance of electrokinetic theory for "soft" particles to bacterial cells: Implications for bacterial adhesion 6462-6472Langmuir2114Jul 5 Bacterial cells and other biological particles carry charged macromolecules on their surface that form a "soft" ion-permeable layer. In this paper, we test the applicability of an electrokinetic theory for soft particles to characterize the electrophoretic mobility (EPM) and adhesion kinetics of bacterial cells. The theory allows the calculation of two parameters-the electrophoretic softness and the fixed charged density that define the characteristics of the polyelectrolyte layer at the soft particle surface. The theory also allows the calculation of an outer-surface potential that may better predict the electrostatic interaction of soft particles with solid surfaces. To verify its relevance for bacterial cells, the theory was applied to EPM measurements of two well-characterized Escherichia coli K12 mutants having lipopolysaccharide (LPS) layers of different lengths and molecular compositions. Results showed that the obtained softness and fixed charge density were not directly related to the known characteristics of the LPS of the selected strains. Interaction energy profiles calculated from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were used to interpret bacterial deposition (adhesion) rates on a pure quartz surface. The outer surface potential failed to predict the low attachment efficiencies of the two bacterial strains. The lack of success in the application of the theory for soft particles to bacterial cells is attributed to chemical and physical heterogeneities of the polyelectrolyte layer at the cell surface.://000230248500048 0743-7463ISI:000230248500048~?>Lee, S. Cho, J. Elimelech, M.2005yA novel method for investigating the influence of feed water recovery on colloidal and NOM fouling of RO and NF membranes496-509!Environmental Engineering Science224Jul-AugA systematic investigation on the role of feed water recovery (or concentration factor) in colloidal and natural organic matter (NOM) fouling of reverse osmosis (RO) and nanofiltration (NF) membranes is reported. Fouling experiments were conducted using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate concentration factor (CF) and feed water recovery as commonly observed in full-scale RO/NF systems. With this novel method, the deterioration in membrane performance due to fouling and recovery-related osmotic pressure buildup can be distinguished. For colloidal fouling of RO membranes, the so-called "cake enhanced osmotic pressure" is a key fouling mechanism resulting in severe decline in permeate flux and significant decrease in salt rejection with increasing CF. On the other hand, NOM-calcium complexation rather than enhanced osmotic pressure is the key mechanism for NOM fouling of NF membranes. The decline in permeate flux and decrease in solute rejection with increasing CF were significant under favorable conditions for fouling, namely at higher initial permeate flux, ionic strength, and calcium ion concentration.://000230184800010 1092-8758ISI:000230184800010M~??5Walker, S. L. Hill, J. E. Redman, J. A. Elimelech, M.2005GInfluence of growth phase on adhesion kinetics of Escherichia coli D21g 3093-3099&Applied And Environmental Microbiology716Jun/The influence of bacterial growth stage and the evolution of surface macromolecules on cell adhesion have been examined by using a mutant of Escherichia coli K-12. To better understand the adhesion kinetics of bacteria in the mid-exponential and stationary growth phases under How conditions, deposition experiments were conducted in a well-controlled radial stagnation point How (RSPF) system. Complementary cell characterization techniques were conducted in combination with the RSPF experiments to evaluate the hydrophobicity, electrophoretic mobility, size, and titratable surface charge of the cells in the two growth phases considered. It was observed that cells in stationary phase were notably more adhesive than those in mid-exponential phase. This behavior is attributed to the high degree of local charge heterogeneity on the outer membranes of stationary-phase cells, which results in decreased electrostatic repulsion between the cells and a quartz surface. The mid-exponential-phase cells, on the other hand, have a more uniform charge distribution on the outer membrane, resulting in greater electrostatic repulsion and, subsequently, less adhesion. Our results suggest that the macromolecules responsible for this phenomenon are outer membrane-bound proteins and lipopolysaccharide-associated functional groups.://000229790900036 0099-2240ISI:000229790900036~?@$Chen, J. C. Elimelech, M. Kim, A. S.2005Monte Carlo simulation of colloidal membrane tiltration: Model development with application to characterization of colloid phase transition291-305Journal Of Membrane Science2551-2Jun 15This study investigates phase transition from a fluid-like polarization layer to a solid cake layer of particle deposits during membrane filtration of interacting colloidal particles. A Monte Carlo simulation model of dead-end filtration is used under the influences of hydrodynamic bias from the permeation flux as well as inter-particle interactions. The model effectively demonstrates the roles of the hydrodynamic drag force and inter-particle potential in governing the volume fraction of the particle deposit. The cake layer volume fraction is shown to be sensitive to the combination of particle surface (zeta) potential, solution ionic strength, particle size, and applied transmembrane pressure. Further application of the model leads to a holistic characterization of the phase transition phenomenon. The onset of phase transition is characterized with flexibility and adaptability with concern for both physico-chemical standards, such as volume fraction and inter-particle separation distance, as well as pragmatic considerations, such as the desire to operate the system below the critical flux and avoidance of irreversible cake formation. © 2005 Elsevier B.V. All rights reserved.://000229517500029 0376-7388ISI:0002295175000298~?ATufenkji, N. Elimelech, M.2005cSpatial distributions of Cryptosporidium oocysts in porous media: Evidence for dual mode deposition 3620-3629"Environmental Science & Technology3910May 15Spatial distributions of Cryptosporidium parvum oocysts in columns packed with uniform glass-bead collectors were measured over a broad range of physicochemical conditions. Oocyst deposition behavior is shown to deviate from predictions based on classical colloid filtration theory (CFT) in the presence of repulsive (unfavorable) colloidal interactions. Specifically, CFT tends to predict greater removal of oocysts (less transport) than that observed in controlled laboratory experiments. Comparison of oocyst retention with results obtained using polystyrene latex particles of similar size suggests that mechanisms controlling particle deposition are the same in both systems. At a given ionic strength, the deposition of Cryptosporidium oocysts is generally greater than that of the microspheres; however, this discrepancy is partly attributable to large differences in oocyst and microsphere zeta potentials. A dual deposition mode (DDM) model is applied which considers the combined influence of "fast" and "slow" oocyst deposition due to the concurrent existence of favorable and unfavorable oocyst-collector interactions. Model simulations of retained oocyst profiles and suspended oocyst concentration at the column effluent are consistent with experimental data. Because classic CFT does not account for the effect of dual mode deposition (i.e., simultaneous "fast" and "slow" oocyst deposition), these observations have important implications for predictions of oocyst transport in subsurface environments, where repulsive electrostatic interactions predominate. Supporting elution experiments further suggest that specific surface interactions between oocyst wall macromolecules and the glass bead collectors could retard or even completely inhibit oocyst release upon perturbation in solution chemistry.://000229193700032 0013-936XISI:000229193700032~?B/McCutcheon, J. R. McGinnis, R. L. Elimelech, M.2005LA novel ammonia-carbon dioxide forward (direct) osmosis desalination process1-11 Desalination1741Apr 1A novel forward (direct) osmosis (FO) desalination process is presented. The process uses an ammonium bicarbonate draw solution to extract water from a saline feed water across a semi-permeable polymeric membrane. Very large osmotic pressures generated by the highly soluble ammonium bicarbonate draw solution yield high water fluxes and can result in very high feed water recoveries. Upon moderate heating, ammonium bicarbonate decomposes into ammonia and carbon dioxide gases that can be separated and recycled as draw solutes, leaving the fresh product water. Experiments with a laboratory-scale FO unit utilizing a flat sheet cellulose tri-acetate membrane demonstrated high product water flux and relatively high salt rejection. The results further revealed that reverse osmosis (RO) membranes are not suitable for the FO process because of relatively low product water fluxes attributed to severe internal concentration polarization in the porous support and fabric layers of the RO membrane.://000228355100001 0011-9164ISI:000228355100001$~?CTufenkji, N. Elimelech, M.2005oBreakdown of colloid filtration theory: Role of the secondary energy minimum and surface charge heterogeneities841-852Langmuir213Feb 1The mechanisms and causes of deviation from the classical colloid filtration theory (CFT) in the presence of repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions were investigated. The deposition behavior of uniform polystyrene latex colloids in columns packed with spherical soda-lime glass beads was systematically examined over a broad range of physicochemical conditions, whereby both the fluid-phase effluent particle concentration and the profile of retained particles were measured. Experiments conducted with three different-sized particles in a simple (1:1) electrolyte solution reveal the controlling influence of secondary minimum deposition on the deviation from CFT. In a second series of experiments, sodium dodecyl sulfate (SDS) was added to the background electrolyte solution with the intent of masking near-neutrally charged regions of particle and collector surfaces. These results indicate that the addition of a small amount of anionic surfactant is sufficient to reduce the influence of certain surface charge inhomogeneities on the deviation from CFT. To verify the validity of CFT in the absence of surface charge heterogeneities, a third set of experiments was conducted using solutions of high pH to mask the influence of metal oxide impurities on glass bead surfaces. The results demonstrate that both secondary minimum deposition and surface charge heterogeneities contribute significantly to the deviation from CFT generally observed in colloid deposition studies. It is further shown that agreement with CFT is obtained even in the presence of an energy barrier (i.e., repulsive colloidal interactions), suggesting that it is not the general existence of repulsive conditions which causes deviation but rather the combined occurrence of "fast" and "slow" particle deposition.://000226614200010 0743-7463ISI:000226614200010~?DKuznar, Z. A. Elimelech, M.2005URole of surface proteins in the deposition kinetics of Cryptosporidium parvum oocysts710-716Langmuir212Jan 18A radial stagnation point flow system was used to investigate the influence of Cryptosporidium parvum surface properties on oocyst deposition kinetics onto solid surfaces. To determine the role of oocyst surface proteins in adhesion, the deposition kinetics of viable oocysts were compared with the deposition kinetics of oocysts treated (inactivated) with either heat or formalin. Results showed a significantly higher deposition rate with formalin and heat-treated oocysts compared to viable oocysts under identical solution ionic strengths. Low deposition rates and corresponding attachment efficiencies were observed with viable oocysts over the entire range of solution conditions investigated, even at high ionic strengths where DLVO theory predicts the absence of an electrostatic energy barrier. An "electrosteric" repulsion between the viable Cryptosporidium oocyst and the quartz substrate, attributed to proteins on the oocyst surface, is surmised to cause this low deposition rate. Inactivation of the oocysts with either formalin or heat resulted in increased attachment efficiencies over the entire range of ionic strengths examined. It is hypothesized that formalin and heat treatments alter the structure of surface proteins and thus reduce steric repulsion. Formalin treatment was also found to impart an increased hydrophobicity to the oocyst surface and thus greater enhancement in oocyst deposition kinetics compared to heat treatment.://000226343100033 0743-7463ISI:000226343100033~?EKuznar, Z. A. Elimelech, M.2004MAdhesion kinetics of viable Cryptosporidium parvum oocysts to quartz surfaces 6839-6845"Environmental Science & Technology3824Dec 15The transport and deposition (adhesion) kinetics of viable Cryptosporidium parvum oocysts onto ultrapure quartz surfaces in a radial stagnation point flow system were investigated. Utilizing an optical microscope and an image-capturing device enabled real time observation of oocyst deposition behavior onto the quartz surface in solutions containing either monovalent (KCl) or divalent (CaCl2) salts. Results showed a significantly lower oocyst deposition rate in the presence of a monovalent salt compared to a divalent salt. With a monovalent salt, oocyst deposition rates and corresponding attachment efficiencies were relatively low, even at high KCl concentrations where Derjaguin-Landau-Verwey-Overbeek (DLVO) theory predicts the absence of an electrostatic energy barrier. On the other hand, in the presence of a divalent salt, oocyst deposition rates increased continuously as the salt concentration was increased over the entire range of ionic strengths investigated. The unusually low deposition rate in a monovalent salt solution is attributed to "electrosteric" repulsion between the Cryptosporidium oocyst and the quartz surface, most likely due to proteins on the oocyst surface that extend into the solution. It is further proposed that specific binding of calcium ions to the oocyst surface functional groups results in charge neutralization and conformational changes of surface proteins that significantly reduce electrosteric repulsion.://000225761800057 0013-936XISI:000225761800057m~?FTufenkji, N. Elimelech, M.2004eDeviation from the classical colloid filtration theory in the presence of repulsive DLVO interactions 10818-10828Langmuir2025Dec 7eA growing body of experimental evidence suggests that the deposition behavior of microbial particles (e.g., bacteria and viruses) is inconsistent with the classical colloid filtration theory (CFT). Well-controlled laboratory-scale column deposition experiments were conducted with uniform model particles and collectors to obtain insight into the mechanisms that give rise to the diverging deposition behavior of microorganisms. Both the fluid-phase effluent particle concentration and the profile of retained particles were systematically measured over a broad range of physicochemical conditions. The results indicate that, in the presence of repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions, the concurrent existence of both favorable and unfavorable colloidal interactions causes significant deviation from the CFT. A dual deposition mode model is presented which considers the combined influence of "fast" and "slow" particle deposition. This model is shown to adequately describe both the spatial distribution of particles in the packed bed and the suspended particle concentration at the column effluent.://000225500700007 0743-7463ISI:000225500700007~?GNg, H. Y. Elimelech, M.2004\Influence of colloidal fouling on rejection of trace organic contaminants by reverse osmosis215-226Journal Of Membrane Science2441-2Nov 15A systematic investigation on the influence of colloidal fouling on removal of trace organics (steroid hormones) and inert organics by reverse osmosis (RO) membranes is reported. Results of laboratory-scale crossflow membrane filtration experiments showed that colloidal fouling caused a marked decrease in rejection of inert organic molecules with molecular weight smaller than about 100 g/mol. While the removal of inert organics was mainly due to steric (size) exclusion, adsorption and diffusion across the membrane polymer played a prominent role in the removal of the steroid hormones by the RO membrane. During membrane fouling, rejection of the inert organics and salt declined to a minimum, but then improved slowly and eventually stabilized at a fixed value. Hormone rejection, on the other hand, decreased rapidly initially, and then gradually slowed down regardless of fouling. This rejection behavior is associated with the decrease in feed hormone concentration due to adsorption and the increase in permeate concentration due to diffusion across the membrane skin layer. The decline in hormone rejection with time was much more severe when colloidal fouling took place. The solute rejection behavior is markedly influenced by the cake-enhanced concentration polarization, whereby the colloidal cake layer hinders back diffusion of solutes from the membrane surface to the bulk solution. The buildup of solutes at the membrane surface results in a higher solute concentration gradient across the membrane and, thus, a greater solute transport through the membrane and a lower observed solute rejection. The rate of decline in permeate flux and solute (hormones, inert organics, and salt) rejection correlated inversely with channel wall shear rate. (C) 2004 Elsevier B.V. All rights reserved.://000225232300021 0376-7388ISI:000225232300021~?HBTufenkji, N. Miller, G. F. Ryan, J. N. Harvey, R. W. Elimelech, M.2004fTransport of Cryptosporidium oocysts in porous media: Role of straining and physicochemical filtration 5932-5938"Environmental Science & Technology3822Nov 15MThe transport and filtration behavior of Cryptosporidium parvum oocysts in columns packed with quartz sand was systematically examined under repulsive electrostatic conditions. An increase in solution ionic strength resulted in greater oocyst deposition rates despite theoretical predictions of a significant electrostatic energy barrier to deposition. Relatively high deposition rates obtained with both oocysts and polystyrene latex particles of comparable size at low ionic strength (1 mM) suggest that a physical mechanism may play a key role in oocyst removal. Supporting experiments conducted with latex particles of varying sizes, under very low ionic strength conditions where physicochemical filtration is negligible, clearly indicated that physical straining is an important capture mechanism. The results of this study indicate that irregularity of sand grain shape (verified by SEM imaging) contributes considerably to the straining potential of the porous medium. Hence, both straining and physicochemical filtration are expected to control the removal of C. parvum oocysts in settings typical of riverbank filtration, soil infiltration, and slow sand filtration. Because classic colloid filtration theory does not account for removal by straining, these observations have important implications with respect to predictions of oocyst transport.://000225272100017 0013-936XISI:000225272100017~?I&Mylon, S. E. Chen, K. L. Elimelech, M.2004Influence of natural organic matter and ionic composition on the kinetics and structure of hematite colloid aggregation: Implications to iron depletion in estuaries 9000-9006Langmuir2021Oct 12-The stability and aggregation behavior of iron oxide colloids in natural waters play an important role in controlling the fate, transport, and bioavailability of trace metals. Time-resolved dynamic light scattering experiments were carried out in a study of the aggregation kinetics and aggregate structure of natural organic matter (NOM) coated hematite colloids and bare hematite colloids. The aggregation behavior was examined over a range of solution chemistries, by adjusting the concentration of the supporting electrolyte-NaCl, CaCl2, or simulated seawater. With the solution pH adjusted so that NOM-coated and bare hematite colloids were at the same zeta potential, we observed a significant difference in colloid stability which results from the stability imparted to the colloids by the adsorbed NOM macromolecules. This enhanced stability of NOM-coated hematite colloids was not observed with CaCl2. Aggregate form expressed as fractal dimension was determined for both NOM-coated and bare hematite aggregates in both NaCl and CaCl2. The fractal dimensions of aggregates formed in the diffusion-limited regime indicate slightly more loosely packed aggregates for bare hematite than theory predicts. For NOM-coated hematite, a small decrease in fractal dimension was observed when the solution composition changed from NaCl to CaCl2. For systems in the reaction-limited regime, the measured fractal dimensions agreed with those in the literature. Colloid aggregation was also studied in synthetic seawater, a mixed cation system to simulate estuarine mixing. Those results describe the important phenomena of iron oxide aggregation and sedimentation in estuaries. When compared to field data from the Mullica Estuary, U.S.A., it is shown that collision efficiency is a good predictor of the iron removal in this natural system.://000224391600011 0743-7463ISI:000224391600011~?JLi, Q. L. Elimelech, M.2004^Organic fouling and chemical cleaning of nanofiltration membranes: Measurements and mechanisms 4683-4693"Environmental Science & Technology3817Sep 1Fouling and subsequent chemical cleaning of nanofiltration (NF) membranes used in water quality control applications are often inevitable. To unravel the mechanisms of organic fouling and chemical cleaning, it is critical to understand the foulant-membrane, foulant-foulant, and foulant-cleaning agent interactions at the molecular level. In this study, the adhesion forces between the foulant and the membrane surface and between the bulk foulant and the fouling layer were determined by atomic force microscopy (AFM). A carboxylate modified AFM colloid probe was used as a surrogate for humic acid, the major organic foulant in natural waters. The interfacial force data were combined with the NF membrane water flux measurements to elucidate the mechanisms of organic fouling and chemical cleaning. A remarkable correlation was obtained between the measured adhesion forces and the fouling and cleaning behavior of the membrane under various solution chemistries. The AFM measurements further confirmed that divalent calcium ions greatly enhance natural organic matter fouling by complexation and subsequent formation of intermolecular bridges among organic foulant molecules. Efficient chemical cleaning was achieved only when the calcium ion bridging was eliminated as a result of the interaction between the chemical cleaning agent and the fouling layer. The cleaning efficiency was highly dependent on solution pH and the concentration of the chemical cleaning agent.://000223678900039 0013-936XISI:000223678900039~?K)Walker, S. L. Redman, J. A. Elimelech, M.2004WRole of cell surface lipopolysaccharides in Escherichia coli K12 adhesion and transport 7736-7746Langmuir2018Aug 31The influence of bacterial surface lipopolysaccharides (LPS) on cell transport and adhesion has been examined by use of three mutants of Escherichia coli K12 with well-characterized LPS of different lengths and molecular composition. Two experimental techniques, a packed-bed column and a radial stagnation point flow system, were employed to investigate bacterial adhesion kinetics onto quartz surfaces over a wide range of solution ionic strengths. Although the two systems capture distinct deposition (adhesion) mechanisms because of their different hydrodynamics, similar deposition kinetics trends were observed for each bacterial strain. Bacterial deposition rates were directly related to the electrostatic double layer interaction between the bacteria and quartz surfaces, in qualitative agreement with classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, DLVO theory does not fully explain the deposition behavior for the bacterial strain with the lengthy, uncharged O-antigen portion of the LPS. Neither the length nor the charge characteristics of the LPS molecule directly correlated to deposition kinetics, suggesting a complex combination of cell surface charge heterogeneity and LPS composition controls the bacterial adhesive characteristics. It is further suggested that bacterial deposition behavior is determined by the combined influence of DLVO interactions, LPS-associated chemical interactions, and the hydrodynamics of the deposition system.://000223567900056 0743-7463ISI:000223567900056R~?L9Nghiem, L. D. McCutcheon, J. Schafer, A. I. Elimelech, M.2004CThe role of endocrine disrupters in water recycling: risk or mania?215-220Water Science And Technology502FThe widespread occurrence of endocrine disrupting chemicals (EDCs), such as steroid hormones, in secondary wastewater effluents has become a major concern in the water recycling practice. This paper investigates the risk of steroid hormone breakthrough during nanofiltration membrane filtration in water recycling applications. The results indicate a dynamic equilibrium between adsorption and desorption of steroid hormone with regard to the membrane. This equilibrium can be pH dependent and there is a possibility for release of steroid hormones at high pH during membrane cleaning procedures or erratic pH variations. Increase in water recovery can severely increase the hormone breakthrough concentration. The results also indicate a possibility of accumulation of steroid hormones in the NF membrane, followed by subsequent release.://000223394900030 0273-1223ISI:000223394900030~?M#Chen, J. C. Li, Q. L. Elimelech, M.2004iIn situ monitoring techniques for concentration polarization and fouling phenomena in membrane filtration83-108)Advances In Colloid And Interface Science1072-3Mar 19Membrane fouling and subsequent permeate flux decline are inevitably associated with pressure-driven membrane processes. Despite the myriad of studies on membrane fouling and related phenomena-concentration polarization, cake formation and pore plugging-the fundamental mechanisms and processes involved are still not fully understood. A key to breakthroughs in understanding of fouling phenomena is the development of novel, non-invasive, in situ quantification of physico-chemical processes occurring during membrane filtration. State-of-the-art in situ monitoring techniques for concentration polarization, cake formation and fouling phenomena in pressure-driven membrane filtration are critically reviewed in this paper. The review addresses the physical principles and applications of the techniques as well as their strengths and deficiencies. Emphasis is given to techniques relevant to fouling phenomena where particles and solutes accumulate on the membrane surface such that pore plugging is negligible. The relevance of the techniques to specific processes and mechanisms involved in membrane fouling is also elaborated and discussed. (C) 2004 Elsevier B.V. All rights reserved.://000220721200002 0001-8686ISI:000220721200002~?N)Redman, J. A. Walker, S. L. Elimelech, M.2004VBacterial adhesion and transport in porous media: Role of the secondary energy minimum 1777-1785"Environmental Science & Technology386Mar 15The adhesion of a well-characterized Escherichia coli bacterial strain to quartz sediment grains in the presence of repulsive electrostatic interactions is systematically examined. An increase in the ionic strength of the pore fluid results in an increase in bacterial attachment, despite DLVO calculations indicating a sizable electrostatic energy barrier to deposition. Bacterial deposition is likely occurring in the secondary energy minimum, which DLVO calculations indicate increases in depth with ionic strength. A decrease in the ionic strength of the pore fluid-thereby eliminating the secondary energy minimum-resulted in release of the majority of previously deposited bacteria, suggesting that these cells were deposited reversibly in the secondary minimum. Additionally, bacterial attachment to a quartz surface in a radial stagnation point flow system was absent at ionic strengths less than 0.01 M and resulted in attachment efficiencies over an order of magnitude lower than in the packed-bed column experiments at higher ionic strengths. Because of the hydrodynamics in the radial stagnation point flow system, this observation supports our conclusion that the majority of bacterial deposition in the packed bed occurs in a secondary energy minimum.://000220193900028 0013-936XISI:000220193900028~?O*Nghiem, L. D. Schafer, A. I. Elimelech, M.2004^Removal of natural hormones by nanofiltration membranes: Measurement, modeling, and mechanisms 1888-1896"Environmental Science & Technology386Mar 15The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.://000220193900042 0013-936XISI:000220193900042~?PLee, S. Cho, J. Elimelech, M.2004_Influence of colloidal fouling and feed water recovery on salt rejection of RO and NF membranes1-12 Desalination1601Jan 5The influence of colloidal fouling and feed water recovery (or concentration factor, CF) on salt rejection of thin-film composite reverse osmosis (RO) and nanofiltration (NF) membranes was investigated. Fouling experiments were carried out using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate the CF and recovery as commonly observed in full-scale RO/NF systems. For feed waters containing only salt (NaCl), permeate flux declined linearly as CF was increased and salt rejection was nearly constant for both RO and NF membranes. On the other hand, a sharp decrease in permeate flux and significant decline in salt rejection with increasing CF were observed under conditions where colloidal fouling takes place. For both RO and NF membranes, the marked permeate flux decline was attributed to the so-called "cake-enhanced osmotic pressure". The decline in salt rejection when colloidal fouling predominated was much more substantial for NF than for RO membranes. In all cases, the decline in salt rejection Was higher under conditions of more severe colloidal fouling, namely at higher ionic strength and initial permeate flux.://000188375200001 0011-9164ISI:000188375200001~?QTufenkji, N. Elimelech, M.2004wCorrelation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media529-536"Environmental Science & Technology382Jan 15A new equation for predicting the single-collector contact efficiency (eta(0)) in physicochemical particle filtration in saturated porous media is presented. The correlation equation is developed assuming that the overall single-collector efficiency can be calculated as the sum of the contributions of the individual transport mechanisms-Brownian diffusion, interception, and gravitational sedimentation. To obtain the correlation equation, the dimensionless parameters governing particle deposition are regressed against the theoretical value of the single-collector efficiency over a broad range of parameter values. Rigorous numerical solution of the convective-diffusion equation with hydrodynamic interactions and universal van der Waals attractive forces fully incorporated provided the theoretical single-collector efficiencies. The resulting equation overcomes the limitations of current approaches and shows remarkable agreement with exact theoretical predictions of the single-collector efficiency over a wide range of conditions commonly encountered in natural and engineered aquatic systems. Furthermore, experimental data are in much closer agreement with predictions based on the new correlation equation compared to other available expressions.://000188124800031 0013-936XISI:000188124800031^~?RHoek, E. M. V. Elimelech, M.2003^Cake-enhanced concentration polarization: A new fouling mechanism for salt-rejecting membranes 5581-5588"Environmental Science & Technology3724Dec 15BResults from well-controlled colloidal fouling experiments with reverse osmosis (RO) and nanofiltration (NF) membranes suggest the existence of a new source of flux decline for salt-rejecting membranes-cake-enhanced osmotic pressure. The physical mechanisms leading to this enhanced osmotic pressure are a combination of hindered back-diffusion of salt ions and altered cross-flow hydrodynamics within colloidal deposit layers, which lead to an enhanced salt concentration polarization layer. A model that accounts for both hindered diffusion of salt ions and altered hydrodynamics within colloidal deposit ("cake") layers is presented. The model successfully links permeate flux and salt rejection to cake-enhanced concentration polarization and provides new insight into the mechanisms through which salt-rejecting membranes foul. Experimental data support the model calculations and highlight the role of enhanced concentration polarization phenomena in the performance (i.e., water flux and salt rejection) of polymeric thin-film composite RO/NF membranes in environmental applications.://000187248000015 0013-936XISI:000187248000015?S Elimelech, M.2003`Particle deposition onto solid surfaces with microscopic charge heterogeneity: The "bump effect"260-260EInternational Conference On Mems, Nano And Smart Systems, Proceedings://000184994600048 ISI:000184994600048~?T;Loveland, J. P. Bhattacharjee, S. Ryan, J. N. Elimelech, M.2003fColloid transport in a geochemically heterogeneous porous medium: aquifer tank experiment and modeling161-182 Journal Of Contaminant Hydrology653-4SepJTo examine colloid transport in geochemically heterogeneous porous media at a scale comparable to field experiments, we monitored the migration of silica-coated zirconia colloids in a two-dimensional layered porous media containing sand coated to three different extents by ferric oxyhydroxides. Transport of the colloids was measured over 1.65 m and 95 days. Colloid transport was modeled by an advection-dispersion-deposition equation incorporating geochemical heterogeneity and colloid deposition dynamics (blocking). Geochemical heterogeneity was represented as favorable (ferric oxyhydroxide-coated) and unfavorable (uncoated sand) deposition surface areas. Blocking was modeled as random sequential adsorption (RSA). Release of deposited colloids was negligible. The time to colloid breakthrough after the onset of blocking increased with increasing ferric oxyhydroxide-coated surface area. As the ferric oxyhydroxide surface area increased, the concentration of colloids in the breakthrough decreased. Model-fits to the experimental data were made by inverse solutions to determine the fraction of surface area favorable for deposition and the deposition rate coefficients for the favorable (ferric oxyhydroxide-coated) and unfavorable sites. The favorable deposition rate coefficient was also calculated by colloid filtration theory. The model described the time to colloid breakthrough and the blocking effect reasonably well and estimated the favorable surface area fraction very well for the two layers with more than 1% ferric oxyhydroxide coating. If mica edges in the uncoated sand were considered as favorable surface area in addition to the ferric oxyhydroxide coatings, the model predicted the favorable surface area fraction accurately for the layer with less than 1% ferric oxyhydroxide coating. (C) 2002 Elsevier Science B.V. All rights reserved.://000185276500002 0169-7722ISI:000185276500002a~?U'Elimelech, M. Chen, J. Y. Kuznar, Z. A.2003pParticle deposition onto solid surfaces with micropatterned charge heterogeneity: The "hydrodynamic bump" effect 6594-6597Langmuir1917Aug 19BA radial stagnation-point flow cell utilizing an optical microscope and an image-capturing device was used to directly observe the deposition kinetics of colloidal particles onto micropatterned glass surfaces with well-defined surface charge features. Surface charge heterogeneity was microfabricated onto glass surfaces by silanizing specified regions of the glass surface by a soft lithographic technique. At a certain combination of solution ionic strengths and particle Peclet numbers, the observed deposition rates deviated from predictions on the basis of a particle-deposition model for surfaces with macroscopic patchwise charge heterogeneity. The results are attributed to the interplay between hydrodynamic and electrostatic double-layer interactions and are explained by a phenomenon we term the "hydrodynamic bump" effect.://000184768600009 0743-7463ISI:000184768600009~?V&Weronski, P. Walz, J. Y. Elimelech, M.2003TEffect of depletion interactions on transport of colloidal particles in porous media372-383(Journal Of Colloid And Interface Science2622Jun 15The influence of depletion interactions on the transport of micrometer-sized, negatively charged polystyrene latex particles through porous media was studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of a packed column of glass beads. The column outlet latex particle concentration profiles and the total amount of particles exiting the column were determined as a function of the concentration of small, silica nanoparticles in the solution and the bulk flow rate. Because of similar charges, the silica particles do not adsorb to either the latex particles or glass beads and thus induce an attractive depletion force between the latex particles and glass bead collectors. The total column outlet latex particle amount was calculated by integrating the measured breakthrough concentration curve and compared to the known amount of injected particles at the column inlet. It was found that the particle recovery was a decreasing function of the silica nanoparticle concentration and the carrier fluid residence time, and an increasing function of the velocity in the bed. In addition, removing the silica nanoparticles from the flowing solution caused a second outlet peak to appear, suggesting that some of the polystyrene particles were captured in secondary energy wells. The experimental data were interpreted using the predicted potential energy profile between a single particle and a glass bead, which was assumed to consist of electrostatic, van der Waals, and depletion components. The results indicate that secondary energy wells significantly affect particle transport behavior through porous media. (C) 2003 Elsevier Science (USA). All rights reserved.://000183355300007 0021-9797ISI:000183355300007~?W.Hoek, E. M. V. Bhattacharjee, S. Elimelech, M.2003JEffect of membrane surface roughness on colloid-membrane DLVO interactions 4836-4847Langmuir1911May 27Recent experimental investigations suggest that interaction of colloidal particles with polymeric membrane surfaces is influenced by membrane surface morphology (roughness). To better understand the consequences of surface roughness on colloid deposition and fouling, it is imperative that models for predicting the Deljaguin-Landau-Verwey-Overbeek (DLVO) interaction energy between colloidal particles and rough membrane surfaces be developed. We present a technique of reconstructing the mathematical topology of polymeric membrane surfaces using statistical parameters derived from atomic force microscopy roughness analyses. The surface element integration technique is used to calculate the DLVO interactions between spherical colloidal particles and the simulated (reconstructed) membrane surfaces. Predictions show that the repulsive interaction energy barrier between a colloidal particle and a rough membrane is lower than the corresponding barrier for a smooth membrane. The reduction in the energy barrier is strongly correlated with the magnitude of surface roughness. It is further suggested that the valleys created by the membrane surface roughness produce wells of low interaction energy in which colloidal particles may preferentially deposit.://000183136900048 0743-7463ISI:000183136900048~?XASong, L. F. Hu, J. Y. Ong, S. L. Ng, W. J. Elimelech, M. Wilf, M.2003dEmergence of thermodynamic restriction and its implications for full-scale reverse osmosis processes213-228 Desalination1553Jul 10{The production rate of permeate in a reverse osmosis (RO) process controlled by mass transfer is proportional to the net driving pressure and the total membrane surface area. This linear relationship may not be the only mechanism controlling the performance of a full-scale membrane process (typically a pressure vessel holding six 1-m-long modules in series) which utilizes highly permeable membranes. The mechanisms that control the performance of an RO process under various conditions were carefully examined in this study. It was demonstrated that thermodynamic equilibrium can impose a strong restriction on the performance of a full-scale RO process under certain circumstances. This thermodynamic restriction arises from the significant increase in osmotic pressure downstream of an RO membrane channel due to the accumulation of rejected salt within the RO channel as a result of permeate water production. Concentration polarization is shown to have a weaker influence on the full-scale RO process performance than the thermodynamic restriction. The behavior of the process under thermodynamic restriction is quite different from the corresponding behavior that is controlled by mass transfer. The transition pressure for an RO process to shift from a mass transfer controlled regime to a thermodynamically restricted regime was determined by the basic parameters of the full-scale RO process.://000182871400001 0011-9164ISI:000182871400001~?YASong, L. F. Hu, J. Y. Ong, S. L. Ng, W. J. Elimelech, M. Wilf, M.2003@Performance limitation of the full-scale reverse osmosis process239-244Journal Of Membrane Science2142Apr 1The mechanisms controlling the performance of a full-scale reverse osmosis (RO) process (typically a pressure vessel holding six I m long modules in series) under various operating conditions are carefully examined in this study. We demonstrate that thermodynamic equilibrium imposes a strong restriction on the performance of a full-scale RO process under certain circumstances. This thermodynamic restriction arises from the significant increase in osmotic pressure downstream of an RO membrane channel (owing to the phenomenon of salt accumulation within the RO channel as a result of permeate production). The behavior of the full-scale RO process under thermodynamic restriction is much different from that of the process when it is controlled by mass transfer. The conditions for an RO process to shift from mass transfer-controlled regime to thermodynamically restricted regime are delineated and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.://000181992000008 0376-7388ISI:000181992000008%~?Z(Tufenkji, N. Redman, J. A. Elimelech, M.2003^Interpreting deposition patterns of microbial particles in laboratory-scale column experiments616-623"Environmental Science & Technology373Feb 1The transport and fate of microbial particles in subsurface environments is controlled by their capture (natural filtration) by sediment grains. Typically, filtration models used to describe microbe removal in porous media predict exponential decrease in microbial particle concentration with travel distance. However, a growing body of laboratory-scale column experiments suggests that the retained microbial particle profiles decay nonexponentially. The observed behavior may be attributed to the heterogeneity in the interactions between microbial particles and sediment grains, most likely due to the inherent variability in the microbial particles. This factor can be incorporated into classical colloid filtration (deposition) theory by inclusion of a distribution in the deposition rate coefficient. We show that certain distributions of the deposition rate coefficient (i.e., log-normal, bimodal, and power-law distributions) give rise to nonexponential deposition patterns. Comparisons of model predictions to experimental data indicate that the observed nonexponential deposition behavior of bacteria and virus particles may be attributed to a broad range (i.e., a power-law distribution) of microbial deposition rates. Other mechanisms such as particle release and blocking by previously deposited microbial particles are also shown to be potential sources of deviation from the classical filtration theory. Our results further suggest that monitoring fluid-phase particle concentration is insufficient for accurate characterization of the deposition and transport behavior of microbial particles in saturated porous media. Rather, the shape of the microbial particle retention profile is shown to be a key indicator of the mechanisms controlling microbial deposition and transport.://000180791100040 0013-936XISI:000180791100040~?[Elimelech, M. Wiesner, M. R.2002'Membrane separations in aquatic systems341-341!Environmental Engineering Science196Nov-Dec://000180396300001 1092-8758ISI:000180396300001i~?\'Hoek, E. M. V. Kim, A. S. Elimelech, M.2002Influence of crossflow membrane filter geometry and shear rate on colloidal fouling in reverse osmosis and nanofiltration separations357-372!Environmental Engineering Science196Nov-DecA laboratory-scale crossflow membrane filtration apparatus was designed to investigate the relative influence of filter geometry and shear rate on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes. An expression that allows clarification of the mechanisms of flux decline due to colloidal fouling in RO and NF separations was derived by combining the solution-diffusion model, film-theory, and a modified cake filtration model. With this new fouling model, the interplay between the salt concentration polarization layer and a growing colloid deposit layer may be quantified. The hydraulic pressure drop across a colloid deposit layer was shown to be negligible compared to cake-enhanced osmotic pressure. The difference in flux decline observed in filters with different channel heights resulted from different cake layer thickness, and thus, different cake-enhanced osmotic pressure. A moderate reduction in the initial concentration polarization and cake-enhanced osmotic pressure was obtained by operating at a higher shear rate within a given filter. However, thicker cakes were produced in the filter with greater channel height regardless of crossflow hydrodynamics, which resulted in greater loss of flux. In all modes of operation for either channel height, salt rejection decreased in proportion to the extent of flux decline. By decreasing channel height, both flux and salt rejection were enhanced by reducing all fouling mechanisms-salt concentration polarization, cake layer resistance, and the cake-enhanced osmotic pressure.://000180396300003 1092-8758ISI:000180396300003~?] Le Gouellec, Y. A. Elimelech, M.2002aControl of calcium sulfate (gypsum) scale in nanofiltration of saline agricultural drainage water387-397!Environmental Engineering Science196Nov-DecA methodology for calcium sulfate (gypsum) scale control in nanofiltration of saline waters is presented. The methodology involves the use of both theoretically and experimentally determined parameters. Pitzer's thermodynamic equations for electrolytes are used to determine the gypsum scaling potential of the feed water based on its ionic composition, whereas the extent of concentration polarization at the membrane surface is determined from the film model. A proportionality factor that relates the kinetic difference between the saturation predicted by the gypsum solubility model and the actual crystallization is determined using data from glassware crystallization experiments. The last step involves an experimentally developed parabolic equation relating antiscalant (polyacrylic acid) dose to the normalized concentration factors of the saline solution. These parameters are combined into a single model for predicting the required antiscalant dose to control calcium sulfate scale in nanofiltration membranes for any given saline solution. The model is tested by nanofiltration membrane experiments utilizing model solutions simulating saline agricultural drainage waters.://000180396300005 1092-8758ISI:000180396300005~?^&Tufenkji, N. Ryan, J. N. Elimelech, M.2002The promise of bank filtration 422A-428A"Environmental Science & Technology3621Nov 1://000179002700017 0013-936XISI:000179002700017~?_+Bhattacharjee, S. Ryan, J. N. Elimelech, M.2002UVirus transport in physically and geochemically heterogeneous subsurface porous media161-187 Journal Of Contaminant Hydrology573-4AugA two-dimensional model for virus transport in physically and geochemically heterogeneous subsurface porous media is presented. The model involves solution of the advection-dispersion equation, which additionally considers virus inactivation in the solution, as well as virus removal at the solid matrix surface due to attachment (deposition), release, and inactivation. Two surface inactivation models for the fate of attached inactive viruses and their subsequent role on virus attachment and release were considered. Geochemical heterogeneity, portrayed as patches of positively charged metal oxyhydroxide coatings on collector grain surfaces, and physical heterogeneity, portrayed as spatial variability of hydraulic conductivity, were incorporated in the model. Both layered and randomly (log-normally) distributed physical and geochemical heterogeneities were considered. The upstream weighted multiple cell balance method was employed to numerically solve the governing equations of groundwater flow and virus transport. Model predictions show that the presence of subsurface layered geochemical and physical heterogeneity results in preferential flow paths and thus significantly affect virus mobility. Random distributions of physical and geochemical heterogeneity have also notable influence on the virus transport behavior. While the solution inactivation rate was found to significantly influence the virus transport behavior, surface inactivation under realistic field conditions has probably a negligible influence on the overall virus transport. It was further demonstrated that large virus release rates result in extended periods of virus breakthrough over significant distances downstream from the injection sites. This behavior suggests that simpler models that account for virus adsorption through a retardation factor may yield a misleading assessment of virus transport in "hydrogeologically sensitive" subsurface environments. (C) 2002 Elsevier Science B.V. All rights reserved.://000177016700002 0169-7722ISI:000177016700002~?` Le Gouellec, Y. A. Elimelech, M.2002QCalcium sulfate (gypsum) scaling in nanofiltration of agricultural drainage water279-291Journal Of Membrane Science2051-2Aug 1Reclamation and reuse of agricultural tile drainage water in the San Joaquin Valley, California, by membrane desalination has been given serious consideration for nearly 30 years. The agricultural drainage water has very high levels of calcium and sulfate ions, rendering it nearly saturated with gypsum in some locations in this region. The present paper focuses on the conditions of membrane surface gypsum scale formation during nanofiltration (NF) of agricultural drainage water. Experimental studies with drainage water samples and model solutions were conducted in laboratory glassware as well as with a small plate-and-frarne cross-flow membrane re-circulation unit. NF membrane experiments consisted of two types: permeate disposal to measure the effect of increasing recovery on the onset of scaling, and feed water re-circulation at a fixed concentration factor to establish performance change over time. An expression relating NF product water recovery to feed water concentration factor enabled numerous membrane scale formation studies that have direct relevance to full-scale NF systems. Glassware experiments showed that magnesium ions decreased the amount of gypsum incipient nuclei because of MgSO40 complexation, which reduces the availability of sulfate ions for nucleus formation. In membrane experiments, model solutions showed that bicarbonate, magnesium ions, and humic acid retarded the onset of gypsum scaling by tying up calcium ions that would have otherwise been used for formation of gypsum incipient nuclei. Both calcium carbonate and gypsum scales may result from particulate deposition rather than membrane surface (wall) crystallization, with the likelihood of particulate fouling increasing with supersaturation. (C) 2002 Elsevier Science B.V. All rights reserved.://000176740900026 0376-7388ISI:000176740900026~?aSeidel, A. Elimelech, M.2002Coupling between chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes: implications for fouling control245-255Journal Of Membrane Science2031-2Jun 30A systematic investigation on the role of hydrodynamics (initial permeate flux and crossflow rate) and divalent cations (calcium) in natural organic matter (NOM) fouling of nanofiltration (NF) membranes is reported. Fouling experiments with a thin-film composite NF membrane were conducted in a bench-scale, crossflow unit at various combinations of calcium ion concentration, initial permeate flux, and crossflow velocity. Results showed that membrane fouling and performance are governed by the coupled influence of chemical and hydrodynamic interactions. Permeation drag and calcium binding to NOM are the major cause for the development of a densely compacted fouling layer on the membrane surface, which leads to severe flux decline. An increase in the shear rate (crossflow velocity) mitigates these effects to some extent by reducing the accumulation of NOM on the membrane and arresting the growth of the fouling layer. The hydrodynamic and chemical interactions involved in NOM fouling are also coupled via the influence of initial permeate flux and crossflow rate on the accumulation of the rejected Ca2+ ions near the membrane surface. At higher initial flux or low crossflow rate, the concentration of rejected Ca2+ at the membrane surface increases due to concentration polarization, thus enhancing fouling by Ca-NOM complex and aggregate formation. The pronounced coupled influence of the initial permeate flux and crossflow velocity on the membrane fouling behavior suggests the possibility of fouling control via optimization of these parameters, thus enabling high product water flux at reduced cost. (C) 2002 Elsevier Science B.V. All rights reserved.://000176241800021 0376-7388ISI:000176241800021~?bLRyan, J. N. Harvey, R. W. Metge, D. Elimelech, M. Navigato, T. Pieper, A. P.2002xField and laboratory investigations of inactivation of viruses (PRD1 and MS2) attached to iron oxide-coated qauartz sand 2403-2413"Environmental Science & Technology3611Jun 1Field and laboratory experiments were conducted to investigate inactivation of viruses attached to mineral surfaces. In a natural gradient transport field experiment, bacteriophage PRD1, radiolabeled with (32)p, Was injected into a ferric oxyhydroxide-coated sand aquifer with bromide and linear alkylbenzene sulfonates. In a zone of the aquifer contaminated by secondary sewage infiltration, small fractions of infective and P-32-labeled PRD1 broke through with the bromide tracer, followed by the slow release of 84% of the P-32 activity and only 0.011% of the infective PRDI. In the laboratory experiments, the inactivation of PRDI, labeled with 35S (protein capsid), and MS2, dual radiolabeled with 35S (protein capsid) and 32p (nucleic acid), was monitored in the presence of groundwater and sediment from the contaminated zone of the field site. Release of infective viruses decreased at a much faster rate than release of the radiolabels, indicating that attached viruses were undergoing surface inactivation. Disparities between P-32 and (35) S release suggest that the inactivated viruses were released in a disintegrated state. Comparison of estimated solution and surface inactivation rates indicates solution inactivation is similar to3 times as fast as surface inactivation. The actual rate of surface inactivation may be substantially underestimated owing to slow release of inactivated viruses.://000176275600032 0013-936XISI:000176275600032{~?c'Chen, J. Y. Klemic, J. F. Elimelech, M.2002Micropatterning microscopic charge heterogeneity on flat surfaces for studying the interaction between colloidal particles and heterogeneously charged surfaces393-396 Nano Letters24Apr0An effective technique for micropatterning microscopic chemical heterogeneity onto solid surfaces for studying colloid interaction with heterogeneously charged surfaces is presented. Charge heterogeneity is micropatterned onto glass surfaces by the chemical modification of specified surface regions with aminosilane. The deposition (adsorption) of colloidal particles onto the micropatterned glass surfaces, under well-controlled laminar flow conditions, is observed in real time using a stagnation point flow cell and an optical microscope with a CCD camera.://000175041800029 1530-6984ISI:000175041800029=~?d<Walker, S. L. Bhattacharjee, S. Hoek, E. M. V. Elimelech, M.2002SA novel asymmetric clamping cell for measuring streaming potential of flat surfaces 2193-2198Langmuir186Mar 19'A novel asymmetric clamping cell is used to measure the potential of macroscopic sample surfaces. The unique design of the cell allows in-situ measurement of potentials of any flat surfaces, either solids (such as glass, plastics, metals, and ceramics) or flexible sheets (like polymer films, papers, foils, and membranes), without having to cut or shape the test surfaces to fit the measuring cell dimensions. The cell enables measurement of the streaming potential through several parallel rectangular channels formed by firmly pressing a grooved spacer against the test surface. The term "asymmetric" specifically refers to the unique configuration of the channels, where one of the walls (the test surface) bears a different charging property (or, more specifically, potential), compared to the other three surfaces of the channel (formed by the spacer). A mathematical formulation on the basis of Smoluchowski-Helmholtz approach reveals that the measured potential in such a cell represents the average potential of the test surface and the spacer material. Several surfaces, including clean glass disk, aminosilane modified glass, polymeric membrane, and poly(methyl methacrylate) (PMMA) plate, were tested using the cell. The potentials of the polymeric membrane obtained using the present cell were compared with the corresponding potentials measured using the traditional rectangular cell, and good agreement between the two measurements was observed. The asymmetric cell can be used in conjunction with standard commercially available streaming potential analyzers.://000174403000036 0743-7463ISI:000174403000036)~?e4Bunn, R. A. Magelky, R. D. Ryan, J. N. Elimelech, M.2002hMobilization of natural colloids from an iron oxide-coated sand aquifer: Effect of pH and ionic strength314-322"Environmental Science & Technology363Feb 1Field and laboratory column experiments were performed to assess the effect of elevated pH and reduced ionic strength on the mobilization of natural colloids in a ferric oxyhydroxide-coated aquifer sediment. The field experiments were conducted as natural gradient injections of groundwater amended by sodium hydroxide additions. The laboratory experiments were conducted in columns of undisturbed, oriented sediments and disturbed, disoriented sediments. In the field, the breakthrough of released colloids coincided with the pH pulse breakthrough and lagged the bromide tracer breakthrough. The breakthrough behavior suggested that the progress of the elevated pH front controlled the transport of the mobilized colloids. In the laboratory, about twice as much colloid release occurred in the disturbed sediments as in the undisturbed sediments. The field and laboratory experiments both showed that the total mass of colloid release increased with increasing pH until the concurrent increase in ionic strength limited release. A decrease in ionic strength did not mobilize significant amounts of colloids in the field. The amount of colloids released normalized to the mass of the sediments was similar for the field and the undisturbed laboratory experiments.://000173626900020 0013-936XISI:000173626900020E~?f+Bhattacharjee, S. Chen, J. C. Elimelech, M.2001ZCoupled model of concentration polarization and pore transport in crossflow nanofiltration 2733-2745 Aiche Journal4712Dec6A coupled model of concentration polarization and pore transport of multicomponent salt mixtures in crossflow nanofiltration rigorously predicts local variations of ionic concentrations, flux and individual ion rejections along a rectangular crossflow filtration channel by a coupled solution of the convective-diffusion and extended Nernst-planck equations. Coupling the pore transport model with the multicomponent convective-diffusion equation in the concentration polarization layer provides a comprehensive understanding of the interplay between concentration polarization and salt rejection. The coupled model is used to predict the local variations of ion rejection, permeate flux and mixture composition in a rectangular crossflow filtration channel for three-component salt mixtures. The total membrane surface concentration of the ions and the ratio of different ions in the mixture (salt ratio) can change considerably along a crossflow filtration channel, and, consequently, cause remarkable variations in intrinsic ion rejections with axial position in the channel.://000172759300012 0001-1541ISI:000172759300012d~?gSenGupta, A. K. Elimelech, M.2001Colloids and Interfaces in Environmental Processes American Chemistry Society, 74th Colloid and Surface Science Symposium - Preface1-2?Colloids And Surfaces A-Physicochemical And Engineering Aspects1911-2Oct 31://000171350400001 0927-7757 Sp. Iss. SIISI:000171350400001~?h5Chen, J. Y. Ko, C. H. Bhattacharjee, S. Elimelech, M.2001_Role of spatial distribution of porous medium surface charge heterogeneity in colloid transport3-15?Colloids And Surfaces A-Physicochemical And Engineering Aspects1911-2Oct 31yThe role of spatial distribution of porous medium patchwise chemical (charge) heterogeneity in colloid transport in packed bed columns is investigated. Colloid transport experiments with carboxyl latex particles flowing through columns packed with chemically heterogeneous sand grains were carried out. Patchwise chemical heterogeneity was introduced to the granular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Colloid transport experiments at various degrees of patchwise charge heterogeneity and several spatial distributions of heterogeneity were conducted at different flow rates and background electrolyte concentrations. Colloid deposition rate coefficients were determined from analysis of particle breakthrough curves as a response to short-pulse colloid injections to the column inlet. Experimental colloid deposition rate coefficients compared well with theoretical predictions based on a colloid transport model that incorporates patchwise chemical heterogeneity. The results revealed the particle deposition rate and transport behavior to be independent of the spatial distribution of porous medium chemical heterogeneity. It is the mean value of chemical heterogeneity rather than its distribution that governs the colloid transport behavior in packed columns, (C) 2001 Elsevier Science B.V. All rights reserved.://000171350400002 0927-7757 Sp. Iss. SIISI:000171350400002P~?i(Grolimund, D. Elimelech, M. Borkovec, M.2001YAggregation and deposition kinetics of mobile colloidal particles in natural porous media179-188?Colloids And Surfaces A-Physicochemical And Engineering Aspects1911-2Oct 31A novel method for assessing the deposition kinetics of colloidal particles in natural porous media is presented. The method is applied for studying the deposition kinetics of in situ mobilized colloidal particles in a non-calcareous soil in mixed electrolytes containing sodium and calcium as counter ions. Particle deposition rate constants were measured by combining deposition experiments in packed columns and aggregation measurements by dynamic light scattering. The relative deposition and aggregation rate constants follow very similar trends, featuring fast (favorable) and slow (unfavorable) regimes at high and low salt concentrations, respectively. These regimes are separated by the critical coagulation or deposition concentrations (CCC or CDC, respectively), which sensitively depend on the type of counterion. In systems containing a single electrolyte, the CCC and CDC follow the classical Schulze-Hardy rule. In mixed sodium-calcium electrolytes, a gradual transition of the CCC and CDC between the values obtained for the corresponding pure (single) electrolyte systems is observed. The present approach provides a facile route for assessing deposition rates of mobile colloidal particles in natural porous media. (C) 2001 Elsevier Science B.V. All rights reserved.://000171350400015 0927-7757 Sp. Iss. SIISI:000171350400015~?j(Vrijenhoek, E. M. Hong, S. Elimelech, M.2001}Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes115-128Journal Of Membrane Science1881Jun 30[Recent studies have shown that membrane surface morphology and structure influence permeability, rejection, and colloidal fouling behavior of reverse osmosis (RO) and nanofiltration (NF) membranes. This investigation attempts to identify the most influential membrane properties governing colloidal fouling rate of RO/NF membranes. Four aromatic polyamide thin-film composite membranes were characterized for physical surface morphology, surface chemical properties, surface zeta potential, and specific surface chemical structure, Membrane fouling data obtained in a laboratory-scale crossflow filtration unit were correlated to the measured membrane surface properties, Results show that colloidal fouling of RO and NF membranes is nearly perfectly correlated with membrane surface roughness, regardless of physical and chemical operating conditions. it is further demonstrated that atomic force microscope (AFM) images of fouled membranes yield valuable: insights into the mechanisms governing colloidal fouling, At the initial stages of fouling, AFM images clearly show that more particles are deposited on rough membranes than on smooth membranes. Particles preferentially accumulate in the "valleys" of rough membranes, resulting in "valley clogging" which causes more severe Aux decline than in smooth membranes. (C) 2001 Elsevier Science B.V, All rights reserved.://000168939300012 0376-7388ISI:000168939300012~?k,Sun, N. Elimelech, M. Sun, N. Z. Ryan, J. N.2001nA novel two-dimensional model for colloid transport in physically and geochemically heterogeneous porous media173-199 Journal Of Contaminant Hydrology493-4JunUA two-dimensional model for colloid transport in geochemically and physically heterogeneous porous media is presented. The model considers patchwise geochemical heterogeneity, which is suitable to describe the chemical variability of many surficial aquifers with ferric oxyhydroxide-coated porous matrix, as well as spatial variability of hydraulic conductivity, which results in heterogeneous flow field. The model is comprised of a transient fluid flow equation, a transient colloid transport equation, and an equation for the dynamics of colloid deposition and release. Numerical simulations were carried out with the model to investigate the colloid transport behavior in layered and randomly heterogeneous porous media. Results demonstrate that physical and geochemical heterogeneities markedly affect the colloid transport behavior. Layered physical or geochemical heterogeneity can result in distinct preferential flow paths of colloidal particles. Furthermore, the combined effect of layered physical and geochemical heterogeneity may result in enhanced or reduced preferential flow of colloids. Random distribution of physical heterogeneity (hydraulic conductivity) results in a random flow field and an irregularly distributed colloid concentration profile in the porous medium. Contrary to random physical heterogeneity, the effect of random patchwise geochemical heterogeneity on colloid transport behavior is not significant. It is mostly the mean value of geochemical heterogeneity rather than its distribution that governs the colloid transport behavior. (C) 2001 Elsevier Science B.V. All rights reserved.://000168794900001 0169-7722ISI:000168794900001 ~?l%Seidel, A. Waypa, J. J. Elimelech, M.2001yRole of charge (Donnan) exclusion in removal of arsenic from water by a negatively charged porous nanofiltration membrane105-113!Environmental Engineering Science182Mar-AprThe removal of arsenic from water by a negatively charged "loose" (porous) nanofiltration (NF) membrane was investigated. To better understand the mechanisms of arsenic removal by the polymeric membrane, its surface charge, pore size, and separation behavior for several salt solutions (NaCl, CaCl2, and Na2SO4) were first investigated. The ability of the membrane to remove inorganic arsenic species-As(III) and As(V)-from water was further evaluated. The removal of As(V) increased from 60 to 90% as the arsenic feed water concentration was increased from 10 to 316 mug/L. Compared to As(V), the rejection of the uncharged As(III) species was significantly lower; the rejection of As(III) decreased from 28 to 5% as the arsenic feed concentration was increased from 10 to 316 mug/L In addition, rejection of As(V) decreased sharply from 85% at pH 8.5 to only 8% at pH 4.5. This behavior is mainly attributed to changes in As(V) speciation with pH (HAsO42- at pH >6.8, H2AsO4- at pH <6.8), and to a lesser extent to a decrease in membrane charge with decreasing pH. The separation of the uncharged As(III), on the other hand, was independent of pH over the studied pH range (removal less than 10%). The results were analyzed in light of the membrane properties (charge and pore size) and arsenic speciation and molecular weight, emphasizing the paramount role of charge (Donnan) exclusion in achieving high rejection of As(V) species, despite the relatively large membrane pore size.://000168238800005 1092-8758ISI:000168238800005A~?m,Sun, N. Sun, N. Z. Elimelech, M. Ryan, J. N.2001tSensitivity analysis and parameter identifiability for colloid transport in geochemically heterogeneous porous media209-222Water Resources Research372FebEffective use of colloid transport models for heterogeneous subsurface porous media requires the development of methodologies to identify the key model parameters. The inverse problem of a two-dimensional model for colloid transport in geochemically heterogeneous porous media is systematically investigated in this paper. Sensitivity analysis prior to the parameter identification provided valuable insights into the identifiability of the six model parameters. The hydraulic conductivity and longitudinal dispersivity were identified from tracer breakthrough data and then were used in the remaining parameter identification. The four colloid deposition and release parameters, favorable (fast) colloid deposition rate coefficient, geochemical heterogeneity, unfavorable (slow) colloid deposition rate coefficient, and colloid release rate coefficient from the unfavorable surface fraction, were found to be highly interrelated, and the inverse solution of the four-parameter set was not unique. When either the geochemical heterogeneity or favorable colloid deposition rate coefficient is known, the other three colloid deposition and release parameters can be identified via the inverse solution if the duration of the colloid injection is sufficiently long. The colloid release rate coefficient, however, cannot be identified when using a short (pulse-like) colloid injection. Neglecting the colloid release rate results in estimation errors of the other model parameters and thus adversely affects the subsequent prediction of colloid transport.://000166582800003 0043-1397ISI:000166582800003~?n*Kim, A. S. Bhattacharjee, S. Elimelech, M.2001UShear-induced reorganization of deformable molecular assemblages: Monte Carlo studies552-561Langmuir172Jan 23The influence of hydrodynamic shear on the shape of deformable molecular assemblages is studied using Monte Carlo simulations. Metropolis Monte Carlo simulations are performed to generate spherical assemblages of amphiphilic molecules by considering coarse statistical mechanical models for the various constituent subunits of the amphiphiles and by avoiding explicit consideration of the solvent molecules. The resulting assemblage is subjected to a unidirectional hydrodynamic shear, and the transition of the system to a secondary equilibrium is studied using a modified Monte Carlo simulation technique that accounts for the systematic force on the assemblage due to the hydrodynamic shear. The influence of hydrodynamic shear on the shape of the assemblage is described qualitatively through several simulation snapshots. The quantitative analysis suggests that the aggregate size, intermolecular interactions between various subunits, and shear rate govern the extent of shear-induced deformation. The three parameters can be combined using a single dimensionless group, the Peclet number. Results indicate that the Peclet number can provide considerable insight into the nature and extent of structural deformation of molecular assemblages in the presence of hydrodynamic shear. There exists a critical Peclet number below which hydrodynamic shear has no effect on the aggregate structure. Above the critical Peclet number, the aspect ratio (a measure of deformation) of the assemblage increases almost linearly with logarithm of the Peclet number.://000166519100044 0743-7463ISI:000166519100044;?o1Elimelech, M. LeGouellec, Y. Nagai, M. Glater, J.1999tFouling of nanofiltration membranes due to calcium sulfate precipitation in treatment of agricultural drainage water538-542Environmental Engineering 1999The feasibility of agricultural drainage water reclamation by nanofiltration (NF) has been investigated. Experimental studies with drainage water samples and model solutions saturated with respect to calcium carbonate and gypsum were conducted to determine scale formation and control by antiscalants in glassware experiments and with a plate-and-frame recirculation NF unit. In order to simulate recovery, feedwater concentration was increased by progressively discarding permeate; the validity of this approach was mathematically demonstrated. Mechanisms for scale formation are shown to be different for CaCO3(s) and CaSO4. 2H(2)O(s). Antiscalants were able to prevent gypsum scaling, as well as calcium carbonate scaling, thereby eliminating the need to acidify the water for pretreatment.://000086435900057 ISI:000086435900057~?pIKuhnen, F. Barmettler, K. Bhattacharjee, S. Elimelech, M. Kretzschmar, R.2000aTransport of iron oxide colloids in packed quartz sand media: Monolayer and multilayer deposition32-41(Journal Of Colloid And Interface Science2311Nov 1The transport and deposition dynamics of hematite (alpha -Fe2O3) colloids in packed quartz sand media are investigated. Column transport experiments were carried out at various solution ionic strengths, colloid concentrations, and flow velocities. A colloid transport model was proposed that includes the dynamics of blocking as well as multilayer deposition that takes place at high ionic strengths where particle-particle interactions are favorable. Blocking dynamics in the model are described by either Langmuirian adsorption (LA) or random sequential adsorption (RSA). Two important model parameters-the particle-matrix collision efficiency and the ionic strength dependent blocking (excluded area) parameter-are estimated from the colloid breakthrough curves using a nonlinear optimization procedure. The collision (attachment) efficiency for particle-particle interactions, on the other hand, was determined independently from colloid aggregation rate measurements. At very low ionic strength, only monolayer deposition is observed and the RSA model gives a better description of the experimental data than the LA model. At higher ionic strengths, multilayer deposition becomes significant and both models yield comparable results. Calculated maximum surface coverages at low ionic strengths were in good agreement with experimentally observed values obtained by scanning electron microscopy. (C) 2000 Academic Press.://000165205200005 0021-9797ISI:000165205200005~?q)Ko, C. H. Bhattacharjee, S. Elimelech, M.2000Coupled influence of colloidal and hydrodynamic interactions on the RSA dynamic blocking function for particle deposition onto packed spherical collectors554-567(Journal Of Colloid And Interface Science2292Sep 15oThe influence of electrostatic double-layer and hydrodynamic interactions on random sequential adsorption (RSA) of colloidal particles onto packed spherical collectors was investigated using inverse analysis of colloid breakthrough data obtained from well-controlled particle deposition experiments. Deposition experiments were carried out using monodisperse aqueous suspensions of positively charged latex colloids and packed columns of negatively charged uniform glass: beads for different combinations of ionic strength, particle size, and approach velocity. From the experimental particle breakthrough data, the initial particle deposition rates and the virial coefficients of the dynamic blocking function based on RSA mechanics were determined. The magnitudes of the virial coefficients were observed to increase from the hard sphere values with increasing flow rates and decreasing ionic strengths of the background electrolyte. Particle size also plays a significant role in governing the deposition dynamics. The deviation from the hard sphere RSA behavior becomes more prominent for larger particles. (C) 2000 Academic Press.://000089390500027 0021-9797ISI:000089390500027~?rKo, C. H. Elimelech, M.2000vThe "shadow effect" in colloid transport and deposition dynamics in granular porous media: Measurements and mechanisms 3681-3689"Environmental Science & Technology3417Sep 1uThe role of hydrodynamic and colloidal interactions in the transport and deposition dynamics of colloidal particles in granular porous media is systematically investigated. Colloid transport experiments were conducted with three suspensions of positively charged colloidal latex particles (133, 288, and 899 nm in diameter) and negatively charged packed quartz grains. The column experiments were carried out under a wide range of solution ionic strengths (10(-5.5)-10(-2.0) M) and approach velocities (10(-4.5)-10(-2.5) mis) until a complete breakthrough was attained, thus allowing unambiguous determination of the maximum attainable surface coverage for each deposition run. Results show that the rate of blocking and the maximum attainable surface coverage are determined by a unique interplay between flow intensity, particle size, and solution ionic strength. It is suggested that the tangential or shear component of the fluid flow around collector grains creates a "shadow zone" on the collector surface down gradient of deposited particles where the probability of subsequent deposition is substantially reduced. The shadow zone is determined by the combined effect of hydrodynamic interaction and electrostatic double layer repulsion. Increasing the approach velocity and particle size and decreasing the solution ionic strength result in a larger area of the shadow zone and hence reduced maximum attainable surface coverages. It is also proposed that sand grain surface roughness influences the dynamics of particle deposition by creating shadow zones down gradient of surface protrusions where particle deposition is significantly hindered.://000089059700034 0013-936XISI:000089059700034~?sChildress, A. E. Elimelech, M.2000`Relating nanofiltration membrane performance to membrane charge (electrokinetic) characteristics 3710-3716"Environmental Science & Technology3417Sep 1The performance (i.e., water flux and solute rejection) of a thin-film composite aromatic polyamide nanofiltration membrane and its relation to membrane surface charge (electrokinetic) characteristics were investigated. Membrane performance and streaming potential measurements were carried out as a function of pH for several solution chemistries, including an indifferent electrolyte, humic acid, and anionic and cationic surfactants. Performance results for the membrane were interpreted by relating the water flux and salt/ion rejection to the membrane charge characteristics. In the case of the indifferent electrolyte (NaCl), water flux and salt passage were maximal at the membrane pore isoelectric point (pH 5) primarily due to decreased electrostatic repulsion and increased pore volume (size) in the cross-linked polymer network, ion rejection is directly related to the membrane pore charge and is attributed to cc-ion electrostatic repulsion (exclusion). At low pH, negative rejection of protons was observed, demonstrating the classical behavior of a more mobile co-ion in a mixture of electrolytes (NaCl and HCl). Suwannee River humic acid was found to have very little effect on the shortterm performance of the membrane, despite its significant influence on membrane zeta-potential. Sodium dodecyl sulfate, on the other hand, had significant effects on the water flux and salt rejection. Association of the surfactant molecules (i.e., hemimicelle formation) at the membrane-solution interface was analyzed in terms of membrane charge characteristics. It is proposed that the adsorbed surfactant molecules in the form of hemimicelles or a bilayer provide an additional filtration layer that results in reduced water flux and increased salt rejection.://000089059700038 0013-936XISI:000089059700038~?t-Elimelech, M. Nagai, M. Ko, C. H. Ryan, J. N.2000xRelative insignificance of mineral grain zeta potential to colloid transport in geochemically heterogeneous porous media 2143-2148"Environmental Science & Technology3411Jun 1The role of zeta-(zeta)potential of mineral grains in the initial deposition kinetics of colloidal particles in geochemically heterogeneous porous media is investigated. Colloid deposition experiments with colloidal silica particles flowing through columns packed with chemically heterogeneous sand were carried out. Patchwise chemical heterogeneity was introduced to the granular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Experimental initial colloid deposition rates and resulting collision efficiencies were compared to theoretical predictions based on the measured average zeta-potential of the chemically heterogeneous sand. It is shown that colloid deposition kinetics are controlled by the degree of patchwise chemical heterogeneity and that use of the measured zeta-potential of the granular porous medium in theoretical predictions leads to erroneous results.://000087394400024 0013-936XISI:000087394400024~?u8Ryan, J. N. Elimelech, M. Baeseman, J. L. Magelky, R. D.2000VSilica-coated titania and zirconia colloids for subsurface transport field experiments 2000-2005"Environmental Science & Technology3410May 15]Silica-coated titania (TiO2) and zirconia (ZrO2) colloids were synthesized in two sizes to provide easily traced mineral colloids for subsurface transport experiments. Electrophoretic mobility measurements showed that coating with silica imparted surface properties similar to pure silica to the titania and zirconia colloids. Measurements of steady electrophoretic mobility and size (by dynamic light scattering) over a 90-day period showed that the silica-coated colloids were stable to aggregation and loss of coating. A natural gradient field experiment conducted in an iron oxide-coated sand and gravel aquifer also showed that the surface properties of the silica-coated colloids were similar. Colloid transport was traced at mu g L-1 concentrations by inductively coupled plasma-atomic emission spectroscopy measurement of Ti and Zr in acidified samples.://000087071900019 0013-936XISI:000087071900019 ~?v+Bhattacharjee, S. Chen, J. Y. Elimelech, M.2000GDLVO interaction energy between spheroidal particles and a fiat surface143-156?Colloids And Surfaces A-Physicochemical And Engineering Aspects1651-3May 30The orientation dependent interaction energy between a spheroidal particle and an infinite planar surface is determined using the surface element integration (SEI) technique. The interaction energy predictions of SEI are shown to be considerably more accurate than the corresponding predictions based on Derjaguin's approximation (DA). Comparison with the Hamaker approach for evaluating the non-retarded van der Waals interaction energy reveals that SEI predicts the orientation dependent interaction energy fbr spheroidal particles with remarkable accuracy. It is further shown that both SEI and DA give nearly identical predictions of the electrostatic double layer interaction energy between a spheroidal particle and a flat plate at high electrolyte concentrations. However, at low electrolyte concentrations, considerable deviations are noted between the predictions of SEI and DA, particularly for very small aspect ratios of the particle (aspect ratio = length of minor axis/length of major axis). It is also noted that when the spheroidal particle is oriented with its major axis parallel to the planar surface, DA incorrectly predicts the interaction energy as that of a spherical particle with a radius equal to the semi-major axis of the spheroid. This limitation of DA is avoided in SEI, which accounts for the dependence of the interaction energy on the actual shape (aspect ratio) of the particle at any orientation. Predictions of the DLVO interaction energy based on SEI indicate that, at high electrolyte concentrations, the orientation dependence of the interaction energy is not significant at large separation distances, and assumption of an equivalent spherical particle may be sufficient. However, significant deviation of the interaction energy from that of a spherical particle is observed at small separation distances, particularly at low electrolyte concentrations. At these small separation distances, where the correct orientation dependence of the interaction energy must be considered for proper calculations of particle interaction phenomena with flat surfaces (e.g. particle deposition), SEI provides a facile route to perform such calculations. (C) 2000 Elsevier Science B.V. All rights reserved.://000085501200011 0927-7757ISI:000085501200011~?wMChildress, A. E. Vrijenhoek, E. M. Elimelech, M. Tanaka, T. S. Beuhler, M. D.1999:Particulate and THM precursor removal with ferric chloride 1054-1061)Journal Of Environmental Engineering-Asce12511NoviPilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California State Project water and Colorado River water. The removal of suspended particles and natural organic matter at various ferric chloride doses and coagulation pHs was assessed through source water and filter effluent measurements of turbidity, particle count, UV254, TOC, and THM formation potential. Overall, it was found that optimal removal of particles and THM precursors by enhanced coagulation with ferric chloride is obtained at high coagulant doses (>16 mg/L) and low pH conditions. Generally, turbidity removal is more efficient and head loss is more moderate at ambient pH compared with pH 5.5. Additionally, filter effluent particle counts were found to be consistent with residual turbidity data. The removal of THM precursors by enhanced coagulation is significantly enhanced at pH 5.5 compared with ambient pH. The reduction in THM formation potential is consistent with the trends observed for the THM precursor removal data (i.e., UV254 and TOC data). Furthermore, specific UV absorbance was used to estimate the proportion of humic substances in the raw waters. Enhanced coagulation was found to be less effective for the source water with the lower specific UV absorbance.://000083216000010 0733-9372ISI:000083216000010?x8Kretzschmar, R. Borkovec, M. Grolimund, D. Elimelech, M.1999BMobile subsurface colloids and their role in contaminant transport121-193Advances In Agronomy, Vol 6666://000080328600003 Advances In AgronomyISI:000080328600003~?y*Bhattacharjee, S. Kim, A. S. Elimelech, M.1999\Concentration polarization of interacting solute particles in cross-flow membrane filtration81-99(Journal Of Colloid And Interface Science2121Apr 1A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted.(C) 1999 Academic Press.://000079227200010 0021-9797ISI:000079227200010X~?zARyan, J. N. Elimelech, M. Ard, R. A. Harvey, R. W. Johnson, P. R.1999aBacteriophage PRD1 and silica colloid transport and recovery in an iron oxide-coated sand aquifer63-73"Environmental Science & Technology331Jan 1Bacteriophage PRD1 and silica colloids were co-injected into sewage-contaminated and uncontaminated zones of an iron oxide-coated sand aquifer on Cape God, MA, and their transport was monitored over distances up to 6 m in three arrays. After deposition, the attached PRD1 and silica colloids were mobilized by three different chemical perturbations (elevated pH, anionic surfactant, and reductant). PRD1 and silica colloids experienced less attenuation in the contaminated zone where adsorbed organic: matter and phosphate may be hindering attachment of PRD1 and silica colloids to the iron oxide coatings. The PRD1 collision efficiencies agree well with collision efficiencies predicted by assuming favorable PRD1 deposition on iron oxide coatings for which the surface area coverage was measured by microprobe analysis of sediment thin sections. zeta potentials of the PRD1, silica colloids, and aquifer grains corroborated the transport results, indicating that electrostatic forces dominated the attachment of PRD1 and silica colloids. Elevated pH was the chemical perturbation most effective at mobilizing the attached PRD1 and silica colloids. Elevated surfactant concentration mobilized the attached PRD1 and silica colloids more effectively in the contaminated zone than in the uncontaminated zone.://000077954100028 0013-936XISI:000077954100028~?{,Bhattacharjee, S. Elimelech, M. Borkovec, M.1998NDLVO interaction between colloidal particles: Beyond Derjaguin's approximation883-903Croatica Chemica Acta714DecVan der Waals and electrostatic double layer interactions between two colloidal particles are evaluated from the corresponding interaction energies per unit area between two infinite flat plates using a recently developed technique, the surface element integration. Application of the technique to two interacting spheres results in predictions of interaction energies that are substantially more accurate compared to the predictions based on conventional Derjaguin's approximation. The superior results of the technique compared to Derjaguin's approximation are attributed to the more rigorous consideration of particle curvature effects in the surface element integration technique.://000077749400019 0011-1643ISI:000077749400019 O~?|SGrolimund, D. Elimelech, M. Borkovec, M. Barmettler, K. Kretzschmar, R. Sticher, H.1998ITransport of in situ mobilized colloidal particles in packed soil columns 3562-3569"Environmental Science & Technology3222Nov 15A systematic investigation of the transport behavior of in situ mobilized soil colloidal particles in their parent soil matrix medium is presented. Particle advection, dispersion, and deposition kinetics were studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of packed soil columns. The transport of the heterogeneous soil particles was compared to the transport of monodisperse carboxyl latex particles to further understand the various particle transport mechanisms. Results show that colloidal particles travel much faster than a conservative tracer (nitrate) due to size exclusion effects, whereby mobile colloidal particles are excluded from small pores within the soil medium. Dispersivity of the natural and latex particles was compared to that of the conservative tracer, and the results indicate that particle dispersivity is greater than the tracer dispersivity. Dispersivity of colloidal particles was shown to he essentially independent of pore water velocity, whereas tracer dispersivity increased with increasing pore water velocity due to a combination of convective and diffusive transport of tracer molecules in small pores within the soil aggregates. The effect of divalent counterions on particle deposition kinetics was also investigated by comparing the results to deposition kinetics with monovalent counterions. Particle deposition rate with Ca2+ was shown to be higher than with Na+, and the critical deposition concentrations with Na+ were greater than those with Ca2+. In contrast to the marked effect of ionic strength and divalent cations, changes in proton activity over more than 1 order of magnitude (from pH 4.0 to 5.5) did not have a significant effect on particle deposition kinetics. Quantitative analysis of the observed particle transport results demonstrates that the transport of the natural colloidal particles in the packed soil columns can be adequately described by the advection-dispersion equation with a first-order, irreversible deposition kinetics term.://000076986800017 0013-936XISI:000076986800017&~?}&Faibish, R. S. Elimelech, M. Cohen, Y.1998Effect of interparticle electrostatic double layer interactions on permeate flux decline in crossflow membrane filtration of colloidal suspensions: An experimental investigation77-86(Journal Of Colloid And Interface Science2041Aug 1A systematic study on the effect of electrostatic double layer interaction on permeate flux decline and deposit cake formation in crossflow membrane filtration of colloidal suspensions is reported. Three monodisperse silica suspensions with diameters of 47, 110, and 310 nm were used as model colloids, and a tabular zirconia membrane with an average pore diameter of 20 nm was used as a model membrane. The magnitude and range of the electrostatic double layer interactions were controlled via changes in solution ionic strength and pH. The coupling between colloidal interactions and hydrodynamic forces was investigated by changing the transmembrane pressure and particle size. The results indicate that the rate of flux decline is strongly dependent on solution ionic strength and, to a much lesser degree, on solution pH (for the investigated pH range 6.1-10.0). Variations in flux decline rate with solution ionic strength are especially significant as the particle size decreases. Particle cake thickness, permeability, and porosity generally increased with a decrease in solution ionic strength for a given particle size. For given physical and chemical conditions, the cake layer porosity increased with decreasing particle size, while cake permeability decreased with decreasing particle size. These trends are consistent with the increased importance of double layer repulsive forces in controlling the cake layer structure as the solution ionic strength and particle size decrease. Pressure relaxation experiments indicated that the particle cake layer is reversible, implying no irreversible deposition (attachment) of silica colloids onto the zirconia membrane surface. (C) 1998 Academic Press.://000075262900010 0021-9797ISI:000075262900010~?~Elimelech, M. Bhattacharjee, S.1998A novel approach for modeling concentration polarization in crossflow membrane filtration based on the equivalence of osmotic pressure model and filtration theory223-241Journal Of Membrane Science1452Jul 8/A theoretical model for prediction of permeate flux during crossflow membrane filtration of rigid hard spherical solute particles is developed. The model utilizes the equivalence of the hydrodynamic and thermodynamic principles governing the equilibrium in a concentration polarization layer. A combination of the two approaches yields an analytical expression for the permeate flux. The model predicts the local variation of permeate flux in a filtration channel, as well as provides a simple expression for the channel-averaged flux. A criterion for the formation of a filter cake is presented and is used to predict the downstream position in the filtration channel where cake layer build-up initiates. The predictions of permeate flux using the model compare remarkably well with a detailed numerical solution of the convective diffusion equation coupled with the osmotic pressure model. Based on the model, a novel graphical technique for prediction of the local permeate flux in a crossflow filtration channel has also been presented. (C) 1998 Elsevier Science B.V.://000074514100007 0376-7388ISI:000074514100007+~?Clark, M. M. Allgeier, S. Amy, G. Chellam, S. DiGiano, F. Elimelech, M. Freeman, S. Jacangelo, J. Jones, K. Laine, J. M. Lozier, J. Marinas, B. Riley, R. Taylor, J. Thompson, M. Vickers, J. Wiesner, M. Zander, A.1998$Committee report: Membrane processes91-105(Journal American Water Works Association906JunThis review focuses on membrane technology research needs in the context of drinking water treatment. It considers practical issues like membrane piloting, scale-up, residuals discharge, and costs, as well as more fundamental issues Like membrane polymers, surface characterization, biofouling, and modeling of the transport of dissolved and particulate species in membrane systems. It is concluded that because the period since this committee's last report has been a fertile one for research, many new questions have arisen on both applied and fundamental issues in the development, use, and understanding of membrane processes in drinking water treatment.://000074328000018 0003-150XISI:000074328000018~?)Bhattacharjee, S. Ko, C. H. Elimelech, M.1998'DLVO interaction between rough surfaces 3365-3375Langmuir1412Jun 9CThe interaction energy between microscopic bodies is almost exclusively determined assuming perfectly smooth and geometrically regular surfaces. Quite often, such interactions fail to explain several colloidal phenomena. These inexplicable behaviors of colloidal systems are generally ascribed to surface chemical and morphological heterogeneities. Here, we employ the surface element integration technique to determine the interaction energy between surfaces containing morphological heterogeneity. Random asperities are generated to represent surface morphological heterogeneity (roughness), and their influence on the DLVO interaction potential is investigated. Incorporation of surface roughness causes a significant reduction in the repulsive interaction energy, the extent of which depends on the size of the asperities and their densities on the surface. Predictions of interaction energy indicate that the DLVO interaction energy profiles for rough surfaces deviate significantly from those derived assuming perfectly smooth surfaces, particularly at very short separation distances.://000074190400034 0743-7463ISI:000074190400034~?MVrijenhoek, E. M. Childress, A. E. Elimelech, M. Tanaka, T. S. Beuhler, M. D.1998=Removing particles and THM precursors by enhanced coagulation139-150(Journal American Water Works Association904AprThe effectiveness of enhanced coagulation for removing particles nad trihalomethane (THM) precursors at various alum dosages and coagulation pH values was assessed. Samples of both source water and filter effluent were examined by counting particles and measuring particle size distribution, turbidity, total organic carbon, ultraviolet light absorbance at 254 nm (UV254), and THM formation potential. Removal of particles and turbidity increased substantially at alum dosages above 20 mg/L. Particle removal was not significantly different at adjusted pH (5.5) compared with ambient pH. Filter effluent particle counts were consistent with residual turbidity data; however, particle counting provided more information on the efficiency of the solid liquid separation. Significantly more THM precursors were removed by enhanced coagulation at pH 5.5 than at ambient pH. Higher dosages were needed to achieve acceptable removal of THM precursors than were needed for removal of particles.://000073134300021 0003-150XISI:000073134300021 ~?.Mazzolani, G. Stolzenbach, K. D. Elimelech, M.1998PGravity-induced coagulation of spherical particles of different size and density334-347(Journal Of Colloid And Interface Science1972Jan 15We consider a dilute homogeneous suspension of rigid spherical particles with different size and density in a motionless Newtonian fluid, These particles are moving under gravity at low Reynolds and Stokes numbers(negligible fluid and particle inertia) and high Peclet numbers (negligible Brownian diffusion), Doublets are formed when two particles in relative motion are brought into contact by the action of the attractive van der Waals force. Trajectory calculations for particles with different densities indicate that as the reduced density ratio increases above unity, the percentage of particles captured on the front hemisphere decreases, and this generally results in smaller collision efficiencies. Furthermore, in contrast to the case of particles with equal density, a maximum of the collision efficiency occurs for a particle size ratio smaller than unity. Above a critical value of the reduced density ratio, the occurrence of a closed region of relative trajectories confines the capture sites mostly to the "rear" hemisphere of each particle. As the reduced density ratio increases above the critical value, this region grows larger and the collision efficiency may be estimated by a closed-form asymptotic solution. (C) 1998 Academic Press.://000072157500018 0021-9797ISI:000072157500018~?%Hong, S. Faibish, R. S. Elimelech, M.1997[Kinetics of permeate flux decline in crossflow membrane filtration of colloidal suspensions267-277(Journal Of Colloid And Interface Science1962Dec 15A series of well-controlled membrane filtration experiments are performed to systematically investigate the dynamic behavior of permeate flux in crossflow membrane filtration of colloidal suspensions. Results are analyzed by a transient permeate flux model which includes an approximate closed-form analytical expression for the change of permeate flux with time. The model is based on a simplified particle mass balance for the early stages of crossflow filtration before a steady-state flux is attained, and Happel's cell model for the hydraulic resistance of the formed particle cake layer. The filtration experiments demonstrate that permeate flux declines faster with increasing feed particle concentration and transmembrane pressure and with a decrease in the particle size of the suspension. It is also shown that crossflow velocity (shear rate) has no effect on permeate flux at the transient stages of crossflow filtration. Pressure relaxation experiments indicate that the particle cake layer is reversible, implying no irreversible deposition (attachment) of particles onto the membrane surface or the accumulated (retained) particles. The experimental results are shown to be in very good agreement with the theoretical predictions, thus verifying the validity of the model for the transient permeate flux in crossflow filtration and the underlying assumptions in the derivation of the model. (C) 1997 Academic Press.://000071939400016 0021-9797ISI:000071939400016F~?Zhu, X. H. Elimelech, M.1997SColloidal fouling of reverse osmosis membranes: Measurements and fouling mechanisms 3654-3662"Environmental Science & Technology3112Dec<The effect of chemical and physical interactions on the fouling rate of cellulose acetate and aromatic polyamide composite reverse osmosis (RO) membranes by silica colloids is investigated. Results of fouling experiments using a laboratory-scale unit demonstrate that colloidal fouling rate increases with increasing solution ionic strength, feed colloid concentration, and permeate water flux through the membrane. It is demonstrated that the rate of colloidal fouling is controlled by a unique interplay between permeation drag and electric double layer repulsion; that is, colloidal fouling of RD membranes involves interrelationship (coupling) between physical and chemical interactions. For solution chemistries typical of natural source waters, permeation drag under normal operating conditions plays a more significant role than chemical interactions and may ultimately control the rate and extent of colloidal fouling. In addition to permeation drag, it is shown that membrane surface morphology has a marked effect an colloidal fouling. The higher fouling propensity of composite polyamide RO membranes compared to cellulose acetate RO membranes is attributed to the pronounced surface roughness of the composite membranes. Implications of the results for developing means to reduce colloidal fouling of RO membranes are discussed.://A1997YJ88200068 0013-936XISI:A1997YJ88200068-~?Bhattacharjee, S. Elimelech, M.1997uSurface element integration: A novel technique for evaluation of DLVO interaction between a particle and a flat plate273-285(Journal Of Colloid And Interface Science1932Sep 15A novel method, the surface element integration (SEI), is developed to determine the van der Waals and electrostatic double layer interactions between a particle and an infinite flat plate from the corresponding interactions per unit area between two infinite flat plates. Comparison with the Hamaker expression for nonretarded van der Waals interaction reveals that the new technique gives the exact interaction energy between a spherical particle and a flat plate. Available analytical expressions for the electrostatic double layer interaction energy between two infinite flat plates, based on the linearized Poisson-Boltzmann equation, are used in SEI to obtain the sphere-flat plate interaction energy. These sphere-hat plate interaction energies determined using SEI are compared with the corresponding interaction energies obtained from a detailed numerical solution of the Poisson-Boltzmann equation based on finite element analysis. The comparisons reveal that SEI scales the flat plate interaction to the corresponding sphere-flat plate geometry exactly, while the scaling based on the conventional Derjaguin approximation technique grossly overpredicts the interaction energy for small particles and low electrolyte concentrations. (C) 1997 Academic Press.://A1997YE45700016 0021-9797ISI:A1997YE45700016$~?(Waypa, J. J. Elimelech, M. Hering, J. G.1997&Arsenic removal by RO and NF membranes102-114(Journal American Water Works Association8910Oct3Bench-scale experiments were performed to assess the effectiveness of reverse osmosis (RO) and nanofiltration (NF) membranes in removing arsenic (As) from synthetic freshwater and source water. The authors examined the effects of operational conditions (applied pressure and feedwater temperature) and solution chemical composition (As oxidation state, pH, and presence of co-occurring inorganic solutes). Both As(V) and As(III) were effectively removed from synthetic freshwater by RO and tight NF membranes over a wide range of operational conditions. The relatively large molecular weight (>125 g/mol) of the As species governed their separation behavior. Applied pressure had little effect on As removal, but an increase in feedwater temperature decreased As removal by a small percentage. Removals of As(III) and As(V) were comparable, with no significant preferential rejection of As(V) over As(III). Variations in solution pH from 4 to 8 also did not affect the removal of As species by the membranes tested, despite changes in the speciation and charge of As (V). Co-occurring inorganic solutes had only a slight effect on As removal. Removal of As from source water was comparable to that obtained with synthetic freshwater, despite the presence of turbidity, natural organic matter, and a variety of co-occurring solutes.://A1997YC65600017 0003-150XISI:A1997YC65600017_~?Hong, S. K. Elimelech, M.1997aChemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes159-181Journal Of Membrane Science1322Sep 3MThe role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated, Results of fouling experiments with three humic acids demonstrate that membrane fouling increases with increasing electrolyte (NaCl) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed fouling layer. In addition to the aforementioned chemical effects, results show that NOM fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion; that is, NOM fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the fouling layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.://A1997XV09500002 0376-7388ISI:A1997XV09500002q~?5Hering, J. G. Chen, P. Y. Wilkie, J. A. Elimelech, M.19976Arsenic removal from drinking water during coagulation800-807)Journal Of Environmental Engineering-Asce1238AugbThe efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water composition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) removal by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restricted than with ferric chloride. For source waters spiked with 20 mu g/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 mu g/L were achieved with both coagulants at neutral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water composition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affected the efficiency of arsenic(III) removal by ferric chloride. Arsenic(III) could not be removed from source waters by coagulation with alum.://A1997XM74400012 0733-9372ISI:A1997XM74400012z?Waypa, J. J. Elimelech, M.1996NRemoving arsenic from water using reverse osmosis and nanofiltration membranes368-373/Water Supply Puzzle: How Does Desalting Fit In?Bench-scale experiments were performed to assess the effectiveness of reverse osmosis and nano-filtration membranes in removing arsenic from synthetic freshwaters and source waters. The effects of operational conditions and solution chemical composition were examined. The removal of As(V) and As(III) were comparable, with no significant preferential rejection of As(V) over As(III). Applied pressure had little effect on arsenic removal but an increase in feedwater temperature resulted in a decrease in arsenic removal by a few percent. Variations in solution pH from 4 to 8 also did not affect the removal of arsenic by the membranes rested, despite changes in the speciation and charge of As(V). The removal of arsenic from source waters was comparable to that obtained with synthetic freshwaters, despite the presence of turbidity, natural organic matter, and a variety of co-occurring solutes.://A1996BH65S00024 ISI:A1996BH65S00024?.Childress, A. E. Deshmukh, S. S. Elimelech, M.1996KZeta potential measurements of reverse osmosis and nanofiltration membranes700-716/Water Supply Puzzle: How Does Desalting Fit In?A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric point of these membranes ranged from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes displayed a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl2 and Na2SO4) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions:, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, Feat humic acid, and Aldrich humic acid, were used to investigate the effect of solution chemistries involved in this investigation included an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.://A1996BH65S00045 ISI:A1996BH65S00045?Hong, S. K. Elimelech, M.1996=Fouling of nanofiltration membranes by natural organic matter717-727/Water Supply Puzzle: How Does Desalting Fit In?*In this study, various physical and chemical factor affecting natural organic matter (NOM) fouling of nanofiltration (NF) membranes were systematically investigated, with an emphasis on the effect of divalent cations (Ca2+). Zeta potential measurements show reduced membrane surface charge in the presence of divalent cations. Results from fouling experiments clearly demonstrate that divalent cations markedly increase the potential for NOM fouling. Increased NOM fouling is attributed to complexation between Ca2+ and NOM which causes a decrease in electrostatic repulsion. Permeation rate also plays a critical role in NOM fouling. Product water flux declines much faster as permeation rate increases. The addition of strong chelating agents (EDTA) to feed water improves membrane performance significantly.://A1996BH65S00046 ISI:A1996BH65S000463~?5Elimelech, M. Zhu, X. H. Childress, A. E. Hong, S. K.1997Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes101-109Journal Of Membrane Science1271Apr 30Laboratory-scale colloidal fouling tests, comparing the fouling behavior of cellulose acetate and aromatic polyamide thin-film composite reverse osmosis (RO) membranes, are reported. Fouling of both membranes was studied at identical initial permeation rates so that the effect of the transverse hydrodynamic force (permeation drag) on the fouling of both membranes is comparable. Results showed a significantly higher fouling rate for the thin-film composite membranes compared to that for the cellulose acetate membranes. Addition of an anionic surfactant (sodium dodecyl sulfate, SDS) to mask variations in chemical and electrokinetic surface characteristics of the cellulose acetate and aromatic polyamide membranes resulted in only a small change in the fouling behavior. The higher fouling late for the thin film composite membranes is attributed to surface roughness which is inherent in interfacially polymerized aromatic polyamide composite membranes. AFM and SEM images of the two membrane surfaces strongly support this conclusion. These surface images reveal that the thin-film composite membrane exhibits large-scale surface roughness of ridge-and-valley structure, while the cellulose acetate membrane surface is relatively smooth.://A1997XC62000011 0376-7388ISI:A1997XC62000011L~?$Johnson, P. R. Sun, N. Elimelech, M.1996XColloid transport in geochemically heterogeneous porous media: Modeling and measurements 3284-3293"Environmental Science & Technology3011Nov1The transport of colloids in geochemically heterogeneous porous media is investigated. A model describing the transport and deposition of colloids onto heterogeneously charged mineral grains is developed and applied to column experiments. The model characterizes mineral grain surfaces according to a patchwise charge distribution, with individual patches being either favorable or unfavorable for deposition depending on their electrostatic charge. Separate rate expressions are used in the model to depict favorable and unfavorable deposition kinetics. Declining deposition kinetics that ape produced when previously retained particles block subsequent attachment of colloids are quantified in the model by dynamic blocking functions, Column experiments involving colloid transport in geochemically heterogeneous porous media were performed using silica colloids and quartz sand. Surface charge heterogeneity was introduced into the porous medium by coating a fraction of the quartz sand with iron oxyhydroxide. Theoretical breakthrough curves generated by the model using experimentally determined parameters compared quite well to the experimental results, demonstrating the importance of geochemically heterogeneous surfaces in determining the transport behavior of colloidal particles in heterogeneous aquatic environments.://A1996VR63100045 0013-936XISI:A1996VR63100045>~?Childress, A. E. Elimelech, M.1996lEffect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes253-268Journal Of Membrane Science1192Oct 16A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl2, Na2SO4, and MgSO4) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.://A1996VJ76200008 0376-7388ISI:A1996VJ76200008~??Hering, J. G. Chen, P. Y. Wilkie, J. A. Elimelech, M. Liang, S.1996"Arsenic removal by ferric chloride155-167(Journal American Water Works Association884AprBench-scale studies were conducted in model freshwater systems to investigate how various parameters affected arsenic removal during coagulation with ferric chloride and arsenic adsorption onto preformed hydrous ferric oxide. Parameters included arsenic oxidation state and initial concentration, coagulant dosage or adsorbent concentration, pH, and the presence of co-occurring inorganic solutes. Comparison of coagulation and adsorption experiments and of experimental results with predictions based on surface complexation modeling demonstrated that adsorption is an important (though not the sole) mechanism governing arsenic removal during coagulation. Under comparable conditions, better removal was observed with arsenic(V) [As(V)] than with arsenic(III) [As(III)] in both coagulation and adsorption experiments. Below neutral pH values, As(III) removal-adsorption was significantly decreased in the presence of sulfate, whereas only a slight decrease in As(V) removal-adsorption was observed. At high pH, removal-adsorption of As(V) was increased in the presence of calcium. Removal of As(V) during coagulation with ferric chloride is both more efficient and less sensitive than that of As(III) to variations in source water composition.://A1996UF42400015 0003-150XISI:A1996UF42400015s~?Elimelech, M. Hering, J. G.1996A Collection of Papers Presented at the Symposium on Colloidal and Interfacial Phenomena in Aquatic Environments, held in Anaheim, CA, USA, 4-6 April 1995 - PrefaceR7-R7?Colloids And Surfaces A-Physicochemical And Engineering Aspects107Feb 20://A1996TW02100001 0927-7757ISI:A1996TW02100001~?Ryan, J. N. Elimelech, M.19961Colloid mobilization and transport in groundwater1-56?Colloids And Surfaces A-Physicochemical And Engineering Aspects107Feb 20Recent held and laboratory experiments have identified colloid-facilitated transport of contaminants as an important mechanism of contaminant migration through groundwater. For colloid-facilitated transport to be important, three criteria must be met: (1) colloids must be generated; (2) contaminants must associate with the colloids; and (3) colloids must be transported through the groundwater. Significant progress in the understanding of colloid generation (by mobilization of existing colloids) and transport (limited by deposition) in model colloid and collector systems has been made in the past few decades. This knowledge of the model systems, however, is inadequate for prediction of colloid behavior in natural groundwater systems. An understanding of colloid behavior in natural systems is essential for predicting the potential for colloid-facilitated transport in a given groundwater. This review presents theories describing colloid mobilization, deposition, and transport, laboratory experiments in model systems designed to test these theories, and applications of these theories to colloid mobilization and transport experiments in natural groundwater systems. Emphasis is placed on mobilization of existing colloids by chemical and physical perturbations, the kinetics and dynamics of colloid deposition (filtration) and the ''blocking'' effect, and the effect of surface chemical heterogeneities on colloid deposition and transport.://A1996TW02100002 0927-7757ISI:A1996TW02100002[~?'Liu, D. L. Johnson, P. R. Elimelech, M.1995\Colloid Deposition Dynamics In Flow-Through Porous-Media - Role Of Electrolyte Concentration 2963-2973"Environmental Science & Technology2912Dec9The role of solution ionic strength and counterion valence in controlling the dynamic (transient) behavior of colloid deposition in granular porous media has been investigated. Packed-bed column experiments were conducted using two different suspensions of positively charged colloidal latex particles and negatively charged glass bead collectors. Variations in the concentration of an indifferent, 1:1 electrolyte solution are used to demonstrate an inverse logarithmic relationship between the average area of collector surface excluded (''blocked'') by deposited colloidal particles and solution ionic strength. Both electrolyte concentration and type influence the dynamics of particle deposition in porous media. A transition from declining deposition rate (''blocking'') to increasing deposition rate (''ripening'') is observed when the concentration of an electrolyte containing divalent counterions is gradually increased. Results from experiments involving irreversible, monolayer particle deposition are used to determine values of the maximum attainable surface coverage for spherical collectors. These values are unique to the collector geometry, flow conditions, and particle sizes used in the experiments. Implications of the results to colloidal transport and mobilization in subsurface aquatic environments are discussed.://A1995TJ35400028 0013-936XISI:A1995TJ35400028 ~?Zhu, X. H. Elimelech, M.1995?Fouling Of Reverse-Osmosis Membranes By Aluminum-Oxide Colloids884-892)Journal Of Environmental Engineering-Asce12112DecFouling experiments of thin film composite and cellulose acetate reverse osmosis membranes by aluminum oxide colloids are reported. Membrane fouling was investigated at various solution chemistries under fixed hydrodynamic conditions. Results show that the fouling rate increases with an increase in the ionic strength of the solution. Fouling was significant at high ionic strengths, including in the presence of background dissolved organic matter, resulting in a gradual decrease in product water flux. Under the chemical conditions tested, colloidal fouling was found to be reversible, thus indicating that pore blockage is not an important factor in colloidal fouling of reverse osmosis membranes. The role of chemical-colloidal interactions in colloidal fouling of reverse osmosis membranes is elucidated. Fouling is controlled by particle-membrane and particle-retained particle interactions, which, in turn, are determined by solution chemistry, chemical properties of colloids and membranes, and the magnitude of permeation drag.://A1995TE94500008 0733-9372ISI:A1995TE94500008~?Song, L. F. Elimelech, M.1995=Theory Of Concentration Polarization In Cross-Flow Filtration 3389-33984Journal Of The Chemical Society-Faraday Transactions9119Oct 7A novel theory is developed for concentration polarization of non-interacting particles in crossflow-filtration systems. This theory reveals that the extent of concentration polarization, as well as the behaviour of the permeate flux, are characterized by an important dimensionless filtration number (N-F = 4 pi a(p)(3) Delta P/3kT). There is a critical value of the filtration number for a given suspension and operational conditions. When the filtration number is smaller than the critical value, a polarization layer exists directly over the membrane surface and the wall particle concentration is determined by the pressure and temperature. At higher filtration numbers, a cake layer of retained particles forms between the polarization layer and the membrane surface. Mathematical models are constructed for both cases and analytical solutions for the permeate flux are derived. An increase in permeate flux with increasing pressure is predicted for all operational conditions.://A1995TA54700011 0956-5000ISI:A1995TA547000113?(Ching, H. W. Elimelech, M. Tanaka, T. S.1993YUse Of Scattered Light Fluctuations To Monitor Coagulation Dynamics With Aluminum Sulfate373-380VAmerican Water Works Association 1993 Annual Conference - Proceedings - Water Research://A1993BC40G00021 ISI:A1993BC40G00021~?Song, L. F. Elimelech, M.1995<Particle Deposition Onto A Permeable Surface In Laminar-Flow165-180(Journal Of Colloid And Interface Science1731JulA theoretical investigation of particle deposition onto a permeable surface in a parallel-plate channel is presented in this paper. The convective diffusion equation is rigorously formulated with the inclusion of lateral transport due to permeation drag and inertial lift, and transport due to gravitational, double layer, and van der Waals forces. A numerical procedure for solving the governing equation is also presented. The effects of particle size, permeation velocity, solution ionic strength, cross-flow velocity, and particle density on the initial rate of particle deposition are investigated. Results point out that the local and average particle deposition rates onto a permeable surface are determined by an interplay between several transport and interaction mechanisms, among which permeation drag, electric double layer repulsion, and inertial lift are most important. (C) 1995 Academic Press, Inc.://A1995RE60100022 0021-9797ISI:A1995RE60100022~?Johnson, P. R. Elimelech, M.1995_Dynamics Of Colloid Deposition In Porous-Media - Blocking Based On Random Sequential Adsorption801-812Langmuir113MarAn improved theoretical model is presented for quantifying the dynamics of colloid deposition in granular porous media. The model characterizes the transient aspects of irreversible particle deposition onto spherical collector surfaces where repulsive electrostatic forces between colloidal particles limit deposition to monolayer coverage. The transient deposition rate normally associated with particle deposition is depicted in the model by a dynamic blocking function derived from random sequential adsorption (RSA) mechanics. The RSA blacking function has a nonlinear power law dependence on surface coverage, in contrast to the linear Langmuirian blocking function used in previous dynamic deposition models for porous media. A technique involving the calculation of the jamming limit from experimental particle breakthrough curves is utilized for determining the excluded area parameter, an integral component of the dynamic blocking function. Parameter estimation and curve fitting techniques are not required by the model as all parameter values are calculated a priori using available theoretical principles. Parameter values are incorporated into the theoretical model to produce theoretical particle breakthrough curves based on both RSA and Langmuirian dynamic blocking functions. A comparison of theoretical results with experimental particle breakthrough curves demonstrates the utility of RSA mechanics as a means of describing particle blocking dynamics associated with colloid deposition in granular porous media.://A1995QP59500023 0743-7463ISI:A1995QP59500023*~?Song, L. F. Elimelech, M.1994ITransient Deposition Of Colloidal Particles In Heterogeneous Porous-Media301-313(Journal Of Colloid And Interface Science1672Oct 15"A general theoretical model for particle deposition and transport in heterogeneous porous media is developed. The model can describe the transient particle deposition and the nonuniform particle coverage of porous media surfaces, resulting from surface charge heterogeneity, surface roughness, or other unevenly dis tributed surface properties. The model is applied to a packed-bed column with spherical collectors whose surfaces are heterogeneously charged. Results indicate that, under unfavorable chemical conditions, it is the degree of surface charge heterogeneity that mainly determines the transient (dynamic) deposition behavior. This transient behavior can be predicted by the flux-correcting function, a function strongly dependent on the charge heterogeneity of solid surfaces. It is further shown that the effect of surface charge heterogeneity on particle deposition dynamics can be quantitatively represented by a few parameters. These parameters are lambda, the fraction of favorable surface sites, and alpha, the collision efficiency of colloidal particles with the unfavorable surface in the patchwise charge distribution model; and psi(0), the average surface potential, and sigma, the standard deviation of surface potential in the normal charge distribution model. (C) 1994 Academic Press, Inc.://A1994PL69000010 0021-9797ISI:A1994PL69000010P~? Elimelech, M.1994Particle Deposition On Ideal Collectors From Dilute Flowing Suspensions - Mathematical Formulation, Numerical-Solution, And Simulations186-212Separations Technology44Oct-This paper presents the quantitative formulation of the convective diffusion equation for particle deposition in ideal deposition systems. Collectors considered include the rotating disk, stagnation-point flow, parallel-plate channel, isolated sphere, and a porous medium composed of uniform spheres. For each collector the complete particle transport equation, proper boundary conditions, and expressions for the particle deposition rate are formulated. Also presented are numerical procedures for solving the convective diffusion equation. Simulations for the effect of various physical and chemical-colloidal variables on the rate of particle deposition are presented and discussed. The theories presented apply to particle deposition from dilute suspensions in which interparticle interactions are negligible.://A1994PJ98600001 0956-9618ISI:A1994PJ98600001~?&Elimelech, M. Chen, W. H. Waypa, J. J.1994lMeasuring The Zeta (Electrokinetic) Potential Of Reverse-Osmosis Membranes By A Streaming Potential Analyzer269-286 Desalination953JulThe use of a novel streaming potential analyzer to measure the zeta potential of cellulose acetate and composite polyamide reverse osmosis membranes is reported. Zeta potentials of these membranes were measured at various solution chemistries. These include effects of salt (NaCl) concentration, solution pH, and the presence of dissolved humic substances. It is demonstrated that streaming potential is a useful tool to measure zeta potential of reverse osmosis membrane surfaces. Results indicate that solution chemistry has a marked effect on the electrokinetic properties of reverse osmosis membranes. Humic substances strongly adsorb onto the surface of reverse osmosis membranes and thus alter the surface charge of the membranes. Furthermore, the zeta potential of reverse osmosis membranes becomes more negative as the NaCl concentration in solution increases, in a marked contrast to conventional electric double layer theories. It appears that the zeta potential of reverse osmosis membranes is strongly influenced by the presence of unreacted chemical substances or impurities on the membrane surface. Various explanations for the behavior of the membranes at the above solution chemistries are evaluated and discussed.://A1994NZ31700002 0011-9164ISI:A1994NZ31700002~?$Glater, J. Hong, S. K. Elimelech, M.1994<The Search For A Chlorine-Resistant Reverse-Osmosis Membrane325-345 Desalination953JulReverse osmosis membranes processing natural and waste waters are often exposed to low concentrations of chlorine in feed water. This biocide is chemically aggressive toward most commercial high performance membrane polymers. Chemical attack by chlorine ultimately results in membrane failure as measured by enhanced passage of both salt and water. Membrane failure is due to certain structural changes within the polymer in response to chlorine exposure. These changes in polyamide type membranes result from chlorine attack on amide nitrogen and aromatic rings. The resulting substitution products may cause deformation in the polymer chain or cleavage at amide linkages. The exact chemical mechanism of chlorine-polymer interaction and subsequent membrane failure is not, as yet, clearly understood. A review of published work on membrane-chlorine interaction will be presented here. Experimental evidence supporting various models for membrane failure will also be documented. In addition, certain common structural features known to enhance chlorine resistance of polymeric membranes are identified. It is anticipated that this paper will stimulate research efforts toward development of polymeric reverse osmosis membranes with high levels of chlorine resistance.://A1994NZ31700006 0011-9164ISI:A1994NZ31700006Y~?(Song, L. F. Johnson, P. R. Elimelech, M.1994TKinetics Of Colloid Deposition Onto Heterogeneously Charged Surfaces In Porous-Media 1164-1171"Environmental Science & Technology286Jun?A general theoretical approach for the calculation of colloid deposition rate onto heterogeneously charged surfaces is presented. Patchwise and random distribution models are used to quantitatively describe surface charge heterogeneity and its effect on the kinetics of colloid deposition. It is shown that unfavorable surfaces with only minor amounts of charge heterogeneity have particle deposition rates that are orders of magnitude larger than similar surfaces having no charge heterogeneity. Furthermore, the sensitivity of particle deposition rate to solution ionic strength decreases as the degree of surface charge heterogeneity increases. Parameters characterizing the surface charge heterogeneity of collectors in porous media are identified from experimental data of colloid deposition by using the inverse procedure of parameter estimation. These heterogeneity parameters can be used in conjunction with current theories of particle deposition to explain experimental results of colloid deposition rates under chemical conditions that are unfavorable for particle deposition.://A1994NP27700034 0013-936XISI:A1994NP27700034D~? Stolzenbach, K. D. Elimelech, M.1994{The Effect Of Particle Density On Collisions Between Sinking Particles - Implications For Particle Aggregation In The Ocean469-4836Deep-Sea Research Part I-Oceanographic Research Papers413MarA theory developed by WACHOLDER and SATHER (1974, Journal of Fluid Mechanics, 65, 417-437) for impermeable spheres moving at low Reynolds numbers predicts that the likelihood of collision between two sinking particles of different size may be essentially zero if the larger one settles faster but is less dense than the smaller. When the ratios of the settling velocity and the excess density of the two particles exceed critical values determined by the theory, the trajectory of the small particle is closed in a region of finite size surrounding the large particle. Small particles overtaken by the large one as it sinks are deflected around this region and collisions arc impossible. These findings are confirmed by laboratory experiments utilizing model particles sinking in a viscous fluid. A review of measured sinking rates and densities of marine particles indicates that a substantial fraction of the particles in the oceanic water column exceed the critical values of settling velocity and excess density with respect to other particles within a factor of 10 or so in size. Thus, aggregation by differential sedimentation is probably significant only between very small and very large particles, for which the effect of particle porosity must also be considered.://A1994NM25200003 0967-0637ISI:A1994NM25200003<~? Elimelech, M.1994iEffect Of Particle-Size On The Kinetics Of Particle Deposition Under Attractive Double-Layer Interactions190-199(Journal Of Colloid And Interface Science1641Apr#The effect of particle size on the kinetics of particle deposition in the presence of attractive double layer interactions has been studied theoretically and experimentally. Particle deposition experiments were carried out with several model suspensions of positively charged latex particles and negatively charged glass beads using the packed bed column technique. The model particles used in the deposition experiments covered a wide size range, from 0.08 to 2.51 mum. Experimental deposition rates were compared to theoretical predictions based on a numerical solution of the convective diffusion equation with colloidal, hydrodynamic, and gravitational forces fully incorporated. Theoretical and experimental results reveal that the enhancement in particle deposition rate (i.e., the deposition rate in the presence of double layer interaction divided by the rate in the absence of double layer interaction) is dependent on particle size. At low ionic strengths, the enhancement in deposition rate passes through a maximum as the particle size increases. This maximum corresponds to particles with a size around 1 mum. It is also concluded that this maximum is determined by the interplay between the size of the particles and the range of the attractive double layer interactions. (C) 1994 Academic Press, Inc.://A1994NA91500022 0021-9797ISI:A1994NA91500022p~?(Ching, H. W. Tanaka, T. S. Elimelech, M.1994@Dynamics Of Coagulation Of Kaolin Particles With Ferric-Chloride559-569Water Research283MarAn optical monitoring technique is used to investigate the dynamics of coagulation of kaolin suspensions with ferric chloride. Particular attention is given to the effects of coagulant dose, solution pH and mixing intensity on coagulation dynamics. Results show that this monitoring method provides valuable information on the dynamics of aggregates in coagulation with Fe(III) salts.://A1994MW93800007 0043-1354ISI:A1994MW938000074~?(Ching, H. W. Elimelech, M. Hering, J. G.1994?Dynamics Of Coagulation Of Clay Particles With Aluminum Sulfate169-189)Journal Of Environmental Engineering-Asce1201Jan-Feb%A novel optical technique is used to investigate the dynamics of coagulation of particle suspensions with aluminum salt. The relative size of aggregates formed during coagulation, expressed as a ''coagulation index,'' can be continuously measured by this technique. Coagulation of clay particles with aluminum sulfate is examined at various aluminum concentrations, solution pH, and mixing intensities. Results indicate that the coagulation index provides valuable information about aggregate dynamics and coagulation mechanisms with aluminum salts.://A1994MT21600012 0733-9372ISI:A1994MT21600012~?Song, L. F. Elimelech, M.1993WCalculation Of Particle Deposition Rate Under Unfavorable Particle Surface Interactions 3443-34524Journal Of The Chemical Society-Faraday Transactions8918Sep 21When repulsive colloidal interactions are involved, calculating the rate of particle deposition becomes particularly difficult. To overcome the difficulty, a new (constant migration flux) boundary condition and a sophisticated numerical procedure are introduced. With these procedures, smooth solutions of the equation are obtained for the entire domain, including the region beyond the energy barrier adjacent to the collector surface. Numerical calculations demonstrate that the dependence of particle deposition rate on flow velocity is quite different from that reported previously. The difficulty of using the 'perfect-sink' boundary condition in numerical solutions and the inadequacy of previous numerical methods are discussed.://A1993LY83800018 0956-5000ISI:A1993LY83800018? Elimelech, M.1993iDeposition Of Colloidal Particles In Porous-Media In The Presence Of Attractive Double-Layer Interactions219-224BManipulation Of Groundwater Colloids For Environmental Restoration://A1993BX82R00032 ISI:A1993BX82R00032~?Song, L. Elimelech, M.1993XDynamics Of Colloid Deposition In Porous-Media - Modeling The Role Of Retained Particles49-63?Colloids And Surfaces A-Physicochemical And Engineering Aspects73Jun 29A model for the dynamics of colloid deposition in porous media is developed by combining macroscopic and microscopic theories of particle deposition. The model considers the non-uniform coverage of collector surfaces by retained particles during the deposition process. A flux-correcting function is introduced that enables the determination of the overall colloid deposition rate as a function of surface coverage. A non-linear dependence of particle deposition rate on surface coverage is obtained, in agreement with experimental data of particle deposition. It is shown that the model is successful in describing the blocking (excluded-area) effect in particle deposition dynamics.://A1993LP04600005 0927-7757ISI:A1993LP04600005 ~?Vanzanten, J. H. Elimelech, M.1992SDetermination Of Absolute Coagulation Rate Constants By Multiangle Light-Scattering1-7(Journal Of Colloid And Interface Science1541Nov://A1992JW75100001 0021-9797ISI:A1992JW75100001=~?Elimelech, M. Song, L. F.1992FDeposition Of Colloids In Porous-Media - Theory And Numerical-Solution26-39gTransport And Remediation Of Subsurface Contaminants - Colloidal, Interfacial, And Surfactant Phenomena491://A1992BV75D00004 ACS SYMPOSIUM SERIESISI:A1992BV75D00004~?Elimelech, M. Song, L. F.1992FDeposition Of Colloids In Porous-Media - Theory And Numerical-Solution26-39Acs Symposium Series491The convective diffusion equation describing the transport of suspended colloidal particles in the vicinity of stationary surfaces in porous media was rigorously formulated by incorporating fundamental theories of mass transport, hydrodynamics of particles in porous media, and colloidal interactions. A finite difference numerical scheme with a variable step size was developed to solve the equation for the concentration distribution of colloidal particles over solid surfaces in porous media, from which the colloid deposition (capture) rates can be evaluated. With the mesh refinement technique employed in the numerical scheme, no oscillations were observed in the numerical solution.://A1992HX62500004 0097-6156ISI:A1992HX625000046~? Elimelech, M.1992HPredicting Collision Efficiencies Of Colloidal Particles In Porous-Media1-8Water Research261Jan]A semi-empirical approach for predicting the collision (attachment) efficiency of particle deposition in porous media has been developed. Based on dimensional analysis, a quantitative relationship between the collision efficiency and a set of parameters characterizing the chemical-colloidal properties of the system has been derived. The results of this analysis show that the collision efficiency can be characterized by a one dimensionless parameter. Experimental collision efficiencies determined from controlled deposition experiments exhibited a strong correlation with this dimensionless parameter.://A1992GU65700001 0043-1354ISI:A1992GU65700001~? Elimelech, M.1991dKinetics Of Capture Of Colloidal Particles In Packed-Beds Under Attractive Double-Layer Interactions337-352(Journal Of Colloid And Interface Science1462Oct 15://A1991GG64000005 0021-9797ISI:A1991GG64000005? Elimelech, M.1990KThe Role Of Colloidal Interactions In The Filtration Of Submicron Particles 1831-1840RAmerican Water Works Association - 1990 Annual Conference Proceedings, Pts 1 And 2://A1990BT11P00131 ISI:A1990BT11P00131~?Elimelech, M. Omelia, C. R.1990=Kinetics Of Deposition Of Colloidal Particles In Porous-Media 1528-1536"Environmental Science & Technology2410Oct://A1990EA64600017 0013-936XISI:A1990EA64600017~?Elimelech, M. Omelia, C. R.1990zEffect Of Particle-Size On Collision Efficiency In The Deposition Of Brownian Particles With Electrostatic Energy Barriers 1153-1163Langmuir66Jun://A1990DK31300023 0743-7463ISI:A1990DK31300023~?Elimelech, M. Omelia, C. R.1990XEffect Of Electrolyte Type On The Electrophoretic Mobility Of Polystyrene Latex Colloids165-178Colloids And Surfaces44Mar://A1990CV40500013 0166-6622ISI:A1990CV40500013~?Adin, A. Elimelech, M.1989.Particle Filtration For Waste-Water Irrigation474-4873Journal Of Irrigation And Drainage Engineering-Asce1153Jun://A1989U793600012 0733-9437ISI:A1989U793600012