Ngai Yin Yip

Ph.D. Candidate, Chemical and Environmental Engineering, Yale University
M.S. and M.Phil. Chemical and Environmental Engineering, Yale University, 2011
B. Eng (First Class Honors) Civil and Environmental Engineering, Nanyang Technological University (Singapore), 2004


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Ngai Yin is a PhD student advised by Professor Menachem Elimelech in the Environmental Engineering Program at Yale University. His research interests are in the general area of membrane technology for sustainable water supply and energy production. His research focuses on high performance polymeric membranes for osmotically-driven membrane processes (ODMPs).

Forward osmosis (FO), a subset of ODMPs, has demonstrated the potential for application in sea and brackish water desalination, wastewater reclamation and industrial wastewater treatment. FO exploits the natural phenomenon of osmosis, which occurs when two solutions of different concentration are placed on opposite sides of a semi-permeable membrane. The osmotic pressure difference drives the permeation of water across the membrane from the dilute solution to the concentrated solution, while the selective property of the membrane retains the solutes in their respective sides.

The ammonia-carbon dioxide FO desalination system, developed here at Yale, enables low-grade geothermal or waste heat from industrial facilities to be utilized as an energy source to drive the separation process. The potential advantage of the technology lies in the production of fresh drinking water with relatively lesser electricity consumption and, hence, at a lower cost.

Pressure retarded osmosis (PRO), the other subset of ODMPs, holds the promise to produce renewable energy from natural and anthropogenic salinity gradients. PRO exploits the same osmotic pressure difference that develops when a semi-permeable membrane separates two solutions of different concentrations, except that a hydraulic pressure is applied on the more concentrated draw solution. As water permeates across the membrane into the pressurized draw solution, a hydroturbine extracts work from the expanding draw solution volume.

Natural salinity gradients, for example those arising from the mixing of freshwater rivers flowing into oceans, have the potential to produce electricity for over half a billion people. Additionally, PRO can use anthropogenic waste streams, such as concentrated brine from a desalination plant, as draw solutions. As such, PRO power generation has the potential to be an alternative source of sustainable energy, and contribute to the alleviation of the energy crisis facing us today.

Prior to his PhD studies, Yip (a name he habitually goes by) completed his Bachelor of Engineering degree in Nanyang Technological University in Singapore, with his research thesis focusing on nanofiltration processes. After graduation he worked for the Singapore government in the National Environment Agency, formulating and implementing policies for the country.

An avid outdoor and sports person, he recently scaled the Dolomites of the Eastern Alps in Italy and the Argentinian Andes. Next, he is planning to SCUBA dive among the pelagic fishes in the seas of Belize.


pdfs and supporting information available on the main publications page.
  1. Lin, S., Yip, N.Y., Cath, T.Y., Osuji, C.O., Elimelech, M. "Hybrid Pressure Retarded Osmosis − Membrane Distillation System for Power Generation from Low-Grade Heat: Thermodynamic Analysis and Energy Efficiency." Environmental Science & Technology, accepted, April 2014.  DOI: 10.1021/es405173b 
  2. Yip, N.Y., Vermaas, D.A., Nijmeijer, K., Elimelech, M. "Thermodynamic, Energy Efficiency, and Power Density Analysis of Reverse Electrodialysis Power Generation with Natural Salinity Gradients." Environmental Science & Technology, Article ASAP, April 2014.  DOI: 10.1021/es5005413 
  3. Lin. S., Yip, N.Y., and Elimelech, M.. "Direct Contact Membrane Distillation with Heat Recovery: Thermodynamic Insights from Module Scale Modeling", Journal of Membrane Science, Volume 453, March 2014, pages 498-515. DOI: 10.1016/j.memsci.2013.11.016
  4. Straub, A.P., Yip, N.Y., and Elimelech, M. "Raising the Bar: Increased Hydraulic Pressure Allows Unprecedented High Power Densities in Pressure-Retarded Osmosis", Environmental Science & Technology Letters, Volume 1, November 2013, pages 55-59. DOI: 10.1021/ez400117d
  5. Yip, N.Y. and Elimelech, M. "Influence of Natural Organic Matter Fouling and Osmotic Backwash on Pressure Retarded Osmosis Energy Production from Natural Salinity Gradients", Environmental Science & Technology, Volume 47, November 2013, pages 12607–12616. DOI: 10.1021/es403207m
  6. Vermaas, D., Veerman, J., Yip, N.Y., Elimelech, M., Saakes, M., and Nijmeijer, K. "High Efficiency in Energy Generation from Salinity Gradients with Reverse Electrodialysis" ACS Sustainable Chemistry & Engineering, Volume 1, October 2013, pages 1295–1302. DOI: 10.1021/sc400150w
  7. Tiraferri, A., Yip, N.Y., Straub, A.P., Romero-Vargas Castrillon, S., and Elimelech, M. "A Method for the Simultaneous Determination of Transport and Structural Parameters of Forward Osmosis Membranes", Journal of Membrane Science, Volume 444, October 2013, pages 523–538. DOI: 10.1016/j.memsci.2013.05.023
  8. Shaffer, D.L., Arias Chavez, L.H., Ben-Sasson, M., Romero-Vargas Castrillon, S., Yip, N.Y., and Elimelech, M. "Desalination and Reuse of High-Salinity Shale Gas Produced Water: Drivers, Technologies, and Future Directions" Environmental Science & Technology, Volume 47, September 2013, pages 9569–9583. DOI: 10.1021/es401966e
  9. Cath, T.Y., Elimelech, M., McCutcheon, J.R., McGinnis, R.L., Achilli, A., Anastasio, D., Brady, A.R., Childress, A.E., Farr, I.V., Hancock, N.T., Lampi, J., Nghiem, L.D., Xie, M., Yip, N.Y. "Standard Methodology for Evaluating Membrane Performance in Osmotically Driven Membrane Processes", Desalination, Volume 312, March 2013, pages 31–38. DOI: 10.1016/j.desal.2012.07.005
  10. Mo, Y.H., Tiraferri, A., Yip, N.Y., Adout, A., Huang, X., and Elimelech, M. "Improved Antifouling Properties of Polyamide Nanofiltration Membranes by Reducing the Density of Surface Carboxyl Groups", Environmental Science & Technology, Volume 46, December 2012, pages 13253–13261. DOI: 10.1021/es303673p
  11. Shaffer, D.L., Yip, N.Y., Gilron J., and Elimelech, M. "Seawater Desalination for Agriculture by Integrated Forward and Reverse Osmosis: Improved Product Water Quality for Potentially Less Energy", Journal of Membrane Science, Volume 415–416, October 2012, pages 1–8. DOI: 10.1016/j.memsci.2012.05.016
  12. Yip, N.Y. and Elimelech, M. "Thermodynamic and Energy Efficiency Analysis of Power Generation from Natural Salinity Gradients by Pressure Retarded Osmosis", Environmental Science & Technology, Volume 46, May 2012, pages 5230–5239. DOI: 10.1021/es300060m 
  13. Yip, N.Y. and Elimelech, M. "Performance Limiting Effects in Power Generation from Salinity Gradients by Pressure Retarded Osmosis", Environmental Science & Technology, Volume 45, December 2011, pages 10273–10282. DOI: 10.1021/es203197e
  14. Hoover, L.A., Phillip, W.A., Tiraferri, A., Yip, N.Y., and Elimelech, M. "Forward with Osmosis: Emerging Applications for Greater Sustainability", Environmental Science & Technology, Volume 45, December 2011, pages 9824–9830. DOI: 10.1021/es202576h
  15. Ang, W.S., Yip, N.Y., Tiraferri, A., and Elimelech, M. "Chemical Cleaning of RO Membranes Fouled by Wastewater Effluent: Achieving Higher Efficiency with Dual-step Cleaning", Journal of Membrane Science, Volume 382, October 2011, pages 100-106. DOI: 10.1016/j.memsci.2011.07.047
  16. Yip, N.Y., Tiraferri, A., Phillip, W.A., Schiffman, J.D., Hoover, L.A., Kim, Y.C., and Elimelech, M. "Thin-Film Composite Pressure Retarded Osmosis Membranes for Sustainable Power Generation from Salinity Gradients", Environmental Science & Technology, Volume 45, May 2011, pages 4360–4369. DOI: 10.1021/es104325z
  17. Tiraferri, A., Yip, N.Y., Phillip, W.A., Schiffman, J.D., Elimelech, M. "Relating Performance of Thin-Film Composite Forward Osmosis Membranes to Support Layer Formation and Structure", Journal of Membrane Science, Volume 367, February 2011, pages 340-352. DOI: 10.1016/j.memsci.2010.11.014
  18. Yip, N.Y., Tiraferri, A., Phillip, W.A., Schiffman, J.D., and Elimelech, M., "High Performance Thin-Film Composite Forward Osmosis Membrane", Environmental Science & Technology, Volume 44, May 2010, pages 3812–3818. DOI: 10.1021/es1002555