Polymer and Separations ResearchLaboratory

(PolySep)

Last update:

08/22/2008

Research Interests

·             Membrane desalination

·             RO desalination process optimal design

·             Real-time energy minimization based control

Current Project

The availability of surface and ground water sources for agricultural, industrial, and personal use is becoming increasingly constrained. In response, high recovery reverse osmosis (RO) water desalination has been touted as a potential technology to mitigate the crisis. However, as water recovery increases the osmotic pressure of the retentate stream increases rapidly and thus increases energy consumption, which already accounts for up to 50% of the total desalination cost. Therefore, there is an urgent need to develop high water recovery RO based processes, while minimizing energy consumption. Significant advances have been made in recent years in the area of high recovery RO including the development of multi-stage operations, integration of RO with inter-stage brine chemical demineralization, innovative membrane spacer designs, and the use of chemical anti-scalants. A formalized analysis of the impact of the above high recovery approaches on energy consumption has not been advanced but is much needed in order to optimize high recovery water desalination processes.

Therefore, a major motivation for my doctoral research is the development of a comprehensive framework for optimizing membrane desalting processes for the new classes of highly permeable RO membranes, which have enabled desalting operations at much lower pressures than previously possible, approaching the limit of thermodynamic equilibrium wherein the retentate osmotic pressure approaches the applied pressure, thus reduces the energy consumption dramatically. Current designs lack a fundamental and rigorous first-principle cost-minimization of membrane desalination processes utilizing low-pressure membranes. Consequently, my research has focused on developing rigorous integrated process and thermodynamic models for optimizing desalination with respect to various process factors, such as feed water chemistry, operating conditions, membrane module properties, brine disposal cost, and the use of energy recovery devices. This includes optimizations of multi-stage and multi-pass membrane process configurations with respect to feed and product water qualities, operating conditions, chemical usage, and water recovery levels. Currently, the developed model is being tested on the Mini-Mobile-Modular (M3) system we recently built.

 

Publications

Zhu, A., Christofides, P. D. and Cohen, Y. Effect of Thermodynamic Restriction on Energy Cost Optimization of RO Membrane Water Desalination, Industrial & Engineering Chemistry Research, 2009, 48(13): 6010-6021.

Zhu, A., Christofides, P. D. and Cohen, Y. Minimization of Energy Consumption for a Two-Pass Membrane Desalination: Effect of Energy Recovery, Membrane Rejection and Retentate Recycling, Journal of membrane science, 2009, 339(1-2): 126-137.

Zhu, A., Christofides, P. D. and Cohen, Y. Energy Consumption Optimization of Reverse Osmosis Membrane Water Desalination Subject to Feed Salinity Fluctuation, Industrial & Engineering Chemistry Research, DOI: 10.1021/ie900729x.

Zhu, A., Christofides, P. D. and Cohen, Y. Energy Consumption Optimization of RO Membrane desalination Subject to Feed Salinity Fluctuation, Proceedings of IFAC International Symposium on Advanced Control of Chemical Processes, Istanbul, Turkey, 2009 (in press).

Zhu, A., Christofides, P. D. and Cohen, Y. On RO Membrane and Energy Costs and Associated Incentives for Future Enhancements of Membrane Permeability, Journal of membrane science, DOI:10.1016/j.memsci.2009.08.006.

Presentations

Zhu, A., Christofides, P. D. and Cohen, Y. Minimization of RO Desalination Cost: Considerations of Membrane Permeability and Feed Salinity Variations, 2009 AIChE Annual Meeting, November 8-13, 2009, Nashville, Tennessee, USA.

Gu, H., Bartmen, A., Zhu, A., Thompson, J., Lam, Y., Uchymiak, M., McCool, B. C., Rahardianto, Christofides, P. D., Cohen, Y and Kaiser, W. A Novel Approach and System for Rapid Field Evaluation of Water Desalination, 2009 AIChE Annual Meeting, November 8-13, 2009, Nashville, Tennessee, USA.