Investigating A New Energy-Efficient Hybrid Ion Exchange-Nanofiltration (HIX-NF) Desalination Process

Lehigh University, Bethlehem PA

Investigators

Abstract

0853124 Sengupta Water desalination is energy-intensive. A typical seawater reverse osmosis (RO) plant requires 1.5 to 2.5 kilowatt hours (kwh) of electricity to produce 1 m3 of treated water; a thermal distillation plant requires five to ten times more. The principal objective of this project is to develop a new hybrid ion exchange-nanofiltration (HIX-NF) process that has the potential to reduce energy consumption of water desalination by two to three times for a wide range of feed water salinities. The proposed process is innovative in its approach for it partially alters the feed water chemistry prior to the membrane treatment. Specifically, it converts chloride, the predominant anion in salt water, into sulfate through a reversible anion exchange process without requiring any regenerant. As a result, RO membranes can be replaced altogether by NF membranes resulting in a marked reduction in energy requirement. Also, NF membrane is more robust and less susceptible to fouling compared to RO, the HIX-NF process has the potential to concentrate the reject stream further, thus reducing the volume of disposable brine. The primary challenge of this research lies in engineering and perfecting the reversible sulfate-chloride anion exchange process, a significant component of the HIX-NF process. For every brackish/sea water composition, there remains a unique sulfate/chloride selectivity (i.e., separation factor value) for anion exchangers to sustain the HIX-NF process. The present body of knowledge on ion exchange fundamentals and our related work strongly suggest that by changing the sizes of the amine functional groups, the relative affinity between divalent sulfate and monovalent chloride can be greatly manipulated for an optimal process performance. In this project, rigorous experimental studies will be conducted with the three following feed water salinities to cover the entire range for the HIX-NF process: 6,000 mg/l, 12,000 mg/l and 30,000 mg/l NaCl concentrations. Two graduate students (one doctoral and one MS) will work on the project. The P.I. plans to recruit one female student from the graduating class. The P.I. gives water related lectures in science classes of Freedom High School in the Lehigh Valley. Due to its global appeal, desalination will continue to be a relevant and interesting topic for high school students.