Development of a New Chlorine and Biofouling Resistant Polyamide Membrane

Mobile reverse osmosis water purification units (ROWPU) have been used by the U.S. military with polyamide spiral-wound elements for over a decade to produce potable water for field applications. Although advances have greatly enhanced performance,improvement of polyamide membrane stability to oxidizing agents such as chlorine and reduced fouling are required to increase membrane life and reduce costs. Recently, a new polyamide membrane (CPTC) has shown promise by displaying resistance to chlorinein laboratory immersion tests. The contact time was 30,000 mg/L-hr, (~6-8 years) of exposure at the 0.5 mg/L level. However, in actual long-term field testing (~2000 hours) on chlorinated waters, the CPTC membranes showed unacceptable performance lossesconsistent with with physicochemical damage and/or biological attack. Work will continue on the CPTC membrane system to identify and resolve this problem. In addition, the pursuit for a low fouling chlorine-resistant membrane will continue by improvingthe understanding of the mechanism of membrane chlorination reactions and associated performance losses. New amine and acid chloride monomers will be synthesized, with the assistance of molecular modeling, to block chlorination sites that are subject toattack and to add low fouling moieties into the polyamide desalination barrier. The total worldwide market for ROWPU-type RO spiral-wound elements, for both military and the private sector, is in excess of $200 million/year. Approximately 75% of thistotal is produced by U.S. companies. Since most membrane manufacturers are U.S. based companies, any product improvement will further strengthen their position in both domestic and overseas markets. The potential use of the proposed membrane improvementsby the Federal government should provide considerable cost savings in element replacement as well as provide increased efficiency in system operation due to minimized fouling and less frequent need for cleaning. Since ROWPU membrane elements are purchasedin large quantities, dertimental effects of long term storage also will be minimized. U.S. membrane companies will benefit in the same manner as the Federal Government, although possibly to a greater extent, since the largest part of their market is inthe private sector.