Development of Improved Membranes for ROWPU Spiral-Wound Elements

Abstract : Mobile reverse osmosis water purification units (ROWPU) have been used by the U. S. Armed Services for over a decade to produce potable water for field applications. Although advancements in the technology of operation and in the performance of the membrane elements have been significantly improved since that time, several major membrane deficiencies still exist. They are: poor lack of chemical stability to oxidants such as chlorine, high fouling rates due to membrane surface roughness and high bacterial attachment counts on the membrane surface leading to biofouling. The ROWPU membrane used today is the seawater polyamide (PA) thin-film composite membrane based on the interfacial reaction of m-phenylenediamine with trimesoyl acid chloride. This program pursues a new approach by utilizing molecular modeling to select new amines and acid chloride combinations. Emphasis focused on synthesis and purification of the new acid chloride, PA membrane development and characterization studies utilizing infrared spectrometry, atomic force microscopy and electron dispersive X-ray to determine surface roughness. Bacterial attachment and mechanisms of the addition of chlorine to the membrane surface were studied extensively. RO field testing on chlorinated feed streams have demonstrated excellent transport properties and chlorine resistance on both brackish water and seawater.