Feasibility of the use of polymer-assisted membrane filtration for brackish water softening

The feasibility of using polymer-assisted ultrafiltration for brackish water softening, i.e. the removal of Na+, K+, Ca2+ Mg2+, Cl-, NO3-, and SO42- from water, was studied. Three weakly basic, cationic water-soluble polymers chitosan, poly(ethylenimine), and poly(diallyl dimethylammonium chloride) were selected. The membranes Amicon YM10, YM30 (regenerated cellulose), and PM10 (polysulfone) were used. Experiments were performed as a function of solution pH. It was shown that the removal of divalent Ca2+ and Mg2+ was more efficient than that of univalent Na+ and K+. In addition, the rejection of anions decreased in the order NO3- > Cl- > SO42-. Finally, the fouling of membranes during filtration was analyzed by conventional cake filtration theory taking into account incompressible or compressible nature of the deposited cake. (C) 2001 Elsevier Science B.V. All rights reserved.