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.