Removal of waterborne microorganisms by filtration using clay-polymer complexes

Abstract

Clay–polymer composites were designed for use in filtration processes for disinfection during the course of water purification. The composites were formed by sorption of polymers based on starch modified with quaternary ammonium ethers onto the negatively charged clay mineral bentonite. The performance of the clay–polymer complexes in removal of bacteria was strongly dependent on the conformation adopted by the polycation on the clay surface, the charge density of the polycation itself and the ratio between the concentrations of clay and polymer used during the sorption process. The antimicrobial effect exerted by the clay–polymer system was due to the cationic monomers adsorbed on the clay surface, which resulted in a positive surface potential of the complexes and charge reversal. Clay–polymer complexes were more toxic to bacteria than the polymers alone. Filtration employing our optimal clay–polymer composite yielded 100% removal of bacteria after the passage of 3 L, whereas an equivalent filter with granular activated carbon (GAC) hardly yielded removal of bacteria after 0.5 L. Regeneration of clay–polymer complexes saturated with bacteria was demonstrated. Modeling of the filtration processes permitted o optimize the design of filters and estimation of experimental conditions for purifying large water volumes in short periods.