THE SEARCH FOR A CHLORINE-RESISTANT REVERSE-OSMOSIS MEMBRANE

Reverse osmosis membranes processing natural and waste waters are ofte n exposed to low concentrations of chlorine in feed water. This biocid e is chemically aggressive toward most commercial high performance mem brane polymers. Chemical attack by chlorine ultimately results in memb rane failure as measured by enhanced passage of both salt and water. M embrane failure is due to certain structural changes within the polyme r in response to chlorine exposure. These changes in polyamide type me mbranes result from chlorine attack on amide nitrogen and aromatic rin gs. The resulting substitution products may cause deformation in the p olymer chain or cleavage at amide linkages. The exact chemical mechani sm of chlorine-polymer interaction and subsequent membrane failure is not, as yet, clearly understood. A review of published work on membran e-chlorine interaction will be presented here. Experimental evidence s upporting various models for membrane failure will also be documented. In addition, certain common structural features known to enhance chlo rine resistance of polymeric membranes are identified. It is anticipat ed that this paper will stimulate research efforts toward development of polymeric reverse osmosis membranes with high levels of chlorine re sistance.