The search for a chlorine-resistant reverse osmosis membrane

Reverse osmosis membranes processing natural and waste waters are often exposed to low concentrations of chlorine in feed water. This biocide is chemically aggressive toward most commercial high performance membrane polymers. Chemical attack by chlorine ultimately results in membrane failure as measured by enhanced passage of both salt and water. Membrane failure is due to certain structural changes within the polymer in response to chlorine exposure. These changes in polyamide type membranes result from chlorine attack on amide nitrogen and aromatic rings. The resulting substitution products may cause deformation in the polymer chain or cleavage at amide linkages. The exact chemical mechanism of chlorine-polymer interaction and subsequent membrane failure is not, as yet, clearly understood. A review of published work on membrane-chlorine interaction will be presented here. Experimental evidence supporting various models for membrane failure will also be documented. In addition, certain common structural features known to enhance chlorine resistance of polymeric membranes are identified. It is anticipated that this paper will stimulate research efforts toward development of polymeric reverse osmosis membranes with high levels of chlorine resistance.