The oxidation of membrane polymer structures after the long-term exposure to chemical cleaning agents in reverse osmosis processes

Abstract

There is few research on the effect of chemical cleaning agents to polymer structure of reverse osmosis membrane surface during the repeated fouling controls. In this study, the oxidation and hardening of RO membrane were investigated after the exposure for 30 days to two commercially available cleaning agents (A and B). After the 30 days of contact with solution containing A and B, the maximum elongation of RO membranes was decreased by 9.2±5.0 % and 19.3±6.7 %, respectively. Specific water fluxes tended to decrease as the increase of exposure time for all tested chemical agents. XPS results showed that the amide bonding of virgin membrane was oxidized, and changed to carboxylic and amine groups after the long-term exposure to chemical cleaning agents. As a results of membrane hardening and oxidation of amide bonding on the membrane polymers, we found that the salt rejection for the RO membranes exposed to A and B were significantly reduced compared to the virgin membrane. Consequently, long-term exposures test should be considered for the minimization of polymer damages on RO membrane surfaces in addition to cleaning efficiency tests.