Hypochlorite treatment on thin film composite RO membrane to improve boron removal performance

Controlled hypochlorite treatment was conducted on three commercial RO membranes to improve their boron removal performance. The effects of hypochlorite treatment on membrane performance, including permeate flux, NaCl rejection as well as boron removal were investigated. The effect of pH of feed water on both original and chlorinated membranes was also investigated. In order to better understand the membrane performance changes related to membrane structure and physicochemical property changes caused by hypochlorite treatment, the membranes before and after chlorination were characterized by XPS, ATR-FTIR, SEM, AFM, surface contact angle, zeta potential and isopropanol (IPA) rejection. The results showed that all the chlorinated membranes had better performance than the original ones, including boron removal, NaCl rejection and permeate flux. Boron can be removed efficiently at pH of 11 after hypochlorite treatment and boron concentration of permeate water was less than 0.5 mg·L− 1. Chlorine had been bound to the surface of the membrane, which led to a more hydrophilic, more negatively charged surface and without change of the morphology. The negative shift of zeta potential and increase of IPA rejection indicated that both electrostatic repulsion and size exclusion effects contributed to the enhanced boron and NaCl rejection.

Research Highlights
► Controlled hypochlorite treatment can improve boron removal of RO membranes.
► Chlorinated membranes have higher flux and higher salt rejection.
► The performance of chlorinated membranes is pH dependant.
► Chlorinated membranes are more hydrophilic, more negatively charged and tighter.