Effects of Membrane Degradation due to Chlorine Exposure on the Removal of Neutral Organic Compounds by Reverse Osmosis for Potable Reuse

Reverse osmosis (RO) is used in advanced water treatment facilities for potable reuse to remove trace organic compounds. Although RO is highly effective, the membranes can degrade over time, especially when exposed to chlorine, other oxidants, and cleaning chemicals. Even low concentrations of chlorine (<0.1 mg/L) can degrade RO membranes, and there is a lack of knowledge on how chlorine degradation affects the rejection of neutral organic compounds. This bench-scale laboratory research examined the change in rejection of a broad spectrum of neutral organic compounds as a function of chlorine exposure. The compounds had molecular weights ranging from 65 to 261 Da, log(Kow) ranging from 0.29 to 4.78, and rejection ranging from ∼0 to >99%. Chlorine exposure periods up to 8370 ppm-h were examined. Rejection decreased as chlorine exposure increased, and the decrease was not linear. Compounds that had an initial rejection between 50 and 95% had a rapid decrease in rejection during the first 230 ppm-h of chlorine exposure, whereas compounds with a new membrane rejection of >95% saw little change in rejection until chlorine exposure exceeded 2640 ppm-h. These results demonstrate a need to monitor organic rejection as RO membranes age.