Extending the life of water reuse reverse osmosis membranes using chlorination

Abstract

Numerous efforts have been made over the years to extend the lifespan of reverse osmosis (RO) membranes. End-of-life RO membranes are periodically replaced and usually discarded in landfills. Periodic membrane modification using chlorination may be an alternative to recover their productivity without compromising process safety. In this research, RO membranes from an engineering-scale ultrafiltration-RO system treating reclaimed water were exposed five times to 2000 ppm-h of chlorine immediately after chemical cleaning. Water, conductivity, ion, and organic permeability coefficients and rejection were related to the chlorine dose. The breakthrough of six naturally occurring viruses with different levels of persistence to wastewater treatment was also monitored. After five chlorine doses, the apparent water permeability was recovered to 1.0–1.5 L m−2 h−1 bar−1, a 3.1-fold increase compared to the end-of-life membranes, with only a 2% decrease in observed salt rejection. Interestingly, apparent conductivity and ion permeability slightly decreased after the first and second chlorine dose, likely because the chlorine removed irreversible fouling/scaling and thus reduced concentration polarization. After the third chlorine dose, as the RO membrane surface oxidized, more monovalent ions permeated through the membrane, while observed divalent ion rejection remained relatively high and constant (>97%). Similarly, the RO permeate dissolved organic carbon concentration and total fluorescence intensity decreased between end-of-life membrane and the second chlorine dose, followed by an increase after the third dose, and only humic substances and building block compounds (<2 kDa) were detected. All viruses were below or near the detection limit, indicating that oxidation did not compromise the integrity of the membrane in its ability to reject virus-sized particles. The results suggest that targeted chlorination may extend RO membrane lifespan by increasing apparent water permeability while maintaining RO-like selectivity.