Ozonation greatly improves ceramic membrane microfiltration efficiency during wastewater reuse: mechanisms and performance
This study investigated the benefits of using in situ ozonation to extend ceramic membrane filtration and mitigate fouling during treatment for wastewater reuse. Pre-ozonation has been proven to diminish ceramic membrane fouling, but in situ ozonation can further sustain ceramic membrane flux. In this study, ceramic membrane filtration cycle times were compared for raw secondary effluent (SE), pre-ozonated SE, and in situ ozonated SE and data were analyzed with respect to changes in organic matter composition. Operational parameters were chosen to simulate typical full-scale operation. Results show that while pre-ozonation (mgO3/mgDOC = 1) can extend filtration cycle time beyond non-ozonated ceramic membrane filtration by approximately 5 times, in situ ozonation, with a residual ozone concentration of only 0.5 ppm on the ceramic membrane surface, extended filtration time by orders of magnitude longer. Like pre-ozonation, in situ ozonation transformed large molecular weight compounds to lower molecular weights, and also reduced organic matter hydrophobicity, mitigating ceramic membrane fouling. However, in situ ozonation also simultaneously provided an oxidative mechanism within the membrane during filtration that pre-ozonation did not. No evidence of a major role of hydroxyl radicals produced via catalytic ozonation with the ceramic membrane material was detected. This work demonstrates the extensive improvements possible for ceramic membrane microfiltration when coupled with in situ ozonation, as part of an alternative water reuse treatment train.