Chemical Cleaning-Triggered Release of Dissolved Organic Matter from a Sludge Suspension in a Ceramic Membrane Bioreactor: A Potential Membrane Foulant

Ceramic membrane bioreactors (MBRs) haveattracted a great deal of interest due to their robustness in thetreatment of various kinds of wastewaters. So far, in situ chemicalcleaning with sodium hypochlorite (NaClO) has been the mostprevalent MBR cleaning method. This study showed that in situNaClO cleaning in MBRs triggered a significant release of dissolvedorganic matter (DOM) from a sludge suspension, while thegenerated DOM could facilitate fouling development, especiallyirreversible fouling in a ceramic MBR. It was found thatbiopolymers with a molecular weight (MW) of >10 kDa andhumic substances could be effectively rejected by the ceramicmembranes. As such, the membrane fouling rate (dTMP/dt) of thesupernatant from a NaClO-treated sludge suspension was closely related to the rejected levels of biopolymers and humic substances.However, hydrophobic DOM and low-MW organics (MW < 500 Da) could easily pass through the membranes, indicating aninsignificant contribution to the observed membrane fouling. Consequently, this study verified the contributions of DOM releasedfrom a sludge suspension after in situ membrane cleaning with NaClO with respect to subsequent membrane fouling development ina ceramic MBR.