A novel approach for fouling mitigation in anaerobic-anoxic-oxic membrane bioreactor (A2O-MBR) by integrating worm predation

Abstract

Membrane fouling is one of the biggest challenges in the widespread application of membrane bioreactors. In this study, a combined system of anaerobic-anoxic-oxic membrane bioreactor (A2O-MBR) and worm reactor (WR) was established for fouling control. In A2O-MBR-WR, the membrane filtration cycle was prolonged by 66.7% due to the confluence of microaerobic treatment and worm predation in WR with the interaction between WR and A2O-MBR. Compared with conventional A2O-MBR, membrane rejection of soluble and colloidal foulants (SCF) in the combined system was decreased by 26.0%, which could be attributed to the higher biodegradability of SCF and the higher bacterial activity in A2O-MBR. Although floc size in A2O-MBR was reduced due to sludge disintegration and worm predation in WR, changes of floc surface properties could counteract this negative effect on fouling. Complex effects of sludge flocs on membrane fouling were further analyzed by the interaction energy between sludge flocs and the clean/fouled membrane based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The energy barriers indicated that flocs in A2O-MBR-WR were difficult to adhere to the membrane and were more likely to detach. Moreover, high-throughput sequencing analysis revealed that the microbial community of the cake layer in the combined system was more even and had a higher proportion of foulants degradation related bacteria, which was beneficial for fouling mitigation. The combination of A2O-MBR and WR has shown significant advantages in membrane fouling mitigation. Keywords: Worm reactor, Membrane fouling, Sludge floc, Interaction energy, Microbial community