Effects of packing carriers and ultrasonication on membrane fouling and sludge properties of anaerobic side-stream reactor coupled membrane reactors for sludge reduction

The aim of this study was to investigate membrane fouling performance of anaerobic side-stream reactor (ASSR) coupled membrane reactors (MBR), and effects of representative enhancement strategy, namely packing carriers and low-strength ultrasonication, on sludge properties and membrane fouling by four pilot-scale MBRs. Compared to anoxic/oxic MBR (AO-MBR) for control, ASSR coupled AO-MBR (ASSR-MBR), ASSR-MBR with ASSR packed with carriers (AP-MBR) and AP-MBR with part of sludge ultrasonicated before fed into ASSR (AUP-MBR) reduced sludge production by 8.4%, 17.5% and 32.9% with efficient pollutants removal. ASSR-MBR showed more severe membrane fouling because inserting ASSR disintegrated sludge floc structure, increased the secretion of extracellular polymeric substances (EPS) and deteriorated viscoelastic property of sludge. Packing carriers in ASSR alleviated membrane fouling of ASSR-MBR by inhibiting EPS-secreting bacteria (Flavobacteriia, gamma-Proteobacteria, delta-Proteobacteria and norank_Saccharibacteria), enlarging particle size and improving dewaterability. AUP-MBR showed the most severe membrane fouling and obvious cake layer fouling because ultrasonication disintegrated sludge to small particles, increased adherence property of EPS, and deteriorated dewaterability and viscoelastic property of sludge. MiSeq sequencing revealed Proteobacteria and Bacteroidetes were responsible for membrane fouling at the phylum level, and norank_Neisseriaceae, Arcobacter, norank_Parcubacteria and Mycobacterium were dominant genera easily attached on membrane surface.