Elucidating the intensifying effect of introducing influent to an anaerobic side-stream reactor on sludge reduction of the coupled membrane bioreactors.

Three anoxic/oxic membrane bioreactors (AO-MBRs) coupled with the anaerobic side-stream reactor (ASSR) with different influent flow distribution ratios (IFDRs) were assessed to elucidate how IFDR in the ASSR affected pollutants removal, sludge reduction, membrane fouling, and potential co-occurrence network of microorganisms. When the IFDR in the ASSR was increased from 0% (ASSR0-MBR), to 25% (ASSR25-MBR) and 75% (ASSR75-MBR), chemical oxygen demand removal was enhanced and nutrient removal was comparable. Compared to ASSR0-MBR, ASSR25- and ASSR75-MBR further improved the sludge reduction by 7.6% and 10.9%, respectively. ASSR25-MBR followed cake-complete model due to the weak membrane surface scouring and high concentration of extracellular polymeric substances, while ASSR0- and ASSR75-MBR fitted cake-standard model. The increased IFDR in the ASSR boosted the relative abundance of hydrolytic and slow-growing bacteria. The co-occurrence networks of sludge reduction, nutrient removal and membrane fouling propensity indicated that the symbiotic relationships were dominant.