A comparison study on membrane fouling in a sponge-submerged membrane bioreactor and a conventional membrane bioreactor

•Less SMP and bound EPS in activated sludge in the SSMBR induced lower RC and RP.•Lower biomass growth and sludge viscosity contributed to lower RC in the SSMBR.•Larger sludge flocs, higher zeta potential and RH led to lower RT in the SSMBR.•Sponge could prevent pore blocking and cake layer formation.•Sponge addition could reduce SMPC and EPSC through adsorption and biodegradation. This study compared membrane fouling in a sponge-submerged membrane bioreactor (SSMBR) and a conventional membrane bioreactor (CMBR) based on sludge properties when treating synthetic domestic wastewater. In the CMBR, soluble microbial products (SMP) in activated sludge were a major contributor for initial membrane fouling and presented higher concentration in membrane cake layer. Afterwards, membrane fouling was mainly governed by bound extracellular polymeric substances (EPS) in activated sludge, containing lower proteins but significantly higher polysaccharides. Sponge addition could prevent cake formation on membrane surface and pore blocking inside membrane, thereby alleviating membrane fouling. The SSMBR exhibited not only less growth of the biomass and filamentous bacteria, but also lower cake layer and pore blocking resistance due to lower bound EPS concentrations in activated sludge. Less membrane fouling in SSMBR were also attributed to larger particle size, higher zeta potential and relative hydrophobicity of sludge flocs.