Performance and membrane fouling of two types of laboratory-scale submerged membrane bioreactors for hospital wastewater treatment at low flux condition

[Display omitted] •Adding sponges into MBR enhanced total nitrogen removal at low flux range.•Movement of sponges reduced cake resistance and thus fouling control.•Sponge-MBR generated less soluble matters in both supernatant and permeate. The performance and membrane fouling of a lab-scale submerged sponge-membrane bioreactor (Sponge-MBR) and a conventional MBR were investigated and compared for hospital wastewater treatment at low fluxes of 2–6LMH. COD removal by the Sponge-MBR was similar to that of the MBR, while the Sponge-MBR achieved 9–16% removed more total nitrogen than the MBR. This was due to 60% of total biomass being entrapped in the sponges, which enhanced simultaneous nitrification denitrification. Additionally, the fouling rates of the Sponge-MBR were 11-, 6.2- and 3.8-times less than those of the MBR at flux rates of 2, 4 and 6LMH, respectively. It indicates the addition of sponge media into a MBR could effectively reduce the fouling caused by cake formation and absorption of soluble substances in a low flux scenario.