Interactions between sludge composition and filtration in submerged membrane bioreactors for municipal wastewater treatment

摘要

This work aims to cha racterize the interactions between the biological activity and membrane filtration in a submerged membrane bioreactor for municipal wastewater treatment. A submerged membrane bioreactor was compared with a conventional activated sludge process (aerobic rea ctor + settler) when both systems are operated with the same conditions (sludge age, HRT, MLSS) and for the same influent characteristics. The MBR was operated at 5 l/h.m~2 for 50 days without backwashes and a very low increase in TMP was observed (7 mbar/day). The MBR allowed a better removal of TSS (99%) but also of COD (93%) than the activated sludge reactor. Concerning the filtration behaviour, even if the MLSS content in the two reactors is the same, the sludge coming from the MBR generates more fouling than the activated sludge. Indeed, the critical flux for the MBR sludge is about 10-15 L/H/m2 against 32-43 L/H/m2 for the activated sludge. The stabilized EPS content in flocs were similar : 25-30 mg proteins/gVSS, 7-8 mg polysaccharides/gVSS and 12-13 mg humics substances/gVSS. However the EPS concentration in supernatants and more particularly the polysaccharides and proteins content are different and much higher in MBR. This could explain the different fouling behaviour of sludges.