Excess Sludge Production in Membrane Bioreactors: A Theoretical Investigation

This paper presents a theoretical investigation on excess sludge production in membrane bioreactors for municipal wastewater treatment. Based on mass balances of sludge and substrate, a formula to predict the excess sludge production in membrane bioreactors is introduced and verified by experimental data. The effects of kinetic parameters and operating conditions on excess sludge production are discussed for strong-, medium-, and low-strength municipal wastewaters, respectively. The strategy for reducing excess sludge production is recommended in order of priority, as sludge retention time-kd-Y-hydraulic retention time. Furthermore, the differences between membrane bioreactors and activated sludge processes are analyzed from the viewpoint of excess sludge production.