Influence of Filtration Aids on Continuous Filtration in Membrane Bioreactors

Abstract

This study investigated the effects of addition of inorganic and organic polymer flocculants as filter aids on mitigation of membrane fouling of membrane bioreactors (MBRs). A series of dead-end filtration batch tests operated at constant pressure were conducted to screen effective filter aid candidates. Continuous MBR operation was carried out subsequently to identify the optimal filter aids selected from the batch tests. Various biomass parameters such as capillary suction time, zeta (ζ) potential, floc size, extracellular polymer substances, and soluble microbial products (SMP) in different MBRs were investigated to study the mechanism leading to the flux improvement. The experimental results demonstrated the significant transmembrane pressure reduction through dosing the selected filter aids. Regular addition of filter aids could extend the stable filtration performance of mixed liquor. Filter aids could mitigate membrane fouling mainly through reducing the concentration of SMP of the mixed liquor. Besides, inorganic additives improved total phosphorus removal of MBR effluent, while organic additives enhanced the sludge dewatering performance through forming fairly large sludge floc size and higher ζ potential. It was also observed that adding filter aids had no negative impact on both chemical oxygen demand and ammonium removal of the MBR system.