Comparative analysis of membrane fouling control by modified microbial flocculant for pre-coagulation in two representative granular sludge-membrane coupling systems

The pre-coagulation process significantly affects the operational efficiency and membrane fouling behavior of membrane bioreactors (MBRs). Nevertheless, the underlying mechanisms remain inadequately elucidated with the development of innovative MBRs. This study evaluated the operational performance of aerobic granular sludge membrane bioreactor (AGMBR) and algal-bacterial aerobic granular sludge membrane bioreactor (ABGMBR) following the application of polymeric aluminum chloride (PAC) and modified microbial flocculant (MMF). The ABGMBR exhibited superior pollutant removal rates and permeate flux compared to the AGMBR owing to its excellent bacteria-algal symbiosis system. PAC/MMF exhibited exceptional flocculation performance, effectively inhibiting foulant adhesion on the membrane surface. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek theory elucidated that the PAC/MMF system hindered the combination of membrane-foulant and foulant-foulant, confirming its efficacy in controlling membrane fouling in AGMBR and ABGMBR. Correlation analysis revealed that PAC/MMF significantly removed the chemical oxygen demand and suspended solids content in raw sewage, which was the primary reason for the alleviation of membrane fouling. This study elucidates the antifouling mechanisms of dual coagulation in granular sludge-membrane systems and offers an economical, efficient, and sustainable strategy for wastewater treatment.