Pre-coagulation for membrane fouling mitigation in an aerobic granular sludge membrane bioreactor: A comparative study of modified microbial and organic flocculants

Coagulation has become a hotspot for membrane fouling control; however, there is a gap in research regarding the application of modified microbial flocculants (MMFs) to mitigate membrane fouling. Herein, we prepared an MMF and compared it with conventional organic flocculants for their effects on mitigating membrane fouling in an aerobic granular sludge membrane bioreactor (AGMBR). The results showed that electrical neutralization played a dominant role in the flocculation process of polymeric aluminum chloride (PAC)/MMF, which exhibited the optimal performance for the removal of pollutants and membrane fouling control. Moreover, the characteristics of the fouled membrane and the fitting of membrane fouling models indicated that the cake layer formation was the main fouling mechanism underlying membrane fouling, and MMF could mitigate the accumulation of foulants on the membrane surface, forming a loose and porous cake layer. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the largest energy barriers of the membrane-foulant and foulant-foulant interactions were observed in the PAC/MMF-AGMBR hybrid system. Furthermore, correlation analysis revealed that total phosphorus, polysaccharide, zeta potential, and particle size had the greatest correlation with the fouling resistance. Thus, this study shows that MMF pre-coagulation is feasible and provides a new method for membrane fouling mitigation in an AGMBR.