Direct and indirect effects of membrane pore size on fouling development in a submerged membrane bioreactor with a symmetric chlorinated poly (vinyl chloride) flat-sheet membrane

Membrane bioreactors (MBRs) have been recognized as a promising wastewater treatment technique because of their superior solid–liquid separation performance; however, fouling development remains a concern. In this study, the relationship between membrane pore size and fouling development is investigated using originally prepared chlorinated polyvinyl chloride (CPVC) flat-sheet membranes with different pore sizes in MBRs; further, the mechanism of fouling development is demonstrated. Under the conditions in this study, the optimal membrane pore size for suppressing fouling development was determined to be in the range of 0.31–0.57 µm. It was also demonstrated that irreversible fouling is closely related to the capture of protein-like compounds inside the membrane; in contrast, it was considered that reversible fouling is caused by gel and cake layers formed on the membrane surface. Moreover, it was indicated that the membrane pore size directly and indirectly affected both reversible and irreversible fouling through the mutual relationship with other membrane characteristics such as the surface roughness. Finally, it is concluded that the optimal membrane pore size for suppressing fouling development is determined by the total filtration resistance caused by irreversible and reversible fouling phenomena.