Membrane fouling characteristics and mitigation in a coagulation-assisted microfiltration process for municipal wastewater pretreatment

Maximizing the energy-profitable treatment of municipal wastewater (MW) is of significance to achieve energy-neutral operation for wastewater treatment plant. Direct membrane filtration technology has been considered as an effective way to separate organic carbon from MW for subsequent anaerobic energy-recovering process, but its application is restrained by severe membrane fouling issues. Thus, it is essential to identify the substances in MW that are responsible for membrane fouling and find out efficient anti-fouling methods. In this work, an integrated approach through combining multivariate curve resolution-alternating least squares analysis with infrared attenuated total reflection mapping was adopted to explore the membrane fouling process, and three coagulants, i.e., polyacrylamide, Al₂(SO₄)₃ and FeCl₃, were individually used to mitigate membrane fouling. Results show that the 1-8 μm biopolymer clusters, i.e., humic-like and protein-like substances, were the predominant foulants in MW. In addition, membrane fouling caused by proteins was found to be more severe than that by humic substances. Coagulation pretreatment was demonstrated to be effective in mitigating membrane fouling. Al₂(SO₄)₃ or FeCl₃ had superior anti-fouling performance comparing to that of polyacrylamide. The dosage of polyacrylamide needs to be optimized according to the actual MW characteristics as its overdose would cause a substantial decline of membrane flux. These results provide a deep understanding of the membrane fouling mechanisms for organic carbon separation from MW and are beneficial for developing efficient and cost-effective membrane fouling mitigation strategies.