Evolution of membrane fouling and cleaning strategy development in municipal wastewater reclamation by nanofiltration

Membrane fouling is a serious concern in municipal wastewater treatment using nanofiltration (NF). The variation of NF membrane fouling at different operational durations were monitored and evaluated to understand the evolution of fouling mechanism in the present study. Six representative cleaning methods were picked for tests to deconstruct the structure and composition of the fouling layers on membrane surface. Characteristics of membrane surface morphology and foulants were analysed using advanced methods to investigate the evolution of membrane fouling. Both the composition and concentration of foulants on membrane surface showed significant variations with time during the whole operational duration, indicating the necessity of clear and precise understanding for the evolution of membrane fouling to expound its mechanism in depth. The fouling layers were mainly composed of hydrophobic organics while most inorganic salts were deposited on the surface or embedded into the upper layer of the cake in a short duration. However, after a long duration, the cake layer became thinner with much higher proportion of hydrophilic organics. Meanwhile, more inorganic foulants penetrated deep into the cake layer or even directly absorbed on the membrane surface, which resulted in more complicated fouling scenarios. Moreover, more efficient and effective targeted cleaning strategies could be further established based on the fouling mechanism identified.