Impacts on characteristics and effluent safety of PVDF ultrafiltration membranes aged by different chemical cleaning types

Chemical cleaning is an effective way to remove the irreversible fouling of ultrafiltration (UF) membranes. However, chemicals can also damage membranes. In order to investigate the effects of chemical cleaning on various properties of the membrane, three chemical agents, sodium hydroxide (NaOH, alkali), sodium hypochlorite (NaClO, disinfector), and citric acid (CA, acid), were used to clean polyvinylidene fluoride (PVDF) UF membranes. After two, six, and ten days of chemical cleaning, a series of changes in the physical and chemical properties proved that the structures of aged membranes were destroyed by the three agents. The aging of the membrane led to a decline in the retention performance, and the effluents were found to contain large amounts of PVDF microplastics (MPs). The concentration of PVDF MPs and the MP release rate increased rapidly with aging time. The proportion of each MP shape was fragment > fiber > sphere, and the proportion decreased with the increase of each MP size. The longer the aging time, the larger the proportion of small-sized MPs. Among the three agents, NaOH may be the most beneficial to the stability of ultrafiltration membrane effluent safety.