The stimulation of microbial activity by microplastic contributes to membrane fouling in ultrafiltration

Research has demonstrated that dissolved organic carbon leaching from plastics can stimulate microbial activity in the ocean. However, similar situation has not been reported in freshwater, like rivers and lakes. The interaction between microplastic and microorganism may probably change water quality, causing operational issues during membrane water treatment, such as increased biofouling, pore blockage or formation of filter cake. In this study, the influence of microplastics (polyethylene, PE) on membrane biofouling and the microbial community during continuous-flow ultrafiltration was investigated. Results demonstrate that PE microplastics stimulate microbial activity in natural surface water and increase the production of extracellular polymeric substances (EPS). The images of scanning electron microscope-energy dispersive spectrometer (SEM-EDS) mapping have confirmed the presence of biofilm covered on the surface of microplastic particles. Biofouling layer became more hydrophobic with a dense and compact surface due to the accumulation of EPS stimulated by microplastics. Specific components of EPS, especially tryptophan-like soluble microbial byproducts with molecular weight distribution from 4 kDa to 30 kDa, were increased with the addition of microplastic and more likely to be entrapped by membrane pores aggravating membrane fouling. The components of EPS stimulated with the presence of microplastic was the main factor that caused membrane fouling. The microbial diversity was also affected with the addition of microplastic. In conclusion, the mechanism of membrane biofouling causing by microplastics in surface water is clear.