Evaluation of Membrane Fouling by Microplastic Particles in Tertiary Wastewater Treatment Processes

Microplastic (MP) pollution in aquatic environments poses substantial ecological, human, and economic threats. A common route of entry for MPs into the aquatic environment is through the effluent from wastewater treatment plants (WWTPs). Although membrane technologies as a tertiary treatment step have shown promise in mitigating the efflux of MPs, little is known about how MPs suspended in wastewater effluent affect membrane performance. One reason is that it is challenging to source MPs for filtration experiments which are representative of those found in WWTPs. As such, this study employed a milling and sieving process to create irregularly shaped polyethylene MPs approximately 10 μm in size which were then suspended in effluent wastewater (taken directly from a secondary clarifier tank). Membrane fouling caused by wastewater/MP interactions was investigated via constant pressure filtration experiments using commercial ultrafiltration and microfiltration membranes. It was found that even low concentrations of MPs in the wastewater increased the extent of membrane fouling. Furthermore, a backwashing process was found to significantly mitigate the effect of MP fouling on the membrane surfaces. The results from this study provide important insights into the governing factors for membrane fouling by MPs in water chemistries representative of WWTP effluents.