Experimental and modeling study on the simultaneous fouling behavior of micro/nanoplastics and bovine serum albumin in ultrafiltration membrane separation

Micro- and nanoplastics (MPs/NPs) are increasingly recognized as serious contaminants of aquatic ecosystems, which enter the marine environment primarily through wastewater treatment plants (WWTPs). Membrane technology is a promising way to mitigate the release of MPs/NPs from WWTPs; however, its applicability is limited by membrane fouling. Therefore, it is essential to explore the effect of MPs/NPs along with other abundant pollutants in wastewater effluent, such as natural organic matter (NOM), on membrane performance. In this study, we investigated the simultaneous fouling behavior of MPs/NPs and bovine serum albumin (BSA), chosen as NOM. It was found that the combined MPs/NPs and BSA ultrafiltration decreases the flux by 13% and increases the fouling resistance by 74%, compared to the single MPs/NPs ultrafiltration. This was attributed to a dense cake layer structure caused by MPs/NPs and BSA. The multi-stage Hermia’s model showed that in the combined foulants filtration, the complete pore blockage time domain was reduced, forming the cake layer at earlier stages than single foulants. Moreover, the interfacial free energy values calculated by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory demonstrated that MPs/NPs and BSA interactions in the feed facilitate the adhesion of MPs/NPs to the membrane surface. Therefore, the cake layer forms earlier, resulting in a higher amount of residual MPs/NPs on the membrane after cleaning. The obtained findings from both experimental and modeling approaches represent the necessity of revising membrane filtration design and operation parameters to prevent and alleviate fouling caused by the simultaneous presence of MPs/NPs and other pollutants in actual wastewater.