Biodegradable Microplastics in Municipal Wastewater and Sludge Treatment Processes: A Review on Occurrence, Fate, and Effects

Biodegradable plastics have emerged as reliable alternatives to conventional plastics for alleviating global plastic pollution. However, biodegradable plastics could also rupture into microplastics and inevitably accumulate in wastewater treatment plants (WWTPs). The fate and effects of biodegradable microplastics (BMPs) in wastewater treatment and sludge disposal processes are of great concern but have not yet been reviewed. This review comprehensively expounded the occurrence, fate, and consequential effects of BMPs in WWTPs. Specifically, the environmental contents of BMPs and the corresponding detection techniques were analyzed and compared with conventional microplastics. Furthermore, the mechanical aging, additive release, extracellular hydrolysis, and microbial biotransformation of BMPs were documented meticulously. Also, the effects of BMPs on microbial community structure and function, as well as pollutant adsorption, were underscored. The obtained knowledge would update our understanding of the risk and control of BMPs in WWTPs. Recommendations for future investigations are made.