Microplastic accumulation hotspots in wastewater treatment plants as leverage points for PET valorization and overall emission mitigation

Wastewater treatment plants (WWTPs) are increasingly recognised as critical control points for mitigating microplastic (MP) emissions, yet their potential role in polymer recovery remains largely unexplored. Among MPs, micro-polyethylene terephthalate (micro-PET), mainly derived from synthetic textile fibers, represents a valuable secondary raw material. This study investigated the fate, removal and recovery potential of MPs and micro-PET along anaerobic digestion, mechanical dewatering and tertiary pile cloth filtration of a full-scale WWTP. Pile cloth filtration proved effective as a refinement step in the water line, achieving an overall MP removal efficiency of 67 ± 12.6%. In the sludge line, anaerobic digestion did not significantly affect MP abundance, whereas mechanical dewatering removed 49.7 ± 32.3 % of MPs via the process water, acting as a barrier to MP release. The water streams identified as potential starting points for the proposed recovery process showed elevated MP concentrations, ranging from 6.86 ± 4.66 MP L−1 in filter wash water to 56.5 ± 12.8 MP L−1 in dewatering water. Micro-PET was detected in filter wash water, supporting the feasibility of the proposed recovery concept; however, its absence in dewatering water suggests that applicability may depend on the composition of the incoming wastewater and on process-specific factors. The optimized separation protocol showed robust and reproducible performance, enabling micro-PET enrichment from complex wastewater- and sludge-derived matrices despite high biomass loads and biofilm-coated particles. Overall, the results suggest that integrating microplastic mitigation with selective polymer recovery could represent a first step towards more resource-oriented wastewater management.