Response mechanisms of enhanced biological phosphorus removal systems to microplastics stress

Enhanced biological phosphorus removal (EBPR) systems play a critical role in wastewater treatment plants (WWTPs) for controlling phosphorus discharge into urban water bodies, thereby mitigating eutrophication risks. Microplastics (MPs) accumulating in WWTPs raise concerns about their impact on EBPR performance. This study investigates the impacts of MPs exposure on EBPR functionality and the associated microbial communities. Results showed that MPs enhanced the stability of EBPR, significantly improved the phosphorus removal efficiency, while inhibited the nitrogen removal efficiency. Microbial community and functional gene analyses revealed that groups exposed to MPs exhibited higher PAOs/GAOs ratios and lower denitrification gene abundance, explaining the observed increase in EBPR stability and decrease in nitrogen removal efficiency. Meanwhile, this study identified Candidatus Accumulibacter vicinus as the dominant Candidatus Accumulibacter lineage in EBPR, challenging the traditional view centered on Ca. Accumulibacter phosphatis. Additionally, the norBC/nosZ ratio was higher in the plastisphere than in activated sludge (AS), indicating that MPs could increase N2O emission risk from WWTPs. Pathogens and antibiotic resistance genes (ARGs), important indicators for wastewater epidemiology, co-enriched on both AS and microplastic surfaces.