Responses of microbial community to the selection pressures of low-concentration contaminants of emerging concern in activated sludge

The activated sludge system used in wastewater treatment plants has demonstrated partial removal capabilities for various contaminants of emerging concern (CECs). However, existing research primarily focuses on the removal efficiency individual or combined CECs, with limited research addressing their impact on microbial community. In this study, three activated sludge systems were developed to investigate the effects of low concentrations of CECs, including five types of antibiotics and five types of non-antibiotic CECs. The results showed that activated sludge could effectively degrade non-antibiotic CECs within 3 -5 days even in the third cycle, whereas the degradation of antibiotics was more variable. Compared to the AA-Group, Alphaproteobacteria, Anaerolineae, Planctomycetes, Gammaproteobacteria, and Bacteroidia shifted to connector in the non-AA treatment as keystones species. Variance partitioning and co-occurrence network analysis showed that CECs exert significant deterministic influences, surpassing traditional environmental factors. Notably, antibiotics promoted microbial interactions more than other CECs, the finding was further validated by null model analysis. Our study provides novel insights into the differential impacts of low-concentration CECs on microbial community dynamics and interactions. Findings highlight the necessity to better understand the complex microbial processes driven by CECs, particularly antibiotics, to further develop more efficient biological treatment pro- cesses for CECs removal.