Deconstructing biotoxicity dynamics in municipal wastewater treatment: Linkages with conventional parameters and process-based insights

Effective conservation of aquatic ecosystem requires a thorough understanding of wastewater biotoxicity dynamics in wastewater treatment plants (WWTPs). This study conducted a comprehensive investigation of four types of biotoxicity (cytotoxicity, acute toxicity, genotoxicity, and neurotoxicity) in extracted wastewater samples from 12 municipal WWTPs across four seasons. In vitro bioassays revealed widespread induction of these biotoxicities in concentrated wastewater. Despite achieving high removal of total organic carbon (TOC, 83.50 % ± 8.38 %), the average removal efficiency of biotoxicities was only 52.77 % ± 17.29 %, with considerable risks remaining in treated wastewater regarding genotoxicity and neurotoxicity. Secondary treatment accounts for 71 %-106 % of total biotoxicity removal (average removal efficiency of 48.08 % ± 16.92 %), while tertiary treatment contributed less (average removal efficiency of 8.34 % ± 17.07 %). Among the evaluated treatment processes, A/A/O-MBR in the secondary phase and multi-component systems in the tertiary phase showed comparatively superior removal capacities. However, operational parameters, such as sludge retention time and hydraulic retention time, showed no significant correlation with biotoxicity removal efficiencies. Similarly, no significant associations were found between effluent biotoxicity levels or removal efficiencies and conventional pollutant parameters, including TOC, NH₄⁺-N, NO₃^--N and TN. The findings of this study underscore the limitations of current treatment processes in addressing biotoxicity risks and highlight the urgent need for toxicity-focused upgrades in WWTPs to ensure safer wastewater discharge.