Molecular insights into bioinhibitory toxicity driven by dissolved organic matter transformation during wastewater...

Wastewater treatment plants (WWTPs) play an important role in transforming wastewater into water that can be safely discharged or reused. However, existing effluent standards primarily focus on regulating concentrations of organic matter, such as chemical oxygen demand (COD) and biochemical oxygen demand (BOD₅), while largely overlooking highly ecotoxic dissolved organic matter (DOM), including trace organic pollutants (TrOPs). This study investigated DOM transformations combined with the dynamics of bioinhibitory toxicity throughout the entire wastewater treatment process to identify potentially toxic organic substances and propose an optimization strategy.The results showed that the anaerobic-anoxic-oxic (A²/O) process converted more DOM into humic-like acids and lignins/CRAM components, and also increased the quantity of aromatic and unsaturated compounds, thereby enhancing the stability of DOM in the effluent. Thus the bioinhibitory rate decreased from 48.58 % to 5.82 %. Among the priority pollutants, bisphenol A (BPA), perfluorooctanoic acid (PFOA), and phenanthrene (PHE) were closely related to bioinhibitory toxicity, followed by CHO and chlorine-containing saturated compounds. These toxic substances accumulated in the anaerobic and anoxic tank, contributing to increased toxicity, but they were effectively transformed and removed in the oxic tank. In addition, the disinfection tank (UV+NaClO) effectively removed strongly aromatic and highly unsaturated DOM, reducing the toxicity of the effluent to a certain extent. However, the generation of chlorine-containing by-products still needs to be closely focused on. Overall, it is essential to develop targeted strategies tailored to the specific functions of each treatment unit to enhance both pollutant and toxicity reduction in existing WWTPs. This study offers a comprehensive perspective on DOM transformation and toxicity evolution throughout the entire municipal wastewater treatment process, thereby facilitating enhanced removal of toxic pollutants and guiding future process upgrades.