Removal of mixed PhACs by combined UV/H₂O₂ and biologically activated carbon process: Toxicity assessment, transformation products and microbial community

This study examined the removal and toxicity reduction of mixed pharmaceutically active compounds (PhACs), including carbamazepine, erythromycin, gemfibrozil, and diclofenac, in the UV/H₂O₂ tandem with biologically activated carbon (UV/H₂O₂-BAC) process and explored potential detoxification mechanisms. Results indicated that the combined process effectively removed the mixed PhACs, with the UV/H₂O₂ segment being the primary contributor. As distinct from concentration removal, the effluent toxicity significantly increased after UV/H₂O₂ treatment. Multi-parameter toxicity assessments indicated that UV/H₂O₂ treatment significantly inhibited the activity of luminescent bacteria, interfered with the developmental toxicity of zebrafish embryos, and affected the oxidative stress and metabolic levels of zebrafish larvae. After BAC treatment, the toxicity of the UV/H₂O₂ effluent significantly decreased, particularly at an empty bed contact time of 45 min. Suspect and non-target screening were used to elucidate further the potential causes of toxicity fluctuations along the treatment flow from the transformation products (TPs) perspective. A total of 58 unique TPs were identified in the tandem process, of which 49 were initially identified in UV/H₂O₂. Over 85% of TPs in UV/H₂O₂ exhibited potential toxicity, with nearly 60% predicted to exhibit higher toxicity than parent. After BAC treatment, above 90% of TPs were effectively reduced. Metagenomics indicated that 8 taxa, including Paracoccus, were potentially dominant functional bacteria involved in the degradation of target substances. This study provided valuable insights into the feasibility and effectiveness of the UV/H₂O₂-BAC process for removing PhACs from the perspective of toxicity reduction.