Comprehensive assessment of 45 antibiotics in ten urban wastewater treatment plants in Northeastern China: Terminal treatment is not a reliable guard.

The increasing presence of antibiotics in urban wastewater has raised significant concerns. Therefore, wastewater treatment plants (WWTPs) face questions about their ability to reliably and effectively remove antibiotics. In this study, data from ten representative WWTPs were systematically evaluated to assess antibiotic occurrence, removal efficiencies, seasonal variations, and ecological risks, revealing the prevalent instability in antibiotic removal capacities of traditional WWTPs. The results showed that the total influent concentrations ranged from 9351.63 to 50126.08 ng/L, with the primary contributors being Norfloxacin (NOR), Ofloxacin (OFX) and Ciprofloxacin (CIP), accounting for 57.63, 18.09 and 9.01 %, respectively. Antibiotic concentrations were significantly higher in winter compared to summer, with winter loads of macrolides, sulfonamides and quinolones exceeding summer levels by 74.09, 86.11 and 38.22 %, respectively. Certain antibiotics, such as Clindamycin hydrochloride (CLH), Roxithromycin (ROX) and Lomefloxacin (LOF), exhibited significant fluctuations. The removal rates of sulfonamides showed a notable decline in winter. Antibiotic emissions from different WWTPs ranged from 20.75 to 284.66 g/day, with Clarithromycin (CLA), Erythromycin (ERY) and OFX being the primary contributors. Additionally, different biological treatment processes do not lead to consistent or predictable variations in antibiotic removal efficiency within WWTPs. More importantly, the study highlighted the current lack of predictive methods for such fluctuations. Correlation analysis between operational parameters and removal rates revealed weak relationships.