Fate of Dissolved Organic Matter and Antibiotics in Conventional Treatment System and Constructed Wetlands System Applied to Source Water Pretreatment: Removal Efficiency and Risk Assessment

In the context of micro-polluted river drinking water sources, implementing water pretreatment systems has played a crucial role in enhancing water quality. Given that conventional pollutants can be effectively controlled, in order to explore the effect on emerging pollutants by source water pretreatment systems, the removal effects of antibiotics by conventional treatment system and constructed wetlands system were compared. In this study, we compared their removal efficiency in two major source water pretreatment systems: Yanlong constructed wetlands and reservoir (YL CWs-R) and the Tongyu water pretreatment system (TYPS), which employ different treatment processes. We also conducted a comprehensive examination of the occurrence and fate of dissolved organic matter (DOM) and antibiotics to explore potential relationship between them. Finally, the selection risks of antibiotics in water source were evaluated. The key findings are as follows: (1) Among 21 antibiotics analyzed, 15 were detected in all samples, with concentrations ranging from 37 to 80 ng/L. In YL CWs-R, the primary unit responsible for antibiotic removal was the submerged plant zone, achieving total removal efficiencies ranging from 10.5 to 90.0%. In TYPS, the biological contact oxidation pool played a comparable role, achieving total removal efficiencies ranging from 17.0 to 81.0%. (2) Redundancy analysis (RDA) revealed a positive correlation between protein-like components and sulfonamides, while humic-like components were negatively correlated with other classes of antibiotics. (3) Among the antibiotics studied, chlortetracycline, cephalexin, norfloxacin, doxycycline, oxytetracycline, and sulfachloropyridazine are classified as low-risk antibiotics, while enrofloxacin falls into the medium-risk category. This study fills a gap in the research about the removal of multiple antibiotics by various water treatment systems applied to source water pretreatment and provides valuable theoretical insights and data to support the establishment of source water pretreatment systems in different regions.