Comprehensive attenuation mechanisms and kinetics of antibiotics in urban sewers: Insights from batch reactor experiments

As emerging contaminants in urban wastewater systems, the comprehensive attenuation mechanisms of antibiotics within sewer networks remain underexplored. This work systematically investigated the in-sewer attenuation mechanisms and kinetics of selected antibiotics (sulfamethoxazole, ofloxacin, roxithromycin, and azithromycin) through laboratory experiments simulating a coupled wastewater-biofilm-sediment sewer environment. By isolating key processes of hydrolysis, sorption-partitioning, and biodegradation, process-specific attenuation rates under varying water temperatures (15 and 25 °C), pH levels (7 and 9), and initial antibiotics concentrations (0.1, 0.2, and 0.5 μg/L) were determined. Biodegradation was the dominant attenuation with rates ranging from 2.67 × 10 −3 to 13.3 × 10 −3 h −1 for the target antibiotics under experimental conditions. Antibiotic concentration was found to be the primary factor influencing biodegradation, exhibiting a non-monotonic and compound-dependent response, while biodegradation also increased with rising temperature. For hydrolysis, elevated temperatures and alkaline conditions accelerated antibiotic attenuation, with rates varying from 0 to 6.09 × 10 −3 h −1 . Antibiotics sorbed to sediments were reduced under higher pH and temperature conditions, with equilibrium sorption-partitioning coefficients of 0.03–2.35 L/kg. Sorption-partitioning affected overall antibiotic attenuation by reducing the aqueous-phase concentration available for biodegradation and hydrolysis. Overall, this study highlights the vital role of urban sewer networks as pretreatment reactors for antibiotics prior to their entry into wastewater treatment plants, and also provides kinetic attenuation rates reference for developing sewer water quality model to quantitatively assess the contribution of urban sewer systems to mitigating aquatic antibiotic risks.