Fate Evaluation of Antibiotics and Metabolites in an Advanced Biological Wastewater Treatment Plant in the Wastewater-Sewage Sludge-Side Continuum: A Holistic Approach

Abstract

This study examined the seasonal fate of 11 antibiotics (eight parent compounds and three metabolites) across all wastewater and sludge treatment units of a large-scale municipal wastewater treatment plant (WWTP). Antibiotics that increased significantly in raw wastewater during the flu season-ciprofloxacin (CIP), sulfamethoxazole (SMX), N-acetyl-sulfamethoxazole (Ac-SMX), trimethoprim (TMP), clarithromycin (CLA), and azithromycin (AZI)-were detected at seasonal concentrations ranging from <10 to 5872.5 ng/L. Owing to the limited removal capacity of the aerated grit chamber and primary clarifier units, antibiotic removal in the pretreatment stage of the plant was poor, ranging from -9.0 to 15.8%. The results indicate that biological treatment is crucial for antibiotic removal, primarily through biodegradation and/or biotransformation in both anoxic and aerobic zones. High removal efficiencies (61.2->95.2%) were achieved for all antibiotics in the biological treatment stage, except TMP. Accordingly, liquid phase removal of the studied antibiotics was classified as: (i) untreated: TMP (-57.6%) and metronidazole (MET) (-1376.8%); (ii) poorly treated: SMX (18.8%); and (iii) moderately to well-treated: CLA (64.6%), AZI (74.6%), CIP (>80.3%), and Ac-SMX (>90.9%). Additionally, antibiotic removal in the liquid phase was further enhanced by sorption onto sewage sludge, particularly for fluoroquinolones (FQs) and macrolides (MLs). Among the antibiotics studied, CIP and CLA were detected in all sludge types (from primary to dewatered sludge) along the plant's sludge line. Besides these, antibiotic concentrations in sidestreams generated in the WWTP occasionally exceeded those in raw wastewater, resulting in an additional average annual antibiotic load of <3.2% (TMP) to 9.2% (CLA) per compound.