Fate and mass loading of antibiotics in hospital and domestic wastewater treatment plants in Bangkok, Thailand

Abstract

Excessive and inappropriate use of antibiotics contributes to the spread of antibiotic resistance in the environment, especially in low-to middle-income countries. This study investigated the occurrence, relative abundance, and fate of eight antibiotics at each treatment stage in four domestic and four hospital wastewater treatment plants (dWWTPs and hWWTPs, respectively), as well as mass loadings into the receiving water environments in Bangkok, Thailand. Samples were prepared by solid-phase extraction and analyzed by high-performance liquid chromatography–tandem mass spectrometry. Antibiotic concentrations were higher in hWWTPs than dWWTPs; approximately 60 times for influents and 10 times for effluents. Ciprofloxacin concentration increased in most dWWTPs, especially in the aeration unit and return sludge, suggesting that it predominantly occurred in the solid phase. Sulfamethoxazole predominantly occurred in the dissolved form, which is more difficult to degrade, and exhibited high concentrations in effluent. Moreover, antibiotic pollutant loadings were approximately 30–3,530 times higher from dWWTPs than from hWWTPs due to higher daily discharges from the domestic sector. These plants are a major point source of antibiotic residue release to aquatic environments; thus, their efficiency should be improved by incorporating advanced treatment processes to ensure effective removal of antibiotics.