Screening and quantitation of residual antibiotics in two different swine wastewater treatment systems during warm and cold seasons.

Due to many occurrences of the illegal addition, misuse and abuse of antibiotics in the swine industry in China, high-resolution mass spectrometry (HRMS) was used to screen and identify these materials in two swine wastewater treatment systems (Swine farm 1: anaerobic digestion - lagoon treatment; Swine farm 2: anaerobic digestion - anoxic treatment - aerobic biological treatment). The results showed that 11 out of 115 antibiotics, including tetracyclines (tetracycline, oxytetracycline, chlortetracycline), sulfonamides (sulfadimidine (SDMD)), macrolides (clarithromycin, tilmicosin (TILM)), fluoroquinolones (ciprofloxacin, ofloxacin, enrofloxacin), β‑lactam (penicillin G), and lincosamides (lincomycin), were identified in the swine farms by screening and confirmation methods through HRMS. The quantification method was carried out using triple-quadrupole tandem mass spectrometry, and the recoveries of 11 analytes in the swine wastewater were above 50%. The investigation results showed that the amount of antibiotic residues during the cold season was much higher than that during the warm season. Among the antibiotics, tetracyclines (average of 58%) were the main antibiotic residues in the two swine farms, with TILM second (33%). Sulfonamides (SDMD) existed only in SF1 and accounted for 10% of the total antibiotic concentration. The average proportion of total antibiotics in the solid and liquid phases were 98.5% and 1.5%, respectively, indicating that antibiotics were mainly adsorbed onto solids, though only SDMD remained relatively high in the liquid phase (5.29%). The degradation data of most of the antibiotics detected in the liquid phase during the wastewater treatments well fitted the simple first-order kinetic model in both SF1 and SF2, and the half-lives of the analytes in SF2 were much shorter than those in SF1. After the wastewater treatment process, approximately 80% of the antibiotics could be removed, but sulfonamides remained at a relatively higher percentage and were the main antibiotics in the effluent (approximately 60%).