Biodegradation and Adsorption of Antibiotics in the Activated Sludge Process

TLDR

The study used two series of batch reactors treating freshwater and saline sewage to investigate removal of 11 antibiotics from six classes in activated sludge. At environmentally relevant concentrations, biodegradation and adsorption were the dominant removal pathways, with cefalexin and the sulfonamides mainly biodegraded, the remaining antibiotics mainly adsorbed (except erythromycin‑H₂O, which persisted), divalent cations in saline sewage reduced fluoroquinolone adsorption yet allowed some biodegradation, and biodegradation followed first‑order kinetics (R² 0.921–0.997).

Abstract

The removal of 11 antibiotics of 6 classes, that is, two β-lactams (ampicillin and cefalexin), two sulfonamides (sulfamethoxazole and sulfadiazine), three fluoroquinolones (norfloxacin, ofloxacin, and ciprofloxacin), one tetracyclines (tetracycline), two macorlides (roxithromycin and anhydro-erythromycin), and one others (trimethoprim), in activated sludge process was investigated using two series of batch reactors treating freshwater and saline sewage respectively. At environmental relevant concentrations tested in this study, biodegradation and adsorption were the major removal routes for the target antibiotics, where volatilization and hydrolysis were neglectable. Among the 11 target antibiotics, cefalexin and the two sulfonamides were predominantly removed by biodegradation in both freshwater and saline sewage systems. Ampicillin, norfloxacin, ciprofloxacin, ofloxacin, tetracycline, roxithromycin, and trimethoprim were mainly removed by adsorption. Divalent cations (Ca2+ and Mg2+) in saline sewage significantly decreased the adsorption of the three fluoroquinolones onto activated sludge. These three fluoroquinolones also exhibited certain biodegradability in the saline activated sludge reactor. Erythromycin-H2O was persistent in both saline and freshwater systems under the experimental conditions and could not be removed at all. Kinetics study showed that biodegradation of cefalexin, the two sulfonamides and the three fluoroquinolones followed first-order model well (R2: 0.921−0.997) with the rate constants ranging from 5.2 × 10−3 to 3.6 × 10−1 h−1.