Removal characteristics and mechanism of antibiotics using constructed wetlands

•Antibiotics from livestock wastewater were treated using constructed wetlands.•There was an inverse removal correlation between sulfonamides and tetracyclines.•Physicochemical property is an important control factor in the CWs.•Sunlight photo-degradation effectively removed enrofloxacin in the CWs.•Microbial activity can be an important removal mechanism for sulfonamides.

The occurrence and removal of antibiotics (sulfamethoxazole (SMZ), sulfathiazole (SFI), sulfamethazine (SMA), trimethoprim (TMP), tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC), and enrofloxacin (EFX)) using constructed wetlands (CWs) for treating livestock wastewater were examined. The levels of antibiotics in the effluents of the CWs were in the order of CTC, SFI, SMZ, SMA, TMP, OTC, EFX and TC, ranging from 47.98 to 6834.66 μg/L, respectively. There was an inverse correlation (p < 0.0493) in the removal of between sulfonamide group (SMZ, SFI, and SMA) and tetracycline group (TC, OTC, and CTC) antibiotics in the effluents of the CWs, indicating that sulfonamide-type antibiotics were more effectively removed in the CWs. Sulfonamide-type antibiotics also have higher pKa values, resulting in more effective adsorption into negatively charged soils through electrostatic interaction. Sunlight photo-degradation experiment showed that EFX was effectively removed (70%) compared to other antibiotics. The microcosm adsorption experiment using wetland soils under biotic and abiotic conditions showed that antibiotics in the biotic system were more effectively removed than abiotic system, indicating that soil-mediated microbial degradation can be a major removal mechanism in the CW soils. The microcosm adsorption experiments using wetland plants (Phragmites australis) showed that the biotic system also removed sulfonamide-type antibiotics more effectively compared to the abiotic system. Our results suggest that the removals of antibiotics in the CWs are mainly mediated by biodegradation and adsorption onto soil and plants. Also, the physicochemical property can be the important factors in the removal of antibiotics in the CWs. Our results imply that the CW system can be used for the removal of antibiotics for treating livestock wastewaters.

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