Occurrence of antibiotics in the different biological treatment processes, reclaimed wastewater treatment plants and effluent-irrigated soils

Abstract

Reclaimed wastewater is increasingly being used for agricultural irrigation to address water scarcity, particularly in arid and semiarid areas. In this study, the occurrence and removal of 24 antibiotics were investigated in two wastewater treatment systems (WWTSs) and their irrigation areas located in the arid northwestern region of China. The different WWTSs included absorption–biodegradation (AB) + anaerobic–anoxic–oxic (AAO) and AAO + AAO + membrane bioreactor (MBR). Nineteen antibiotics were detected, with concentrations ranging from low to 60.8 μg/L. The dominant antibiotic classes were quinolones (QNs) and macrolides (MLs) in winter, and MLs and sulfonamides (SAs) in summer. The AAO + AAO + MBR system exhibited better removal efficiencies for most antibiotics, improving their adsorption and biodegradation. Except for ofloxacin (OFC) and norfloxacin (NFC), the concentrations of the detected antibiotics were higher in summer than in winter. However, the antibiotic removal efficiency increased by 2–141% in summer compared to winter due to the increase in microbial activity with temperature. Even though reclaimed treatment water plants contributed to the removal of antibiotics, residual antibiotics still affected the soil environment after green irrigation. In irrigated soil, QNs were predominantly detected, with a maximum concentration of 150.9 ng/kg for NFC. An ecological risk assessment showed that OFC, NFC, enrofloxacin, and lomefloxacin presented low or medium ecological risks in at least two irrigated sites. Thus, more attention should be given to the reuse of reclaimed wastewater, as it may pose toxicity risks to organisms in the soil environment.