Removal of trace antibiotics from wastewater: A systematic study of nanofiltration combined with ozone-based advanced oxidation processes

• Nanofiltration was efficient in removing antibiotics from WWTP effluent.
• UV/O3 process could effectively eliminate antibiotics in NF concentrate.
• Biodegradability and toxicity of NF concentrate were improved by UV/O3 treatment.
• Zero discharge of micropollutants from WWTPs is possible by the proposed scheme.

This work did a systematic investigation on removal of trace antibiotics from wastewater treatment plant (WWTP) effluent through nanofiltration (NF), and disposal of the NF concentrate by advanced oxidation processes (AOPs). Four antibiotics, namely, norfloxacin (NOR), ofloxacin (OFL), roxithromycin (ROX) and azithromycin (AZI), which had high detection frequencies in effluents from WWTPs in Dalian (China), were selected as the target micropollutants. High rejections of antibiotics (>98%) were obtained in all sets of NF experiments. UV254 photolysis, ozonation and UV/O3 process were employed to treat NF concentrate. Results demonstrated that UV254 photolysis was not effective in degrading the four antibiotics, while ozone-based processes exhibited high removal efficiencies in 30 min. A synergetic effect between O3 and UV was observed in degradation of the selected antibiotics during UV/O3 treatment. Generation of hydroxyl radicals in the process was testified using electron paramagnetic resonance (EPR) spin trapping technology. In treatment of NF concentrate from real secondary effluent, UV/O3 process achieved excellent removal efficiencies of antibiotics (>87%), a partial removal of dissolved organic carbon (DOC) (40%), an increase of BOD5/COD ratio (4.6 times), and a reduction of acute toxicity (58%). The study revealed that nanofiltration could efficiently remove antibiotics from WWTP effluent, and meanwhile, UV/O3 process was able to further eliminate the antibiotics in the NF concentrate effectively.

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