Removal of antibiotics in conventional and advanced wastewater treatment: Implications for environmental discharge and wastewater recycling

Removal of 28 human and veterinary antibiotics was assessed in a conventional (activated sludge) and advanced (microfiltration/reverse osmosis) wastewater treatment plant (WWTP) in Brisbane, Australia. The dominant antibiotics detected in wastewater influents were cephalexin (med. 4.6 μg L−1, freq. 100%), ciprofloxacin (med. 3.8 μg L−1, freq. 100%), cefaclor (med. 0.5 μg L−1, freq. 100%), sulphamethoxazole (med. 0.36 μg L−1, freq. 100%) and trimethoprim (med. 0.34 μg L−1, freq. 100%). Results indicated that both treatment plants significantly reduced antibiotic concentrations with an average removal rate from the liquid phase of 92%. However, antibiotics were still detected in both effluents from the low-to-mid ng L−1 range. Antibiotics detected in effluent from the activated sludge WWTP included ciprofloxacin (med. 0.6 μg L−1, freq. 100%), sulphamethoxazole (med. 0.27 μg L−1, freq. 100%) lincomycin (med. 0.05 μg L−1, freq. 100%) and trimethoprim (med. 0.05 μg L−1, freq. 100%). Antibiotics identified in microfiltration/reverse osmosis product water included naladixic acid (med. 0.045 μg L−1, freq. 100%), enrofloxacin (med. 0.01 μg L−1, freq. 100%), roxithromycin (med. 0.01 μg L−1, freq. 100%), norfloxacin (med. 0.005 μg L−1, freq. 100%), oleandomycin (med. 0.005 μg L−1, freq. 100%), trimethoprim (med. 0.005 μg L−1, freq. 100%), tylosin (med. 0.001 μg L−1, freq. 100%), and lincomycin (med. 0.001 μg L−1, freq. 66%). Certain traditional parameters, including nitrate concentration, conductivity and turbidity of the effluent were assessed as predictors of total antibiotic concentration, however only conductivity demonstrated any correlation with total antibiotic concentration (p=0.018, r=0.7). There is currently a lack of information concerning the effects of these chemicals to critically assess potential risks for environmental discharge and water recycling.