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.