Quantifying the fate and risk assessment of different antibiotics during wastewater treatment using a Monte Carlo simulation

With increasing antibiotic use, more antibiotics are being discharged into wastewater treatment plants, which are not designed to effectively remove emerging pollutants. A fate model based on a Monte Carlo simulation was established by combining secondary and tertiary treatment processes to investigate the fate of six types of antibiotics during various treatment processes. The results showed that the distribution of the antibiotic concentrations in wastewater influent was strongly dependent on antibiotic type. During the secondary and tertiary wastewater processes, norfloxacin and ciprofloxacin showed higher average removals (71.5 +/- 3.8% and 78.4 +/- 6.9%) during secondary treatment than the other four types of antibiotics. The total antibiotic removal efficiencies depended mainly on the tertiary process, with average removals of 97.9% by reverse osmosis, 93.0% by ozone oxidation, and 84.2% by powder activated carbon adsorption when combined with conventional sludge-based wastewater treatment. Reverse osmosis showed high removal efficiencies for all six antibiotics, with no particular selectivity. Ozone treatment showed significant negative correlations between antibiotics removal and molecular weight (r: -0.965, p = 0.002), Log octanol-water partition coefficient (r: -0.921, p = 0.009), and acid dissociation constant (r: -0.847, p = 0.033). After the reverse osmosis-based combination treatment, all antibiotics had risk quotients <1, indicated that reverse osmosis could significantly reduce the toxicity of antibiotics to the environment. After ozone- and powder activated carbon-based combination treatments, the remaining erythromycin and ciprofloxacin in effluent still had risk quotients >1. These results can be used to support the optimization of combined treatment of wastewater and risk assessments of antibiotics in the environment. (C) 2017 Elsevier Ltd. All rights reserved.