Biological and chemical-ozone oxidation of emerging micropollutants in wastewater treatment plants

Pharmaceuticals are found in significant quantities in municipal wastewater, probably because of their incomplete biotransformation by human or animal metabolization. They are not completely eliminated through conventional wastewater treatment and are subsequently released into the aquatic environment. More advanced treatment is required for the effective reduction of the quantity of pharmaceuticals entering the environment. Among the available technical treatments, tertiary ozonation has proved an economically feasible and highly effectivewayof removing awide range of contaminants. Like other oxidative treatments, ozonation leads to major changes in the water composition. Consequently, it is important to evaluate the toxic potential of the treated effluent through relevant ecotoxicological end points. This pilot study took place at the Bellecombe WWTP (France). A mixture of municipal and hospital wastewater was treated by conventional activated sludge (CAS) followed by tertiary ozonation at three transferred ozone doses ranging from 0.45 to 2.30 mg O3/mg DOC with a hydraulic contact time of 5 minutes. To characterize the removal efficiencies of both CAS and CAS with tertiary ozonation, 12 pharmaceuticals were tested. Endocrine disruption tests were conducted to assess the toxic potential of the effluents. The overall elimination yields achieved by CAS were 48% with a high standard deviation (above 18%). The addition of tertiary ozonation greatly improved the global removal to 92% (+/- 4%) for an average transferred ozone dose of 0.45 mg O3/mg DOC. Increasing the ozone dose to 1.30 mg O3/mg DOC significantly enhanced the removal of the pharmaceuticals, with kO3 below 105 M-1.s-1. In addition, estrogenic, androgenic, and glucocorticoid endocrine disruption were all reduced in the ozonation stage. Ozonation proved to be highly effective in removing pharmaceuticals at low ozone doses, while simultaneously reducing the potential of endocrine disruption activities compared with biological treatment by conventional activated sludge.