Treatment of a biological effluent containing metronidazole

Emerging pollutants like metronidazole (MNZ) affect the removal efficiency of conventional activated sludge (CAS) based wastewater treatment plants and can escape traditional treatment facilities. Advanced oxidation processes (AOPs) and membrane filtration could complement the existing processes to completely eliminate pollutants of emerging concern in wastewaters. This work investigated the application of photochemical processes for treating a synthetic wastewater effluent from CAS treatment and membrane filtration of the biological effluents after CAS experiments with MNZ, caffeine (CAF) and ibuprofen (IBU). Photochemical experiments were conducted in a batch photochemical reactor. The influence of different chemical species such as H₂O₂, Fe(II), K₂S₂O₈ and TiO₂ and of pH value in the system were studied in terms of TOC removal and MNZ degradation. The application of UV/K₂S₂O₈/Fe(II) resulted in 78 % TOC removal in the effluent. Complete degradation of MNZ was observed after 30 min of treatment in the following experiments: UV/H₂O₂/Fe(II) at pH 3 and UV/K₂S₂O₈. Moreover, the effluents were treated by means of a membrane bioreactor (MBR). Polycarbonate track-etch membranes of 50 and 100 nm pore size were used. The results obtained showed that the carbon removal by the MBR was comparable with the conventional biological treatment. Rejection of MNZ depends on the presence/absence of other emerging contaminants in the wastewater effluents.