Catalytic ozonation promoted by Mn-doped sludge-based catalyst treating refractory industrial wastewater

Attributed to the refractory characteristic of industrial wastewater, it usually needs advanced treatment. Moreover, massive hazardous activated waste sludge generated from wastewater treatment introduces additional ecological risks. In this study, sludge-based catalysts were prepared by doping Mn to treat typical refractory wastewater of petrochemical secondary wastewater. Results showed that the Mn-doped catalyst (PS-M700) prepared by pyrolysis at 700 degree celsius was optimal for the catalytic ozonation of petrochemical secondary wastewater. The optimal ozone and catalyst dosage were 216 mg/L and 1.0 g/L, respectively. Catalytic ozonation of petrochemical secondary wastewater using PS-M700 showed an excellent TOC removal efficiency of 56.6 %. In addition, hydroxyl radicals ((OH)-O-center dot) played a major role in the catalytic ozonation of the petrochemical secondary wastewater. Results of excitation-emission matrix fluorescence spectroscopy showed that catalytic ozonation can further enhance the removal efficiency of not readily biodegradable compounds compared to ozone alone. Moreover, the catalytic ozonation process mainly targeted substances within the molecular weight (MW) < 1 kDa range in petrochemical secondary wastewater. In addition, transformation processes occurred between pollutants of different MW. Fourier Transform ion cyclotron resonance mass spectrometry showed that oxygen (CHO), nitrogen (CHONO) and sulfur (CHOS) containing contaminants were decreased by 6.0 % (2359 vs 2216), 34.9 % (2505 vs 1631) and 62.8 % (1227 vs 456). The present study shows the satisfactory prospect of a sustainable "wastes-treating-wastes" process for wastewater treatment.