Cutting oil-water emulsion wastewater treatment by microwave assisted catalytic wet peroxide oxidation

Cutting-oil in water emulsions (COWE) suppose an environmental threat due to their high volume, stability and low biodegradability (BOD5/COD: 0.07). So far, these effluents have been treated by physical methods which merely transfer the pollutants into another phase. In this work, Microwave-assisted Catalytic Wet Peroxide Oxidation (MW-CWPO) is used for the first time in the degradation of COWE 0.5%w, using graphite as catalyst. Working at pH(0): 9, graphite: 10 g/L, 15.7 g/L H2O2, at MW power of 800 W by pulsation method, complete demulsification and 82% Total Organic Carbon (TOC) removal is achieved in only 10 min. Furthermore, the remaining TOC in solution is mainly ascribed to malonic, acetic and formic acids, which results in readily biodegradable effluents (BOD5/COD: 0.93). The degradation mechanism is a complex combination of H2O2-mediated adsorption of the pollutants onto the graphite's surface and its subsequent oxidation mediated by hot-spots induced by MW radiation. This work also studies the influence of pH(0), catalyst load and H2O2 dosage in COWE degradation. Finally, catalyst stability upon 3 consecutive cycles was tested and various techniques are proposed and examined for catalyst regeneration.