Interaction effects of various reaction parameters on the treatment of sulfidic spent caustic through electro-photo-Fenton

In this research, the interaction effects between pH (range from 2 to 5), temperature (20-60 degrees C), current density (5-20 mA/cm(2)), hydrogen peroxide per chemical oxygen demand H2O2COD, and 80 min. The interaction effects of hydrogen peroxide with pH; hydrogen peroxide with temperature; and temperature with reaction time were considered essential, which indicated the dependency among the factors. However, the interaction effect between pH and hydrogen peroxide was found so significant for chemical pollutant removal due to the activity of both iron ions and hydrogen peroxide. The pH reduction step of spent caustic (pH < 5) could lead toward the COD removal of 45% in the form of hydrogen sulfide gas. Complementary tests were run on the precipitated chemical sludge at optimal conditions to find organic contaminants, which indicated the chemical sludge mainly contains FeSO4 and Na2SO4. It was shown that advanced oxidation process for the degradation of contaminants was efficient and pollutants did not add to the sediment in the sludge phase.