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

  • K. Nasr Esfahani
  • M. FarhadianEmail author
  • A. R. Solaimany Nazar
Original Paper


In this research, the interaction effects between pH (range from 2 to 5), temperature (20–60 °C), current density (5–20 mA/cm2), hydrogen peroxide per chemical oxygen demand \( \frac{{{\text{H}}_{2} {\text{O}}_{2} }}{\text{COD}} \) (0.2–0.75), and reaction time (45–135 min) for spent caustic wastewater treatment were assessed through electro-photo-Fenton oxidation process by using response surface methodology. The optimum conditions for Esfahan oil refinery’s spent caustic wastewater treatment with an experimental COD removal of 97% were obtained at 4.5 (pH), 60 °C, 16.6 mA/cm2, 0.69 (\( \frac{{{\text{H}}_{2} {\text{O}}_{2} }}{\text{COD}} \)), 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.

Graphical abstract


AOP Electro-photo Fenton RSM Sulfidic spent caustic Wastewater treatment 





Chemical oxygen demand


Advanced oxidation processes


Response surface methodology


Wet air oxidation


Occupational Safety and Health Administration


Central composite design



This study was supported by the University of Isfahan and a grant from EORC [Grant Numbers D234]. The authors wish to acknowledge the co-operation of EORC’s R&D department for providing wastewater samples and laboratory equipment.


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Copyright information

© Islamic Azad University (IAU) 2019

Authors and Affiliations

  1. 1.Department of Chemical Engineering, Faculty of EngineeringUniversity of IsfahanIsfahanIran
  2. 2.Utility PlantEsfahan Oil Refining CompanyIsfahanIran
  3. 3.Environmental Research InstituteUniversity of IsfahanIsfahanIran

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