Performance of integrated treatment system of photofenton and membrane bioreactor for synthetic spent caustic wastewater

Abstract

The potential of a combined integrated treatment system using photo-Fenton process and membrane bioreactor (MBR) was studied in the treatment of spent caustic wastewater with initial COD and sulfide of 1990-2740 mg/L and 82-165 mg/L, respectively and at biodegradability level (BOD5/COD) of 0.39-0.52. Photo- Fenton process was carried out to reduce influent toxicity that can destroy living microorganism in the MBR. Molar ratio of hydrogen peroxide to COD values ([H2O2/COD]), ferrous ion to hydrogen peroxide [Fe2+/H2O2], and reaction time were studied on degradation of chemicals contained in the wastewater within the range of 1.5-2.5, 0.05-0.15 and 0-60 minutes. A statistical experimental design using central composite design (CCD) was employed to describe the relationship of individual and combined parameters towards the degradation. The optimum conditions were selected based on the highest percentage of COD and sulfide removal as well as acceptable BOD5/COD with minimum value of molar ratio [H2O2/COD] and [Fe2+/H2O2] within reaction time range. Optimum conditions for molar ratio [H2O2/COD] and [Fe2+/H2O2] at pH of 3 were 1.5 and 0.05 with reaction time of 47.84 minutes. The optimum condition for MBR was evaluated based on critical flux value. It was observed that critical flux was achieved at flux of 6 and 9.5 L m-2 h-2. The achievement of optimal conditions for both processes led to the assessment of the integrated treatment. It was found that the overall percentage removal of COD and sulfide were 99.27–99.92% and 100% leading to final effluent with COD and sulfide concentrations of 20 mg/L and 0.001 mg/L, respectively. It can be concluded that the integrated treatment system combining photo-Fenton and MBR could be an efficient alternative method for spent caustic wastewater.