Assessment of sulfate radical-based advanced oxidation and electrocoagulation processes for spent caustic treatment from olefin unit

The treatment of the spent caustic effluent from an olefin plant applying the sulfate radical-based advanced oxidation process (SR-AOP) and its combination with the electrocoagulation process (AOP + EC) have been evaluated. For this purpose, the iron plate was selected as anode and cathode in the EC process. Box-Behnken design based on response surface methodology was used for optimization. Accordingly, the maximum removal were obtained at pH of 3.9 and 3.4, reaction time of 64.6 and 84.5 min, and persulfate concentration of 3.6 and 3.9 g/L for AOP and AOP + EC processes, respectively. Additionally, the experimental results reveal the higher final efficiency of AOP + EC in comparison with AOP as the former yielded a Chemical oxygen demand (COD) reduction of 92% under optimum operating conditions. Moreover, as ANOVA represents the good coefficients for the COD removal, pH has the most significant influence on the treatment process. Definitive agreements between the experimental data and the statistical ones were obtained from the correlations for the COD at the optimum conditions. The study results indicate that the AOP + EC processes could be used as a complementary facility to reduce the amount of COD of spent caustic from an olefin plant.