Treatment of spent caustic wastewater by electro-Fenton process: Kinetics and cost analysis

Abstract

Spent caustic is a highly contaminated wastewater from critical industries with complicated chemistry and different environmental adverse effects. Conventional wastewater remediation approaches are not effective enough for the remediation of spent caustic. Hence in this study, Electro-Fenton (EF) technology as a subsection of Advanced Oxidation Processes (AOPs) was applied for the removal of chemical oxygen demand (COD) in spent caustic effluent. For statistical analysis and experimental design of each factor including H2O2/COD, current density, pH, and treatment time on the COD removal (response), the Box Behnken Design (BBD) was used. The optimal conditions for operating factors were as the following: H2O2/COD = 0.73, pH= 5.46, current density = 18.83 mA/cm2 and treatment time= 69.88 min. In these conditions, the actual and predicted COD removal was 93.0% and, 94.38%, respectively. Finally, it concludes that Electro-Fenton technology was reliable and outstandingly efficient for COD removal in spent caustic wastewater. The kinetic studies confirmed that the removal of COD tracked the first-order kinetic model and the constant reaction rate and half-life of COD removal kinetic were 0.0257 min−1 and 27 min, respectively. The operating costs analysis showed that the Electro-Fenton process had lower operating costs and it can be a good opportunity for the treatment of spent caustic wastewater on an industrial scale. The operational cost for this process was found to be 1.562$ M−3kg−1COD removal.