Kinetic, statistical, and cost evaluations in the remediation of spent caustic wastewater by photo-electro-Fenton process

Unsystematic monitoring in disposal and treatment of spent caustic wastewater, reducing energy resources, threatening our environment, and deteriorating water security challenge. In this context, spent caustic wastewater should be effectively remediated regarding its environmentally malign properties due to the presence of different contaminants with complicated formulations. Thus, in this research, the remediation of spent caustic effluent was investigated by the photo-electro-Fenton (PEF) as an advanced oxidation process (AOP). The Box–Behnken design (BBD) was applied for empirical outline and statistical interpretation of each variable, H₂O₂-to-COD ratio, pH, current density, and reaction temperature on the elimination of chemical oxygen demand (COD). The optimum points of variables were as follows: current density at 15.2 mA/cm², H₂O₂-to-COD ratio at 0.57, pH at 3.9, and treatment time of 71 min. In this condition, the predicted and real values of COD removal percent were 96.20 and 97.0%, respectively. The kinetic analysis showed that the COD removal pursued the first-order kinetic model, and the half-life and reaction rate constant in the kinetic were 14.5 min and 0.0479 min⁻¹, respectively. The considered specific energy consumption (SEC) value in the PEF process was 22.71 kWh/m³ removal, showing that this process could be a cost-effective technique for the remediation of spent caustic effluent on a laboratory works. Therefore, based on the overall results, PEF can be a promising and highly effective process for the COD elimination in spent caustic wastewater.