Spent caustic oxidation using electro-generated Fenton's reagent in a batch reactor

Abstract

This work shows the results of four Electro-Fenton laboratory tests to reduce the chemical oxygen demand (COD) in spent caustic solutions. The treatment consisted of (i) a pH reduction followed by (ii) an Electro-Fenton process, which was analyzed in this work. The Fenton's reagent was produced in a specially designed reactor, where the waste stream flowed through a labyrinth made by ferrous plates. These plates acted as sacrificial anodes—releasing Fe^{2 +} cations to the solution, where H₂O₂ was also added. The Electro-Fenton process was analyzed varying the ferrous ion concentration ([Fe^{+ 2}]), the spent caustic's initial temperature and the initial pH. Close to 95% removal of COD (from 8800 mg L^{− 1}) was achieved at a pH of 4, a temperature of 40°C and 100 mg L^{− 1} of Fe^{+ 2} (applying 1 A). Two models were considered to simulate the behavior of the reactor considering (i) axial dispersion and (ii) kinetic rate, respectively. The model that was based on kinetics, proved to be the slightly closest fit to the experimental values.

Keywords:

• Electro Fenton
• Fenton reagent
• electrochemical oxidation
• spent caustic

Acknowledgments

The authors would like to acknowledge the financial support of the Chilean Comisión de Investigación en Ciencias y Tecnología, Conicyt (Proyecto Regular FONDECYT 1085118) and project USM 27.07.28.