Pyrite as a sustainable catalyst in electro-Fenton process for improving oxidation of sulfamethazine. Kinetics, mechanism and toxicity assessment

The degradation of 0.20 mM sulfamethazine (SMT) solutions was investigated by heterogeneous electro-Fenton (EF) process using pyrite as source of Fe2+ (catalyst) and pH regulator in an undivided electro-chemical cell equipped either with a Pt or a BDD anode and carbon-felt as cathode. Effect of pyrite concentration and applied current on the oxidative degradation kinetics and mineralization efficiency has been studied. The higher oxidation power of the process, named "Pyrite-EF" using BDD anode was demonstrated. Pyrite-EF showed a better performance for the oxidation/mineralization of the drug SMT in comparison to the classic EF process: 95% and 87% TOC removal by Pyrite-EF with BDD and Pt anodes, respectively, versus 90% and 83% by classical EF with BDD and Pt anodes, respectively. The rate constant of the oxidation of SMT by (OH)-O-center dot was determined by the competition kinetics method and found to be 1.87 x 10(9) mol(-1) L s(-1). Based on the identified reaction intermediates by HPLC and GS-MS, as well as released SO42-, NH4+ and NO3- ions, a plausible reaction pathway was proposed for the mineralization of SMT during Pyrite-EF process. Toxicity assessment by means of Microtox method revealed the formation of some toxic intermediates during the treatment. However, toxicity of the solution was removed at the end of treatment. (C) 2016 Elsevier Ltd. All rights reserved.