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

•Degradation of drug sulfamethazine by electro-Fenton-pyrite using BDD and Pt anodes.•Almost total mineralization (96%) of 55.6 mg L−1 sulfamethazine aqueous solution.•Absolute rate constant for the oxidation of SMT by OH of (1.87 ± 0.01) × 109 M−1 s−1.•Identification of 6 aromatic intermediates and 6 short-chain carboxylic acids.•Toxicity assessment by bioluminescence inhibition of Vibrio fischeri.

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 electrochemical 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 was determined by the competition kinetics method and found to be 1.87 × 109 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.

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