Combined Electro-Fenton and Anodic Oxidation Processes at a Sub-Stoichiometric Titanium Oxide (Ti4O7) Ceramic Electrode for the Degradation of Tetracycline in Water

Busisiwe N Zwane,Valérie Bonniol,Eddy Petit,Babatunde A Koiki,Marc Cretin,Nonhlangabezo Mabuba,Geoffroy Lesage,Benjamin O Orimolade,Chaimaa Gomri,Omotayo A Arotiba,Matthieu Rivallin

doi:10.3390/w13192772

Abstract

The mineralization of tetracycline by electrochemical advanced oxidation processes (EAOPs) as well as the study of the toxicity of its intermediates and degradation products are presented. Electro-Fenton (EF), anodic oxidation (AO), and electro-Fenton coupled with anodic oxidation (EF/AO) were used to degrade tetracycline on carbon felt (cathode) and a sub-stoichiometric titanium oxide (Ti4O7) layer deposited on Ti (anode). As compared to EF and AO, the coupled EF/AO system resulted in the highest pollutant removal efficiencies: total organic carbon removal was 69 ± 1% and 68 ± 1%, at 20 ppm and 50 ppm of initial concentration of tetracycline, respectively. The effect of electrolysis current on removal efficiency, mineralization current efficiency, energy consumption, and solution toxicity of tetracycline mineralization were investigated for 20 ppm and 50 ppm tetracycline. The EF/AO process using a Ti4O7 anode and CF cathode provides low energy and high removal efficiency of tetracycline caused by the production of hydroxyl radicals both at the surface of the non-active Ti4O7 electrode and in solution by the electro-Fenton process at the cathodic carbon felt. Complete removal of tetracycline was observed from HPLC data after 30 min at optimized conditions of 120 mA and 210 mA for 20 ppm and 50 ppm tetracycline concentrations. Degradation products were elucidated, and the toxicity of the products were measured with luminescence using Microtox® bacteria toxicity test.

Highlights

Using the combined EF/anodic oxidation (AO) system, this study investigates the extent of mineralization, the toxicity of oxidation by-products, and degradation pathways resulting from the degradation of tetracycline
A similar trend was observed with ppm TC where ± 1%, 61 ± 2% and 68 ± 1% total organic carbon (TOC) removal was recorded using EF, AO, and electro-Fenton coupled with anodic oxidation (EF/AO) respectively (Table 1)
The mineralization of tetracycline by electrochemical advanced oxidation processes (EAOPs) using Ti4 O7 as anode and carbon felt as the cathode was successful

Summary

Introduction

Antibiotics are a class of pharmaceuticals that are extensively used to treat and prevent disease in humans and animals [5]. The concentrations of these antibiotics have been found to range between 116 and 750 ng/L in wastewater influents and 52 to 85 ng/L in effluents, worldwide [6]. Tetracycline is an antibiotic used widely for human, animal, and agricultural purposes [3]. Due to the wide usage and poor absorption of tetracycline, it is excreted through feces and urine and has been found in surface water, ground water, and wastewater in many places around the world [2,7]

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Results

Conclusion