Comparative degradation of benzoic acid and its hydroxylated derivatives by electro-Fenton technology using BDD/carbon-felt cells

Abstract

This study aims the oxidation comparison of the benzoic acid and its hydroxylated derivatives by the electro-Fenton process using BDD/Carbon-felt cells. In this context, the degradation process of benzoic acid, constituting the parent molecule of several phenolic compounds, was undertaken by electro-Fenton method adopting the Response Surface Methodology (RSM); precisely the Centered Composite Design (CCD). The optimum conditions determined (Fe2+ concentration = 0.03 mM, applied current =300 mA, benzoic acid concentration = 0.2 mM and electrolysis time =60 min), were applied to degrade a series of hydroxybenzoic acids, namely; salicylic, protocatechic, and gallic acids. The degradation rates for all these acids were in the following order: Gallic acid > protocatechic acid > salicylic acid > benzoic acid, and their almost total degradation was achieved in two hours. Mineralization of the benzoic acid and its hydroxylated derivatives was followed by the chemical oxygen demand (COD) analysis, where a complete mineralization was achieved within 4 h for protocatechic and gallic acids and within 5 h for benzoic and salicylic acids. This result highlights the potential application of electro-Fenton process using BDD/Carbon-felt cells to the complete removal of aromatic carboxylic acids from contaminated water.