Anodic oxidation of 2,4-dihydroxybenzoic acid for wastewater treatment

Dihydroxybenzoic acid (2,4-DHBA) is used as an intermediate chemical reactant in industrial synthetic processes. Disinfection of water contaminated by 2,4-DHBA, using chlorinating techniques, generates trihalomethane compounds, so that alternative degradation techniques are of interest. The electrochemical oxidation of 2,4-dihydroxybenzoic acid (2,4-DHBA) at a platinized titanium electrode was investigated. An electroanalytical study by linear and cyclic voltammetry showed adsorption of the reagent at the electrode surface. Mathematical treatment of cyclic voltammetry curves indicates Langmuir type adsorption. For electrolysis, working in the oxygen evolution region causes an increase in electroactive electrode surface area and better mass transfer at the electrode. For example, for an initial 2,4-DHBA concentration of 0.3 kg m^–3 and a current density of 300 A m^–2, almost complete conversion of the pollutant is obtained after passing 4 A h, together with a TOC decrease of 30%. Byproducts of electrodegradation include 2,3,4- and 2,4,5-trihydroxybenzoic acids (THBA), maleic acid, glyoxalic acid and oxalic acid. The faradaic yield is less than 18%, due to oxygen evolution during electrolysis.