Removal of Benzoic Acid Derivatives from Aqueous Effluents by the Catalytic Decomposition of Hydrogen Peroxide

Abstract

The batch catalytic oxidation of a synthetic effluent containing benzoic acid derivatives (p-hydroxybenzoic, gallic and vanillic acids) using hydrogen peroxide and Cu2+ ions at temperatures from 25 to 80 °C, hydrogen peroxide concentrations from 0.22 to 9.3 gl−1, catalyst concentrations from 6 to 300 mgl−1 and initial pH values from 1.7 to 10 has been investigated. At the conditions under consideration, total organic carbon (TOC) removal rates generally increased with increasing temperature, hydrogen peroxide and catalyst concentrations. Alkaline or strongly acidic conditions (i.e. pH values outside the range 3–7) appeared to have a detrimental effect on total oxidation rates. The Cu2+/H2O2 system was found to be capable of removing most of the organic carbon at relatively short times and moderate temperatures with 85% and nearly 100% TOC removal being recorded after 120min at 60 °C and 60 min at 80 °C, respectively. In this respect, the Cu2+/H2O2 system was found to be more effective than the typical Fenton's reagent (Fe2+/H2O2). The hydrogen peroxide catalytic decomposition (in the absence of organics) has also been investigated. Copper and iron ions were both capable of rapidly decomposing hydrogen peroxide; at temperatures higher than ambient, Cu2+-catalysed decomposition was always faster than the Fe2+-catalysed one.