Efficient electrochemical advanced degradation of Red CL and Red WB dyes from the tanning industry using a...

Electrochemical oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) with a BDD anode have been comparatively assessed to remediate solutions of Red CL and/or Red WB azo dyes from real raw water. For the EO process in 50 mM Na₂SO₄ at pH 3.0, the main oxidant was the heterogeneous ^•OH generated at the anode, whereas in EF and PEF, the cathodic production of H₂O₂ and the addition of 0.50 mM Fe²⁺ catalyst additionally originated homogeneous ^•OH that enhanced the oxidation of organics. In PEF, the solution was illuminated with a 6 W UVA light. An almost total discoloration was always found operating with a 1:1 mixture of 200 mg L^-1 of both dyes in 60 min, whose efficiency increased in the order of EO < EF < PEF. The HPLC analysis of the dye mixture treated by PEF disclosed that its degradation process agreed with its discoloration. A high 74% of COD was reduced due to the oxidative action of hydroxyl radicals and the photolysis of final Fe(III)-carboxylate species with UVA irradiation. The process was accompanied by an energy consumption of 0.76 kWh (g COD)^-1, a value similar to the energy consumed by the applied UVA light.