A first pre-pilot system for the combined treatment of dye pollutants by electrocoagulation/EAOPs

BACKGROUND: Based on promising results obtained at laboratory scale with a two-step electrochemical treatment of Tartrazine solutions by electrocoagulation (EC) coupled with electrochemical advanced oxidation processes (EAOPs), this work addresses its scale-up to degrade 1.85 dm(3) of solutions of this dye. Monopolar and bipolar configurations have been compared in EC. The effect of supporting electrolyte, pH, applied current, dye concentration and electrolysis time has been assessed. RESULTS: Electrocoagulation with four Fe electrodes was first optimized for the treatment of 278 mg dm(-3) Tartrazine solutions. The bipolar series configuration led to enhanced coagulation due to the larger electrode consumption. Solutions with 0.05 mol dm(-3) NaCl at pH 6.3 were quickly decolorized with 60% total organic carbon removal, being more convenient than Na2SO4 and NaNO3 electrolytes due to the synergistic action of coagulation and oxidation by active chlorine. Among the EAOPs, carried out with a Ti/IrO2-RuO2 anode and an air-diffusion cathode to electrogenerate H2O2, electro-Fenton (EF) with 0.5 mmol dm(-3) Fe2+ was much better than electro-oxidation owing to the oxidative action of active chlorine and (OH)-O-center dot formed in the bulk from Fenton's reaction. Photoelectro-Fenton (PEF) was even better by the additional photolysis of by-products under incident UVA photons. CONCLUSIONS: The use of an EC reactor in bipolar configuration for 12.5 min at 1.50 A followed by PEF treatment for 360 min at 1.50-2.00 A ensured mineralization >90%, which encourages further optimization at larger scale for the treatment of a variety of organic pollutants in real wastewaters. (C) 2014 Society of Chemical Industry