This paper investigates the electrochemical oxidation of the reactive dyes reactive blue 4 (RB-4) and reactive orange 16 (RO-16) on RuO2 dimensionally stable anode (DSA®) electrodes. Electrolysis was achieved under galvanostatic control as a function of supporting electrolyte and electrode composition. The electrolyses, performed in either the presence or absence of NaCl, were able to promote efficient color removal; moreover, at low chloride concentration (0.01 mol L-1), total color removal was obtained after just 10 min of electrolysis, and a significant increase in total dye combustion was achieved for all the studied anodes in chloride medium (reaching ca. 80% - chemical oxygen demand - COD removal). No significant enhancement in dye color removal or mineralization was observed upon increasing chloride concentration. The influence of oxide composition on dye elimination seems to be significant in both media (with or without chloride), being Ti/Ru0.30Ti0.70O2, the most active material for organic compound oxidation. The oxygen evolution reaction (OER) was shown to be a limiting reaction in both supporting electrolytes; i.e., NaCl and Na2SO4, and its competition with organic compound oxidation remained an obstacle. The adsorbable organo halogens (AOX) formation study revealed that there is slight consumption of the undesirable species formed within the first minutes of the electrolysis, being Ti/(RuO2)0.70(Ta2O5) 0.30 the most environmentally friendly composition. Both anode composition and chloride concentration affect the formation of these undesirable compounds.
reactive dyes; electrochemical oxidation; DSA® electrodes; wastewater; AOX
