Fenton and Electro-Fenton Methods for Oxidation of H-Acid and Reactive Black 5

Oxidative treatment of H-acid (HA) and Reactive Black 5 (RB5) using Fenton reagent (Fe2+/H2O2) and the electro-Fenton (EF) method is reported. Optimization of doses of ferrous iron and hydrogen peroxide was carried out in each case using HA; and the oxidation of RB5 was also carried out under the optimized conditions. Approximately 71% chemical oxygen demand (COD) was removed in 2 h using the conventional Fenton method at optimized doses: Fe2+=0.3 g/L (5.37 mM), H2O2=6 mL/L (53.0 mM), H2O2/Fe2+=10. In contrast, more than 92% COD was removed in 15 min using the EF method with an optimized Fe2+ dose of 0.130 g/L (2.34 mM) and 8 ml/L (70.6 mM) of H2O2. The pseudo-first-order rate constants (k) for the Fenton reagent and EF method were 0.054 and 0.38 min^-1. The COD removal through the EF method was seven times faster. The calculated energy requirement of the EF method was 0.82 kg COD/kW·h at the minimum applied current (0.25 A) when approximately 92.5% COD was removed. In the case of RB5, about 67 and 87% COD was removed under optimized Fenton and electro-Fenton conditions, respectively. The higher efficiency of the EF method was attributed to incremental addition of Fe2+ and accompanying higher H2O2/Fe2+ molar ratio. The results are discussed in the light of the mechanism for Fentonʹs oxidation.