Destruction of EDTA using Fenton and photo-Fenton-like reactions under UV-A irradiation

Degradation experiments using 5 mmol/l ethylenediaminetetraacetic acid (EDTA) solutions at pH 3 were performed in the presence of H2O2 and metals such as Fe2+, Fe3+, Cu2+ and mixtures of Fe2+/Cu2+ and Fe3+/Cu2+ under UV-A irradiation (366 nm)—photo-Fenton and photo-Fenton-like reactions—at different metal/EDTA concentration ratios in order to determine the best conditions for EDTA photochemical removal. Analogous dark reactions were performed for comparison. The reaction course was monitored by both EDTA and TOC determinations. Hydrogen peroxide demand was also evaluated in all cases. In terms of TOC removal, photo-Fenton-like reactions were remarkably more efficient than the analogous Fenton-like reactions. When EDTA was monitored, Fenton-like reactions showed variable performances, being more efficient with EDTA:Fe2+ and EDTA:Fe3+ ratios of 1:1. However, in these both cases, reaction rates were lower than the ones obtained under irradiation. Total mineralization ranged from 31% (Cu2+ system) to 92% (Fe2+, Fe3+, Fe3++Cu2+ and Fe2++Cu2+ systems) after 4 h of irradiation. Percentage of TOC removal was higher in the presence of iron because some photoactive intermediates were probably formed during EDTA degradation.