Degradation of photographic developers by Fenton’s reagent: condition optimization and kinetics for metol oxidation

The potential of the Fenton’s reagent for oxidation of p-aminophenols, which are the main developers used in white and black processes, was assessed. Metol [N-methyl-p-aminophenol] was chosen as a model. Degradation of this compound by Fenton’s reagent was examined under dark conditions as a function of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H2O2, 9.0×10−4 M Fe2+, pH 3–5 and room temperature, the initial COD of a 5×10−3 M metol solution was reduced by about 50% within 2 h. After this time, additional COD reduction was very slow (about 20% in five days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavage products. Metol conversion behaved as a first-order reaction with respect to metol and Fe2+. Complete destruction of residual organic matter could be achieved at high temperatures (about 60°C) or by using the photo-Fenton reaction, which thus opens up prospects for an effective treatment of p-aminophenols in effluents from photographic processes.