N-methyl-p-aminophenol (metol) ozonation in aqueous solution: kinetics, mechanism and toxicological characterization of ozonized samples

The ozonation of metol, one of the main constituents of photographic developers, has been studied in aqueous solution in the pH range 2.0–7.0. Main reaction mechanisms have been assessed on the basis of observed reaction intermediates and products at varying pH of the solution. The effect of manganese addition—MnII ions or solid MnO2—to the reacting system has also been evaluated. The capability of the ozonation treatment to reduce the toxicity of metol-containing aqueous solutions, with respect to selected organisms, such as algae, has also been studied according to reported standard procedures. The results of toxicological assessments show that high levels of detoxification are achieved after 20 min of ozonation treatment and that longer treatments cause an increase in the toxicity of the solution due to the formation of secondary reaction products. The adoption of proper chemical and fluid dynamic submodels enabled the estimation of the reaction kinetics of ozone that attack to the substrate.