Assessment of key processes that govern the degradation of mixtures in photo-Fenton systems

Abstract

This work focuses on the use of the photo-Fenton process for the treatment of dye mixtures with different compositions. The statistical design of experiments for mixtures and the response surface methodology were used to assess the effect of the dye proportions on both the discoloration rates and the mineralization efficiency. The initial concentrations of catalyst and oxidant, as well as the temperature and the initial pH, were kept constant for all tests. The discoloration rates were followed in terms of the UV–vis absorption spectra evolution, whereas the mineralization efficiencies were assessed by analyzing the decrease of total organic carbon and the consumption of H2O2. The treatment times required for a discoloration of 50% were fitted to a quadratic model (R2 = 0.9347). In addition, within the tested experimental domain, mineralization degrees of at least 80% were achieved after 180 min under all conditions. The analysis of the involved processes shows that the shape of the obtained response surface may be explained by taking into account three key factors: (i) the relative contributions of the internal filter effects, (ii) the inactivation of the catalyst due to the formation of relatively inert coordination complexes with some of the target pollutants, and (iii) the in situ formation of intermediate organic species that can reduce Fe(III) and enhance the catalyst activity.