Changes of excitation/emission matrixes of wastewater caused by Fenton- and Fenton-like treatment and their associations with the generation of hydroxyl radicals, oxidation of effluent organic matter and degradation of trace-level organic pollutants.

Changes of fluorescence excitation emission matrixes (EEM) of wastewater caused by Fenton process (FP) and Fenton-like process (FLP) were quantified in this study. Their association with the generation of hydroxyl radicals, formation of oxidation products of effluent organic matter (EfOM) and degradation of pharmaceuticals and personal care products (PPCPs) were examined as well. Both FP and FLP caused a consistent decrease of EfOM fluorescence. This decrease was most prominent in the EEM region associated with soluble microbial products (SMPs). Measurements of the consumption of the radical probe pCBA and calculations of OH· radicals exposures showed that relative changes of EEM quantified using alternative parameters (such as humic region response or peak intensity relative change) were predictive of OH· exposures irrespective of whether the wastewater was treated with FP or FLP at any Fe doses and treatment times. The generation of EfOM oxidation products such as formate, oxalate and acetate was also correlated with EEM changes. Similar observations were obtained for PPCPs whose removal was interpreted based on first-order kinetics. Values of selected parameters representing correlations between PPCPs oxidation and EfOM fluorescence decreases were strongly correlated with the intrinsic rates of the oxidation of trace-level organic species by OH· radicals.