UV-assisted persulfate oxidation: the influence of cation type in the persulfate salt on the degradation kinetics of an azo dye pollutant

With the aim to investigate the influence of UV-assisted persulfate oxidation operating parameters (cation type in persulfate salt, persulfate concentration and initial pH), the empirical/modeling approach applying full factorial experimental design (FFD) combined with response surface methodology (RSM) and mechanistic modeling (MM) was used. The efficiency of UV-assisted persulfate oxidation as a wastewater treatment method and the dependence on the aforementioned process parameters was evaluated in the case study where an azo dye (C.I. Acid Orange 7—AO7) was used as a model pollutant in water matrix. The FFD matrix with three independent variables representing the studied process parameters established experimental combinations, on which the UV-assisted persulfate oxidation process response, the AO7 decolorization rate was determined and correlated using RSM over quadratic polynomial equations, i.e. RSM model. The significance and accuracy of the developed RSM model was evaluated on the basis of analysis of variance and obtained statistical parameters (R2, F, p), used also to examine the influence of studied process parameters. It was determined that the persulfate salt is the most influential process parameter, followed by rather high combined influence of initial pH and cation type, indicating the practical implications regarding the cation type. The MM used to describe the UV-assisted persulfate oxidation system showed high accuracy in predicting the AO7 degradation monitored over several parameters (decolorization, degradation of naphthalene and benzene structures, as well as overall mineralization) as well as high flexibility covering the broad pH range of application set by different cation type ion the persulfate salt.