Catalytic activity of the SO4− radical for photodegradation of the azo dye Cibacron Brilliant Yellow 3 and 3,4-dichlorophenol: Optimization by application of response surface methodology

Advanced oxidation processes (AOP) generate in situ active radicals with a high oxidation potential, allowing for the destruction of polluting agents through organic compound mineralization. The use of experimental design is a tool that allows adjustment of factors to obtain an optimal response in experimental analysis. We used multivariate analysis to optimize the process of organic removal from wastewater in a cylindrical reactor, using UV radiation (254 nm) and peroxodisulfate as an oxidant. We used 3,4-dichlorophenol and Cibacron Brillant Yellow 3 (CBY-3) as model organic compounds. Both of these compounds are characteristic polluting agents present in industrial wastewater. We used a factorial 2n design to obtain the best experimental conditions to efficiently remove the compounds from the solution, using time and oxidant concentration as experimental variables. The initial concentration of both compounds was 100 ppm, and we obtained 90% dichlorophenol removal, with a rate constant of 0.0386 min−1. Degradation of azo dye was more efficient reaching 98%, with a rate constant of 0.0908 min−1. In both cases, the optimal time for reducing the maximum concentration was 60 min of irradiation. Total organic carbon (TOC) reduction was analyzed to determine the efficiency of the UV/K2S2O8 process in mineralization, where we obtained 90% TOC reduction for both organic compounds. At the same time, the dye compound, CBY-3, whose organic structure is more complex, generated nitrate and chloride ions as mineralization products. The efficient mineralization of both compounds is based on the in situ formation of the strong oxidant sulfate anion radical (E = 2.5–3.1 V).