Structural aspects of the degradation of sulfoaromatics by the UV/H2O2 process

The influence of structure of sulfoaromatics (SulfoArs) on photooxidative treatment by UV/H2O2 process was investigated. In that purpose, benzenesulfonic acids with different substituents in para position (H, OH, CH3, Cl, NH2) were chosen as representatives of SulfoArs water pollutants. The effects of operational parameters of UV/H2O2 process and structural features of SulfoArs on their degradation kinetics were investigated by statistical/empirical approach employing the design of experiments and response surface methodology. Different optimal conditions yielding maximal degradation rates were established. The observed degradation rate constants and reaction rate constants of SulfoArs with hydroxyl radicals follow the different decreasing orders indicating the competitive kinetics with by-products formed through the structurally influenced degradation pathways. The mineralization kinetics is correlated with the degradation pathways of studied SulfoArs, the shared sequence within, and the influence of inorganic ions present in the reaction mixture upon the elimination of parent substituents. It was determined that the changes of biodegradability and toxicity toward Vibrio fischeri during UV/H2O2 treatment are related to the preferable degradation route including the elimination of parent substituent and subsequent hydroxylation. In the observed treatment period biodegradability was significantly improved in all cases, while the toxicity levels were higher than those of parent pollutants.