Identifying oxidation intermediates formed during ozone–UV of fulvic acid

摘要

The purpose of this study was to determine the different classes and yields of oxidation intermediates, compared ozone (O-3), ultraviolet (UV) irradiation and the combined O-3-UV advanced oxidation process, as well as investigated on the effects of irradiation time, UV intensity, O-3 dosage on the removal of fulvic acid (FA), which is regarded as the main disinfection by-products (DBPs) precursor. Based on that, the knowledge gap of DBPs generated was made up. The results showed that by UV irradiation and O-3 oxidation, FA broke down into smaller molecules which were more hydrophilic, namely formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, glyoxal, methylglyoxal, formic, fumaric, benzoic, protocatechuic and 3-hydroxybenzoic acids. Meanwhile, unsaturated conjugated double bonds in the structure of FA were destroyed, which lead to UV254 decrease. Due to the synergistic effect of O-3-UV, dissolved organic carbon and UV254 significantly decreased and remained stable after the reaction of 10 min, indicating that O-3-UV system had a stronger potential of mineralization and lower selectivity. Besides, the kinds and concentration levels of the intermediates were obviously reduced with increase in light intensity. Furthermore, in O-3-UV system with high O-3 dosage, fumaric and benzoic acid concentration gradually decreased, which were relatively inert to O-3. Due to the fact that the high concentration level of center dot OH radical that could mineralize some organics which could not be mineralized by O-3.