Oxidation of salicylic acid in water by the O3 and UV/O3 processes: removal and reaction byproducts

In this study, the removal of salicylic acid (SA) in water by ozone (O-3) and ultraviolet/ozone (UV/O-3) processes was investigated. Results showed that more than 50% of SA (10 mg/L) could be effectively removed after 1 min during these two processes. However, the UV/O-3 process was much more effective than the O-3 process for SA mineralization, and the total organic carbon reduction after 30 min was 69.5% and 28.1%, respectively. In the two processes, the optimum pH value for SA removal was 4.3, while that for SA mineralization was 10.0. Both bicarbonate and dissolved organic carbon significantly inhibited SA removal during the two processes. Eleven oxidation byproducts were detected in O-3 process, but only four byproducts were observed in UV/O-3 process. Three hydroxylation aromatic products were identified as the initial byproducts during SA degradation. Glyoxylic acid monohydrate, glycolic acid, and oxalic acid were accumulated in O-3 process but not observed in UV/O-3 process. Oxalic acid was the only detected small molecular byproduct in UV/O-3 process, and it could be further mineralized, thereby indicating that UV/O-3 had a greater potential for degrading both SA and its reaction byproducts.