Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution

Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045 mM 2,4-D using O3, O3/UV, UV/TiO2 and O3/UV/TiO2 systems were compared, and influence of reaction temperature on the mineralization in O3/UV/TiO2 system was investigated. 2,4-D degradations by O3, O3/UV and UV/TiO2 systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O3/UV/TiO2 system, and further enhancements were observed with larger O3 supplies. The enhancements were attributed to hydroxyl radical (OH) generation from more than one reaction pathway. The degradation and removal in O3/UV/TiO2 system were very efficient with reaction temperature fixed at 20 °C. It was suspected that reaction temperature might have influenced OH generation in the system, which needs further attention.