Degradation of ortho-toluidine from aqueous solution by the TiO2/O3 process

In this work, the degradation and mineralization of ortho-toluidine (OT) that is one of the constituents of petrochemical wastewater was investigated by the TiO2/O3 process. The influence of some operational parameters such as concentration of pollutant (30–90 mg L^-1), initial pH and amounts of TiO2 was investigated. A radical mechanism with the formation of an anion radical superoxide radical prior to hydroxyl radical is suggested for describing the interaction between ozone and TiO2. These results were not similar to the ozonation process alone, in which higher pH had a positive effect on the removal of OT because of the generation of hydroxyl radicals. In optimum pH for the ozonation and O3/TiO2 processes, the degradation efficiency of the OT was 89.5 and 96%, respectively, at 60 min of reaction. Furthermore, it was made clear that in catalytic ozonation, the degradation efficiency of the OT was higher at neutral pH conditions (pH = 7). The removal of chemical oxygen demand (COD) was increased from 47.5% (only ozonation) to 73% (O3/TiO2) after 90 min of reaction. The kinetics of degradation was pseudo-first order; the degradation and relative mineralization of the OT were calculated by HPLC and COD tests, respectively.