Photocatalytic bleaching of p-nitrosodimethylaniline and a comparison to the performance of other AOP technologies

In this paper, the performance of a developed photo reactor has been studied using the process of bleaching of p-nitrosodimethylaniline (RNO). The effect of available surface area in the reactor has been tested with the TiO2 suspension system as reference, as well as the influence of operating parameters as pH and aerobic/anaerobic conditions. The bleaching of RNO by UV light alone was found to be significantly slower compared to the bleaching observed when applying photocatalysis, but the initial bleaching rate when applying TiO2 in suspension was still 7 times faster compared to the most efficient immobilized TiO2 treatment set up. An approximate linear correlation between the surface area of the TiO2 available for reaction and the initial rate of bleaching was found. In addition, the kinetics of the photocatalytic bleaching was found to obey L–H kinetics. The pH of the solution was found to influence the rate of bleaching presumably due to the change in the surface charge of TiO2. Also aerobic/anaerobic conditions and the presence of hydroxyl radical scavenger had a profound influence on the bleaching rate, where the reductive bleaching process was found to be much faster than the oxidative bleaching paths. When comparing the obtained rates of bleaching of RNO in the photocatalytic reactors to two competitive AOPs, UV/S2O82− and conductive-diamond electrochemical oxidation (CDEO), the CDEO process was the most energy efficient for bleaching of RNO.