No abstract

Chloride and carbonates have the potential to impact pathway, kinetics, and efficiency of oxidation reactions, both as radical scavengers and as metal complexing agents. Traditionally, it is assumed that they have an overall negative impact on the activated persulfate performance. This study investigated the influence of carbonates and chloride on the reactivity of persulfate for three different activation techniques to produce reactive free sulfate radicals; heat, alkaline and iron activation. By using p-nitrosodimethylaniline as model target compound, it was demonstrated that iron activation at neutral pH was not affected by Cl(-) or HCO(3)(-), alkaline activation was enhanced by Cl(-) and even more by CO(3)(2-), and heat activation was enhanced by Cl(-), and no effect from HCO(3)(-) was observed. At pH 2 destruction of perchloroethylene by iron activated persulfate was significantly affected by chloride. Reaction rates decreased, but the overall oxidation efficiency was unaffected up to 28 mM Cl(-). The effect of chloride and carbonates is caused by direct attack of produced reactive chlorine, or carbonate species or by catalysis of the propagation reactions resulting in more sulfate radicals. These results show that carbonate and chloride might play an important role in activated persulfate applications and should not strictly be considered as scavengers.

In the present paper, research on the electrochemical bleaching of p-nitrosodimethylaniline (RNO) in different electrolyte systems is presented with special attention to the role of RNO as a selective hydroxyl radical probe compound. At a Ti/Pt 90 -Ir 10 anode, RNO was found to be bleached in 0.050 M sodium sulphate electrolyte due to lattice active oxygen without hydroxyl radicals being intermediately present. In 0.050 M sodium chloride, the bleaching rate was greatly enhanced due to indirect bulk oxidation by active chlorine species, again without the presence of hydroxyl radicals in the oxidation mechanisms. Under galvanostatic electrolysis, a linear relationship was found between the concentration of added chloride to a supporting sodium sulphate electrolyte and the first order rate constant of the bleaching reaction, showing the importance of the indirect bulk chlorine bleaching in chloride electrolyte systems. In this fashion both the chemically bonded active oxygen and the chemical bulk oxidation by active chlorine species proved to be valid bleaching pathways of RNO that according to these findings cannot be regarded as a fully selective hydroxyl radical probe compound. In addition, the difference in the mechanisms of chloride electrolysis at Ti/ Pt 90 -Ir 10 and Si-BDD anodes was clearly demonstrated using t-BuOH as hydroxyl radical scavenger.

a b s t r a c tIn 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 TiO 2 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 TiO 2 in suspension was still 7 times faster compared to the most efficient immobilized TiO 2 treatment set up. An approximate linear correlation between the surface area of the TiO 2 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 TiO 2 . 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/S 2 O 8 2− and conductive-diamond electrochemical oxidation (CDEO), the CDEO process was the most energy efficient for bleaching of RNO.