Effects of nitrate on the UV photolysis of H₂O₂ for VOCs degradation in an aqueous solution

The major objective of this study was to delineate the effect of nitrate on the UV oxidation of benzene and toluene, dissolved in less than 100 μg l-1, by conducting a bench-scale operation at various reaction times and with various initial concentrations of H2O2 and NO3-. The oxidation of benzene and toluene can be expected to be only about 10% and 18%, respectively, through the photolysis of H2O2 (initial conc. of 50 mg l-1), where the reactor was operated at a reaction time of 2 min, with an initial NO3 - N concentration of 5 mg l-1. Nitrate clearly hindered UV oxidation when the initial H2O2 concentration in the reactor was less than 50 mg l-1. Even if approximately 40% removal could be achieved under the conditions mentioned above (an initial H2O2 concentration of 200 mg l-1 at a reaction time of 9 min, with a high UV dose), the operating conditions for the 40% removal might be beyond the practical limits applied for effluents discharged from wastewater treatment plants. The results of the experiment also indicate that benzene and toluene can be oxidized in very limited amounts through direct photolysis, without additional oxidation by hydroxyl radicals.