Nitroaromatic hydrocarbon ozonation in water. 2. Combined ozonation with hydrogen peroxide or UV radiation

The combined ozonation of nitrobenzene and 2,6-dinitrotoluene with hydrogen peroxide and UV radiation has been studied. Effects of variables such as pH, hydroxyl radical scavengers, ozone feed rate, or hydrogen peroxide to ozone feed molar ratios have been investigated. Results are also compared to those obtained from UV radiation and single ozonation (Beltran et al., 1998). Quantum yields of nitrobenzene and 2,6-dinitrotoluene at 254 nm were found to be 7.0 X 10(-3) and 2.2 X 10(-2) mol einstein(-1), respectively. Removal rates of nitrobenzene through single or combined ozonation with hydrogen peroxide at concentration lower than 10(-2) M are similar while under the same conditions combined ozonation of 2,6-dinitrotoluene leads to higher removal rates than single ozonation. Also, the latter compound is removed faster by UV radiation alone and UV/O-3 oxidation than by single ozonation. Rate constants of the reaction between the hydroxyl radical and nitrobenzene and 2,6-dinitrotoluene were found to be 2.9 X 10(9) and 7.5 X 10(8) M-1 s(-1), respectively. Nitrophenols and 2,6-dinitrobenzaldehyde appear to be some of the principal intermediates formed in the treatment of nitrobenzene and 2,6-dinitrotoluene, respectively, regardless of oxidation techniques applied. Apart from economic considerations UV/O-3 oxidation is the technique among those studied leading to the highest removal rates.