Aniline degradation in aqueous solution by UV-aeration and UV-microO3 processes: Efficiency, contribution of radicals and byproducts

The use of combination of air and UV irradiation for organic matters removal has drawn attention since degradation efficiency would be significantly enhanced in the presence of oxygen. Considering the fact that a low-pressure mercury UV lamp (emitting at 254 nm and 185 nm) could dissociate oxygen in gas phase and generate ozone, UV irradiation with addition of ozone enriched air, generated by the same UV lamp, was introduced. This technology was called UV-microO(3) because the concentration of ozone generated by UV irradiation was relatively low (lower than 1 mg L-1). The degradation of aniline by UV-aeration and UV-microO(3) processes was comparatively analyzed. It was shown that aniline underwent much faster and more complete degradation in UV-microO(3) process than in UV-aeration system. Hydroxyl radical ((OH)-O-center dot) exposure in UV-microO(3) process was 2.46 times of that in UV-aeration system. Furthermore, increasing inlet air flow rate would be of benefit to maintaining high dissolved oxygen (DO) level in UV-aeration system, thus the aniline removal was improved. While concentration of ozone generated by UV irradiation increased at first and then declined as the air flow rate increased from 1.8 L min(-1) to 4.8 L min(-1) in UV-microO(3) process, and similar trend for aniline removal rate was observed. The contributions of radicals on aniline removal in UV-aeration and UV-microO(3) processes were calculated to be 23.1% and 67.7%. The formation of 4-aminophenol, 4-Hydroxydiphenylamine, azobenzene and 4-Phenylazophenol was observed as the major intermediates in UV-aeration and UV-microO(3) processes, mechanism of aniline degradation was proposed based on experimental evidence. (C) 2013 Elsevier B.V. All rights reserved.