The effect of humic acids on nitrobenzene oxidation by ozonation and O3/UV processes

Three types of commercially available humic acids from different sources were used to simulate natural organic matter in water for the investigation of nitrobenzene oxidation by ozonation and O3/UV. Despite the structural differences among the Fluka, Aldrich and Suwanee River humic acids as reflected by the UV absorptivity, their effects on nitrobenzene removal rate was observed to be similar for the two processes. Removal rate of nitrobenzene was hindered by the addition of humic acids in ozonation as well as in O3/UV processes. However, the hindrance by the humic acids was more pronounced in O3/UV as compared to the ozonation process. The effect of humic acid in O3/UV was primarily a UV light screening. Addition of humic acids above a certain concentration did not cause any further retardation on nitrobenzene removal rate by ozonation and O3/UV. Accumulation of hydrogen peroxide as well as probable formation of peroxy radicals in the solutions might induce chain promoting reactions to produce hydroxyl radical during the nitrobenzene oxidation. For waters containing high levels of humic acid, ozonation alone might be as effective as O3/UV process for the removal of nitrobenzene.