Comparison of the chemical effects of ozone and of irradiation on organic impurities in water

Depending on the reaction conditions, radiation and ozone yield the same reactive intermediates in aqueous oxygenated solutions. In both systems the -OH radical can become the main species for the oxidation of organic impurities. The oxidizing intermediate produced by ozone has been identified by comparing its reaction selectivities with those known for the -OH radicals initiated by high-energy irradiation. The conditions have been investigated (pH-range and solutes) for which the predecomposition of ozone to -OH radicals becomes effective before ozone reacts directly with dissolved solutes. Because many moles of -OH radicals are necessary to eliminate one mole of an organic solute by oxidation (TOC-reduction), the cost of the oxidizing agent is a determining factor for a cost/benefit evaluation. The yield of -OH radicals per decomposed ozones is about 0.5 when compared with a radiation chemical yield of G(-OH)=2.9. The -OH radicals initiated by ozone in alkaline aqueous solutions cost 1 to 2 orders of magnitude less than those produced by gamma radiation. Therefore, other potential advantages of radiation would have to bear a large part of the cost, if radiation is to be competitive with ozone to eliminate dissolved impurities in water. (Author)