Reductive Destruction of Water Contaminants during Treatment with Hydroxyl Radical Processes

• Published in: Environmental science & technology 1995-06, Vol.29 (6), p.1710-1712
• Main Authors: Peyton, Gary R., Bell, Oliver J., Girin, Elizaveta, LeFaivre, Mary H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemicals; Chemistry; Exact sciences and technology; Industrial wastewaters; Pollution; Wastewaters; Water pollution; Water treatment; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es00006a041

During an ongoing study of the destruction of energetic compounds by photolytic and free-radical treatment processes, we performed a series of treatability experiments in which photolytic ozonation (O sub(3)/UV) was used to treat 2,4-dinitrotoluene (DNT) in aqueous solutions containing relatively high concentrations of ethanol in order to simulate the treatment of wastewater from the manufacturing process. Unsuccessful attempts to analyze these data in terms of competition between DNT and ethanol for the hydroxyl radical led us to the conclusion that an active species other than OH was at least partially responsible for the observed DNT destruction, since DNT was removed considerably faster than could be accounted for by hydroxyl radical alone under those conditions. Since the solutions treated were sparged with an ozone-oxygen mixture during treatment, the ethanol radical ( alpha -hydroxyethyl radical) formed by OH attack on ethanol should be rapidly consumed by the nearly diffusion-controlled reaction with oxygen to form the corresponding peroxyl radical. The equilibrium concentration of oxygen was not measured during these experiments but was estimated to have been approximately 1 mM since ozone was generated from oxygen rather than air. Therefore, peroxyl radical reaction with DNT was considered as an explanation for the enhanced DNT removal that was observed. Both oxidative attack at the alpha -hydrogens and reductive attack to yield a radical anion, oxygen, and acetaldehyde were considered as possibilities. Although ethanol peroxyl radical can rapidly eliminate superoxide, which can act as a reducing agent, no examples of direct electron transfer from peroxyl radicals to substrate to yield reduced substrate, oxygen, and stable organic product (acetaldehyde in the case of ethanol) could be found in the peroxyl radical literature. Therefore, the possibility that some ethanol radicals were able to reduce DNT rather than being consumed by oxygen was also considered. Preliminary kinetic analysis of the treatability data proved to be consistent with all three of the above possibilities, requiring further experimentation.