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Laboratory Investigations Of Mechanisms For 1,4-Dioxane Destruction By Ozone In Water (Presentation)
Citation:
Sumner, A. L. AND M. A. SIMON. Laboratory Investigations Of Mechanisms For 1,4-Dioxane Destruction By Ozone In Water (Presentation). Presented at The Seventh International Conference Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 24 - 27, 2010.
Impact/Purpose:
To perform laboratory-scale testing to determine whether *OH chemistry is responsible for the observed decays in 1,4-dioxane from treatment with ozone alone and with potential catalysts, including hydrogen peroxide, iron(II), and an olefin (trichloroethylene, TCE).
Description:
Advances in analytical detection methods have made it possible to quantify 1,4-dioxane contamination in groundwater, even a well-characterized sites where it had not been previously detected. Although 1,4-dioxane is difficult to treat because of its chemical and physical properties, recent bench- and pilot-scale testing has shown better-than-expected effectiveness using ozone with and without hydrogen peroxide. However, the reaction rate of ozone with 1,4-dioxane is too slow to account for the decreases in 1,4-dioxane concentration observed during in-situ treatment of groundwater. It was hypothesized that constituents of the groundwater, such as iron and olefins, acted as catalysis to produce hydroxyl radicals (*OH) in situ during treatment with ozone. The hydroxyl radical has a 109 higher reaction rate for the destruction of 1,4-dioxane than does ozone. The goal of this work was to perform laboratory-scale testing to determine whether *OH chemistry is responsible for the observed decays in 1,4-dioxane from treatment with ozone alone and with potential catalysts, including hydrogen peroxide, iron(II), and an olefin (trichloroethylene, TCE). An indirect chemical probe method, similar to those used previously to detect *OH in various matrices, was chosen. The chemical probe, salicyclic acid (SA), was selected because it reacts readily with *OH at a known rate and can be easily measured. The decays of 1,4-dioxane and salicyclic acid were monitored during ozonation and in the presence of several potential catalysts. The observed ratios of the 1,4-dioxane and SA decay rates were compared to their known relative reaction rates to determine whether ozone or *OH was more effective in removing the analytes under each test condition. The results suggest that *OH chemistry was more responsible for the observed decay even in the absence of the potential catalysts. In fact, treatment with hydrogen peroxide and ozone resulted in absolute decay rates for 1,4-dioxane and SA that were slower than treatment with ozone alone.