The natural activation ability of subsurface media to promote in-situ chemical oxidation of 1,4-dioxane

The ability of soils and sediments to promote in-situ activation of persulfate and persulfate combined with hydrogen peroxide was investigated for treatment of 1,4-dioxane (dioxane). Experiments were conducted with both batch-reactor and column systems to examine reaction rates and activation mechanisms. Four soils and aquifer sediments were used. ICP-MS and XRD analyses were used to characterize geochemical properties of the solutions and sediments, while EPR spectroscopy was used to characterize radical formation. For the batch experiments, degradation of dioxane was significantly greater in the presence of each of the four subsurface geomedia compared to the controls with no geomedia. This indicates that all four geomedia induced oxidant activation, thereby enhancing dioxane degradation. Dioxane degradation was significantly enhanced by the addition of peroxide to the persulfate solution. It is hypothesized that iron associated with the geomedia is primarily responsible for activation, and that the degree of degradation enhancement relates in part to dissolved-phase iron content. EPR results indicate that manganese oxides and soil organic matter may also have contributed to some degree to persulfate activation, and that manganese oxides enhanced activation of peroxide under the study conditions. Approximately 10% of dioxane was degraded in the miscible-displacement experiments, consistent with the short residence time compared to dioxane's half-life. The pseudo first-order rate coefficients obtained from the batch and column experiments were similar. The results of this study indicate that subsurface geomedia can induce activation of persulfate and peroxide to enhance in-situ chemical oxidation applications.