ORCID Profile
0000-0002-0882-4413
Current Organisation
Washington State University
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Publisher: American Society of Civil Engineers (ASCE)
Date: 04-2011
Publisher: American Chemical Society (ACS)
Date: 16-07-2010
DOI: 10.1021/ES1013714
Abstract: Base is the most commonly used activator of persulfate for the treatment of contaminated groundwater by in situ chemical oxidation (ISCO). A mechanism for the base activation of persulfate is proposed involving the base-catalyzed hydrolysis of persulfate to hydroperoxide anion and sulfate followed by the reduction of another persulfate molecule by hydroperoxide. Reduction by hydroperoxide decomposes persulfate into sulfate radical and sulfate anion, and hydroperoxide is oxidized to superoxide. The base-catalyzed hydrolysis of persulfate was supported by kinetic analyses of persulfate decomposition at various base:persulfate molar ratios and an increased rate of persulfate decomposition in D(2)O vs H(2)O. Stoichiometric analyses confirmed that hydroperoxide reacts with persulfate in a 1:1 molar ratio. Addition of hydroperoxide to basic persulfate systems resulted in rapid decomposition of the hydroperoxide and persulfate and decomposition of the superoxide probe hexachloroethane. The presence of superoxide was confirmed with scavenging by Cu(II). Electron spin resonance spectroscopy confirmed the generation of sulfate radical, hydroxyl radical, and superoxide. The results of this research are consistent with the widespread reactivity reported for base-activated persulfate when it is used for ISCO.
Publisher: American Society of Civil Engineers (ASCE)
Date: 04-2012
Publisher: American Chemical Society (ACS)
Date: 04-02-2009
DOI: 10.1021/ES802505S
Abstract: Superoxide is unreactive in deionized water, but aqueous systems containing added solvents, including H2O2 at >100 mM, show significantly increased reactivity of superoxide with oxidized organic compounds such as highly chlorinated aliphatics. The potential for solid surfaces to similarly increase the reactivity of superoxide in water was investigated. Heterogeneous birnessite (gamma-MnO2)-catalyzed decomposition of H2O2 promoted the degradation of the superoxide probe hexachloroethane (HCA) at H202 concentrations as low as 7.5 mM, while no measurable HCA degradation was found in parallel homogeneous iron(III)-EDTA-H2O2 systems at H2O2 concentrations <100 mM. Electron spin resonance spectroscopy confirmed that superoxide was the dominant reactive species generated in the birnessite-catalyzed decomposition of H2O2. Increased superoxide reactivity was also found in aqueous superoxide-glass bead heterogeneous systems, and the rates of HCA degradation increased as a function of the surface area of the glass beads. The results of this research show that, similar to the addition of solvents, the presence of surfaces also enhances the reactivity of superoxide in water, possibly by altering the superoxide solvation shell. On the basis of these findings, superoxide generated in catalyzed H2O2 propagations (CHP modified Fenton's reagent) used for in situ chemical oxidation (ISCO) may have greater reactivity with highly oxidized contaminants than previously thought.
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.CHEMOSPHERE.2013.05.050
Abstract: The water quality parameters nitrate-nitrogen, dissolved organic carbon, and suspended solids were correlated with photodegradation rates of the herbicides atrazine and 2,4-D in s les collected from four sites in the Columbia River Basin, Washington, USA. Surface water s les were collected in May, July, and October 2010 and analyzed for the water quality parameters. Photolysis rates for the two herbicides in the surface water s les were then evaluated under a xenon arc l . Photolysis rates of atrazine and 2,4-D were similar with rate constants averaging 0.025 h(-1) for atrazine and 0.039 h(-1) for 2,4-D. Based on multiple regression analysis, nitrate-nitrogen was the primary predictor of photolysis for both atrazine and 2,4-D, with dissolved organic carbon also a predictor for some sites. However, at sites where suspended solids concentrations were elevated, photolysis rates of the two herbicides were controlled by the suspended solids concentration. The results of this research provide a basis for evaluating and predicting herbicide photolysis rates in shallow surface waters.
Publisher: American Chemical Society (ACS)
Date: 07-01-2010
DOI: 10.1021/JF903501C
Abstract: Highly halogenated organic compounds, which include polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs) formed during the synthesis of pentachlorophenol and chlorophenoxy herbicides, are often found as contaminants in less toxic nonaqueous media, such as waste oil, oily sludges, or biosolids. Superoxide is highly reactive with halogenated compounds when both are dissolved in nonaqueous media however, superoxide is most economically generated in water, where it is unreactive with most organic compounds. Superoxide reactivity was investigated in organic solvent-water systems as a basis for treating halogenated contaminants in less toxic nonaqueous media. Such a process could potentially render a contaminated oil or sludge nonhazardous, providing a mechanism for waste volume reduction. Increasing amounts of water added to acetone and dimethyl sulfoxide systems decreased the activity of superoxide in the solvent, but enough activity remained for effective treatment. Superoxide was then generated in the aqueous phase of two-phase water-organic solvent systems, and significant superoxide activity was achieved in the organic media with the addition of phase transfer catalysts (PTCs) to transfer superoxide into the nonaqueous phase. The results of this research demonstrate that superoxide, which can be generated in water electrochemically or through the catalytic decomposition of peroxygens, has the potential to be transferred to oils, sludges, and other less toxic nonaqueous media to destroy highly refractory contaminants such as PCBs, PCDDs, and other halogenated contaminants.
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