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Colorado State University, Fort Collins

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Browsing Colorado State University, Fort Collins by Subject "1,4-dioxane"

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    Catalytic strategies for enhancing electrochemical oxidation of 1,4-dioxane: TiO2 dark activation and microbial stimulation
    (Colorado State University. Libraries, 2016) Jasmann, Jeramy R., author; Borch, Thomas, advisor; Blotevogel, Jens, advisor; Farmer, Delphine, committee member; Neilson, James, committee member; Sanford, William, committee member; Elliot, Michael, committee member
    1,4-dioxane, a probable human carcinogen, is an emerging contaminant currently being reviewed by the U.S. Environmental Protection Agency for possible health-based maximum contaminant level regulations. As both stabilizer in commonly used chlorinated solvents and as a widely used solvent in the production of many pharmaceuticals, personal care products, (PPCPs), 1,4-dioxane has been detected in surface water, groundwater and wastewater around the U.S. It is resistant to many of the traditional water treatment technologies such as sorption to activated carbon, air stripping, filtering and anaerobic biodegradation making 1,4-dioxane removal difficult and/or expensive. State-of-the art technologies for the removal of 1,4-dioxane usually apply advanced oxidation processes (AOPs) using strong oxidants in combination with UV-light and sometimes titanium dioxide (TiO2) catalyzed photolysis. These approaches require the use of expensive chemical reagents and are limited to ex situ (i.e. pump and treat) applications. Here, at Colorado State University’s Center for Contaminant Hydrology, innovative flow-through electrolytic reactors have been developed for treating groundwater contaminated with organic pollutants. The research presented in this dissertation has investigated catalytic strategies for enhancing electrochemical oxidation of 1,4-dioxane in flow-through reactors. Two types (abiotic and biotic) of catalysis were also explored: (1) dark, electrolytic activation of insulated, inter-electrode TiO2 pellets to catalyze the degradation of organic pollutants in the bulk solution by reactive oxygen species (ROS), and (2) adding permeable electrodes upstream of dioxane-degrading microbes, Pseudonocardia dioxanivorans CB1190, to pre-treat mixed contaminant water and provide O2 stimulation to these aerobic bacteria. For the abiotic form of catalysis, we characterized the properties of novel TiO2 inter-electrode material, and elucidated the properties most important to its catalytic activity, using 1,4-dioxane as the model contaminant. The TiO2 was novel in its use as an “inter-electrode” catalyst (not coated on the electrode and not used as a TiO2 slurry) and in the mechanism of its catalytic activation occurring in dark (not photocatalysis) and insulated (not typical electrocatalysis) conditions. Further studies were performed using electrochemical batch reactors and probe molecules in order to gain mechanistic insights into dark catalysis provided by detached TiO2 pellets in an electrochemical system. The results of our investigations show that electrolytic treatment, when used in combination with this catalytically active inter-electrode material, can successfully and efficiently degrade 1,4-dioxane. Benefits of catalyzed electrolysis as a green remediation technology are that (1) it does not require addition of chemicals during treatment, (2) it has low energy requirements that can be met through the use of solar photovoltaic modules, and (3) it is very versatile in that it could be applied in situ for contaminated groundwater sites or installed in-line on above-ground reactors to remediate contaminated groundwater. Although, 1,4-dioxane appears to be resistant to natural attenuation via anaerobic biodegradation, some aerobic bacteria have been shown to metabolize and co-metabolize 1,4-dioxane. For example, growth-supporting aerobic metabolism/degradation of 1,4-dioxane by Pseudonocardia dioxanivorans CB1190, has been demonstrated in laboratory studies. However, previous studies showed that this biodegradation process is inhibited by the presence of chlorinated solvents such as 1,1,1-trichlorethane (1,1,1-TCA) and trichloroethene (TCE). This could dramatically impact the success for in situ 1,4-dioxane biodegradation with P. dioxanivorans since chlorinated solvents are common co-contaminants of 1,4-dioxane. Our previous investigations into electrolytic treatment of organic pollutants both ex and in situ showed that effective degradation of chlorinated solvents like TCE was achievable. In addition, the electrolysis of water generates molecular O2 required by the CB1190 bacteria as well. This led us to hypothesize that the generation of O2 could enhance aerobic biodegradation processes, and the concurrent degradation of co-solvents could reduce their inhibitory impact on 1,4-dioxane biodegradation. In flow-through sand column studies presented here, we investigate the electrolytic stimulation of Pseudonocardia dioxanivorans CB1190, with the expectation that anodic O2 generation would enhance aerobic biodegradation processes, and concurrent degradation of TCE would reduce the expected inhibitory impact on 1,4-dioxane biodegradation. Results show that when both electrolytic and biotic processes are combined, oxidation rates of 1,4-dioxane substantially increased suggesting that aerobic biodegradation processes had been successfully stimulated. In summary, the results of this dissertation provide evidence of (1) efficient removal of recalcitrant 1,4-dioxane, especially with the addition of inter-electrode TiO2 catalysts, (2) elucidate possible mechanistic pathways for electro-activated dark TiO2 catalysis, and (3) provide evidence for successful synergistic performance for electro-bioremediation treatment during simulated mixed, contaminant plume conditions.
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    ItemOpen Access
    Reactor design for electrochemical oxidation of the persistent organic pollutant 1,4-dioxane in groundwater
    (Colorado State University. Libraries, 2018) Cottrell, P. Maxine, author; Blotevogel, Jens, advisor; Sale, Tom C., advisor; Dandy, David, committee member
    The common industrial solvent stabilizer and wetting agent 1,4-dioxane (DX) is one of the most widely occurring organic groundwater contaminants in the United States today. It is a probable human carcinogen, highly mobile in groundwater, and resistant to anaerobic biodegradation. The ineffectiveness of conventional treatment approaches such as stripping and sorption to activated carbon results in a critical need of advanced technologies for the treatment of DX in groundwater. Previous studies have shown that electrochemical oxidation is able to fully mineralize 1,4-dioxane, but testing has thus far been limited to proof-of-principle bench-scale experiments. Consequently, this study addresses the design of a configurable mobile pilot-scale reactor that can be used to test electrochemical degradation performance under site-specific conditions and with different dimensionally stable electrode materials. The goal of this reactor design is to accommodate straightforward scale-up for field applications, and low cost of production so that ultimately multiple modular units can be deployed to operate in series or in parallel. Assessment of critical design parameters in a bench-scale reactor showed that DX degradation rates almost doubled when no inter-electrode solid media were used. No significant differences were observed between operating the reactor in continuous versus batch mode. An additional 57% degradation rate improvement was achieved when the batch reactor was operated with 30-minute polarity reversals as compared with constant polarity. Bench-scale reactor and initial pilot reactor tests with Ti/IrO2-Ta2O5 electrodes were run using a synthetic groundwater solution containing DX in NaCl electrolyte, revealing substantial effects of scale, while DX degradation kinetics were similar. Groundwater from a contaminated industrial site was then treated in the pilot reactor with an apparent anode surface area per order of magnitude DX removal (ASAAO) of 305 h*m2/m3 at an electric energy consumption per order of magnitude DX removal (EEO) of 152 kWh/m3, with relatively minor production of undesirable by-products. The contaminated site groundwater was also treated in a commercial bench-scale reactor with a Magnéli-phase titanium oxide anode, resulting in an ASAAO of 28 h*m2/m3 at an EEO of 176 kWh/m3, but with a high yield of carbon tetrachloride (CCl4) and chlorate (ClO3-), and minor formation of perchlorate (ClO4-). In comparison of the surface-area normalized rates of removal, the commercial reactor was faster than the pilot reactor, but it consumed more energy per order reduction and generated more undesirable reaction by-products, commonly referred to as disinfection by-products (DBPs). Future testing at contaminated field sites will reveal the efficacy of our newly designed reactor, and thus electrochemical treatment, for the remediation of groundwater contaminated with DX and other persistent organic pollutants.