Matching Items (3)
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- All Subjects: Soil remediation
- All Subjects: Syngas Fermentation
- Creators: Rittmann, Bruce E
- Creators: Chen, Tengfei
Description
The world currently faces hundreds of millions of cubic meters of soil contaminated with petroleum crude oil residuals. The application of ozone gas (O3) to contaminated soil is an effective means to oxidize petrogenic compounds and, when used with bioremediation, remove the oxidized byproducts. The overarching goal of this dissertation was to evaluate two areas of potential concern to large-scale O3 deployment: the capacity of O3-treated petroleum contaminated soils to support seed germination before bioremediation and the transport characteristics of O3 in soil columns. A matched study comparing the germination outcomes of radish (Raphanus sativus L.), grass (Lagurus ovatus), and lettuce (Lactuca sativa) in soils contaminated with three crude oils at various O3 total-dose levels showed that radish germination was sensitive to the soluble byproducts of oxidized petroleum (assayed as dissolved organic carbon [DOC]), but not sensitive to the unreacted petroleum (total petroleum hydrocarbon [TPH]). A multivariable logistic regression model based on the radish results showed that adverse germination outcomes varied with the DOC concentration and that DOC ecotoxicity decreased with increasing O3 dose-level and background organic material. The model was used to create a risk management map of conditions that created 10%, 25%, and 50% extra risks of adverse radish germination. Thus, while O3 effectively lowered TPH in soils, the byproducts exhibited ecotoxicity that inhibited radish germination. On the other hand, the sensitivity of radish germination to oxidized petroleum byproducts could be utilized to assess ecological risk. The feasibility of gas transport in the soil matrix is also of paramount concern to field-scale utilization of O3. A matched study comparing TPH removal at three field-relevant loading rates (4, 12, or 36 mgozone/ gsoil/ hr) and various total dose-levels showed an anisotropic pattern along the axial distance favoring the column inlet end. The asymmetry decreased as loading rate decreased and with concurrent improvements in O3-transport distance, O3 utilization, and heat balance. Overall, a low O3 loading rate significantly improved O3 transport and utilization efficiency, while also better distributing reaction-generated heat along the gas flow path for a depth typically utilized in bioremediation field settings.
ContributorsYavuz, Burcu Manolya (Author) / Rittmann, Bruce E (Thesis advisor) / Delgado, Anca G (Committee member) / Westerhoff, Paul (Committee member) / Arizona State University (Publisher)
Created2022
Description
Petroleum contamination is ubiquitous during extraction, transportation, refining, and storage. Contamination damages the soil’s ecosystem function, reduces its aesthetics, and poses a potential threat to human beings. The overall goals of this dissertation are to advance understanding of the mechanisms behind ozonation of petroleum-contaminated soil and to configure an effective integrated bioremediation + ozonation remedial strategy to remove the overall organic carbon. Using a soil column, I conducted batch ozonation experiments for different soils and at different moisture levels. I measured multiple parameters: e.g., total petroleum hydrocarbons (TPH) and dissolved organic carbon (DOC), to build a full understanding of the data that led to the solid conclusions. I first demonstrated the feasibility of using ozone to attack heavy petroleum hydrocarbons in soil settings. I identified the physical and chemical hurdles (e.g., moisture, mass transfer, pH) needed to be overcome to make the integration of chemical oxidation and biodegradation more efficient and defines the mechanisms behind the experimental observations. Next, I completed a total carbon balance, which revealed that multiple components, including soil organic matter (SOM) and non-TPH petroleum, competed for ozone, although TPH was relatively more reactive. Further experiments showed that poor soil mixing and high soil-moisture content hindered mass transfer of ozone to react with the TPH. Finally, I pursued the theme of optimizing the integration of ozonation and biodegradation through a multi-stage strategy. I conducted multi-stages of ozonation and bioremediation for two benchmark soils with distinctly different oils to test if and how much ozonation enhanced biodegradation and vice versa. With pH and moisture optimized for each step, pre-ozonation versus post-ozonation was assessed for TPH removal and mineralization. Multi-cycle treatment was able to achieve the TPH regulatory standard when biodegradation alone could not. Ozonation did not directly enhance the biodegradation rate of TPH; instead, ozone converted TPH into DOC that was biodegraded and mineralized. The major take-home lesson from my studies is that multi-stage ozonation + biodegradation is a useful remediation tool for petroleum contamination in soil.
ContributorsChen, Tengfei (Author) / Rittmann, Bruce E. (Thesis advisor) / Westerhoff, Paul (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Delgado, Anca G (Committee member) / Arizona State University (Publisher)
Created2018
Description
The increasing concentrations of greenhouse gases into the atmosphere call for urgent measures to use non-fossil feedstock for fuels and chemicals. Synthesis gas (or syngas) is a mixture of three gases: hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2). Syngas already is widely used as a non-fossil fuel and a building block for a variety of chemicals using the Fischer-Tropsch process. Recently, syngas fermentation has attracted attention as a more sustainable way for the conversion of syngas to chemicals, since its biocatalysts are self-generating, are resilient, and can utilize a wide range of syngas compositions. However, syngas fermentation has technical and economic limitations. This dissertation, by contributing to the understanding of syngas fermentation, helps to overcome the limitations. A bibliometric analysis showed the topic’s landscape and identified that mass transfer is the biggest challenge for the process. One means to improve syngas mass transfer is to use the membrane biofilm reactor, or MBfR, to deliver syngas to the microorganisms. MBfR experiments delivering pure H2 demonstrated that the H2:IC ratio (IC is inorganic carbon) controlled the overall production rate of organic compounds and their carbon-chain length. Organic chemicals up to eight carbons could be produced with a high H2:IC ratio. A novel asymmetric membrane dramatically improved mass transfer rates for all syngas components, and its low selectivity among them made it ideal for high-rate syngas fermentation. MBfR experiments using syngas and the asymmetric membrane, as well as a conventional symmetric membrane, confirmed that the key parameter for generating long-chain products was a high H2:IC ratio. The fast mass transfer rate of the asymmetric membrane allowed a very high areal production rate of acetate: 253 g.m-2.d-1, the highest reported to date. Since the membrane delivered H2 and C from the syngas feed, the relatively low selectivity of the asymmetric membrane favored acetogenesis over microbial chain elongation. A techno-economic analysis of the MBfR showed that the cost to produce acetate was less than its market price. All results presented in this dissertation support the potential of syngas fermentation using the MBfR as a means to produce commodity chemicals and biofuels from syngas.
ContributorsCalvo Martinez, Diana Carolina (Author) / Rittmann, Bruce E (Thesis advisor) / Torres, César I (Thesis advisor) / Kralmajnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2021