Matching Items (4)
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- All Subjects: Bioengineering
- Creators: Rittmann, Bruce E.
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
On average, our society generates ~0.5 ton of municipal solid waste per person annually. Biomass waste can be gasified to generate synthesis gas (syngas), a gas mixture consisting predominantly of CO, CO2, and H2. Syngas, rich in carbon and electrons, can fuel the metabolism of carboxidotrophs, anaerobic microorganisms that metabolize CO (a toxic pollutant) and produce biofuels (H2, ethanol) and commodity chemicals (acetate and other fatty acids). Despite the attempts for commercialization of syngas fermentation by several companies, the metabolic processes involved in CO and syngas metabolism are not well understood. This dissertation aims to contribute to the understanding of CO and syngas fermentation by uncovering key microorganisms and understanding their metabolism. For this, microbiology and molecular biology techniques were combined with analytical chemistry analyses and deep sequencing techniques. First, environments where CO is commonly detected, including the seafloor, volcanic sand, and sewage sludge, were explored to identify potential carboxidotrophs. Since carboxidotrophs from sludge consumed CO 1000 faster than those in nature, mesophilic sludge was used as inoculum to enrich for CO- and syngas- metabolizing microbes. Two carboxidotrophs were isolated from this culture: an acetate/ethanol-producer 99% phylogenetically similar to Acetobacterium wieringae and a novel H2-producer, Pleomorphomonas carboxidotrophicus sp. nov. Comparison of CO and syngas fermentation by the CO-enriched culture and the isolates suggested mixed-culture syngas fermentation as a better alternative to ferment CO-rich gases. Advantages of mixed cultures included complete consumption of H2 and CO2 (along with CO), flexibility under different syngas compositions, functional redundancy (for acetate production) and high ethanol production after providing a continuous supply of electrons. Lastly, dilute ethanol solutions, typical of syngas fermentation processes, were upgraded to medium-chain fatty acids (MCFA), biofuel precursors, through the continuous addition of CO. In these bioreactors, methanogens were inhibited and Peptostreptococcaceae and Lachnospiraceae spp. most likely partnered with carboxidotrophs for MCFA production. These results reveal novel microorganisms capable of effectively consuming an atmospheric pollutant, shed light on the interplay between syngas components, microbial communities, and metabolites produced, and support mixed-culture syngas fermentation for the production of a wide variety of biofuels and commodity chemicals.
ContributorsEsquivel Elizondo, Sofia Victoria (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Delgado, Anca G. (Committee member) / Torres, Cesar I. (Committee member) / Arizona State University (Publisher)
Created2017
Description
Seeking to address sustainability issues associated with food waste (FW), and fat, oil, and grease (FOG) waste disposal, the City of Mesa commissioned the Biodesign Swette Center for Environmental Biotechnology (BSCEB) at Arizona State University (ASU) to study to the impact of implementing FW/FOG co-digestion at the wastewater treatment plant (WWTP). A key issue for the study was the “souring” of the anaerobic digesters (ADs), which means that the microorganism responsible for organic degradation were deactivated, causing failure of the AD. Several bench-scale reactors soured after the introduction of the FW/FOG feed streams. By comparing measurements from stable with measurements from the souring reactors, I identified two different circumstances responsible for souring events. One set of reactors soured rapidly after the introduction of FW/FOG due to the digester’s hydraulic retention times (HRT) becoming too short for stable operation. A second set of reactors soured after a long period of stability due to steady accumulation of fatty acids (FAs) that depleted bicarbonate alkalinity. FA accumulation was caused by the incomplete hydrolysis/fermentation of feedstock protein, leading to insufficient release of ammonium (NH4+). In contrast, carbohydrates were more rapidly hydrolyzed and fermented to FAs.
The most important contribution of my research is that I identified several leading indicators of souring. In all cases of souring, the accumulation of soluble chemical oxygen demand (SCOD) was an early and easily quantified indicator. A shift in effluent FA concentrations from shorter to longer species also portended souring. A reduction in the yield of methane (CH4) per mass of volatile suspended solids removed (VSSR) also identified souring conditions, but its variability prevented the methane yield from providing advanced warning to allow intervention. For the rapidly soured reactors, reduced bicarbonate alkalinity was the most useful warning sign, and an increasing ratio of SCOD to bicarbonate alkalinity was the clearest sign of souring. Because I buffered the slow-souring reactors with calcium carbonate (CaCO3), I could not rely on bicarbonate alkalinity as an indicator, which put a premium on SCOD as the early warning. I implemented two buffering regimes and demonstrated that early and consistent buffering could lead to reactor recovery.
The most important contribution of my research is that I identified several leading indicators of souring. In all cases of souring, the accumulation of soluble chemical oxygen demand (SCOD) was an early and easily quantified indicator. A shift in effluent FA concentrations from shorter to longer species also portended souring. A reduction in the yield of methane (CH4) per mass of volatile suspended solids removed (VSSR) also identified souring conditions, but its variability prevented the methane yield from providing advanced warning to allow intervention. For the rapidly soured reactors, reduced bicarbonate alkalinity was the most useful warning sign, and an increasing ratio of SCOD to bicarbonate alkalinity was the clearest sign of souring. Because I buffered the slow-souring reactors with calcium carbonate (CaCO3), I could not rely on bicarbonate alkalinity as an indicator, which put a premium on SCOD as the early warning. I implemented two buffering regimes and demonstrated that early and consistent buffering could lead to reactor recovery.
ContributorsKupferer III, Rick Anthony (Author) / Rittmann, Bruce E. (Thesis advisor) / Young, Michelle N (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2020
Description
Carbon dioxide (CO2) levels in the atmosphere have reached unprecedented levels due to increasing anthropogenic emissions and increasing energy demand. CO2 capture and utilization can aid in stabilizing atmospheric CO2 levels and producing carbon-neutral fuels. Utilizing hollow fiber membranes (HFMs) for microalgal cultivation accomplishes that via bubbleless gas-transfer, preventing CO2 loss to the atmosphere. Various lengths and geometries of HFMs were used to deliver CO2 to a sodium carbonate solution. A model was developed to calculate CO2 flux, mass-transfer coefficient (KL), and volumetric mass-transfer coefficient (KLa) based on carbonate equilibrium and the alkalinity of the solution. The model was also applied to a sparging system, whose performance was compared with that of the HFMs. Typically, HFMs are operated in closed-end mode or open-end mode. The former is characterized by a high transfer efficiency, while the latter provides the advantage of a high transfer rate. HFMs were evaluated for both modes of operation and a varying inlet CO2 concentration to determine the effect of inert gas and water vapor accumulation on transfer rates. For pure CO2, a closed-end module operated as efficiently as an open-end module. Closed-end modules perform significantly worse when CO2-enriched air was supplied. This was shown by the KLa values calculated using the model. Finally, a mass-balance model was constructed for the lumen of the membranes in order to provide insight into the gas-concentration profiles inside the fiber lumen. For dilute CO2 inlet streams, accumulation of inert gases -- nitrogen (N2), oxygen (O2), and water vapor (H2O) -- significantly affected module performance by reducing the average CO2 partial pressure in the membrane and diminishing the amount of interfacial mass-transfer area available for CO2 transfer.
ContributorsShesh, Tarun (Author) / Rittmann, Bruce E. (Thesis advisor) / Green, Matthew (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2018