Matching Items (7)

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Microbially Induced Desaturation and Precipitation (MIDP) Pressure Contours

Description

This thesis is part of a larger research project, conducted by Elizabeth Stallings Young, which aims to improve understanding about the factors controlling the process of MIDP and the interaction

This thesis is part of a larger research project, conducted by Elizabeth Stallings Young, which aims to improve understanding about the factors controlling the process of MIDP and the interaction between the biochemical reactions and the hydrological properties of soils treated with MIDP. Microbially Induced Desaturation and Precipitation (MIDP) is a bio-geotechnical process by which biogenic gas production and calcite mineral bio-cementation are induced in the pore space between the soil particles, which can mitigate earthquake induced liquefaction (Kavazanjian et al. 2015). In this process substrates are injected which stimulate indigenous nitrate reducing bacteria to produce nitrogen and carbon dioxide gas, while precipitating calcium carbonate minerals. The biogenic gas production has been shown to dampen pore pressure build up under dynamic loading conditions and significantly increase liquefaction resistance (Okamura and Soga 2006), while the precipitation of calcium carbonate minerals cements adjacent granular particles together. The objective of this thesis was to analyze the recorded pore pressure development as a result of biogenic gas formation and migration, over the entire two-dimensional flow field, by generating dynamic pressure contour plots, using MATLAB and ImageJ software. The experiment was run in a mesoscale tank that was approximately 114 cm tall, 114 cm wide and 5.25 cm thick. Substrate was flushed through the soil body and the denitrifying reaction occurred, producing gas and correspondingly, pressure. The pressure across the tank was recorded with pore pressure sensors and was loaded into a datalogger. This time sensitive data file was loaded into a MATLAB script, MIDPCountourGen.m, to create pressure contours for the tank. The results from this thesis include the creation of MIDPContourGen.m and a corresponding How-To Guide and pore pressure contours for the F60 tank. This thesis concluded that the MIDP reaction takes a relatively short amount of time and that the residual pressure in the tank after the water flush on day 17 offers a proof of effect of the MIDP reaction.

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Date Created
  • 2020-05

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Assessment of the Vertical Stratification of Microbial Community Structure in Permafrost Peatlands

Description

Peatlands are a type of wetlands where the rate of accumulation of organic matter exceed the rate of decomposition and have accumulated more than 30 cm of peat (Joosten and

Peatlands are a type of wetlands where the rate of accumulation of organic matter exceed the rate of decomposition and have accumulated more than 30 cm of peat (Joosten and Clark, 2002). Peatlands store approximately 30% of all terrestrial carbon as recalcitrant peat, partially decomposed plant and microbial biomass, while simultaneously producing almost 40% of the globally emitted methane (Schmidt et al., 2016), making peatlands an important component of the carbon budgets. Published research indicates that the efficiency of carbon usage among microbial communities can determine the soil-carbon response to rising temperatures (Allison et al. 2010). By determining carbon consumption in peatland soils, total community respiration response, and community structure change with additions, models of carbon use efficiency in permafrost peatlands will be well-informed and have a better understanding of how the peatlands will respond to, and utilize, increased availability of carbon compounds due to the melting permafrost. To do this, we will sequence Lutose deep core samples to observe baseline microbial community structure at different depths and different age-gradients, construct substrate incubations of glucose and propionate and observe community respiration response via a gas chromatography flame ionization detector, track the glucose and propionate additions with high-performance liquid chromatography (HPLC), and sequence the samples once more to determine if there was a deviation from the initial community structure obtained prior to the incubations. We found that our initial sequencing data was supported by previous work (Lin et al., 2014), however we were unable to sequence samples post-incubation due to time constraints. In this sequencing analysis we found that the strongest variable that made samples biologically similar was the age-gradient site in which they were extracted. We found that the group with glucose additions produced the most carbon dioxide compared with the other treatments, but was not the treatment that dominated the production of methane. Finally, in the HPLC samples that were analyzed, we found that glucose is likely forming the most by-product accumulation from mass balance calculations, while propionate is likely forming the least. Future experimentation should focus on the shortcomings of this experiment. Further analysis of 16S rRNA sequencing data from after the incubations should be analyzed to determine the change in microbial community structure throughout the experiment. Furthermore, HPLC analysis for the several samples need to be done and followed up with mass balance to determine where the added glucose and propionate are being allocated within the soil. Once these pieces of the puzzle are put into place, our original question of how the microbial community structure changes at different depths and age-gradients within permafrost peatlands will be conclusively answered.

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Date Created
  • 2018-05

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Estimation of Pressuremeter Modulus From Shear Wave Velocity In the Sonoran Desert

Description

Laterally-loaded short rigid drilled shaft foundations are the primary foundation used within the electric power transmission line industry. Performance of these laterally loaded foundations is dependent on modulus of the

Laterally-loaded short rigid drilled shaft foundations are the primary foundation used within the electric power transmission line industry. Performance of these laterally loaded foundations is dependent on modulus of the subsurface, which is directly measured by the Pressuremeter (PMT). The PMT test provides the lateral shear modulus at intermediate strains, an equivalent elastic modulus for lateral loading, which mimics the reaction of transmission line foundations within the elastic range of motion. The PMT test, however, is expensive to conduct and rarely performed. Correlations of PMT to blow counts and other index properties have been developed but these correlations have high variability and may result in unconservative foundation design. Variability in correlations is due, in part, because difference of the direction of the applied load and strain level between the correlated properties and the PMT. The geophysical shear wave velocity (S-wave velocity) as measured through refraction microtremor (ReMi) methods can be used as a measure of the small strain, shear modulus in the lateral direction. In theory, the intermediate strain modulus of the PMT is proportional to the small strain modulus of S-wave velocity. A correlation between intermediate strain and low strain moduli is developed here, based on geophysical surveys conducted at fourteen previous PMT testing locations throughout the Sonoran Desert of central Arizona. Additionally, seasonal variability in S-wave velocity of unsaturated soils is explored and impacts are identified for the use of the PMT correlation in transmission line foundation design.

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Date Created
  • 2018

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Pore-scale Study of Bio-mineral and Bio-gas Formations in Porous Media

Description

The potential of using bio-geo-chemical processes for applications in geotechnical engineering has been widely explored in order to overcome the limitation of traditional ground improvement techniques. Biomineralization via urea hydrolysis,

The potential of using bio-geo-chemical processes for applications in geotechnical engineering has been widely explored in order to overcome the limitation of traditional ground improvement techniques. Biomineralization via urea hydrolysis, referred to as Microbial or Enzymatic Induced Carbonate Precipitation (MICP/EICP), has been shown to increase soil strength by stimulating precipitation of calcium carbonate minerals, bonding soil particles and filling the pores. Microbial Induced Desaturation and Precipitation (MIDP) via denitrification has also been studied for its potential to stabilize soils through mineral precipitation, but also through production of biogas, which can mitigate earthquake induced liquefaction by desaturation of the soil. Empirical relationships have been established, which relate the amount of products of these biochemical processes to the engineering properties of treated soils. However, these engineering properties may vary significantly depending on the biomineral and biogas formation mechanism and distribution patterns at pore-scale. This research focused on the pore-scale characterization of biomineral and biogas formations in porous media.

The pore-scale characteristics of calcium carbonate precipitation via EICP and biogenic gas formation via MIDP were explored by visual observation in a transparent porous media using a microfluidic chip. For this purpose, an imaging system was designed and image processing algorithms were developed to analyze the experimental images and detect the nucleation and growth of precipitated minerals and formation and migration mechanisms of gas bubbles within the microfluidic chip. Statistical analysis was performed based on the processed images to assess the evolution of biomineral size distribution, the number of precipitated minerals and the porosity reduction in time. The resulting images from the biomineralization study were used in a numerical simulation to investigate the relation between the mineral distribution, porosity-permeability relationships and process efficiency. By comparing biogenic gas production with abiotic gas production experiments, it was found that the gas formation significantly affects the gas distribution and resulting degree of saturation. The experimental results and image analysis provide insight in the kinetics of the precipitation and gas formation processes and their resulting distribution and related engineering properties.

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Created

Date Created
  • 2019

Self-Burrowing Mechanism and Robot Inspired by Razor Clams

Description

The Atlantic razor clam burrows underground with effectiveness and efficiency by coordinating shape changings of its shell and foot. Inspired by the burrowing strategy of razor clams, this research is

The Atlantic razor clam burrows underground with effectiveness and efficiency by coordinating shape changings of its shell and foot. Inspired by the burrowing strategy of razor clams, this research is dedicated to developing a self-burrowing technology for active underground explorations by investigating the burrowing mechanism of razor clams from the perspective of soil mechanics. In this study, the razor clam was observed to burrow out of sands simply by extending and contracting its foot periodically. This upward burrowing gait is much simpler than its downward burrowing gait, which also involves opening/closing of the shell and dilation of the foot. The upward burrowing gait inspired the design of a self-burrowing-out soft robot, which drives itself out of sands naturally by extension and contraction through pneumatic inflation and deflation. A simplified analytical model was then proposed and explained the upward burrowing behavior of the robot and razor clams as the asymmetric nature of soil resistances applied on both ends due to the intrinsic stress gradient of sand deposits. To burrow downward, additional symmetry-breaking features are needed for the robot to increase the resistance in the upward burrowing direction and to decrease the resistance in the downward burrowing direction. A potential approach is by incorporating friction anisotropy, which was then experimentally demonstrated to affect the upward burrowing of the soft robot. The downward burrowing gait of razor clams provides another inspiration. By exploring the analogies between the downward burrowing gait and in-situ soil characterization methods, a clam-inspired shape-changing penetrator was designed and penetrated dry granular materials both numerically and experimentally. Results demonstrated that the shell opening not only contributes to forming a penetration anchor by compressing the surrounding particles, but also reduces the foot penetration resistance temporally by creating a stress arch above the foot; the shell closing facilitates the downward burrowing by reducing the friction resistance to the subsequent shell retraction. Findings from this research shed lights on the future design of a clam-inspired self-burrowing robot.

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Created

Date Created
  • 2020

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Reductive dechlorination sustained by microbial chain elongation

Description

Trichloroethene (TCE) is a ubiquitous soil and groundwater contaminant. The most common bioremediation approach for TCE relies on the process of reductive dechlorination by Dehalococcoides mccartyi. D. mccartyi use TCE,

Trichloroethene (TCE) is a ubiquitous soil and groundwater contaminant. The most common bioremediation approach for TCE relies on the process of reductive dechlorination by Dehalococcoides mccartyi. D. mccartyi use TCE, dichloroethene, and vinyl chloride as electron acceptors and hydrogen as an electron donor. At contaminated sites, reductive dechlorination is typically promoted by adding a fermentable substrate, which is broken down to short chain fatty acids, simple alcohols, and hydrogen. This study explored microbial chain elongation (MCE), instead of fermentation, to promote TCE reductive dechlorination. In MCE, microbes use simple substrates (e.g., acetate, ethanol) to build medium chain fatty acids and also produce hydrogen during this process. Soil microcosm using TCE and acetate and ethanol as MCE substrates were established under anaerobic conditions. In soil microcosms with synthetic groundwater and natural groundwater, ethene was the main product from TCE reductive dechlorination and butyrate and hydrogen were the main products from MCE. Transfer microcosms using TCE and either acetate and ethanol, ethanol, or acetate were also established. The transfers with TCE and ethanol showed the faster rates of reductive dechlorination and produced more elongated products (i.e., hexanoate). The microbial groups enriched in the soil microcosms likely responsible for chain elongation were most similar to Clostridium genus. These investigations showed the potential for synergistic microbial chain elongation and reductive dechlorination of chlorinated ethenes.

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Date Created
  • 2019

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Exploring microbial chain elongation for production of organics and hydrogen in soils

Description

This research explores microbial chain elongation as a pathway for production of complex organic compounds in soils with implication for the carbon cycle. In chain elongation, simple substrates such as

This research explores microbial chain elongation as a pathway for production of complex organic compounds in soils with implication for the carbon cycle. In chain elongation, simple substrates such as ethanol and short chain carboxylates such as acetate can be converted to longer carbon chain carboxylates under anaerobic conditions through cyclic, reverse β oxidation. This pathway elongates the carboxylate by two carbons. The chain elongation process is overall thermodynamically feasible, and microorganisms gain energy through this process. There have been limited insights into the versatility of chain elongating substrates, understanding the chain elongating microbial community, and its importance in sequestering carbon in the soils.

We used ethanol, methanol, butanol, and hydrogen as electron donors and acetate and propionate as electron acceptors to test the occurrence of microbial chain elongation in four soils with different physicochemical properties and microbial communities. Common chain elongation products were the even numbered chains butyrate, caproate, and butanol, the odd numbered carboxylates valerate and heptanoate, along with molecular hydrogen. At a near neutral pH and mesophilic temperature, we observed a stable and sustained production of longer fatty acids along with hydrogen. Microbial community analysis show phylotypes from families such as Clostridiaceae, Bacillaceae, and Ruminococcaceae in all tested conditions. Through chain elongation, the products formed are less biodegradable. They may undergo transformations and end up as organic carbon, decreasing the greenhouse gas emissions, thus, making this process important to study.

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Created

Date Created
  • 2018