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- Genre: Doctoral Dissertation
Description
Water contamination with nitrate (NO3−) (from fertilizers) and perchlorate (ClO4−) (from rocket fuel and explosives) is a widespread environmental problem. I employed the Membrane Biofilm Reactor (MBfR), a novel bioremediation technology, to treat NO3− and ClO4− in the presence of naturally occurring sulfate (SO42−). In the MBfR, bacteria reduce oxidized pollutants that act as electron acceptors, and they grow as a biofilm on the outer surface of gas-transfer membranes that deliver the electron donor (hydrogen gas, (H2). The overarching objective of my research was to achieve a comprehensive understanding of ecological interactions among key microbial members in the MBfR when treating polluted water with NO3− and ClO4− in the presence of SO42−. First, I characterized competition and co-existence between denitrifying bacteria (DB) and sulfate-reducing bacteria (SRB) when the loading of either the electron donor or electron acceptor was varied. Then, I assessed the microbial community structure of biofilms mostly populated by DB and SRB, linking structure with function based on the electron-donor bioavailability and electron-acceptor loading. Next, I introduced ClO4− as a second oxidized contaminant and discovered that SRB harm the performance of perchlorate-reducing bacteria (PRB) when the aim is complete ClO4− destruction from a highly contaminated groundwater. SRB competed too successfully for H2 and space in the biofilm, forcing the PRB to unfavorable zones in the biofilm. To better control SRB, I tested a two-stage MBfR for total ClO4− removal from a groundwater highly contaminated with ClO4−. I document successful remediation of ClO4− after controlling SO4 2− reduction by restricting electron-donor availability and increasing the acceptor loading to the second stage reactor. Finally, I evaluated the performance of a two-stage pilot MBfR treating water polluted with NO3− and ClO4−, and I provided a holistic understanding of the microbial community structure and diversity. In summary, the microbial community structure in the MBfR contributes to and can be used to explain/predict successful or failed water bioremediation. Based on this understanding, I developed means to manage the microbial community to achieve desired water-decontamination results. This research shows the benefits of looking "inside the box" for "improving the box".
ContributorsOntiveros-Valencia, Aura (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Torres, Cesar I. (Committee member) / Arizona State University (Publisher)
Created2014
Description
The overall goal of this dissertation is to advance understanding of biofilm reduction of oxidized contaminants in water and wastewater. Chapter 1 introduces the fundamentals of biological reduction of three oxidized contaminants (nitrate, perchlorate, and trichloriethene (TCE)) using two biofilm processes (hydrogen-based membrane biofilm reactors (MBfR) and packed-bed heterotrophic reactors (PBHR)), and it identifies the research objectives. Chapters 2 through 6 focus on nitrate removal using the MBfR and PBHR, while chapters 7 through 10 investigate simultaneous reduction of nitrate and another oxidized compound (perchlorate, sulfate, or TCE) in the MBfR. Chapter 11 summarizes the major findings of this research. Chapters 2 and 3 demonstrate nitrate removal in a groundwater and identify the maximum nitrate loadings using a pilot-scale MBfR and a pilot-scale PBHR, respectively. Chapter 4 compares the MBfR and the PBHR for denitrification of the same nitrate-contaminated groundwater. The comparison includes the maximum nitrate loading, the effluent water quality of the denitrification reactors, and the impact of post-treatment on water quality. Chapter 5 theoretically and experimentally demonstrates that the nitrate biomass-carrier surface loading, rather than the traditionally used empty bed contact time or nitrate volumetric loading, is the primary design parameter for heterotrophic denitrification. Chapter 6 constructs a pH-control model to predict pH, alkalinity, and precipitation potential in heterotrophic or hydrogen-based autotrophic denitrification reactors. Chapter 7 develops and uses steady-state permeation tests and a mathematical model to determine the hydrogen-permeation coefficients of three fibers commonly used in the MBfR. The coefficients are then used as inputs for the three models in Chapters 8-10. Chapter 8 develops a multispecies biofilm model for simultaneous reduction of nitrate and perchlorate in the MBfR. The model quantitatively and systematically explains how operating conditions affect nitrate and perchlorate reduction and biomass distribution via four mechanisms. Chapter 9 modifies the nitrate and perchlorate model into a nitrate and sulfate model and uses it to identify operating conditions corresponding to onset of sulfate reduction. Chapter 10 modifies the nitrate and perchlorate model into a nitrate and TCE model and uses it to investigate how operating conditions affect TCE reduction and accumulation of TCE reduction intermediates.
ContributorsTang, Youneng (Author) / Rittmann, Bruce E. (Thesis advisor) / Westerhoff, Paul (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Halden, Rolf (Committee member) / Arizona State University (Publisher)
Created2012
Description
Contamination by chlorinated ethenes is widespread in groundwater aquifers, sediment, and soils worldwide. The overarching objectives of my research were to understand how the bacterial genus Dehalococcoides function optimally to carry out reductive dechlorination of chlorinated ethenes in a mixed microbial community and then apply this knowledge to manage dechlorinating communities in the hydrogen-based membrane biofilm reactor (MBfR). The MBfR is used for the biological reduction of oxidized contaminants in water using hydrogen supplied as the electron donor by diffusion through gas-transfer fibers. First, I characterized a new anaerobic dechlorinating community developed in our laboratory, named DehaloR^2, in terms of chlorinated ethene turnover rates and assessed its microbial community composition. I then carried out an experiment to correlate performance and community structure for trichloroethene (TCE)-fed microbial consortia. Fill-and-draw reactors inoculated with DehaloR^2 demonstrated a direct correlation between microbial community function and structure as the TCE-pulsing rate was increased. An electron-balance analysis predicted the community structure based on measured concentrations of products and constant net yields for each microorganism. The predictions corresponded to trends in the community structure based on pyrosequencing and quantitative PCR up to the highest TCE pulsing rate, where deviations to the trend resulted from stress by the chlorinated ethenes. Next, I optimized a method for simultaneous detection of chlorinated ethenes and ethene at or below the Environmental Protection Agency maximum contaminant levels for groundwater using solid phase microextraction in a gas chromatograph with a flame ionization detector. This method is ideal for monitoring biological reductive dechlorination in groundwater, where ethene is the ultimate end product. The major advantage of this method is that it uses a small sample volume of 1 mL, making it ideally suited for bench-scale feasibility studies, such as the MBfR. Last, I developed a reliable start-up and operation strategy for TCE reduction in the MBfR. Successful operation relied on controlling the pH-increase effects of methanogenesis and homoacetogenesis, along with creating hydrogen limitation during start-up to allow dechlorinators to compete against other microorgansims. Methanogens were additionally minimized during continuous flow operation by a limitation in bicarbonate resulting from strong homoacetogenic activity.
ContributorsZiv-El, Michal (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Halden, Rolf U. (Committee member) / Arizona State University (Publisher)
Created2012
Description
ABSTRACT
Sustainable global energy production is one of the grand challenges of the 21st century. Next-generation renewable energy sources include using photosynthetic microbes such as cyanobacteria for efficient production of sustainable fuels from sunlight. The cyanobacterium Synechocystis PCC 6803 (Synechocystis) is a genetically tractable model organism for plant-like photosynthesis that is used to develop microbial biofuel technologies. However, outside of photosynthetic processes, relatively little is known about the biology of microbial phototrophs such as Synechocystis, which impairs their development into market-ready technologies. My research objective was to characterize strategic aspects of Synechocystis biology related to its use in biofuel production; specifically, how the cell surface modulates the interactions between Synechocystis cells and the environment. First, I documented extensive biofouling, or unwanted biofilm formation, in a 4,000-liter roof-top photobioreactor (PBR) used to cultivate Synechocystis, and correlated this cell-binding phenotype with changes in nutrient status by developing a bench-scale assay for axenic phototrophic biofilm formation. Second, I created a library of mutants that lack cell surface structures, and used this biofilm assay to show that mutants lacking the structures pili or S-layer have a non-biofouling phenotype. Third, I analyzed the transcriptomes of cultures showing aggregation, another cell-binding phenotype, and demonstrated that the cells were undergoing stringent response, a type of conserved stress response. Finally, I used contaminant Consortia and statistical modeling to test whether Synechocystis mutants lacking cell surface structures could reduce contaminant growth in mixed cultures. In summary, I have identified genetic and environmental means of manipulating Synechocystis strains for customized adhesion phenotypes, for more economical biomass harvesting and non-biofouling methods. Additionally, I developed a modified biofilm assay and demonstrated its utility in closing a key gap in the field of microbiology related to axenic phototrophic biofilm formation assays. Also, I demonstrated that statistical modeling of contaminant Consortia predicts contaminant growth across diverse species. Collectively, these findings serve as the basis for immediately lowering the cost barrier of Synechocystis biofuels via a more economical biomass-dewatering step, and provide new research tools for improving Synechocystis strains and culture ecology management for improved biofuel production.
Sustainable global energy production is one of the grand challenges of the 21st century. Next-generation renewable energy sources include using photosynthetic microbes such as cyanobacteria for efficient production of sustainable fuels from sunlight. The cyanobacterium Synechocystis PCC 6803 (Synechocystis) is a genetically tractable model organism for plant-like photosynthesis that is used to develop microbial biofuel technologies. However, outside of photosynthetic processes, relatively little is known about the biology of microbial phototrophs such as Synechocystis, which impairs their development into market-ready technologies. My research objective was to characterize strategic aspects of Synechocystis biology related to its use in biofuel production; specifically, how the cell surface modulates the interactions between Synechocystis cells and the environment. First, I documented extensive biofouling, or unwanted biofilm formation, in a 4,000-liter roof-top photobioreactor (PBR) used to cultivate Synechocystis, and correlated this cell-binding phenotype with changes in nutrient status by developing a bench-scale assay for axenic phototrophic biofilm formation. Second, I created a library of mutants that lack cell surface structures, and used this biofilm assay to show that mutants lacking the structures pili or S-layer have a non-biofouling phenotype. Third, I analyzed the transcriptomes of cultures showing aggregation, another cell-binding phenotype, and demonstrated that the cells were undergoing stringent response, a type of conserved stress response. Finally, I used contaminant Consortia and statistical modeling to test whether Synechocystis mutants lacking cell surface structures could reduce contaminant growth in mixed cultures. In summary, I have identified genetic and environmental means of manipulating Synechocystis strains for customized adhesion phenotypes, for more economical biomass harvesting and non-biofouling methods. Additionally, I developed a modified biofilm assay and demonstrated its utility in closing a key gap in the field of microbiology related to axenic phototrophic biofilm formation assays. Also, I demonstrated that statistical modeling of contaminant Consortia predicts contaminant growth across diverse species. Collectively, these findings serve as the basis for immediately lowering the cost barrier of Synechocystis biofuels via a more economical biomass-dewatering step, and provide new research tools for improving Synechocystis strains and culture ecology management for improved biofuel production.
ContributorsAllen, Rebecca Custer (Author) / Curtiss Iii, Roy (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Vermaas, Willem (Committee member) / Arizona State University (Publisher)
Created2016
Description
Microbial Electrochemical Cell (MXC) technology harnesses the power stored in wastewater by using anode respiring bacteria (ARB) as a biofilm catalyst to convert the energy stored in waste into hydrogen or electricity. ARB, or exoelectrogens, are able to convert the chemical energy stored in wastes into electrical energy by transporting electrons extracellularly and then transferring them to an electrode. If MXC technology is to be feasible for ‘real world’ applications, it is essential that diverse ARB are discovered and their unique physiologies elucidated- ones which are capable of consuming a broad spectrum of wastes from different contaminated water sources.
This dissertation examines the use of Gram-positive thermophilic (60 ◦C) ARB in MXCs since very little is known regarding the behavior of these microorganisms in this setting. Here, we begin with the draft sequence of the Thermincola ferriacetica genome and reveal the presence of 35 multiheme c-type cytochromes. In addition, we employ electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA) to gain insight into the presence of multiple pathways for extracellular electron transport (EET) and current production (j) limitations in T. ferriacetica biofilms.
Next, Thermoanaerobacter pseudethanolicus, a fermentative ARB, is investigated for its ability to ferment pentose and hexose sugars prior to using its fermentation products, including acetate and lactate, for current production in an MXC. Using CA, current production is tracked over time with the generation and consumption of fermentation products. Using CV, the midpoint potential (EKA) of the T. pseudethanolicus EET pathway is revealed.
Lastly, a cellulolytic microbial consortium was employed for the purpose ofassessing the feasibility of using thermophilic MXCs for the conversion of solid waste into current production. Here, a highly enriched consortium of bacteria, predominately from the Firmicutes phylum, is capable of generating current from solid cellulosic materials.
This dissertation examines the use of Gram-positive thermophilic (60 ◦C) ARB in MXCs since very little is known regarding the behavior of these microorganisms in this setting. Here, we begin with the draft sequence of the Thermincola ferriacetica genome and reveal the presence of 35 multiheme c-type cytochromes. In addition, we employ electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA) to gain insight into the presence of multiple pathways for extracellular electron transport (EET) and current production (j) limitations in T. ferriacetica biofilms.
Next, Thermoanaerobacter pseudethanolicus, a fermentative ARB, is investigated for its ability to ferment pentose and hexose sugars prior to using its fermentation products, including acetate and lactate, for current production in an MXC. Using CA, current production is tracked over time with the generation and consumption of fermentation products. Using CV, the midpoint potential (EKA) of the T. pseudethanolicus EET pathway is revealed.
Lastly, a cellulolytic microbial consortium was employed for the purpose ofassessing the feasibility of using thermophilic MXCs for the conversion of solid waste into current production. Here, a highly enriched consortium of bacteria, predominately from the Firmicutes phylum, is capable of generating current from solid cellulosic materials.
ContributorsLusk, Bradley (Author) / Torres, César I (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2015