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Description
Bioremediation of trichloroethene (TCE) using Dehalococcoides mccartyi-containing microbial cultures is a recognized and successful remediation technology. Our work with an upflow anaerobic sludge blanket (UASB) reactor has shown that high-performance, fast-rate dechlorination of TCE can be achieved by promoting bioflocculation of Dehalococcoides mccartyi-containing cultures. The bioreactor achieved high maximum conversion rates of 1.63 ± 0.012 mmol Cl- Lculture-1 h-1 at an HRT of 3.6 hours and >97% dechlorination of TCE to ethene while continuously fed 2 mM TCE. The UASB generated bioflocs from a microbially heterogeneous dechlorinating culture and produced Dehalococcoides mccartyi densities of 1.73x10-13 cells Lculture-1 indicating that bioflocculation of Dehalococcoides mccartyi-containing cultures can lead to high density inocula and high-performance, fast-rate bioaugmentation culture for in situ treatment. The successful operation of our pilot scale bioreactor led to the assessment of the technology as an onsite ex-situ treatment system. The bioreactor was then fed TCE-contaminated groundwater from the Motorola Inc. 52nd Street Plant Superfund site in Phoenix, AZ augmented with the lactate and methanol. The bioreactor maintained >99% dechlorination of TCE to ethene during continuous operation at an HRT of 3.2 hours. Microbial community analysis under both experimental conditions reveals shifts in the community structure although maintaining high rate dechlorination. High density dechlorinating cultures containing bioflocs can provide new ways to 1) produce dense bioaugmentation cultures, 2) perform ex-situ bioremediation of TCE, and 3) increase our understanding of Dehalococcoides mccartyi critical microbial interactions that can be exploited at contaminated sites in order to improve long-term bioremediation schemes.
ContributorsFajardo-Williams, Devyn (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Torres, César I (Committee member) / Popat, Sudeep C (Committee member) / Arizona State University (Publisher)
Created2015
Description
Photosynthesis converts sunlight to biomass at a global scale. Among the photosynthetic organisms, cyanobacteria provide an excellent model to study how photosynthesis can become a practical platform of large-scale biotechnology. One novel approach involves metabolically engineering the cyanobacterium Synechocystis sp. PCC 6803 to excrete laurate, which is harvested directly.
This work begins by defining a working window of light intensity (LI). Wild-type and laurate-excreting Synechocystis required an LI of at least 5 µE/m2-s to sustain themselves, but are photo-inhibited by LI of 346 to 598 µE/m2-s.
Fixing electrons into valuable organic products, e.g., biomass and excreted laurate, is critical to success. Wild-type Synechocystis channeled 75% to 84% of its fixed electrons to biomass; laurate-excreting Synechocystis fixed 64 to 69% as biomass and 6.6% to 10% as laurate. This means that 16 to 30% of the electrons were diverted to non-valuable soluble products, and the trend was accentuated with higher LI.
How the Ci concentration depended on the pH and the nitrogen source was quantified by the proton condition and experimentally validated. Nitrate increased, ammonium decreased, but ammonium nitrate stabilized alkalinity and Ci. This finding provides a mechanistically sound tool to manage Ci and pH independently.
Independent evaluation pH and Ci on the growth kinetics of Synechocystis showed that pH 8.5 supported the fastest maximum specific growth rate (µmax): 2.4/day and 1.7/day, respectively, for the wild type and modified strains with LI of 202 µE/m2-s. Half-maximum-rate concentrations (KCi) were less than 0.1 mM, meaning that Synechocystis should attain its µmax with a modest Ci concentration (≥1.0 mM).
Biomass grown with day-night cycles had a night endogenous decay rate of 0.05-1.0/day, with decay being faster with higher LI and the beginning of dark periods. Supplying light at a fraction of daylight reduced dark decay rate and improved overall biomass productivity.
This dissertation systematically evaluates and synthesizes fundamental growth factors of cyanobacteria: light, inorganic carbon (Ci), and pH. LI remains the most critical growth condition to promote biomass productivity and desired forms of biomass, while Ci and pH now can be managed to support optimal productivity.
This work begins by defining a working window of light intensity (LI). Wild-type and laurate-excreting Synechocystis required an LI of at least 5 µE/m2-s to sustain themselves, but are photo-inhibited by LI of 346 to 598 µE/m2-s.
Fixing electrons into valuable organic products, e.g., biomass and excreted laurate, is critical to success. Wild-type Synechocystis channeled 75% to 84% of its fixed electrons to biomass; laurate-excreting Synechocystis fixed 64 to 69% as biomass and 6.6% to 10% as laurate. This means that 16 to 30% of the electrons were diverted to non-valuable soluble products, and the trend was accentuated with higher LI.
How the Ci concentration depended on the pH and the nitrogen source was quantified by the proton condition and experimentally validated. Nitrate increased, ammonium decreased, but ammonium nitrate stabilized alkalinity and Ci. This finding provides a mechanistically sound tool to manage Ci and pH independently.
Independent evaluation pH and Ci on the growth kinetics of Synechocystis showed that pH 8.5 supported the fastest maximum specific growth rate (µmax): 2.4/day and 1.7/day, respectively, for the wild type and modified strains with LI of 202 µE/m2-s. Half-maximum-rate concentrations (KCi) were less than 0.1 mM, meaning that Synechocystis should attain its µmax with a modest Ci concentration (≥1.0 mM).
Biomass grown with day-night cycles had a night endogenous decay rate of 0.05-1.0/day, with decay being faster with higher LI and the beginning of dark periods. Supplying light at a fraction of daylight reduced dark decay rate and improved overall biomass productivity.
This dissertation systematically evaluates and synthesizes fundamental growth factors of cyanobacteria: light, inorganic carbon (Ci), and pH. LI remains the most critical growth condition to promote biomass productivity and desired forms of biomass, while Ci and pH now can be managed to support optimal productivity.
ContributorsNguyen, Binh Thanh (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Westerhoff, Paul (Committee member) / Arizona State University (Publisher)
Created2015
Description
Microbial electrochemical cells (MXCs) offer an alternative to methane production in anaerobic water treatment and the recapture of energy in waste waters. MXCs use anode respiring bacteria (ARB) to oxidize organic compounds and generate electrical current. In both anaerobic digestion and MXCs, an anaerobic food web connects the metabolisms of different microorganisms, using hydrolysis, fermentation and either methanogenesis or anode respiration to break down organic compounds, convert them to acetate and hydrogen, and then convert those intermediates into either methane or current. In this dissertation, understanding and managing the interactions among fermenters, methanogens, and ARB were critical to making developments in MXCs. Deep sequencing technologies were used in order to identify key community members, understand their role in the community, and identify selective pressures that drove the structure of microbial communities. This work goes from developing ARB communities by finding and using the best partners to managing ARB communities with undesirable partners. First, the foundation of MXCs, namely the ARB they rely on, was expanded by identifying novel ARB, the genus Geoalkalibacter, and demonstrating the presence of ARB in 7 out of 13 different environmental samples. Second, a new microbial community which converted butyrate to electricity at ~70% Coulombic efficiency was assembled and demonstrated that mixed communities can be used to assemble efficient ARB communities. Third, varying the concentrations of sugars and ethanol fed to methanogenic communities showed how increasing ED concentration drove decreases in methane production and increases in both fatty acids and the propionate producing genera Bacteroides and Clostridium. Finally, methanogenic batch cultures, fed glucose and sucrose, and exposed to 0.15 – 6 g N-NH4+ L-1 showed that increased NH4+ inhibited methane production, drove fatty acid and lactate production, and enriched Lactobacillales (up to 40% abundance) above 4 g N-NH4+ L-1. Further, 4 g N-NH4+ L-1 improved Coulombic efficiencies in MXCs fed with glucose and sucrose, and showed that MXC communities, especially the biofilm, are more resilient to high NH4+ than comparable methanogenic communities. These developments offer new opportunities for MXC applications, guidance for efficient operation of MXCs, and insights into fermentative microbial communities.
ContributorsMiceli, Joseph (Author) / Torres, César I (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Rittmann, Bruce (Committee member) / Arizona State University (Publisher)
Created2015
Description
This study reports on benzene and toluene biodegradation under different dissolved oxygen conditions, and the goal of this study is to evaluate and model their removal.
Benzene and toluene were tested for obligate anaerobic degradation in batch reactors with sulfate as the electron acceptor. A group of sulfate-reducing bacteria capable of toluene degradation was enriched after 252 days of incubation. Those cultures, originated from anaerobic digester, were able to degrade toluene coupled to sulfate reduction with benzene coexistence, while they were not able to utilize benzene. Methanogens also were present, although their contribution to toluene biodegradation was not defined.
Aerobic biodegradation of benzene and toluene by Pseudomonas putida F1 occurred, and biomass production lagged behind substrate loss and continued after complete substrate removal. This pattern suggests that biodegradation of intermediates, rather than direct benzene and toluene transformation, caused bacterial growth. Supporting this explanation is that the calculated biomass growth from a two-step model basically fit the experimental biomass results during benzene and toluene degradation with depleted dissolved oxygen.
Catechol was tested for anaerobic biodegradation in batch experiments and in a column study. Sulfate- and nitrate-reducing bacteria enriched from a wastewater treatment plant hardly degraded catechol within 20 days. However, an inoculum from a contaminated site was able to remove 90% of the initial 16.5 mg/L catechol, and Chemical Oxygen Demand was oxidized in parallel. Catechol biodegradation was inhibited when nitrite accumulated, presumably by a toxic catechol-nitrite complex.
The membrane biofilm reactor (MBfR) offers the potential for biodegrading benzene in a linked aerobic and anaerobic pathway by controlling the O2 delivery. At an average benzene surface loading of 1.3 g/m2-day and an average hydraulic retention time of 2.2 day, an MBfR supplied with pure O2 successfully achieved 99% benzene removal at steady state. A lower oxygen partial pressure led to decreased benzene removal, and nitrate removal increased, indicating multiple mechanisms, including oxygenation and nitrate reduction, were involved in the system being responsible for benzene removal. Microbial community analysis indicated that Comamonadaceae, a known aerobic benzene-degrader and denitrifier, dominated the biofilm at the end of operation.
Benzene and toluene were tested for obligate anaerobic degradation in batch reactors with sulfate as the electron acceptor. A group of sulfate-reducing bacteria capable of toluene degradation was enriched after 252 days of incubation. Those cultures, originated from anaerobic digester, were able to degrade toluene coupled to sulfate reduction with benzene coexistence, while they were not able to utilize benzene. Methanogens also were present, although their contribution to toluene biodegradation was not defined.
Aerobic biodegradation of benzene and toluene by Pseudomonas putida F1 occurred, and biomass production lagged behind substrate loss and continued after complete substrate removal. This pattern suggests that biodegradation of intermediates, rather than direct benzene and toluene transformation, caused bacterial growth. Supporting this explanation is that the calculated biomass growth from a two-step model basically fit the experimental biomass results during benzene and toluene degradation with depleted dissolved oxygen.
Catechol was tested for anaerobic biodegradation in batch experiments and in a column study. Sulfate- and nitrate-reducing bacteria enriched from a wastewater treatment plant hardly degraded catechol within 20 days. However, an inoculum from a contaminated site was able to remove 90% of the initial 16.5 mg/L catechol, and Chemical Oxygen Demand was oxidized in parallel. Catechol biodegradation was inhibited when nitrite accumulated, presumably by a toxic catechol-nitrite complex.
The membrane biofilm reactor (MBfR) offers the potential for biodegrading benzene in a linked aerobic and anaerobic pathway by controlling the O2 delivery. At an average benzene surface loading of 1.3 g/m2-day and an average hydraulic retention time of 2.2 day, an MBfR supplied with pure O2 successfully achieved 99% benzene removal at steady state. A lower oxygen partial pressure led to decreased benzene removal, and nitrate removal increased, indicating multiple mechanisms, including oxygenation and nitrate reduction, were involved in the system being responsible for benzene removal. Microbial community analysis indicated that Comamonadaceae, a known aerobic benzene-degrader and denitrifier, dominated the biofilm at the end of operation.
ContributorsLiu, Zhuolin (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2015
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
Description
Microbial electrochemical cells (MXCs) serve as an alternative anaerobic technology to anaerobic digestion for efficient energy recovery from high-strength organic wastes such as primary sludge (PS). The overarching goal of my research was to address energy conversion from PS to useful resources (e.g. hydrogen or hydrogen peroxide) through bio- and electro-chemical anaerobic conversion processes in MXCs.
First, a new flat-pate microbial electrolysis cell (MEC) was designed with high surface area anodes using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. Through the improved design, operation, and electrochemical characterization, the applied voltages were reduced from 1.1 to ~0.85 V, at 10 A m-2. Second, PS conversion was examined through hydrolysis, fermentation, methanogenesis, and/or anode respiration. Since pretreatment often is required to accelerate hydrolysis of organic solids, I evaluated pulsed electric field technology on PS showing a modest improvement of energy conversion through methanogenesis and fermentation, as compared to the conversion from waste activated sludge (WAS) or WAS+PS. Then, a two-stage system (prefermented PS-fed MEC) yielded successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (CR, 80%), and COD-removal efficiency (85%). However, overall PS conversion to electrical current (or CR) through pre-fermentation and MEC, was just ~16%. Next, a single-stage system (direct PS-fed MEC) with semi-continuous operation showed 34% CR at a 9-day hydraulic retention time. The PS-fed MEC also showed an important pH dependency, in which high pH (> 8) in the anode chamber improved anode respiration along with methanogen inhibition. Finally, H2O2 was produced in a PS-fed microbial electrochemical cell with a low energy requirement (~0.87 kWh per kg H2O2). These research developments will provide groundbreaking knowledge for MXC design, commercial application, and anaerobic energy conversion from other high-strength organic wastes to resources.
First, a new flat-pate microbial electrolysis cell (MEC) was designed with high surface area anodes using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. Through the improved design, operation, and electrochemical characterization, the applied voltages were reduced from 1.1 to ~0.85 V, at 10 A m-2. Second, PS conversion was examined through hydrolysis, fermentation, methanogenesis, and/or anode respiration. Since pretreatment often is required to accelerate hydrolysis of organic solids, I evaluated pulsed electric field technology on PS showing a modest improvement of energy conversion through methanogenesis and fermentation, as compared to the conversion from waste activated sludge (WAS) or WAS+PS. Then, a two-stage system (prefermented PS-fed MEC) yielded successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (CR, 80%), and COD-removal efficiency (85%). However, overall PS conversion to electrical current (or CR) through pre-fermentation and MEC, was just ~16%. Next, a single-stage system (direct PS-fed MEC) with semi-continuous operation showed 34% CR at a 9-day hydraulic retention time. The PS-fed MEC also showed an important pH dependency, in which high pH (> 8) in the anode chamber improved anode respiration along with methanogen inhibition. Finally, H2O2 was produced in a PS-fed microbial electrochemical cell with a low energy requirement (~0.87 kWh per kg H2O2). These research developments will provide groundbreaking knowledge for MXC design, commercial application, and anaerobic energy conversion from other high-strength organic wastes to resources.
ContributorsKi, Dong Won (Author) / Torres, César I (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Parameswaran, Prathap (Committee member) / Popat, Sudeep C (Committee member) / Arizona State University (Publisher)
Created2016
Description
To address sustainability issues in wastewater treatment (WWT), Siemens Water Technologies (SWT) has designed a "hybrid" process that couples common activated sludge (AS) and anaerobic digestion (AD) technologies with the novel concepts of AD sludge recycle and biosorption. At least 85% of the hybrid's AD sludge is recycled to the AS process, providing additional sorbent for influent particulate chemical oxygen demand (PCOD) biosorption in contact tanks. Biosorbed PCOD is transported to the AD, where it is converted to methane. The aim of this study is to provide mass balance and microbial community analysis (MCA) of SWT's two hybrid and one conventional pilot plant trains and mathematical modeling of the hybrid process including a novel model of biosorption. A detailed mass balance was performed on each tank and the overall system. The mass balance data supports the hybrid process is more sustainable: It produces 1.5 to 5.5x more methane and 50 to 83% less sludge than the conventional train. The hybrid's superior performance is driven by 4 to 8 times longer solid retention times (SRTs) as compared to conventional trains. However, the conversion of influent COD to methane was low at 15 to 22%, and neither train exhibited significant nitrification or denitrification. Data were inconclusive as to the role of biosorption in the processes. MCA indicated the presence of Archaea and nitrifiers throughout both systems. However, it is inconclusive as to how active Archaea and nitrifiers are under anoxic, aerobic, and anaerobic conditions. Mathematical modeling confirms the hybrid process produces 4 to 20 times more methane and 20 to 83% less sludge than the conventional train under various operating conditions. Neither process removes more than 25% of the influent nitrogen or converts more that 13% to nitrogen gas due to biomass washout in the contact tank and short SRTs in the stabilization tank. In addition, a mathematical relationship was developed to describe PCOD biosorption through adsorption to biomass and floc entrapment. Ultimately, process performance is more heavily influenced by the higher AD SRTs attained when sludge is recycled through the system and less influenced by the inclusion of biosorption kinetics.
ContributorsYoung, Michelle Nichole (Author) / Rittmann, Bruce E. (Thesis advisor) / Fox, Peter (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2011
Description
Large-scale cultivation of photosynthetic microorganisms for the production of biodiesel and other valuable commodities must be made more efficient. Recycling the water and nutrients acquired from biomass harvesting promotes a more sustainable and economically viable enterprise. This study reports on growing the cyanobacterium Synechocystis sp. PCC 6803 using permeate obtained from concentrating the biomass by cross-flow membrane filtration. I used a kinetic model based on the available light intensity (LI) to predict biomass productivity and evaluate overall performance.
During the initial phase of the study, I integrated a membrane filter with a bench-top photobioreactor (PBR) and created a continuously operating system. Recycling permeate reduced the amount of fresh medium delivered to the PBR by 45%. Biomass production rates as high as 400 mg-DW/L/d (9.2 g-DW/m2/d) were sustained under constant lighting over a 12-day period.
In the next phase, I operated the system as a sequencing batch reactor (SBR), which improved control over nutrient delivery and increased the concentration factor of filtered biomass (from 1.8 to 6.8). I developed unique system parameters to compute the amount of recycled permeate in the reactor and the actual hydraulic retention time during SBR operation. The amount of medium delivered to the system was reduced by up to 80%, and growth rates were consistent at variable amounts of repeatedly recycled permeate. The light-based model accurately predicted growth when biofilm was not present. Coupled with mass ratios for PCC 6803, these predictions facilitated efficient delivery of nitrogen and phosphorus. Daily biomass production rates and specific growth rates equal to 360 mg-DW/L/d (8.3 g/m2/d) and 1.0 d-1, respectively, were consistently achieved at a relatively low incident LI (180 µE/m2/s). Higher productivities (up to 550 mg-DW/L/d) occurred under increased LI (725 µE/m2/s), although the onset of biofilm impeded modeled performance.
Permeate did not cause any gradual growth inhibition. Repeated results showed cultures rapidly entered a stressed state, which was followed by widespread cell lysis. This phenomenon occurred independently of permeate recycling and was not caused by nutrient starvation. It may best be explained by negative allelopathic effects or viral infection as a result of mixed culture conditions.
During the initial phase of the study, I integrated a membrane filter with a bench-top photobioreactor (PBR) and created a continuously operating system. Recycling permeate reduced the amount of fresh medium delivered to the PBR by 45%. Biomass production rates as high as 400 mg-DW/L/d (9.2 g-DW/m2/d) were sustained under constant lighting over a 12-day period.
In the next phase, I operated the system as a sequencing batch reactor (SBR), which improved control over nutrient delivery and increased the concentration factor of filtered biomass (from 1.8 to 6.8). I developed unique system parameters to compute the amount of recycled permeate in the reactor and the actual hydraulic retention time during SBR operation. The amount of medium delivered to the system was reduced by up to 80%, and growth rates were consistent at variable amounts of repeatedly recycled permeate. The light-based model accurately predicted growth when biofilm was not present. Coupled with mass ratios for PCC 6803, these predictions facilitated efficient delivery of nitrogen and phosphorus. Daily biomass production rates and specific growth rates equal to 360 mg-DW/L/d (8.3 g/m2/d) and 1.0 d-1, respectively, were consistently achieved at a relatively low incident LI (180 µE/m2/s). Higher productivities (up to 550 mg-DW/L/d) occurred under increased LI (725 µE/m2/s), although the onset of biofilm impeded modeled performance.
Permeate did not cause any gradual growth inhibition. Repeated results showed cultures rapidly entered a stressed state, which was followed by widespread cell lysis. This phenomenon occurred independently of permeate recycling and was not caused by nutrient starvation. It may best be explained by negative allelopathic effects or viral infection as a result of mixed culture conditions.
ContributorsThompson, Matthew (Author) / Rittmann, Bruce E. (Thesis advisor) / Fox, Peter (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2015
Description
Creating sustainable alternatives to fossil fuel resources is one of the greatest
challenges facing mankind. Solar energy provides an excellent option to alleviate modern dependence on fossil fuels. However, efficient methods to harness solar energy are still largely lacking. Biomass from photosynthetic organisms can be used as feedstock to produce traditional fuels, but must be produced in great quantities in order to meet the demands of growing populations. Cyanobacteria are prokaryotic photosynthetic microorganisms that can produce biomass on large scales using only sunlight, carbon dioxide, water, and small amounts of nutrients. Thus, Cyanobacteria are a viable option for sustainable production of biofuel feedstock material. Photobioreactors (PBRs) offer a high degree of control over the temperature, aeration, and mixing of cyanobacterial cultures, but cannot be kept sterile due to the scales necessary to meet domestic and global energy demands, meaning that heterotrophic bacteria can grow in PBRs by oxidizing the organic material produced and excreted by the Cyanobacteria. These heterotrophic bacteria can positively or negatively impact the performance of the PBR through their interactions with the Cyanobacteria. This work explores the microbial ecology in PBR cultures of the model cyanobacterium Synechocystis sp. PCC6803 (Synechocystis) using microbiological, molecular, chemical, and engineering techniques. I first show that diverse phylotypes of heterotrophic bacteria can associate with Synechocystis-based PBRs and that excluding them may be impossible under typical PBR operating conditions. Then, I demonstrate that high-throughput sequencing can reliably elucidate the structure of PBR microbial communities without the need for pretreatment to remove Synechocystis 16S rRNA genes, despite the high degree of polyploidy found in Synechocystis. Next, I establish that the structure of PBR microbial communities is strongly influenced by the microbial community of the inoculum culture. Finally, I show that maintaining available phosphorus in the culture medium promotes the production and enrichment of Synechocystis biomass in PBRs by reducing the amount of soluble substrates available to heterotrophic bacteria. This work presents the first analysis of the structure and function of microbial communities associated with Synechocystis-based PBRs.
challenges facing mankind. Solar energy provides an excellent option to alleviate modern dependence on fossil fuels. However, efficient methods to harness solar energy are still largely lacking. Biomass from photosynthetic organisms can be used as feedstock to produce traditional fuels, but must be produced in great quantities in order to meet the demands of growing populations. Cyanobacteria are prokaryotic photosynthetic microorganisms that can produce biomass on large scales using only sunlight, carbon dioxide, water, and small amounts of nutrients. Thus, Cyanobacteria are a viable option for sustainable production of biofuel feedstock material. Photobioreactors (PBRs) offer a high degree of control over the temperature, aeration, and mixing of cyanobacterial cultures, but cannot be kept sterile due to the scales necessary to meet domestic and global energy demands, meaning that heterotrophic bacteria can grow in PBRs by oxidizing the organic material produced and excreted by the Cyanobacteria. These heterotrophic bacteria can positively or negatively impact the performance of the PBR through their interactions with the Cyanobacteria. This work explores the microbial ecology in PBR cultures of the model cyanobacterium Synechocystis sp. PCC6803 (Synechocystis) using microbiological, molecular, chemical, and engineering techniques. I first show that diverse phylotypes of heterotrophic bacteria can associate with Synechocystis-based PBRs and that excluding them may be impossible under typical PBR operating conditions. Then, I demonstrate that high-throughput sequencing can reliably elucidate the structure of PBR microbial communities without the need for pretreatment to remove Synechocystis 16S rRNA genes, despite the high degree of polyploidy found in Synechocystis. Next, I establish that the structure of PBR microbial communities is strongly influenced by the microbial community of the inoculum culture. Finally, I show that maintaining available phosphorus in the culture medium promotes the production and enrichment of Synechocystis biomass in PBRs by reducing the amount of soluble substrates available to heterotrophic bacteria. This work presents the first analysis of the structure and function of microbial communities associated with Synechocystis-based PBRs.
ContributorsZevin, Alexander Simon (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Vermaas, Willem Fj (Committee member) / Arizona State University (Publisher)
Created2015
Description
Microbial electrochemical cells (MXCs) are promising platforms for bioenergy production from renewable resources. In these systems, specialized anode-respiring bacteria (ARB) deliver electrons from oxidation of organic substrates to the anode of an MXC. While much progress has been made in understanding the microbiology, physiology, and electrochemistry of well-studied model ARB such as Geobacter and Shewanella, tremendous potential exists for MXCs as microbiological platforms for exploring novel ARB. This dissertation introduces approaches for selective enrichment and characterization of phototrophic, halophilic, and alkaliphilic ARB. An enrichment scheme based on manipulation of poised anode potential, light, and nutrient availability led to current generation that responded negatively to light. Analysis of phototrophically enriched communities suggested essential roles for green sulfur bacteria and halophilic ARB in electricity generation. Reconstruction of light-responsive current generation could be successfully achieved using cocultures of anode-respiring Geobacter and phototrophic Chlorobium isolated from the MXC enrichments. Experiments lacking exogenously supplied organic electron donors indicated that Geobacter could produce a measurable current from stored photosynthate in the dark. Community analysis of phototrophic enrichments also identified members of the novel genus Geoalkalibacter as potential ARB. Electrochemical characterization of two haloalkaliphilic, non-phototrophic Geoalkalibacter spp. showed that these bacteria were in fact capable of producing high current densities (4-8 A/m2) and using higher organic substrates under saline or alkaline conditions. The success of these selective enrichment approaches and community analyses in identifying and understanding novel ARB capabilities invites further use of MXCs as robust platforms for fundamental microbiological investigations.
ContributorsBadalamenti, Jonathan P (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Rittmann, Bruce E. (Committee member) / Torres, César I (Committee member) / Vermaas, Willem (Committee member) / Arizona State University (Publisher)
Created2013