Matching Items (82)
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
Obesity is a worldwide epidemic accompanied by multiple comorbidities. Bariatric surgery is currently the most efficient treatment for morbid obesity and its comorbidities. The etiology of obesity is unknown, although genetic, environmental, and most recently, microbiome elements have been recognized as contributors to this rising epidemic. The role of the gut microbiome in weight-loss or weight-gain warrants investigation, and bariatric surgery provides a good model to study influences of the microbiome on host metabolism. The underlying goals of my research were to analyze (i) the factors that change the microbiome after bariatric surgery, (ii) the effects of different types of bariatric surgeries on the gut microbiome and metabolism, (iii) the role of the microbiome on the success of bariatric surgery, and (iv) temporal and spatial changes of the microbiome after bariatric surgery.
Roux-en-Y gastric bypass (RYGB) rearranges the gastrointestinal tract and reduces gastric acid secretions. Therefore, pH could be one of the factors that change microbiome after RYGB. Using mixed-cultures and co-cultures of species enriched after RYGB, I showed that as small as 0.5 units higher gut pH can aid in the survival of acid-sensitive microorganisms after RYGB and alter gut microbiome function towards the production of weight loss-associated metabolites. By comparing microbiome after two different bariatric surgeries, RYGB and laparoscopic adjustable gastric banding (LAGB), I revealed that gut microbiome structure and metabolism after RYGB are remarkably different than LAGB, and LAGB change microbiome minimally. Given the distinct RYGB alterations to the microbiome, I examined the contribution of the microbiome to weight loss. Analyses revealed that Fusobacterium might lessen the success of RYGB by producing putrescine, which may enhance weight-gain and could serve as biomarker for unsuccessful RYGB.
Finally, I showed that RYGB alters the luminal and the mucosal microbiome. Changes in gut microbial metabolic products occur in the short-term and persist over the long-term. Overall, the work in this dissertation provides insight into how the gut microbiome structure and function is altered after bariatric surgery, and how these changes potentially affect the host metabolism. These findings will be helpful in subsequent development of microbiome-based therapeutics to treat obesity.
Roux-en-Y gastric bypass (RYGB) rearranges the gastrointestinal tract and reduces gastric acid secretions. Therefore, pH could be one of the factors that change microbiome after RYGB. Using mixed-cultures and co-cultures of species enriched after RYGB, I showed that as small as 0.5 units higher gut pH can aid in the survival of acid-sensitive microorganisms after RYGB and alter gut microbiome function towards the production of weight loss-associated metabolites. By comparing microbiome after two different bariatric surgeries, RYGB and laparoscopic adjustable gastric banding (LAGB), I revealed that gut microbiome structure and metabolism after RYGB are remarkably different than LAGB, and LAGB change microbiome minimally. Given the distinct RYGB alterations to the microbiome, I examined the contribution of the microbiome to weight loss. Analyses revealed that Fusobacterium might lessen the success of RYGB by producing putrescine, which may enhance weight-gain and could serve as biomarker for unsuccessful RYGB.
Finally, I showed that RYGB alters the luminal and the mucosal microbiome. Changes in gut microbial metabolic products occur in the short-term and persist over the long-term. Overall, the work in this dissertation provides insight into how the gut microbiome structure and function is altered after bariatric surgery, and how these changes potentially affect the host metabolism. These findings will be helpful in subsequent development of microbiome-based therapeutics to treat obesity.
ContributorsIlhan, Zehra Esra (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / DiBaise, John K. (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / Rittmann, Bruce E. (Committee member) / Arizona State University (Publisher)
Created2016
Description
The advantages and challenges of combining zero-valent iron (ZVI) and microbial reduction of trichloroethene (TCE) and perchlorate (ClO4-) in contaminated soil and groundwater are not well understood. The objective of this work was to identify the benefits and limitations of simultaneous application of ZVI and bioaugmentation for detoxification of TCE and ClO4- using conditions relevant to a specific contaminated site. We studied conditions representing a ZVI-injection zone and a downstream zone influenced Fe (II) produced, for simultaneous ZVI and microbial reductive dechlorination applications using bench scale semi-batch microcosm experiments. 16.5 g L-1 ZVI effectively reduced TCE to ethene and ethane but ClO4- was barely reduced. Microbial reductive dechlorination was limited by both ZVI as well as Fe (II) derived from oxidation of ZVI. In the case of TCE, rapid abiotic TCE reduction made the TCE unavailable for the dechlorinating bacteria. In the case of perchlorate, ZVI inhibited the indigenous perchlorate-reducing bacteria present in the soil and groundwater. Further, H2 generated by ZVI reactions stimulated competing microbial processes like sulfate reduction and methanogenesis. In the microcosms representing the ZVI downstream zone (Fe (II) only), we detected accumulation of cis-dichloroethene (cis-DCE) and vinyl chloride (VC) after 56 days. Some ethene also formed under these conditions. In the absence of ZVI or Fe (II), we detected complete TCE dechlorination to ethene and faster rates of ClO4- reduction. The results illustrate potential limitations of combining ZVI with microbial reduction of chlorinated compounds and show the potential that each technology has when applied separately.
ContributorsMohana Rangan, Srivatsan (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Delgado, Anca G (Committee member) / Lowry, Gregory V. (Committee member) / Arizona State University (Publisher)
Created2017
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
Biological soil crusts (BSCs), topsoil microbial assemblages typical of arid land ecosystems, provide essential ecosystem services such as soil fertilization and stabilization against erosion. Cyanobacteria and lichens, sometimes mosses, drive BSC as primary producers, but metabolic activity is restricted to periods of hydration associated with precipitation. Climate models for the SW United States predict changes in precipitation frequency as a major outcome of global warming, even if models differ on the sign and magnitude of the change. BSC organisms are clearly well adapted to withstand desiccation and prolonged drought, but it is unknown if and how an alteration of the precipitation frequency may impact community composition, diversity, and ecosystem functions. To test this, we set up a BSC microcosm experiment with variable precipitation frequency treatments using a local, cyanobacteria-dominated, early-succession BSC maintained under controlled conditions in a greenhouse. Precipitation pulse size was kept constant but 11 different drought intervals were imposed, ranging between 416 to 3 days, during a period of 416 days. At the end of the experiments, bacterial community composition was analyzed by pyrosequencing of the 16s rRNA genes in the community, and a battery of functional assays were used to evaluate carbon and nitrogen cycling potentials. While changes in community composition were neither marked nor consistent at the Phylum level, there was a significant trend of decreased diversity with increasing precipitation frequency, and we detected particular bacterial phylotypes that responded to the frequency of precipitation in a consistent manner (either positively or negatively). A significant trend of increased respiration with increasingly long drought period was detected, but BSC could recover quickly from this effect. Gross photosynthesis, nitrification and denitrification remained essentially impervious to treatment. These results are consistent with the notion that BSC community structure adjustments sufficed to provide significant functional resilience, and allow us to predict that future alterations in precipitation frequency are unlikely to result in severe impacts to BSC biology or ecological relevance.
ContributorsMyers, Natalie Kristine (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Hall, Sharon (Committee member) / Turner, Benjamin (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2013
Description
Phytoplankton comprise the base of the marine food web, and, along with heterotrophic protists, they are key players in the biological pump that transports carbon from the surface to the deep ocean. In the world's subtropical oligotrophic gyres, plankton communities exhibit strong seasonality. Winter storms vent deep water into the euphotic zone, triggering a surge in primary productivity in the form of a spring phytoplankton bloom. Although the hydrographic trends of this "boom and bust" cycle have been well studied for decades, community composition and its seasonal and annual variability remains an integral subject of research. It is hypothesized here that proportions of different phytoplankton and protistan taxa vary dramatically between seasons and years, and that picoplankton represent an important component of this community and contributor to carbon in the surface ocean. Monthly samples from the Bermuda Atlantic Time-series Study (BATS) site were analyzed by epifluorescence microscopy, which permits classification by morphology, size, and trophic type. Epifluorescence counts were supplemented with flow cytometric quantification of Synechococcus, Prochlorococcus, and autotrophic pico- and nanoeukaryotes. Results from this study indicate Synechococcus and Prochlorococcus, prymnesiophytes, and hetero- and mixotrophic nano- and dinoflagellates were the major players in the BATS region plankton community. Ciliates, cryptophytes, diatoms, unidentified phototrophs, and other taxa represented rarer groups. Both flow cytometry and epifluorescence microscopy revealed Synechococcus to be most prevalent during the spring bloom. Prymnesiophytes likewise displayed distinct seasonality, with the highest concentrations again being noted during the bloom. Heterotrophic nano- and dinoflagellates, however, were most common in fall and winter. Mixotrophic dinoflagellates, while less abundant than their heterotrophic counterparts, displayed similar seasonality. A key finding of this study was the interannual variability revealed between the two years. While most taxa were more abundant in the first year, prymnesiophytes experienced much greater abundance in the second year bloom. Analyses of integrated carbon revealed further stark contrasts between the two years, both in terms of total carbon and the contributions of different groups. Total integrated carbon varied widely in the first study year but displayed less fluctuation after June 2009, and values were noticeably reduced in the second year.
ContributorsHansen, Amy (Author) / Neuer, Susanne (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Sommerfeld, Milton (Committee member) / Arizona State University (Publisher)
Created2010
Description
Trichloroethene (TCE) and hexavalent chromium [Cr(VI)] are toxic and carcinogenic contaminants found in drinking water resources across the United States. A series of Bench-scale treatability studies were conducted to evaluate the effectiveness of a consortium of facultative and strictly anaerobic bacteria, KB-1®, to remove TCE and Cr(VI) from a contaminated aquifer in San Diego. These series of treatability studies were also performed to prepare data and mature packed sediment columns for the deployment of the In Situ Microcosm Array (ISMA), a diagnostic device for determining optimal treatments for a contaminated aquifer, at this particular site. First, a control panel for the ISMA’s Injection Module (IM) was created in order to deliver nutrients to the columns. Then, a column treatability study was performed in order to produce columns with an established KB-1® consortium, so that all TCE in the column influent was converted to ethene by the time it had exited the column. Finally, a batch bottle treatability study was performed to determine KB-1®’s effectiveness at remediating both TCE and Cr(VI) from the San Diego ground-water samples. The results from the column study found that KB-1® was able to reduce TCE in mineral media. However, in the presence of site ground-water for the batch bottle study, KB-1® was only able to reduce Cr(VI) and no TCE dechlorination was observed. This result suggests that the dechlorinating culture cannot survive prolonged exposure to Cr(VI). Therefore, future work may involve repeating the batch bottle study with Cr(VI) removed from the groundwater prior to inoculation to determine if KB-1® is then able to dechlorinate TCE.
ContributorsDuong, Benjamin Taylor (Author) / Halden, Rolf (Thesis director) / Torres, Cesar (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Barrett, The Honors College (Contributor) / School of Dance (Contributor) / Chemical Engineering Program (Contributor)
Created2013-05
Description
The effect of ammonium on microbial fermentation was investigated to improve the efficiency of microbial electrochemical cells (MXC). Electron balances of anaerobic microbial cultures with varying ammonium concentrations (reported as g N-NH4+/L) were used to study the distribution of electrons from different fermentable substrates to acetate, propionate, and methane. Results showed that with a high ammonium concentration (between 2.25 to 3g N-NH4+/L) fewer electrons routed to methane during the fermentation of 300 me-eq./L of electron donors .The majority of electrons (~ 60-80%) in the serum bottles experiments were routed to acetate and propionate for all fermentable substrates with high ammonium concentration. While methane cannot be utilized by anode respiring bacteria (ARBs) to produce current, both acetate and propionate can, which could lead to higher Coulombic efficiencies in MXCs. Experiments in microbial electrolysis cells (MECs) with glucose, lactate, and ethanol were performed. MEC experiments showed low percentage of electrons to current (between 10-30 %), potentially due to low anode surface area (~ 3cm2) used during these experiments. Nevertheless, the fermentation process observed in the MECs was similar to serum bottles results which showed significant diversion of electrons to acetate and propionate (~ 80%) for a control concentration of 0.5 g N-NH4+/L .
ContributorsLozada Guerra, Suyana Patricia (Co-author) / Joseph, Miceli (Co-author) / Krajmalnik-Brown, Rosa (Thesis director) / Torres, Cesar (Committee member) / Young, Michelle (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2013-05
Description
With global warming becoming a more serious problem and mankind's alarming dependency on fossil fuels, the need for a sustainable and environmentally friendly fuel source is becoming more important. Biofuels produced from photosynthetic microorganisms like algae or cyanobacteria offer a carbon neutral replacement for petroleum fuel sources; however, with the technology and information available today, the amount of biomass that would need to be produced is not economically feasible. In this work, I examined a possible factor impacting the growth of a model cyanobacterium, Synechocystis sp. PCC6803, which is heterotrophic bacteria communities accompanying the cyanobacteria. I experimented with three variables: the type of heterotrophic bacteria strain, the initial concentration of heterotrophic bacteria, and the addition of a carbon source (glucose) to the culture. With experimental information, I identified if given conditions would increase Synechocystis growth and thus increase the yield of biomass. I found that under non-limiting growth conditions, heterotrophic bacteria do not significantly affect the growth of Synechocystis or the corresponding biomass yield. The initial concentration of heterotrophic bacteria and the added glucose also did not affect the growth of Synechocystis. I did see some nutrient recycling from the heterotrophic bacteria as the phosphate levels in the growth medium were depleted, which was apparent from prolonged growth phase and higher levels of reactive phosphate in the media.
ContributorsCahill, Brendan Robert (Author) / Rittmann, Bruce (Thesis director) / Krajmalnik-Brown, Rosa (Committee member) / W. P. Carey School of Business (Contributor) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2015-12
Description
The human gut microbiome is a complex community of microorganisms. These microbes play an important role in host health by contributing essential compounds and acting as a barrier against pathogens. However, these communities and associated functions can be impacted by factors like disease and diet. In particular, microbial fermentation of dietary components like polysaccharides, proteins, and fats that reach the gut are being examined to better understand how these biopolymers are utilized and affect community structure. Thus, evaluating the accuracy of methods used to quantify specific macromolecules is crucial to gaining a precise understanding of how gut microbes hydrolyze those substrates. This study presents findings on the accuracy of the Megazyme RS kit (Rapid) modified for high performance liquid chromatography (HPLC) readings and the DC Protein Assay when performed on samples from complex gut media with potato starch treatments and bovine serum albumin (BSA) treatments. Overall, our data indicates that the megazyme RS kit needs further modification to detect expected starch content with the HPLC and that the DC Protein Assay is not suitable for specific protein analysis.
ContributorsKlein, Rachel Marie (Author) / Krajmalnik-Brown, Rosa (Thesis director) / Marcus, Andrew (Committee member) / School of Life Sciences (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05