Matching Items (402)
ContributorsWard, Geoffrey Harris (Performer) / ASU Library. Music Library (Publisher)
Created2018-03-18
Description
To further the efforts producing energy from more renewable sources, microbial electrochemical cells (MXCs) can utilize anode respiring bacteria (ARB) to couple the oxidation of an organic substrate to the delivery of electrons to the anode. Although ARB such as Geobacter and Shewanella have been well-studied in terms of their microbiology and electrochemistry, much is still unknown about the mechanism of electron transfer to the anode. To this end, this thesis seeks to elucidate the complexities of electron transfer existing in Geobacter sulfurreducens biofilms by employing Electrochemical Impedance Spectroscopy (EIS) as the tool of choice. Experiments measuring EIS resistances as a function of growth were used to uncover the potential gradients that emerge in biofilms as they grow and become thicker. While a better understanding of this model ARB is sought, electrochemical characterization of a halophile, Geoalkalibacter subterraneus (Glk. subterraneus), revealed that this organism can function as an ARB and produce seemingly high current densities while consuming different organic substrates, including acetate, butyrate, and glycerol. The importance of identifying and studying novel ARB for broader MXC applications was stressed in this thesis as a potential avenue for tackling some of human energy problems.
ContributorsAjulo, Oluyomi (Author) / Torres, Cesar (Thesis advisor) / Nielsen, David (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Popat, Sudeep (Committee member) / Arizona State University (Publisher)
Created2013
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
Intimate coupling of Ti2 photocatalysis and biodegradation (ICPB) offers potential for degrading biorecalcitrant and toxic organic compounds much better than possible with conventional wastewater treatments. This study reports on using a novel sponge-type, Ti2-coated biofilm carrier that shows significant adherence of Ti2 to its exterior and the ability to accumulate biomass in its interior (protected from UV light and free radicals). First, this carrier was tested for ICPB in a continuous-flow photocatalytic circulating-bed biofilm reactor (PCBBR) to mineralize biorecalcitrant organic: 2,4,5-trichlorophenol (TCP). Four mechanisms possibly acting of ICPB were tested separately: TCP adsorption, UV photolysis/photocatalysis, and biodegradation. The carrier exhibited strong TCP adsorption, while photolysis was negligible. Photocatalysis produced TCP-degradation products that could be mineralized and the strong adsorption of TCP to the carrier enhanced biodegradation by relieving toxicity. Validating the ICPB concept, biofilm was protected inside the carriers from UV light and free radicals. ICPB significantly lowered the diversity of the bacterial community, but five genera known to biodegrade chlorinated phenols were markedly enriched. Secondly, decolorization and mineralization of reactive dyes by ICPB were investigated on a refined Ti2-coated biofilm carrier in a PCBBR. Two typical reactive dyes: Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86), showed similar first-order kinetics when being photocatalytically decolorized at low pH (~4-5), which was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on Ti2, radical scavenging by phosphate or carbonate, or both. In the PCBBR, photocatalysis alone with Ti2-coated carriers could remove RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD. Finally, three low-temperature sintering methods, called O, D and DN, were compared based on photocatalytic efficiency and Ti2 adherence. The DN method had the best Ti2-coating properties and was a successful carrier for ICPB of RB5 in a PCBBR.
ContributorsLi, Guozheng (Author) / Rittmann, Bruce E. (Thesis advisor) / Halden, Rolf (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2011
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
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
The purpose of this study was to observe the effectiveness of the phenylalanyl arginine β-naphthylamide dihydrochloride inhibitor and Tween 20 when combined with an antibiotic against Escherichia. coli. As antibiotic resistance becomes more and more prevalent it is necessary to think outside the box and do more than just increase the dosage of currently prescribed antibiotics. This study attempted to combat two forms of antibiotic resistance. The first is the AcrAB efflux pump which is able to pump antibiotics out of the cell. The second is the biofilms that E. coli can form. By using an inhibitor, the pump should be unable to rid itself of an antibiotic. On the other hand, using Tween allows for biofilm formation to either be disrupted or for the biofilm to be dissolved. By combining these two chemicals with an antibiotic that the efflux pump is known to expel, low concentrations of each chemical should result in an equivalent or greater effect on bacteria compared to any one chemical in higher concentrations. To test this hypothesis a 96 well plate BEC screen test was performed. A range of antibiotics were used at various concentrations and with varying concentrations of both Tween and the inhibitor to find a starting point. Following this, Erythromycin and Ciprofloxacin were picked as the best candidates and the optimum range of the antibiotic, Tween, and inhibitor were established. Finally, all three chemicals were combined to observe the effects they had together as opposed to individually or paired together. From the results of this experiment several conclusions were made. First, the inhibitor did in fact increase the effectiveness of the antibiotic as less antibiotic was needed if the inhibitor was present. Second, Tween showed an ability to prevent recovery in the MBEC reading, showing that it has the ability to disrupt or dissolve biofilms. However, Tween also showed a noticeable decrease in effectiveness in the overall treatment. This negative interaction was unable to be compensated for when using the inhibitor and so the hypothesis was proven false as combining the three chemicals led to a less effective treatment method.
ContributorsPetrovich Flynn, Chandler James (Author) / Misra, Rajeev (Thesis director) / Bean, Heather (Committee member) / Perkins, Kim (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
ContributorsBolari, John (Performer) / ASU Library. Music Library (Publisher)
Created2018-10-04
Description
The mechanisms of extracellular respiration in Geobacter sulfurreducens, commonly considered to be a model organism for anode respiration, are yet to be completely understood. The interplay between electron and proton transport especially could be a key to gaining further insights. One way to investigate the mechanisms of extracellular respiration under varying environmental conditions is by analyzing the electrochemical response of the biofilm with respect to pH, buffer concentrations, and acetate concentrations. I seek to increase the understanding of the electrochemical response of the G. sulfurreducens biofilm through electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques in concert with chronoamperometry. I used Geobacter sulfurreducens PCA biofilms in single-chamber electrochemical cells (approximately 100 mL volume) with a small gold working electrode (3.14 mm2). I observed limitations in the initial methods used for media replacement. I tracked changes in the CV data, such as EKA (midpoint potential), as a function of pH and buffer concentration. The media replacement method developed demonstrates success in pH experiments that will be transferrable to other environmental conditions to study electron transport. The experiments revealed that the clarity of data collected is dependent on the quality of the biofilm. A high quality biofilm is characterized by a high current density and normal growth behavior. The general trends seen in these experiments are that as pH increases the potential decreases, and as buffer concentration increases the potential decreases and pH increases. Acetate-free conditions in the reactor were unable to be achieved as characterized by non-zero current densities in the acetate-free experiments.
ContributorsHolzer, Denton Gene (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Yoho, Rachel (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05