Barrett, The Honors College Thesis/Creative Project Collection
Barrett, The Honors College at Arizona State University proudly showcases the work of undergraduate honors students by sharing this collection exclusively with the ASU community.
Barrett accepts high performing, academically engaged undergraduate students and works with them in collaboration with all of the other academic units at Arizona State University. All Barrett students complete a thesis or creative project which is an opportunity to explore an intellectual interest and produce an original piece of scholarly research. The thesis or creative project is supervised and defended in front of a faculty committee. Students are able to engage with professors who are nationally recognized in their fields and committed to working with honors students. Completing a Barrett thesis or creative project is an opportunity for undergraduate honors students to contribute to the ASU academic community in a meaningful way.
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- Creators: Chemical Engineering Program
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
Description
Microbial fuel cells (MFCs) promote the sustainable conversion of organic matter in black water to electrical current, enabling the production of hydrogen peroxide (H2O2) while making waste water treatment energy neutral or positive. H2O2 is useful in remote locations such as U.S. military forward operating bases (FOBs) for on-site tertiary water treatment or as a medical disinfectant, among many other uses. Various carbon-based catalysts and binders for use at the cathode of a an MFC for H2O2 production are explored using linear sweep voltammetry (LSV) and rotating ring-disk electrode (RRDE) techniques. The oxygen reduction reaction (ORR) at the cathode has slow kinetics at conditions present in the MFC, making it important to find a catalyst type and loading which promote a 2e- (rather than 4e-) reaction to maximize H2O2 formation. Using LSV methods, I compared the cathodic overpotentials associated with graphite and Vulcan carbon catalysts as well as Nafion and AS-4 binders. Vulcan carbon catalyst with Nafion binder produced the lowest overpotentials of any binder/catalyst combinations. Additionally, I determined that pH control may be required at the cathode due to large potential losses caused by hydroxide (OH-) concentration gradients. Furthermore, RRDE tests indicate that Vulcan carbon catalyst with a Nafion binder has a higher H2O2 production efficiency at lower catalyst loadings, but the trade-off is a greater potential loss due to higher activation energy. Therefore, an intermediate catalyst loading of 0.5 mg/cm2 Vulcan carbon with Nafion binder is recommended for the final MFC design. The chosen catalyst, binder, and loading will maximize H2O2 production, optimize MFC performance, and minimize the need for additional energy input into the system.
ContributorsStadie, Mikaela Johanna (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2015-05
Description
In this Honors thesis, direct flame solid oxide fuel cells (DFFC) were considered for their feasibility in providing a means of power generation for remote powering needs. Also considered for combined heat and fuel cell power cogeneration are thermoelectric cells (TEC). Among the major factors tested in this project for all cells were life time, thermal cycle/time based performance, and failure modes for cells. Two types of DFFC, anode and electrolyte supported, were used with two different fuel feed streams of propane/isobutene and ethanol. Several test configurations consisting of single cells, as well as stacked systems were tested to show how cell performed and degraded over time. All tests were run using a Biologic VMP3 potentiostat connected to a cell placed within the flame of a modified burner MSR® Wisperlite Universal stove. The maximum current and power output seen by any electrolyte supported DFFCs tested was 47.7 mA/cm2 and 9.6 mW/cm2 respectively, while that generated by anode supported DFFCs was 53.7 mA/cm2 and 9.25 mW/cm2 respectively with both cells operating under propane/isobutene fuel feed streams. All TECs tested dramatically outperformed both constructions of DFFC with a maximum current and power output of 309 mA/cm2 and 80 mW/cm2 respectively. It was also found that electrolyte supported DFFCs appeared to be less susceptible to degradation of the cell microstructure over time but more prone to cracking, while anode supported DFFCs were dramatically less susceptible to cracking but exhibited substantial microstructure degradation and shorter usable lifecycles. TECs tested were found to only be susceptible to overheating, and thus were suggested for use with electrolyte supported DFFCs in remote powering applications.
ContributorsTropsa, Sean Michael (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2014-05
Description
In microbial fuel cells (MFCs) the biocathode is developed as a potential alternative to chemical cathodic catalysts, which are deemed as expensive and unsustainable for applications. These cells utilize different types of microorganisms as catalysts to promote biodegradation of organic matter while simultaneously converting energy released in metabolic reactions into electrical energy. Most current research have focused more on the anodic microbes, including the current generating bacteria species, anodic microbial community composition, and the mechanisms of the extracellular electron transfer. Compared to the anode, research on the microbes of the biocathode of the MFCs are very limited and are heavily focused on the role of the bacteria in the system. Thus, further understand of the mechanism of the microbial community in the biocathode will create new engineering applications for sustainable energy. Previous research conducted by Strycharz-Glaven et al. presented an electrochemical analysis of a Marinobacter-dominated biocathode communitygrown on biocathodes in sediment/seawater-based MFCs. Chronoamperometry results indicated that current densities up to -0.04 A/m2 were produced for the biocathode. Cyclic voltammetry responses indicated a midpoint potential at 0.196 V ± 0.01 V. However, the reactor design for these experiments showed that no oxygen is supplied to the electrochemical system. By incorporating an air diffusion membrane to the cathode of the reactor, chronoamperometry results have produced current density in the system up to -0.15 A/m2. Cyclic voltammetry results have also displayed a midpoint potential of 0.25 V ± 0.01 V under scan rates of 0.2 mV/s. Thus, this electrochemical setup has increased the current output of the system.
ContributorsWang, Zixuan (Author) / Torres, Cesar (Thesis director) / Hart, Steven (Committee member) / Materials Science and Engineering Program (Contributor) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Microbial fuel cells (MFCs) facilitate the conversion of organic matter to electrical current to make the total energy in black water treatment neutral or positive and produce hydrogen peroxide to assist the reuse of gray water. This research focuses on wastewater treatment at the U.S. military forward operating bases (FOBs). FOBs experience significant challenges with their wastewater treatment due to their isolation and dangers in transporting waste water and fresh water to and from the bases. Even though it is theoretically favorable to produce power in a MFC while treating black water, producing H2O2 is more useful and practical because it is a powerful cleaning agent that can reduce odor, disinfect, and aid in the treatment of gray water. Various acid forms of buffers were tested in the anode and cathode chamber to determine if the pH would lower in the cathode chamber while maintaining H2O2 efficiency, as well as to determine ion diffusion from the anode to the cathode via the membrane. For the catholyte experiments, phosphate and bicarbonate were tested as buffers while sodium chloride was the control. These experiments determined that the two buffers did not lower the pH. It was seen that the phosphate buffer reduced the H2O2 efficiency significantly while still staying at a high pH, while the bicarbonate buffer had the same efficiency as the NaCl control. For the anolyte experiments, it was shown that there was no diffusion of the buffers or MFC media across the membrane that would cause a decrease in the H2O2 production efficiency.
ContributorsThompson, Julia (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Anaerobic digestion (AD), a common process in wastewater treatment plants, is traditionally assessed with Biochemical Methane Potential (BMP) tests. Hydrolysis is considered its rate-limiting step. During my research, I assessed the impact of pretreatment on BMPs and microbial electrochemical cells (MECs). In the first set of experiments, BMP tests were performed using alkaline and thermal pretreated waste activated sludge (WAS), a control group, and a negative control group as samples and AD sludge (ADS) as inoculum. The data obtained suggested that BMPs do not necessarily require ADS, since samples without inoculum produced 5-20% more CH4. However, ADS appears to reduce the initial methanogenesis lag in BMPs, as no pH inhibition and immediate CH4 production were observed. Consumption rate constants, which are related to hydrolysis, were calculated using three methods based on CH4 production, SSCOD concentration, and the sum of both, called the lumped parameter. All the values observed were within literature values, yet each provide a different picture of what is happening in the system. For the second set of experiments, the current production of 3 H-type MECs were compared to the CH4 production of BMPs to assess WAS solids' biodegradability and consumption rates relative to the pretreatment methods employed for their substrate. BMPs fed with pretreated and control WAS solids were performed at 0.42 and 1.42 WAS-to-ADS ratios. An initial CH4 production lag of about 12 days was observed in the BMP assays, but MECs immediately began producing current. When compared in terms of COD, MECs produced more current than the BMPs produced CH4, indicating that the MEC may be capable of consuming different types of substrate and potentially overestimating CH4 production in anaerobic digesters. I also observed 2 to 3 different consumption events in MECs versus 3 for BMP assays, but these had similar magnitudes, durations, and starting times in the control and thermal pretreated WAS-fed assays and not in alkaline assays. This might indicate that MECs identified the differences of alkaline pretreatment, but not between control WAS and thermal pretreated WAS. Furthermore, HPLC results suggest at least one hydrolysis event, as valerate, butyrate, and traces of acetate are observed in the reactors' effluents. Moreover, a possible inhibition of valerate-fixing microbial communities due to pretreatment and the impossibility of valerate consumption by ARB might explain its presence in the reactors' effluents.
ContributorsBrown Munoz, Francisco (Author) / Torres, Cesar (Thesis director) / Rittmann, Bruce E. (Committee member) / Chemical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Alternative ion exchange membranes for implementation in a peroxide production microbial electrochemical cel (PP-MEC) are explored through membrane stability tests with NaCl electrolyte and stabilizer EDTA at varying operational pHs. PP-MEC performance parameters \u2014 H2O2 concentration, current density, coulombic efficiency and power input required \u2014 are optimized over a 7 month continuous operation period based on their response to changes in HRT, EDTA concentration, air flow rate and electrolyte. I found that EDTA was compatible for use with the membranes. I also determined that AMI membranes were preferable to CMI and FAA because it was consistently stable and maintained its structural integrity. Still, I suggest testing more membranes because the AMI degraded in continuous operation. The PP-MEC produced up to 0.38 wt% H2O2, enough to perform water treatment through the Fenton process and significantly greater than the 0.13 wt% batch PP-MEC tests by previous researchers. It ran at > 0.20 W-hr/g H2O2 power input, ~ three orders of magnitude less than what is required for the anthraquinone process. I recommend high HRT and EDTA concentration while running the PP- MEC to increase H2O2 concentration, but low HRT and low EDTA concentration to decrease power input required. I recommend NaCl electrolyte but suggest testing new electrolytes that may control pH without degrading H2O2. I determined that air flow rate has no effect on PP-MEC operation. These recommendations should optimize PP-MEC operation based on its application.
ContributorsChowdhury, Nadratun Naeem (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Biofuels are a carbon-neutral energy source proving to be a sustainable alternative to greenhouse gas-emitting fossil fuels that are accelerating the detrimental effects of anthropogenic climate change. A developing system aimed at more efficiently producing biofuels is called Microbial Electro-Photosynthesis (MEPS). In MEPS, a Synechocystis sp. PCC 6803 mutant lacking photosystem II (PSII) receives electrons by a hydroduroquinone (DQH2) mediator from a more efficient water-splitting electrochemical cell, rather than splitting water itself using PSII. However, growth of the Synechocystis cells prior to use in MEPS requires an organic carbon source, leading to internally-stored electron sources, namely glycogen, that compete with preferred DQH2 mediator-delivered electrons. In this study, the effects of organic carbon source (pyruvate, acetate, glucose, and no carbon source) and light condition (light or dark) on the physiology and P700+ reduction kinetics of photoheterotrophically grown Synechocystis mutants were studied with the hope of identifying a maintenance culturing method that allowed for both cell viability and mitigated glycogen storage. While no significant decreases in internal electron-sources were found with these methods, it was observed that Synechocystis cells fed pyruvate in the light had most successfully reduced competition between internal electron sources and preferred DQH2-delivered electrons. This study suggests that these experiments be re-run after removing exogenous carbon sources and that the nutrients available to the cells and their effects on pyruvate and acetate uptake be further investigated.
ContributorsMangus, Anna Michelle (Author) / Torres, Cesar (Thesis director) / Lewis, Christine (Committee member) / Chemical Engineering Program (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12