Matching Items (19)
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- All Subjects: Environmental engineering
- Creators: Torres, César I
Description
Uranium (U) contamination has been attracting public concern, and many researchers are investigating principles and applications of U remediation. The overall goal of my research is to understand the versatile roles of sulfate-reducing bacteria (SRB) in uranium bioremediation, including direct involvement (reducing U) and indirect involvement (protecting U reoxidation). I pursue this goal by studying Desulfovibro vuglaris, a representative SRB. For direct involvement, I performed experiments on uranium bioreduction and uraninite (UO2) production in batch tests and in a H2-based membrane biofilm reactor (MBfR) inoculated with D. vuglaris. In summary, D. vuglaris was able to immobilize soluble U(VI) by enzymatically reducing it to insoluble U(IV), and the nanocrystallinte UO2 was associated with the biomass. In the MBfR system, although D. vuglaris failed to form a biofilm, other microbial groups capable of U(VI) reduction formed a biofilm, and up to 95% U removal was achieved during a long-term operation. For the indirect involvement, I studied the production and characterization of and biogenic iron sulfide (FeS) in batch tests. In summary, D. vuglaris produced nanocrystalline FeS, a potential redox buffer to protect UO2 from remobilization by O2. My results demonstrate that a variety of controllable environmental parameters, including pH, free sulfide, and types of Fe sources and electron donors, significantly determined the characteristics of both biogenic solids, and those characteristics should affect U-sequestrating performance by SRB. Overall, my results provide a baseline for exploiting effective and sustainable approaches to U bioremediation, including the application of the novel MBfR technology to U sequestration from groundwater and biogenic FeS for protecting remobilization of sequestrated U, as well as the microbe-relevant tools to optimize U sequestration applicable in reality.
ContributorsZhou, Chen (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2014
Description
This research explores microbial chain elongation as a pathway for production of complex organic compounds in soils with implication for the carbon cycle. In chain elongation, simple substrates such as ethanol and short chain carboxylates such as acetate can be converted to longer carbon chain carboxylates under anaerobic conditions through cyclic, reverse β oxidation. This pathway elongates the carboxylate by two carbons. The chain elongation process is overall thermodynamically feasible, and microorganisms gain energy through this process. There have been limited insights into the versatility of chain elongating substrates, understanding the chain elongating microbial community, and its importance in sequestering carbon in the soils.
We used ethanol, methanol, butanol, and hydrogen as electron donors and acetate and propionate as electron acceptors to test the occurrence of microbial chain elongation in four soils with different physicochemical properties and microbial communities. Common chain elongation products were the even numbered chains butyrate, caproate, and butanol, the odd numbered carboxylates valerate and heptanoate, along with molecular hydrogen. At a near neutral pH and mesophilic temperature, we observed a stable and sustained production of longer fatty acids along with hydrogen. Microbial community analysis show phylotypes from families such as Clostridiaceae, Bacillaceae, and Ruminococcaceae in all tested conditions. Through chain elongation, the products formed are less biodegradable. They may undergo transformations and end up as organic carbon, decreasing the greenhouse gas emissions, thus, making this process important to study.
We used ethanol, methanol, butanol, and hydrogen as electron donors and acetate and propionate as electron acceptors to test the occurrence of microbial chain elongation in four soils with different physicochemical properties and microbial communities. Common chain elongation products were the even numbered chains butyrate, caproate, and butanol, the odd numbered carboxylates valerate and heptanoate, along with molecular hydrogen. At a near neutral pH and mesophilic temperature, we observed a stable and sustained production of longer fatty acids along with hydrogen. Microbial community analysis show phylotypes from families such as Clostridiaceae, Bacillaceae, and Ruminococcaceae in all tested conditions. Through chain elongation, the products formed are less biodegradable. They may undergo transformations and end up as organic carbon, decreasing the greenhouse gas emissions, thus, making this process important to study.
ContributorsJoshi, Sayalee (Author) / Delgado, Anca G (Thesis advisor) / Torres, César I (Committee member) / van Paassen, Leon (Committee member) / Arizona State University (Publisher)
Created2018
Description
Microbial electrochemical cells (MxCs) are a novel technology that use anode-respiring bacteria (ARB) to bioremediate wastewaters and respire an electrical current, which can then be used directly to produce value-added products like hydrogen peroxide (H2O2). Ninety-five percent of the world’s H2O2 is currently produced using the anthraquinone process, whose production requires expensive and potentially carcinogenic catalysts and high amounts of electricity. However, the amount of H2O2 that can be produced from these microbial peroxide-producing cells (MPPCs) has not been thoroughly investigated. Predicting potential H2O2 production in MxCs is further complicated by a lack of mathematical models to predict performance utilizing complex waste streams like primary sludge (PS).
A reactor design methodology was developed for MPPCs to systematically optimize H2O2 production with minimal energy consumption. H2O2 stability was evaluated with different catholytes, membranes, and catalysts materials, and the findings used to design and operate long-term a dual-chamber, flat-plate MPPC using different catholytes, ferrochelating stabilizers, and hydraulic retention times (HRT). Up to 3.1 ± 0.37 g H2O2 L-1 was produced at a 4-h HRT in an MPPC with as little as 1.13 W-h g-1 H2O2 power input using NaCl catholytes. Attempts to improve H2O2 production by using weak acid buffers as catholytes or ferrochelating stabilizers failed for different reasons.
A non-steady-state mathematical model, MYAnode, was developed combinging existing wastewater treatment, anode biofilm, and chemical speciation models to predict MxC performance utilizing complex substrates. The model simulated the large-scale trends observed when operating an MPPC with PS substrate. At HRTs ≥ 12-d, the model demonstrated up to 20% Coulombic recovery. At these conditions, ARB required additional alkalinity production by ≥ 100 mgVSS/L of acetoclastic methanogens to prevent pH inhibition when little influent alkalinity is available. At lower HRTs, methanogens are unable to produce the alkalinity required to prevent ARB inhibition due to washout and rapid acidification of the system during fermentation. At ≥ 100 mgVSS/L of methanogens, increasing the diffusion layer thickness from 500 to 1000 μm improved Coulombic efficiency by 13.9%, while increasing particulate COD hydrolysis rates to 0.25/d only improved Coulombic efficiency by 3.9%.
A reactor design methodology was developed for MPPCs to systematically optimize H2O2 production with minimal energy consumption. H2O2 stability was evaluated with different catholytes, membranes, and catalysts materials, and the findings used to design and operate long-term a dual-chamber, flat-plate MPPC using different catholytes, ferrochelating stabilizers, and hydraulic retention times (HRT). Up to 3.1 ± 0.37 g H2O2 L-1 was produced at a 4-h HRT in an MPPC with as little as 1.13 W-h g-1 H2O2 power input using NaCl catholytes. Attempts to improve H2O2 production by using weak acid buffers as catholytes or ferrochelating stabilizers failed for different reasons.
A non-steady-state mathematical model, MYAnode, was developed combinging existing wastewater treatment, anode biofilm, and chemical speciation models to predict MxC performance utilizing complex substrates. The model simulated the large-scale trends observed when operating an MPPC with PS substrate. At HRTs ≥ 12-d, the model demonstrated up to 20% Coulombic recovery. At these conditions, ARB required additional alkalinity production by ≥ 100 mgVSS/L of acetoclastic methanogens to prevent pH inhibition when little influent alkalinity is available. At lower HRTs, methanogens are unable to produce the alkalinity required to prevent ARB inhibition due to washout and rapid acidification of the system during fermentation. At ≥ 100 mgVSS/L of methanogens, increasing the diffusion layer thickness from 500 to 1000 μm improved Coulombic efficiency by 13.9%, while increasing particulate COD hydrolysis rates to 0.25/d only improved Coulombic efficiency by 3.9%.
ContributorsYoung, Michelle Nichole (Author) / Rittmann, Bruce E. (Thesis advisor) / Torres, César I (Committee member) / Marcus, Andrew K (Committee member) / Arizona State University (Publisher)
Created2018
Description
Productivity in the construction industry is an essential measure of production efficiency and economic progress, quantified by craft laborers' time spent directly adding value to a project. In order to better understand craft labor productivity as an aspect of lean construction, an activity analysis was conducted at the Arizona State University Palo Verde Main engineering dormitory construction site in December of 2016. The objective of this analysis on craft labor productivity in construction projects was to gather data regarding the efficiency of craft labor workers, make conclusions about the effects of time of day and other site-specific factors on labor productivity, as well as suggest improvements to implement in the construction process. Analysis suggests that supporting tasks, such as traveling or materials handling, constitute the majority of craft labors' efforts on the job site with the highest percentages occurring at the beginning and end of the work day. Direct work and delays were approximately equal at about 20% each hour with the highest peak occurring at lunchtime between 10:00 am and 11:00 am. The top suggestion to improve construction productivity would be to perform an extensive site utilization analysis due to the confined nature of this job site. Despite the limitations of an activity analysis to provide a complete prospective of all the factors that can affect craft labor productivity as well as the small number of days of data acquisition, this analysis provides a basic overview of the productivity at the Palo Verde Main construction site. Through this research, construction managers can more effectively generate site plans and schedules to increase labor productivity.
ContributorsFord, Emily Lucile (Author) / Grau, David (Thesis director) / Chong, Oswald (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
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
The finite supply of current energy production materials has created opportunities for the investigation of alternative energy sources in many fields. One example is the use of microorganisms in bioenergy applications, such as microbial fuel cells. Present in many types of environments, microorganisms with the ability to respire solid electron acceptors have become of increasing relevance to alternative energy and wastewater treatment research. In this dissertation, several aspects of anode respiration are investigated, with the goal of increasing the limited understanding of the mechanisms of electron transport through the use of advanced electrochemical methods. Biofilms of Geobacter sulfurreducens, the model anode respiring organism, as well as its alkaliphilic relative, Geoalkalibacter ferrihydriticus, were investigated using chronoamperometry, electrochemical impedance spectroscopy, and cyclic voltammetry.
In G. sulfurreducens, two distinct pathways of electron transport were observed through the application of advanced electrochemical techniques on anode biofilms in microbial electrochemical cells. These pathways were found to be preferentially expressed, based on the poised anode potential (redox potential) of the electrode. In Glk. ferrihydriticus, four pathways for electron transport were found, showing an even greater diversity in electron transport pathway utilization as compared to G. sulfurreducens. These observations provide insights into the diversity of electron transport pathways present in anode-respiring bacteria and introduce the necessity of further characterization for pathway identification.
Essential to science today, communication of pressing scientific issues to the lay audience may present certain difficulties. This can be seen especially with the topics that are considered socio-scientific issues, those considered controversial in society but not for scientists. This dissertation explores the presentation of alternative and renewable energy technologies and climate change in undergraduate education. In introductory-level Biology, Chemistry, and Physics textbooks, the content and terminology presented were analyzed for individual textbooks and used to evaluate discipline-based trends. Additional extensions were made between teaching climate change with the active learning technique of citizen science using past research gains from studies of evolution. These observations reveal patterns in textbook content for energy technologies and climate change, as well as exploring new aspects of teaching techniques.
In G. sulfurreducens, two distinct pathways of electron transport were observed through the application of advanced electrochemical techniques on anode biofilms in microbial electrochemical cells. These pathways were found to be preferentially expressed, based on the poised anode potential (redox potential) of the electrode. In Glk. ferrihydriticus, four pathways for electron transport were found, showing an even greater diversity in electron transport pathway utilization as compared to G. sulfurreducens. These observations provide insights into the diversity of electron transport pathways present in anode-respiring bacteria and introduce the necessity of further characterization for pathway identification.
Essential to science today, communication of pressing scientific issues to the lay audience may present certain difficulties. This can be seen especially with the topics that are considered socio-scientific issues, those considered controversial in society but not for scientists. This dissertation explores the presentation of alternative and renewable energy technologies and climate change in undergraduate education. In introductory-level Biology, Chemistry, and Physics textbooks, the content and terminology presented were analyzed for individual textbooks and used to evaluate discipline-based trends. Additional extensions were made between teaching climate change with the active learning technique of citizen science using past research gains from studies of evolution. These observations reveal patterns in textbook content for energy technologies and climate change, as well as exploring new aspects of teaching techniques.
ContributorsYoho, Rachel Ann (Author) / Torres, César I (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Popat, Sudeep C (Committee member) / Vanmali, Binaben H (Committee member) / Arizona State University (Publisher)
Created2016
Description
The application of microalgal biofilms in wastewater treatment has great advantages such as abolishing the need for energy intensive aerators and recovering nutrients as energy, thus reducing the energy requirement of wastewater treatment several-fold. A 162 cm2 algal biofilm reactor with good wastewater treatment performance and a regular harvesting procedure was studied at lab scale to gain an understanding of effectual parameters such as hydraulic retention time (HRT; 2.6 and 1.3 hrs), liquid level (LL; 0.5 and 1.0 cm), and solids retention time (SRT; 3 and 1.5 wks). A revised synthetic wastewater “Syntho 3.7” was used as a surrogate of domestic primary effluent for nutrient concentration consistency in the feed lines. In the base case (2.6 hr HRT, 0.5 cm LL, and 3 wk SRT), percent removals of 69 ± 2 for total nitrogen (TN), 54 ± 21 for total phosphorous (TP), and 60 ± 7 for chemical oxygen demand (COD) were achieved and 4.0 ± 1.6 g/m2/d dry biomass was produced. A diffusion limitation was encountered when increasing the liquid level, while the potential to further decrease the HRT remains. Nonlinear growth kinetics was observed in comparing SRT variations, and promoting autotrophic growth seems possible. Future work will look towards producing a mathematical model and further testing the aptness of this system for large-scale implementation.
ContributorsHalloum, Ibrahim (Author) / Torres, César I (Thesis advisor) / Popat, Sudeep C (Committee member) / Rittmann, Bruce E. (Committee member) / Arizona State University (Publisher)
Created2016
Description
One solution to mitigating global climate change is using cyanobacteria or single-celled algae (collectively microalgae) to replace petroleum-based fuels and products, thereby reducing the net release of carbon dioxide. This work develops and evaluates a mechanistic kinetic model for light-dependent microalgal growth. Light interacts with microalgae in a variety of positive and negative ways that are captured by the model: light intensity (LI) attenuates through a microalgal culture, light absorption provides the energy and electron flows that drive photosynthesis, microalgae pool absorbed light energy, microalgae acclimate to different LI conditions, too-high LI causes damage to the cells’ photosystems, and sharp increases in light cause severe photoinhibition that inhibits growth. The model accounts for all these phenomena by using a set of state variables that represent the pooled light energy, photoacclimation, PSII photo-damage, PSII repair inhibition and PSI photodamage. Sets of experiments were conducted with the cyanobacterium Synechocystis sp. PCC 6803 during step-changes in light intensity and flashing light. The model was able to represent and explain all phenomena observed in the experiments. This included the spike and depression in growth rate following an increasing light step, the temporary depression in growth rate following a decreasing light step, the shape of the steady-state growth-irradiance curve, and the “blending” of light and dark periods under rapid flashes of light. The LI model is a marked improvement over previous light-dependent growth models, and can be used to design and interpret future experiments and practical systems for generating renewable feedstock to replace petroleum.
ContributorsStraka, Levi (Author) / Rittmann, Bruce E. (Thesis advisor) / Fox, Peter (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2017
Description
Accidental wetlands have been created on the bed of the Salt River and are fed by storm-water outfalls discharging at various sections of the Phoenix Metropolitan Area. Water discharges from these outfalls throughout the year, during both dry conditions (base flow) and during rain events (storm flow). In this study, DOC content and composition was studied during these two flow conditions, in the outfalls and along the wetland flow path. The importance of DOC lies in its role in transporting carbon via water movement, between different parts of a landscape, and therefore between pools in the ecosystem. Urbanization has influenced content and composition of DOC entering the accidental urban wetland via outfalls as they represent watersheds from different areas in Phoenix. First, DOC load exhibited higher quantities during stormflow compared to baseflow conditions. Second, DOC load and fluorescence analysis outcomes concluded the outfalls are different from each other. The inputs of water on the north side of the channel represent City of Phoenix watersheds were similar to each other and had high DOC load. The northern outfalls are both different in load and composition from the outfall pipe on the southern bank of the wetland as it represents South Mountain watershed. Fluorescence analysis results also concluded compositional changes occurred along the wetland flow path during both stormflow and baseflow conditions. In this study, it was explored how urbanization and the associated changes in hydrology and geomorphology have affected a desert wetland's carbon content.
ContributorsBone, Stephanie Rosalia (Author) / Hartnett, Hilairy (Thesis director) / Palta, Monica (Committee member) / Mascaro, Giuseppe (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Trichloroethene (TCE) and hexavalent chromium (Cr (VI)) are ubiquitous subsurface contaminants affecting the water quality and threatening human health. Microorganisms capable of TCE and Cr (VI) reductions can be explored for bioremediation at contaminated sites. The goal of my dissertation research was to address challenges that decrease the efficiency of bioremediation in the subsurface. Specifically, I investigated strategies to (i) promote improve microbial reductive dechlorination extent through the addition of Fe0 and (ii) Cr (VI) bio-reduction through enrichment of specialized microbial consortia. Fe0 can enhance microbial TCE reduction by inducing anoxic conditions and generating H2 (electron donor). I first evaluated the effect of Fe0 on microbial reduction of TCE (with ClO4– as co-contaminant) using semi-batch soil microcosms. Results showed that high concentration of Fe0 expected during in situ remediation inhibited microbial TCE and ClO4– reduction when added together with Dehalococcoides mccartyi-containing cultures. A low concentration of aged Fe0 enhanced microbial TCE dechlorination to ethene and supported complete microbial ClO4– reduction. I then evaluated a decoupled Fe0 and biostimulation/bioaugmentation treatment approach using soil packed columns with continuous flow of groundwater. I demonstrated that microbial TCE reductive dechlorination to ethene can be benefitted by Fe0 abiotic reactions, when biostimulation and bioaugmentation are performed downstream of Fe0 addition. Furthermore, I showed that ethene production can be sustained in the presence of aerobic groundwater (after Fe0 exhaustion) by the addition of organic substrates. I hypothesized that some lessons learned from TCE Bioremediation can be applied also for other pollutants that can benefit from anaerobic reductions, like Cr (VI). Bioremediation of Cr (VI) has historically relied on biostimulation of native microbial communities, partially due to the lack of knowledge of the benefits of adding enriched consortia of specialized microorganisms (bioaugmentation). To determine the merits of a specialized consortium on bio-reduction of Cr (VI), I first enriched a culture on lactate and Cr (VI). The culture had high abundance of putative Morganella species and showed rapid and sustained Cr (VI) bio-reduction compared to a subculture grown with lactate only (without Morganella). Overall, this dissertation work documents possible strategies for synergistic abiotic and biotic chlorinated ethenes reduction, and highlights that specialized consortia may benefit Cr (VI) bio-reduction.
ContributorsMohana Rangan, Srivatsan (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Delgado, Anca G (Thesis advisor) / Torres, César I (Committee member) / van Paassen, Leon (Committee member) / Arizona State University (Publisher)
Created2022