Browsing by Author "He, Zhen"

Now showing 1 - 20 of 72
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    3D Hybrid of Layered MoS2/Nitrogen-Doped Graphene Nanosheet Aerogels: An Effective Catalyst for Hydrogen Evolution in Microbial Electrolysis Cells
    Hou, Yang; Zhang, Bo; Wen, Zhenhai; Cui, Shumao; Guo, Xiaoru; He, Zhen; Chen, Junhong (The Royal Society of Chemistry, 2014-06-18)
    Microbial fuel cells (MFCs) have been conceived and intensively studied as a promising technology to achieve sustainable wastewater treatment. However, doubts and debates arose in recent years regarding the technical and economic viability of this technology on a larger scale and in a real-world applications. Hence, it is time to think about and examine how to recalibrate this technology's role in a future paradigm of sustainable wastewater treatment. In the past years, many good ideas/approaches have been proposed and investigated for MFC application, but information is scattered. Various review papers were published on MFC configuration, substrates, electrode materials, separators and microbiology but there is lack of critical thinking and systematic analysis of MFC application niche in wastewater treatment. To systematically formulate a strategy of (potentially) practical MFC application and provide information to guide MFC development, this perspective has critically examined and discussed the problems and challenges for developing MFC technology, and identified a possible application niche whereby MFCs can be rationally incorporated into the treatment process. We propose integration of MFCs with other treatment technologies to form an MFC-centered treatment scheme based on thoroughly analyzing the challenges and opportunities, and discuss future efforts to be made for realizing sustainable wastewater treatment.
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    Advanced Technologies for Resource Recovery and Contaminants Removal from Landfill Leachate
    Iskander, Syeed Md (Virginia Tech, 2019-04-25)
    Landfill leachate contains valuable, recoverable organics, water, and nutrients. This project investigated leachate treatment and resource recovery from landfill leachates by innovative methods such as forward osmosis (FO), bioelectrochemical systems (BES), and advanced oxidation. In this study, a microbial fuel cell (MFC) removed 50-75% of the ammonia from a leachate through the electricity driven movement of ammonium to the cathode chamber followed by air stripping at high pH (> 9). During this process, the MFC system removed 53-64% of the COD, producing a net energy of 0.123 kWh m-3. Similarly, an integrated microbial desalination cell (MDC) in an FO system recovered 11-64% of the ammonia from a leachate; this was affected by current generation and hydraulic retention time in the desalination chamber. The MDC-FO system recovered 51.5% of the water from a raw leachate. This increased to 83.5% when the FO concentrate was desalinated in the MDC and then recirculated through the FO unit. In addition, the project investigated humic acid (HA) recovery from leachate during the synergistic incorporation of FO, HA recovery, and Fenton's oxidation to enhance leachate treatment and to reduce Fenton's reagent requirements. This led to the investigation of harmful disinfection byproducts (DBPs) formation during Fenton's oxidation of landfill leachate. The removal of leachate UV-quenching substances (humic, fulvic, and hydrophilic acids) using an MFC and a chemical oxidant (i.e., sodium percarbonate) with a focus on energy production and cost efficiency were also studied. BES treatment can reduce leachate organics concentrations; lower UV absorbance; recover ammonia; and, in combination with FO, recover water. Although BES is promising, significant work is needed before its use in landfill leachate becomes practical. FO application to leachate treatment must consider the choice of an appropriate draw solute, which should require minimal effort for regeneration. Resources like HA in leachate deserve more attention. Further efforts can focus on purification and application of the recovered products. The emerging issue of DBP formation in leachate treatment also requires attention due to the potential environmental and human health effects. The broader impact of this study is the societal benefit from more sustainable and cost-efficient leachate treatment.
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    Advancing Forward Osmosis for Energy-efficient Wastewater Treatment towards Enhanced Water Reuse and Resource Recovery
    Zou, Shiqiang (Virginia Tech, 2019-05-30)
    Current treatment of wastewater can effectively remove the contaminants; however, the effluent is still not widely reused because of some undesired substances like pathogens and trace organic chemicals. To promote water reuse, membrane-based technologies have emerged as a robust and more efficient alternative to current treatment practice. Among these membrane processes, forward osmosis (FO) utilizes an osmotic pressure gradient across a semi-permeable membrane to reclaim high-quality water. Still, several key challenges remain to be addressed towards broader FO application, including energy-intensive draw regeneration to yield product water and salinity buildup in the feed solution. To bypass energy-intensive draw regeneration, commercial solid fertilizers was utilized as a regeneration-free draw solute (DS), harvesting fresh water towards direct agricultural irrigation. However, using nutrient-rich fertilizers as DS resulted in an elevated reverse solute flux (RSF). This RSF, known as the cross-membrane diffusion of DS to the feed solution, led to deteriorated solute buildup on the feed side, reduced osmotic driving force, increased fouling propensity, and higher operation cost. To effectively mitigate solute buildup while achieving energy-efficient water reclamation, a parallel electrodialysis (ED) device was integrated to FO for DS recovery in the feed solution. The salinity in the feed solution was consistently controlled below 1 mS cm-1 via the hybrid FO-ED system. Considering solute buildup is merely a consequence of RSF, direct control of RSF was further investigated via operational strategy (i.e., an electrolysis-assisted FO) and membrane modification (i.e., surface coating of zwitterion-functionalized carbon nanotubes). Significantly reduced RSF (> 50% reduction) was obtained in both approaches with minor energy/material investment. With two major bottlenecks being properly addressed for energy-efficient water reclamation, FO was further integrated with a microbial electrolysis cell (MEC) to achieve integrated nutrient-energy-water recovery from high-strength wastewater (i.e., the digestor centrate). The abovementioned research projects are among the earliest efforts to address multiple key challenges of FO during practical application, serving as a cornerstone to facilitate the transformation of current water/wastewater treatment plant to resource recovery hub in order to ensure global food-energy-water security.
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    Advancing Microbial Desalination Cell towards Practical Applications
    Ping, Qingyun (Virginia Tech, 2016-11-03)
    Conventional desalination plant, municipal water supply and wastewater treatment system are among the most electricity-intensive facilities. Microbial Desalination Cell (MDC) has emerged as a promising technique to capture the chemical energy stored in wastewater directly for desalination, which has the potential to solve the high energy consumption issue in desalination industry as well as wastewater treatment system. The MDC is composed of two critical components, the electrodes (anode and cathode), and the ion-exchange membranes separating the two electrodes which drive anions migrate towards the anode, and cations migrate towards the cathode. The multiple components allow us to manipulate the configuration to achieve most efficient desalination performance. By coupling with Donnan Dialysis or Microbial Fuel Cell, the device can effectively achieve boron removal which has been a critical issue in desalination plants. The uncertainty of water quality of the final desalinated water caused by contaminant back diffusion from the wastewater side can be theoretically explained by two mechanisms, Donnan exchange and molecule transport which are controlled by bioelectricity and concentration gradient. Scaling and fouling is also a factor needs to be taken into consideration when operating the MDC system in real world. With mathematical modeling, we can provide insight to bridge the gap between lab-scale experiments and industrial applications. This study is expected to provide guidance to enhance the efficiency as well as the reliability and controllability of MDC for desalination.
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    Aerosolization of Ebola Virus Surrogates in Wastewater Systems
    Lin, Kaisen (Virginia Tech, 2016-09-26)
    Recent studies have shown that Ebola virus can persist in wastewater, and the potential for the virus to be aerosolized and pose a risk of inhalation exposure has not been evaluated. We considered this risk for three wastewater systems: toilets, a lab-scale model of an aeration basin, and a lab-scale model of converging sewer pipes. We measured the aerosol size distribution generated by each system, spiked Ebola virus surrogates into each system, and determined the emission rate of viruses into the air. While the number of aerosols released ranged from 105 to 107 per flush from the toilets or per minute from the lab-scale models, the total volume of aerosols generated by these systems was ~10-8 to 10-7 mL per flush or per minute in all cases. The Ebola virus surrogates MS2 and Phi6, spiked into toilets at an initial concentration of 107 PFU mL-1, were not detected in air after flushing. Airborne concentrations of MS2 and Phi6 were ~20 PFU L-1 and ~0.1 PFU L-1, respectively, associated with the aeration basin and sewer models. This corresponds to emission rates of 547 PFU min-1 and 3.8 PFU min-1 of MS2 and Phi6, respectively, for the aeration basin and 79 PFU min-1 and 0.3 PFU min-1 for the sewer model. Since information on the aerosolization of Ebola virus is quite limited, these emission rates can greatly help inform risk assessment of inhalation exposure to Ebola virus.
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    Anammox-based Technologies for Sustainable Mainstream Wastewater Treatment: Process Development, Microbial Ecology and Mathematical Modeling
    Li, Xiaojin (Virginia Tech, 2018-03-08)
    The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. The key objectives of this dissertation are to develop nitritation-anammox process to treat wastewater with low-nitrogen strength, understand the fundamental microbiology, and optimize its operation through experimental studies and mathematic modeling. Chapter 2 showed that the nitritation-anammox process has been successfully developed in an upflow membrane-aerated biofilm reactor, where pure oxygen was delivered via gas-permeable membrane module. Chapter 3 demonstrated that hybrid anaerobic reactor (HAR) could be an effective pretreatment method to provide a relatively low COD/N ratio for nitritation-anammox reactor. In Chapter 4, a novel mathematical model has been proposed to evaluate the minimum DO requirement for the nitritation-anammox reactor to achieve the maximum TN removal under various COD/N scenarios (controlled by HRTHAR). Chapters 5 and 6 designed an OsAMX system by linking nitritation-anammox to forward osmosis to remove the reverse-fluxed ammonium while using ammonium bicarbonate as a draw solute. The microbial community structures and dynamics, spatial distributions in these bioreactors were characterized by high-throughput sequencing and fluorescent in situ hybridization techniques. The studies in this dissertation have demonstrated that nitritation-anammox process is a promising alternative for sustainable mainstream treatment with the appropriate pretreatment approach and operation optimization.
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    Bioaugmentation and Retention of Anammox Granules to a Mainstream Deammonification Bio-Oxidation Pilot with a Post Polishing Anoxic Partial Denitrification/Anammox Moving Bed Biofilm Reactor
    Campolong, Cody James (Virginia Tech, 2019-03-25)
    The Chesapeake Bay watershed has seen an increase in population, nutrient loading, and stringent effluent limits; therefore, cost-effective technologies must be explored and implemented to intensify the treatment of regional wastewater. This work describes the bioaugmentation and retention of anammox (AMX) granules in a continuous adsorption/bio-oxidation (A/B) mainstream deammonification pilot-scale process treating domestic wastewater. The AMX granules were collected from the underflow of a sidestream DEMON® process. The bioaugmentation rate was based on several factors including full-scale sidestream DEMON® wasting rate and sidestream vs mainstream AMX activity. The retention of bioaugmented AMX granules required a novel settling column at the end of the deammonification step. The settling column was designed to provide a surface overflow rate (SOR) that allowed dense AMX granules to settle into the underflow and less dense floccular biomass to outselect into the overflow. B-Stage was operated to out-select nitrite oxidizing bacteria (NOB) by maintaining an ammonia residual (>2 mg NH4-N/L), a relatively high dissolved oxygen (DO) (>1.5 mg O2/L) concentration, an aggressive solids retention time (SRT) for NOB washout, and intermittent aeration for transient anoxia. AMX activity was not detected in the mainstream at any time. The settling column AMX retention quantification suggested but did not confirm AMX were maintained in the mainstream. NOB were not suppressed during this study and no nitrite accumulation was present in the mainstream process. It was theorized that AMX granules were successfully settled into the settling column underflow and accumulated in the intermittently mixed sidestream biological phosphorus reactor (SBPR) where they disintegrated. This work also describes optimization of carbon addition to an anoxic partial denitrification anammox (PdN/A) moving bed biofilm reactor (MBBR) testing glycerol, acetate, and methanol as carbon sources to maximize total inorganic nitrogen (TIN) removal through the anammox pathway and to minimize effluent TIN. A carbon feeding strategy was developed and was evaluated by the extent of partial denitrification vs full denitrification (partial denitrification efficiency, PdN efficiency). All three carbon sources were capable of high TIN removal, low effluent TIN, and moderate to high PdN efficiency. Average TIN removal for glycerol was 10.0 ± 3.6 mg TIN/L, for acetate it was 8.7 ± 2.9 mg TIN/L, and for methanol it was 11.5 ± 5.6 mg TIN/L. Average effluent TIN for glycerol was 6.0 ± 4.0 mg TIN/L, for acetate it was 5.0 ± 1.1 mg TIN/L, and for methanol it was 4.3 ± 1.5 mg TIN/L. Average PdN efficiency for glycerol was 91.0 ± 9.0%, for acetate it was 88.0 ± 7.7%, and for methanol it was 74.0 ± 8.5%. When PdN efficiency was factored into the cost of each carbon source, methanol was 5.83% cheaper than glycerol per mass TIN removed and 59.0% cheaper than acetate per mass TIN-N removed.
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    Bioelectricity inhibits back diffusion from the anolyte into the desalinated stream in microbial desalination cells
    Ping, Qingyun; Porat, Oded; Dosoretz, Carlos G.; He, Zhen (Pergamon-Elsevier, 2016-01-01)
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    Bioelectrochemical production of hydrogen in an innovative pressure-retarded osmosis/microbial electrolysis cell system: experiments and modeling
    Yuan, Heyang; Lu, Yaobin; Abu-Reesh, Ibrahim M.; He, Zhen (Biomed Central, 2015-08-14)
    Background While microbial electrolysis cells (MECs) can simultaneously produce bioelectrochemical hydrogen and treat wastewater, they consume considerable energy to overcome the unfavorable thermodynamics, which is not sustainable and economically feasible in practical applications. This study presents a proof-of-concept system in which hydrogen can be produced in an MEC powered by theoretically predicated energy from pressure-retarded osmosis (PRO). The system consists of a PRO unit that extracts high-quality water and generates electricity from water osmosis, and an MEC for organic removal and hydrogen production. The feasibility of the system was demonstrated using simulated PRO performance (in terms of energy production and effluent quality) and experimental MEC results (e.g., hydrogen production and organic removal). Results The PRO and MEC models were proven to be valid. The model predicted that the PRO unit could produce 485 mL of clean water and 579 J of energy with 600 mL of draw solution (0.8 M of NaCl). The amount of the predicated energy was applied to the MEC by a power supply, which drove the MEC to remove 93.7 % of the organic compounds and produce 32.8 mL of H2 experimentally. Increasing the PRO influent volume and draw concentration could produce more energy for the MEC operation, and correspondingly increase the MEC hydraulic retention time (HRT) and total hydrogen production. The models predicted that at an external voltage of 0.9 V, the MEC energy consumption reached the maximum PRO energy production. With a higher external voltage, the MEC energy consumption would exceed the PRO energy production, leading to negative effects on both organic removal and hydrogen production. Conclusions The PRO-MEC system holds great promise in addressing water-energy nexus through organic removal, hydrogen production, and water recovery: (1) the PRO unit can reduce the volume of wastewater and extract clean water; (2) the PRO effluents can be further treated by the MEC; and (3) the osmotic energy harvested from the PRO unit can be applied to the MEC for sustainable bioelectrochemical hydrogen production.
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    Bioelectrochemical Systems: Microbiology, Catalysts, Processes and Applications
    Yuan, Heyang (Virginia Tech, 2017-11-01)
    The treatment of water and wastewater is energy intensive, and there is an urgent need to develop new approaches to address the water-energy challenges. Bioelectrochemical systems (BES) are energy-efficient technologies that can treat wastewater and simultaneously achieve multiple functions such as energy generation, hydrogen production and/or desalination. The objectives of this dissertation are to understand the fundamental microbiology of BES, develop cost-effective cathode catalysts, optimize the process engineering and identify the application niches. It has been shown in Chapter 2 that electrochemically active bacteria can take advantage of shuttle-mediated EET and create optimal anode salinities for their dominance. A novel statistical model has been developed based on the taxonomic data to understand and predict functional dynamics and current production. In Chapter 3, 4 and 5, three cathode catalyst (i.e., N- and S- co-doped porous carbon nanosheets, N-doped bamboo-like CNTs and MoS2 coated on CNTs) have been synthesized and showed effective catalysis of oxygen reduction reaction or hydrogen evolution reaction in BES. Chapter 6, 7 and 8 have demonstrated how BES can be combined with forward osmosis to enhance desalination or achieve self-powered hydrogen production. Mathematical models have been developed to predict the performance of the integrated systems. In Chapter 9, BES have been used as a research platform to understand the fate and removal of antibiotic resistant genes under anaerobic conditions. The studies in this dissertation have collectively demonstrated that BES may hold great promise for energy-efficient water and wastewater treatment.
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    C-13 Pathway Analysis for the Role of Formate in Electricity Generation by Shewanella Oneidensis MR-1 Using Lactate in Microbial Fuel Cells
    Luo, Shuai; Guo, Weihua; Nealson, Kenneth H.; Feng, Xueyang; He, Zhen (Nature Publishing Group, 2016-02-12)
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    Cathode-enhanced wastewater treatment in bioelectrochemical systems
    Jain, Akshay; He, Zhen (Nature Research, 2018-12-05)
    Bioelectrochemical systems (BES) have been intensively studied as a new technology for wastewater treatment. However, the treatment efficiency of BES anodes is limited and the anode effluent usually cannot be directly discharged or reused. To enhance the treatment, BES cathodes may be used for additional treatment of selected contaminants. This has been investigated in a number of approaches, which can be grouped into cathode-stimulated treatment and cathode-supported treatment. The former involves electron transfer directly to reduce contaminants like nitrate or dye compounds, while the latter can accomplish contaminant removal by aerobic oxidation, algal growth, production of strong oxidants for advanced oxidation, and/or membrane treatment. This paper aims to provide a concise view and discussion on the cathode-promoted wastewater treatment in BES, analyze challenges pertaining to the cathode treatment, and offer suggestions on the future development of BES for maximized treatment performance.
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    Challege and Opportunities of Membrane Bioelctrochemical Reactors for Wastewater Treatment
    Li, Jian (Virginia Tech, 2016-04-26)
    Microbial fuel cells (MFCs) are potentially advantageous as an energy-efficient approach for wastewater treatment. Integrating membrane filtration with MFCs could be a viable option for advanced wastewater treatment with a low energy input. Such an integration is termed as membrane bioelectrochemical reactors (MBERs). Comparing to the conventional membrane bioreactors or anaerobic membrane bioreactors, MBER could be a competitive technology, due to the its advantages on energy consumption and nutrients removal. By installing the membrane in the cathodic compartment or applying granular activated carbon as fluidized bed materials, membrane fouling issue could be alleviated significantly. In order to drive MBER technology to become a more versatile platform, applying anion exchange membrane (AEM) could be an option for nutrients removal in MBERs. Wastewater can be reclaimed and reused for subsequent fermentation use after a series MFC-MBR treatment process. Such a synergistic configuration not only provide a solution for sustainable wastewater treatment, but also save water and chemical usage from other non-renewable resource. Integrating membrane process with microbial fuel cells through an external configuration provides another solution on sustainable wastewater treatment through a minimal maintenance requirement.
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    CNT@TiO2 nanohybrids for high-performance anode of lithium-ion batteries
    Wen, Zhenhai; Ci, Suqin; Mao, Shun; Cui, Shumao; He, Zhen; Chen, Junhong (Springer, 2013-11-22)
    This work describes a potential anode material for lithium-ion batteries (LIBs), namely, anatase TiO2 nanoparticle-decorated carbon nanotubes (CNTs@TiO2). The electrochemical properties of CNTs@TiO2 were thoroughly investigated using various electrochemical techniques, including cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic cycling, and rate experiments. It was revealed that compared with pure TiO2 nanoparticles and CNTs alone, the CNT@TiO2 nanohybrids offered superior rate capability and achieved better cycling performance when used as anodes of LIBs. The CNT@TiO2 nanohybrids exhibited a cycling stability with high reversible capacity of about 190 mAh g-1 after 120-cycles at a current density of 100-mA-g-1 and an excellent rate capability (up to 100 mAh g-1 at a current density of 1,000-mA-g-1).
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    Computational investigation of the flow field contribution to improve electricity generation in granular activated carbon-assisted microbial fuel cells
    Zhao, Lei; Li, Jian; Battaglia, Francine; He, Zhen (Elsevier, 2016-11-30)
    Microbial fuel cells (MFCs) offer an alternative approach to treat wastewater with less energy input and direct electricity generation. To optimize MFC anodic performance, adding granular activated carbon (GAC) has been proved to be an effective way, most likely due to the enlarged electrode surface for biomass attachment and improved mixing of the flow field. The impact of a flow field on the current enhancement within a porous anode medium (e.g., GAC) has not been well understood before, and thus is investigated in this study by using mathematical modeling of the multi-order Butler-Volmer equation with computational fluid dynamics (CFD) techniques. By comparing three different CFD cases (without GAC, with GAC as a nonreactive porous medium, and with GAC as a reactive porous medium), it is demonstrated that adding GAC contributes to a uniform flow field and a total current enhancement of 17%, a factor that cannot be neglected in MFC design. However, in an actual MFC operation, this percentage could be even higher because of the microbial competition and energy loss issues within a porous medium. The results of the present study are expected to help with formulating strategies to optimize MFC with a better flow pattern design. (C) 2016 Elsevier B.V. All rights reserved.
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    Computational Modeling of Planktonic and Biofilm Metabolism
    Guo, Weihua (Virginia Tech, 2017-10-16)
    Most of microorganisms are ubiquitously able to live in both planktonic and biofilm states, which can be applied to dissolve the energy and environmental issues (e.g., producing biofuels and purifying waste water), but can also lead to serious public health problems. To better harness microorganisms, plenty of studies have been implemented to investigate the metabolism of planktonic and/or biofilm cells via multi-omics approaches (e.g., transcriptomics and proteomics analysis). However, these approaches are limited to provide the direct description of intracellular metabolism (e.g., metabolic fluxes) of microorganisms. Therefore, in this study, I have applied computational modeling approaches (i.e., 13C assisted pathway and flux analysis, flux balance analysis, and machine learning) to both planktonic and biofilm cells for better understanding intracellular metabolisms and providing valuable biological insights. First, I have summarized recent advances in synergizing 13C assisted pathway and flux analysis and metabolic engineering. Second, I have applied 13C assisted pathway and flux analysis to investigate the intracellular metabolisms of planktonic and biofilm cells. Various biological insights have been elucidated, including the metabolic responses under mixed stresses in the planktonic states, the metabolic rewiring in homogenous and heterologous chemical biosynthesis, key pathways of biofilm cells for electricity generation, and mechanisms behind the electricity generation. Third, I have developed a novel platform (i.e., omFBA) to integrate multi-omics data with flux balance analysis for accurate prediction of biological insights (e.g., key flux ratios) of both planktonic and biofilm cells. Fourth, I have designed a computational tool (i.e., CRISTINES) for the advanced genome editing tool (i.e., CRISPR-dCas9 system) to facilitate the sequence designs of guide RNA for programmable control of metabolic fluxes. Lastly, I have also accomplished several outreaches in metabolic engineering. In summary, during my Ph.D. training, I have systematically applied computational modeling approaches to investigate the microbial metabolisms in both planktonic and biofilm states. The biological findings and computational tools can be utilized to guide the scientists and engineers to derive more productive microorganisms via metabolic engineering and synthetic biology. In the future, I will apply 13C assisted pathway analysis to investigate the metabolism of pathogenic biofilm cells for reducing their antibiotic resistance.
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    Controlled Evaluation of Silver Nanoparticle Dissolution: Surface Coating, Size and Temperature Effects
    Liu, Chang (Virginia Tech, 2020-03-30)
    The environmental fate and transport of engineered nanomaterials have been broadly investigated and evaluated in many published studies. Silver nanoparticles (AgNPs) represent one of the most widely manufactured nanomaterials. They are currently being incorporated into a wide range of consumer products due to their purported antimicrobial properties. However, either the AgNPs themselves or dissolved Ag+ ions has a significant potential for the environmental release. The safety issues for nanoparticles are continuously being tested because of their potential danger to the environment and human health. Studies have explored the toxicity of AgNPs to a variety of organisms and have shown such toxicity is primarily driven by Ag+ ion release. Dissolution of nanoparticles is an important process that alters their properties and is a critical step in determining their safety. Therefore, studying nanoparticles' dissolution can help in the current move towards safer design and application of nanoparticles. This research endeavor sought to acquire comprehensive kinetic data of AgNP dissolution to aid in the development of quantitative risk assessments of AgNP fate. To evaluate the dissolution process in the absence of nanoparticle aggregation, AgNP arrays were produced on glass substrates using nanosphere lithography (NSL). Changes in the size and shape of the prepared AgNP arrays were monitored during the dissolution process by atomic force microscopy (AFM). The dissolution of AgNP is affected by both internal and external factors. First, surface coating effects were investigated by using three different coating agents (BSA, PEG1000, and PEG5000). Capping agent effects nanoparticle transformation rate by blocking reactants from the nanoparticle surface. Coatings prevented dissolution to different extents due to the various way they were attached to the AgNP surface. Evidence for the existence of bonds between the coating agents and the AgNPs was obtained by surface enhanced Raman spectroscopy. Moreover, to study the size effects on AgNP dissolution, small, medium, and large sized AgNPs were used. The surrounding medium and temperature were the two variables that were included in the size effects study. Relationships were established between medium concentration and dissolution rate for three different sized AgNP samples. By using the Arrhenius equation to plot the reaction constant vs. reaction temperature, the activation energy of AgNPs of different sizes were obtained and compared.
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    Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production
    Tse, Hei Tsun; Luo, Shuai; Li, Jian; He, Zhen (Springer, 2016-11-01)
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    Detection of Environmental Contaminants in Water Utilizing Raman Scanning for E. coli Phenotype Changes
    Flick, Hunter James (Virginia Tech, 2019-05-30)
    Raman spectroscopy and its counterpart surface-enhanced Raman scattering (SERS) have proven to be effective methods for detecting miniscule changes in the phenotypes of E. coli and other single-celled organisms to aid in the detection of new strains for industrial use and discovery of new antibiotics. The purpose of this study is to develop a method to quickly and accurately detect contaminants in water samples through phenotype changes in E. coli measured through SERS. Contaminated Luria-Bertani (LB) media was inoculated with LB with an OD600 of 1, grown for two hours, and then dried on a flat piece of aluminum foil. These samples were then Raman scanned and processed to determine contaminant-induced changes to the phenotypes of the E. coli. Three types of tests were run to show the effectiveness of this method: single-component, multicomponent, and impure water sources. In single-component tests, it was found that differences due to NaCl contamination could be detected to 5.0E-9 weight percent (wt %), ethanol (EtOH) to 5.0E-7 volumetric percent (% v/v), citric acid (CA) to 2.8E-4 wt %, acetic acid (AA) to 2.6E-4 wt %, kanamycin to 2.5E-11 wt %, ampicillin to 2.5E-10 wt %, CoCl2 to trace amounts, and silver nanoparticles (AgNP) to 5.2E-7 wt %. Many of these are below the detection limits of analytical instrumentation, but their effects on E. coli phenotypes were detectable by Raman spectroscopy. Multicomponent tests showed that in a mixture, the most toxic or most concentrated contaminants have the most effect on cell phenotype. However, it was shown that similar concentrations of similar contaminants may be difficult to discern with current methods. This behavior was also seen in the impure water samples, showing that tap water behaves the closest to a DI control, followed by running water, and finally stagnant bodies. This new method of monitoring E. coli phenotypes with Raman spectroscopy as a biosensor shows promise for the fast, portable, and accurate determination of environmental contaminants with a broad-spectrum and very low detection limits.