http://hdl.handle.net/1957/496 Sat, 25 May 2013 03:34:04 GMT 2013-05-25T03:34:04Z http://hdl.handle.net/1957/31098 Bacterial community analysis, new exoelectrogen isolation and enhanced performance of microbial electrochemical systems using nano-decorated anodes Xu, Shoutao Microbial electrochemical systems (MESs) have attracted much research attention in recent years due to their promising applications in renewable energy generation, bioremediation, and wastewater treatment. In a MES, microorganisms interact with electrodes via electrons, catalyzing oxidation and reduction reactions at the anode and the cathode. The bacterial community of a high power mixed consortium MESs (maximum power density is 6.5W/m²) was analyzed by using denature gradient gel electrophoresis (DGGE) and 16S DNA clone library methods. The bacterial DGGE profiles were relatively complex (more than 10 bands) but only three brightly dominant bands in DGGE results. These results indicated there are three dominant bacterial species in mixed consortium MFCs. The 16S DNA clone library method results revealed that the predominant bacterial species in mixed culture is Geobacter sp (66%), Arcobacter sp and Citrobacter sp. These three bacterial species reached to 88% of total bacterial species. This result is consistent with the DGGE result which showed that three bright bands represented three dominant bacterial species. Exoelectrogenic bacterial strain SX-1 was isolated from a mediator-less microbial fuel cell by conventional plating techniques with ferric citrate as electron acceptor under anaerobic conditions. Phylogenetic analysis of the 16S rDNA sequence revealed that it was related to the members of Citrobacter genus with Citrobacter sp. sdy-48 being the most closely related species. The bacterial strain SX-1 produced electricity from citrate, acetate, glucose, sucrose, glycerol, and lactose in MFCs with the highest current density of 205 mA/m² generated from citrate. Cyclic voltammetry analysis indicated that membrane associated proteins may play an important role in facilitating electron transfer from the bacteria to the electrode. This is the first study that demonstrates that Citrobacter species can transfer electrons to extracellular electron acceptors. Citrobacter strain SX-1 is capable of generating electricity from a wide range of substrates in MFCs. This finding increases the known diversity of power generating exoelectrogens and provids a new strain to explore the mechanisms of extracellular electron transfer from bacteria to electrode. The wide range of substrate utilization by SX-1 increases the application potential of MFCs in renewable energy generation and waste treatment. Anode properties are critical for the performance of microbial electrolysis cells (MECs). Inexpensive Fe nanoparticle modified graphite disks were used as anodes to preliminarily investigate the effects of nanoparticles on the performance of Shewanella oneidensis MR-1 in MECs. Results demonstrated that average current densities produced with Fe nanoparticle decorated anodes were up to 5.9-fold higher than plain graphite anodes. Whole genome microarray analysis of the gene expression showed that genes encoding biofilm formation were significantly up-regulated as a response to nanoparticle decorated anodes. Increased expression of genes related to nanowires, flavins and c-type cytochromes indicate that enhanced mechanisms of electron transfer to the anode may also have contributed to the observed increases in current density. The majority of the remaining differentially expressed genes were associated with electron transport and anaerobic metabolism demonstrating a systemic response to increased power loads. The carbon nanotube (CNT) is another form of nano materials. Carbon nanotube (CNT) modified graphite disks were used as anodes to investigate the effects of nanostructures on the performance S. oneidensis MR-1 in microbial electrolysis cells (MECs). The current densities produced with CNT decorated anodes were up to 5.6-fold higher than plain graphite anodes. Global transcriptome analysis showed that cytochrome c genes associated with extracellular electron transfer are up-expressed by CNT decorated anodes, which is the leading factor to contribute current increase in CNT decorated anode MECs. The up regulated genes encoded to flavin also contribute to current enhancement in CNT decorated anode MECs. Graduation date: 2013 Fri, 15 Jun 2012 00:00:00 GMT http://hdl.handle.net/1957/31098 2012-06-15T00:00:00Z http://hdl.handle.net/1957/30841 High frequency water vapor density measurements using the beat frequency method Elorriaga Montenegro, Estefania This document describes the design and deployment of a first generation water vapor density sensing unit, the HumiSense. This device is based on an open, air-filled capacitor which is part of a resonant circuit. The frequency of the resonant circuit mixed with a fixed frequency oscillator is the basis of the method to generate a signal that is associated to the change in water vapor density within the open capacitor with time. The physical testing results were inconclusive given that there were many unresolved artifacts in the data. Several suggestions for improving the device for future device generations were provided. Graduation date: 2013 Fri, 15 Jun 2012 00:00:00 GMT http://hdl.handle.net/1957/30841 2012-06-15T00:00:00Z http://hdl.handle.net/1957/21923 Modeling phosphorus sequestration and release in an Upper Klamath Basin wetland Mulford, Emily L. Upper Klamath Lake (UKL) and Agency Lake (AL) in southern Oregon are both hypereutrophic, in large part due to natural and anthropogenic loading of phosphorus (P), resulting in annual blooms of blue-green algae. Reduction of P loading to the lake is considered crucial to reduce the blue-green algae blooms, maintain water quality, and increase the fish populations within the lake. Restoration of fringe wetlands is one potential way to reduce external P loading to the lake. However, upon the initial period of flooding, restored wetlands have been found to also be a source of P into the lake, as a result of P resuspension due to years of soil disturbance. We adapted a mass balance model of the biological P uptake and release to examine how P wetland dynamics change over the course of a year in restored wetlands in the Upper Klamath Basin. Our analyses focused on 1) comparing the P release and sequestration processes over each season, 2) examining whether wetlands around the lakes act as a net source or sink of P to UKL, 3) investigating wetland management strategies to determine if there is any one that is most successful at sequestering P, and 4) if release and sequestration of P in restored wetlands contribute to the P dynamics of the broader ecosystem in the UKL. Results from this model indicate resuspension of P in the wetlands is high throughout the year, yet outflow only occurs during the first 16 days of the summer, and macrophyte uptake and sedimentation of P are most important in sequestering P. Additionally, our findings indicate that two of the modeled management strategies are successful at preventing P from reaching the lakes, and that wetlands around the lake act as a net sink of P to UKL over time. However, the reduction or termination of external loading is not likely to reduce the algal blooms in the lakes, as the amount of P recycled from the lake sediments each year far exceeds the capabilities of the current wetlands. Graduation date: 2012 Fri, 01 Jul 2011 00:00:00 GMT http://hdl.handle.net/1957/21923 2011-07-01T00:00:00Z http://hdl.handle.net/1957/20249 Photobiological hydrogen production from the cyanobacterium Synechocystis sp. PCC 6803 encapsulated in sol-gel processed silica Dickson, David J. Photobiological hydrogen production from live cells of the cyanobacterium Synechocystis sp. PCC 6803 encapsulated in silica gel was investigated. Hydrogen is a dense energy carrier with potential to reduce dependence on fossil fuels, provided a renewable and sustainable means of production can be achieved. Under certain conditions, Synechocystis sp. PCC 6803 can produce molecular hydrogen through the activity of a reversible [Ni-Fe] hydrogenase using energy derived from photosynthesis. The current work improved hydrogen production through encapsulation of viable cells in silica gel and through manipulation of the phycobilisomes (PBS), the light harvesting antennae. First, various formulations of silicon alkoxide-derived gels were screened with a high throughput screening assay to verify the organism could be successfully encapsulated and hydrogen production was comparable to similar cells in liquid culture. It was found that wild-type (wt) Synechocystis sp. PCC 6803 and a mutant known as M55 are both amenable to encapsulation within gels derived from tetraethoxysilane (TEOS) precursors of low silica content, and observed hydrogen production was comparable to liquid cultures. Subsequent investigations explored the effects of encapsulation stress and possible effects of gel additives on the photosynthetic activity and efficiency of this organism. Synechocystis sp. PCC 6803 was found to be moderately robust against salt stress, somewhat sensitive to ethanol stress, and very sensitive to osmotic stresses and interference with excitation transfer created by polyethylene glycol and glycerol, respectively. Finally, three PBS mutants known as ΔcpcAB, ΔapcE, and ΔapcF were evaluated for glycogen accumulation, pigment content, hydrogen production, photosynthetic activity, and suitability for silica sol-gel encapsulation. The ΔcpcAB strain lacks PBS rods, the ΔapcE strain completely lacks a functional PBS, and the ΔapcF strain has a functional PBS with disrupted excitation transfer to the photosystems. Under 200 μEm⁻²s⁻¹ light, all strains accumulated similar levels of glycogen, and the ΔapcE and ΔapcF strains produced similar levels of hydrogen while the ΔcpcAB strain produced less hydrogen compared to wt cells, although its photosynthetic efficiency was actually improved. Under 400μEm⁻²s⁻¹ light, the ΔapcE and ΔapcF mutants both produced approximately 25% more hydrogen than wt cells from the same amount of glycogen, accumulating a 1.2% headspace hydrogen concentration. Hydrogen production from cells encapsulated in gels derived from aqueous precursors was approximately 3.5 times higher than similar cells in liquid culture, and more than double that from cells in alkoxide-derived gels. This investigation demonstrates the efficacy of silica sol-gel encapsulation as a tool to enhance photobiological hydrogen production from Synechocystis sp. PCC 6803 and that manipulation of photoantennae can lead to improved hydrogen production. Graduation date: 2011 Fri, 25 Feb 2011 00:00:00 GMT http://hdl.handle.net/1957/20249 2011-02-25T00:00:00Z