Ann D. Christy

Effect of external resistance on bacterial diversity and metabolism in cellulose-fed microbial fuel cells.

External resistance affects the performance of microbial fuel cells (MFCs) by controlling the flow of electrons from the anode to the cathode. The purpose of this study was to determine the effect of external resistance on bacterial diversity and metabolism in MFCs. Four external resistances (20, 249, 480, and 1000 Ω) were tested by operating parallel MFCs independently at constant circuit loads for 10 weeks. A maximum power density of 66 mW m(-2) was achieved by the 20 Ω MFCs, while the MFCs with 249, 480, and 1000 Ω external resistances produced 57.5, 27, and 47 mW m(-2), respectively. Denaturing gradient gel electrophoresis analysis of partial 16S rRNA genes showed clear differences between the planktonic and anode-attached populations at various external resistances. Concentrations of short chain fatty acids were higher in MFCs with larger circuit loads, suggesting that fermentative metabolism dominated over anaerobic respiration using the anode as the final electron acceptor.

Suppression of methanogenesis in cellulose-fed microbial fuel cells in relation to performance, metabolite formation, and microbial population.

The objective of this work was to evaluate methanogenesis in relation to the changes in performance and microbial diversity of cellulose-fed microbial fuel cells (MFCs). Replicate MFCs were inoculated with a ruminal microbial consortium and operated under 20 (R20Ω) or 100 Ω (R100Ω) external resistances. During the first week of operation, 0.31 and 0.44 mmol l(-1) of methane were produced in the R20Ω and R100Ω MFCs, respectively. Methanogenesis was, however, suppressed to undetectable levels within 90 days of operation, accompanied with increased current production and improved coulombic efficiency. Suppressed methanogenesis coincided with changes in the concentrations of short chain fatty acids and a decrease in the microbial diversity. The results demonstrated that methanogenesis was active during the early stage of cellulose-fed MFCs but this activity declined over prolonged operation.

Development of a continuous system for sanitizing whole apples with aqueous ozone

Alternative and economical methods for reducing the bacterial load on cider apples are needed by small cider producers to comply with U.S. Food and Drug Administration (FDA) regulations for food safety. In 1996, the Centers for Disease Control and Prevention reported that several illnesses and one death were attributed to Escherichia coli O157:H7 contaminated apple cider. Currently the only option available for cider producers to avoid an FDA required warning label on their product is pasteurization. The equipment needed for pasteurization can be expensive and is limited to liquids only. Ozone (O 3 ) is a potent disinfectant that shows great potential for food sanitizing applications. This article summarizes the design and construction of a benchtop prototype chamber and related components for the treatment of whole cider apples with ozonated washwater prior to grinding and pressing for cider. Preliminary performance data on residual ozone concentrations produced in the washwater are also presented. A maximum residual dissolved concentration of 34 ppm was achieved over a 0.5 to 1.5 min contact time per apple.

Characterization and performance of anodic mixed culture biofilms in submersed microbial fuel cells

Microbial fuel cells (MFCs) were designed for laboratory scale experiments to study electroactive biofilms in anodic chambers. Anodic biofilms and current generation during biofilm growth were examined using single chambered MFCs submersed in algal catholyte. A culture of the marine green alga Nanochloropsis salina was used as a biocatholyte, and a rumen fluid microbiota was the anodic chamber inoculum. Electrical impedance spectroscopy was performed under varying external resistance once a week to identify mass transport limitations at the biofilm-electrolyte interface during the four-week experiment. The power generation increased from 249 to 461mWm-2 during the time course. Confocal laser scanning microscopy imaging showed that the depth of the bacterial biofilm on the anode was about 65μm. There were more viable bacteria on the biofilm surface and near the biofilm-electrolyte interface as compared to those close to the anode surface. The results suggest that biofilm growth on the anode creates a conductive layer, which can help overcome mass transport limitations in MFCs.

Acetone-butanol-ethanol fermentation of corn stover: current production methods, economic viability and commercial use

Biobutanol is a next-generation liquid biofuel with properties akin to those of gasoline. There is a widespread effort to commercialize biobutanol production from agricultural residues, such as corn stover, which do not compete with human and animal foods. This pursuit is backed by extensive government mandates to expand alternative energy sources. This review provides an overview of research on biobutanol production using corn stover feedstock. Structural composition, pretreatment, sugar yield (following pretreatment and hydrolysis) and generation of lignocellulose-derived microbial inhibitory compounds (LDMICs) from corn stover are discussed. The review also discusses different Clostridium species and strains employed for biobutanol production from corn stover-derived sugars with respect to solvent yields, tolerance to LDMICs and in situ solvent recovery (integrated fermentation). Further, the economics of cellulosic biobutanol production are highlighted and compared to corn starch-derived ethanol and gasoline. As discussed herein, the economic competitiveness of biobutanol production from corn stover largely depends on feedstock processing and fermentation process design.

Effectiveness of Rice Agricultural Waste, Microbes and Wetland Plants in the Removal of Reactive Black-5 Azo Dye in Microcosm Constructed Wetlands.

Azo dyes are commonly generated as effluent pollutants by dye using industries, causing contamination of surface and ground water. Various strategies are employed to treat such wastewater; however, a multi-faceted treatment strategy could be more effective for complete removal of azo dyes from industrial effluent than any single treatment. In the present study, rice husk material was used as a substratum in two constructed wetlands (CWs) and augmented with microorganisms in the presence of wetland plants to effectively treat dye-polluted water. To evaluate the efficiency of each process the study was divided into three levels, i.e., adsorption of dye onto the substratum, phytoremediation within the CW and then bioremediation along with the previous two processes in the augmented CW. The adsorption process was helpful in removing 50% dye in presence of rice husk while 80% in presence of rice husk biocahr. Augmentation of microorganisms in CW systems has improved dye removal efficiency to 90%. Similarly presence of microorganisms enhanced removal of total nitrogen (68% 0 and Total phosphorus (75%). A significant improvement in plant growth was also observed by measuring plant height, number of leaves and leave area. These findings suggest the use of agricultural waste as part of a CW substratum can provide enhanced removal of textile dyes.

LONGITUDINAL SURVEY OF FEMALE FACULTY IN BIOLOGICAL AND AGRICULTURAL ENGINEERING

Female faculty in biological and agricultural engineering (BAE) were surveyed in 1998 to examine their professional experiences, motivations, and insights. Approximately 7% of all BAE faculty were women in 1998, and the total number of women in the population was 57. Results, based on a 61% response rate, showed that 60% of the population was at the assistant professor rank. Respondents reported that BAE departments provided a supportive environment and believed that the attraction of women to BAE was due to its emphasis on biological systems, as well as biological engineerings relative newness and lack of long-standing stereotypes of male dominance. Full results of the original survey were published in the Journal of Women and Minorities in Science and Engineering in 2000. We re-surveyed the population of women in BAE in 2006 because we believe that longitudinal data on this population will provide interesting insights into this group and its experiences in the profession, and may suggest ways to increase female representation among engineering faculty. The population is now comprised of 89 women and represents approximately 11% of BAE faculty. Approximately 85% of all women in the original 1998 survey population are included in the current population. Reasons given by those exiting the population include staying in academia but moving to non-BAE departments such as chemical engineering or bioengineering, being promoted to academic leadership positions without retaining primary BAE status, or pursuing other non-academic professional opportunities. Forty-nine percent of the population are now assistant professors, and the number of BAE full professors increased from 10% in 1998 to 19% in 2006. A significant number of women BAE faculty have engineers and/or faculty members within their immediate families; two respondents are second-generation women engineers. The reported self-confidence level of women faculty is 65%, the same as the 1998 survey. Ninety-five percent of respondents act as mentors to others (up from 72% in 1998). Eighty-four percent of respondents do not feel that they have experienced space inequities, and 73% do not believe they have experienced salary inequities. Lack of support for dual-career couples and other family issues were mentioned by 48% of respondents as issues that could be addressed to improve the climate for women faculty in BAE; these issues were mentioned more often in 2006 than in 1998.

A Microbial Fuel Cell Coupling Anaerobic Degradation of Agricultural Lignocellulose Wastes to Electricity Generation

Microbial fuel cells (MFCs) are bio-electro-chemical reactors in which renewable biomass resources are used as fuels to generate electricity. The objectives of this study were (i) to evaluate electricity generation from cellulose in an MFC with rumen microbes as biocatalysts, and (ii) to analyze the microbial diversity that developed in the MFC. The anode was inoculated with rumen microorganisms, and suspended cellulose powder was the sole substrate in the anodic chamber. Power density reached 55.3 mW·m-2 without the addition of external redox mediators. Electricity generation involved anode-attached and suspended microorganisms working in a concert to link cellulose hydrolysis to anaerobic respiration and electrode reduction. The results also demonstrate that the current could be sustained for over 1440 hours with cellulose as the sole substrate. Denaturing gradient gel electrophoresis of PCR amplified 16s rDNA revealed that microbial communities changed when different substrates were used as fuel in MFCs. Results suggested that microbial consortia composed of both anode-biofilm and suspended microbes could evolve within an MFC’s environment. Phylogenetic analysis by the use of rDNA clone libraries, showed differences between the two communities in the cellulose- MFC. This study demonstrates that rumen microbes are capable of hydrolyzing cellulose with concomitant transfer of electrons to an electrode. In addition it adds to the diversity of microorganisms that have been shown to produce electricity in MFCs, and expands the range of suitable substrates to include cellulose, a most abundant plant biomass component readily available as a waste material in many parts of the world.

Ternary Diagram Modeling of Soil Texture Data for Predicting Subsurface Fracturing in Glacially Related Fine-Grained Materials

Fractures play an important role in the movement of water and contaminants through soil materials. The objectives of this research were: (1) to determine the best model for predicting fracturing, which could serve as a practical tool to anticipate and investigate fractures in glacially related fine-grained soil materials, and (2) to identify those soil textures most likely to support fracturing. A dataset based on Ohio soils observed in the field to be fractured was extended to cover a wider range of textures through performing controlled laboratory fracturing experiments. The 30 data produced by these laboratory experiments were added to the 143 field data and together used to develop five statistical and graphical methods: the silhouette method, the girth method, the hexagonal field method, Weltjes method, and a non-statistical best-fit method. The best predictive model of the five was the non-statistical best-fit method. When plotted on a USDA ternary diagram, soils with 6% clay were predicted to support fracturing. All texture classes of soils were identified as able to sustain fracturing except the loamy sand and sand classes. This graphical model can be useful to explain how fractures are created in glacially related fine-grained materials and may be a practical tool allowing geologists and field engineers to anticipate fractures without resorting to more costly methods such as soil borings, soil pits, or excavations.

Engaging Students to Prepare them for the Engineering Profession and Reflect upon their Undergraduate Career

An undergraduate professional development course for students in food, agricultural, and biological engineering features several instructional activities for engaging those students. The goals of the course are to: (1.) Prepare students to enter the engineering profession including developing improved personal skills and confidence for interviewing and pursuing professional licensing; (2.) Introduce professional development business topics; (3.) Instill the need for life-long learning after graduation; (4.) Explore the ethical expectations within the engineering profession; and (5.) Enable students to reflect upon and articulate what they have learned during their engineering education. Students submit weekly assignments (15 draft documents) and one professional portfolio summarizing their undergraduate career and organized by ABET a-k outcome. Methods and classroom activities are presented along with four years of assessment data.