Conceptual and Mathematical Models of Batch Simultaneous Saccharification and Fermentation: Dimensionless Groups for Predicting Process Dynamics

This paper describes a modeling effort demonstrating that dimensionless groupings of classical process parameters can be used to predicting process dynamics of batch simultaneous saccharification and fermentation (SSF) processes. Michaelis–Menten enzyme kinetics and Monod growth kinetics were employed, and inhibition of enzyme action and inhibition of microbial growth were neglected. The SSF process was characterized by the relative durations of three phases: A microbially-limited phase, a hydrolysis-limited phase, and a monosaccharide-depletion phase. The duration of these three phases were interrelated, and well predicted by the dimensionless magnitude of the monosaccharide peak (MSP). Thus, the MSP could be used as a single-value descriptor of an SSF process. The dimensionless ratio of the initial hydrolysis rate to the initial substrate consumption rate was shown to predict MSP, and an overall system time constant was shown to predict the total run time of a batch SSF process

Why They Leave: Understanding Student Attrition from Engineering Majors

A large number of students leave engineering majors prior to graduation despite efforts to increase retention rates. To improve retention rates in engineering programs, the reasons why students leave engineering must be determined. In this paper, we review the literature on attrition from engineering programs to identify the breadth of factors that contribute to students’ decisions to leave. Fifty studies on student attrition from engineering programs were included in the primary part of this literature review. In the second half of the work, an additional twenty-five studies that focused on methods of increasing student retention, were examined. Six broad factors driving students to leave engineering were identified by examining the attrition literature: classroom and academic climate, grades and conceptual understanding, self-efficacy and self-confidence, high school preparation, interest and career goals, and race and gender. Evidence from the retention studies suggests that successful efforts to increase retention act on one or more of these factors. A clear gap in the literature is that of economics: the costs associated with losing students, and the costs associated with implementing retention strategies, are virtually unmentioned

A Coarse Techno-Economic Model of a Combined Fermentation-Catalysis Route to Sorbic Acid

The conversion of biomass into bulk chemicals provides the potential for multiple environmental and economic benefits. While current research in industrial biotechnology focuses primarily on biocatalysts, a significant opportunity exists when combining biological and chemical catalysis into one process train. This hybrid process approach will potentially produce a wide array of economically viable molecules. One test-case of this hybrid approach is the production of sorbic acid via biocatalytic conversion of glucose to 4-Hydroxy-6-methyl-2-pyrone (HMP), followed by catalytic conversion of HMP to sorbic acid. Current collaborative research has developed this process to the stage where gram-quantities of biologically-produced HMP have been delivered to catalysis to produce butyl sorbate (a hydrolysis step can then take this to sorbic acid). Although the final process details needed for a detailed technoeconomic analyses are several years away, it is desirable to understand a coarse structure of the economics of such a process. Such an understanding can provide insight into opportunities for process improvement, as well as into fundamental technoeconomic limitations of the approach. To this end, we have developed a spreadsheet-based model of this hybrid process and have estimated the sorbic acid production cost from the process, which are then compared to current wholesale prices. We also report results of a comprehensive sensitivity analysis to demonstrate potential process improvements

Techno-economic Analysis of Farm Scale Plug-flow Anaerobic Digestion

Treating animal wastes through anaerobic digestion (AD) yields methane-rich biogas that can be used for power generation or heating, and a nutrient-rich digestate that can be land applied as fertilizer. Anaerobic digestion also reduces odors from stored and land applied manures. Despite these benefits, AD deployment rates in the United States (US) are only 5% for dairy farms identified as being suitable for AD by the US Environmental Protection Agency. The objective of this study was to analyze the economic and technical limitations of farm-scale plug-flow anaerobic digesters using a simple model permitting insight into the fundamental constraints on the technology. A model was developed to determine the cost of methane produced via AD based on operation size. For context, the cost of ADmethane was then compared to commercial methane costs (i.e., natural gas). The analysis shows how critical farm size is to making AD-methane cost-competitive with natural gas. At low herd sizes (below 400 animals), carbon credits and odor reductions alone appear insufficient to overcome the relatively low commercial energy rates in the US. However, moderate reductions in digester cost and interest rate, coupled with moderate increases in amortization period, and/or natural gas prices appear could make AD more competitive with commercial energy in the US even at relatively small herd sizes (ca. 200 animals)

A Success Enhancement Program after the First Test in Freshman Engineering

All first-year engineering students at the University of Tennessee take a common sequence of two-4 hour Physics for Engineers classes. The classes cover typical introduction to engineering topics, as well as basic physics concepts. The classes are divided into modules, with each module lasting approximately three weeks. There is a 50-minute test at the end of each module, which is worth 11% of the student’s grade

Epigenetics and the exposomes: Obesity and beyond

The specific genetic alterations that result in diseases and complex syndromes have been and continue to be identified. Search for the origins of disease have led to investigations into the roles of dietary and environmental factors as potential triggers or modifiers of risk. Genome-wide association studies have identified concepts such as the rare variant-common disease hypothesis and the common variant-common disease hypothesis. Through association studies, unique gene-environment interactions, which may occur with or without specific periods of permissiveness or vulnerabilities, have also been identified. Major conditions where the role of exposomes and epigenetics are rapidly evolving are obesity, neurological disorders, immune disorders and cancers. These concepts are particularly intriguing in the context of obesity

A Rose by Any Other Name: An Analysis of Agricultural and Biological Engineering Undergraduate Curricula

The objective of this study was to assess the extent to which a common thread exists among all of the ag-based biological systems engineering programs across the U.S. through a course-by-course analysis of individual program curricula. Publically available curricula were used to determine the coursework requirements for 88 unique curricula in the U.S. Due to the lack of standardization of course titles in the discipline, disciplinary courses were grouped into themes, and summary tables showing the distribution of courses by theme in the different curricula were made. In addition, a self-organizing map was made using the categorized data to provide visual mapping of curricular similarity among programs. Results indicate that although all programs require similar basic math, science, and engineering fundamentals, there is wide variety in the discipline-specific requirements. For example, the two most common discipline-specific themes are required by only 61% and 75% of programs (basic engineering applied to agricultural and biological systems, and instrumentation and controls, respectively). Furthermore, results show that the name of the program and/or option generally conveys limited information about the content of the curriculum, although some differentiation between agricultural engineering programs and biological engineering programs is evident

An Engineering-Economic Model for Analyzing Dairy Plug-Flow Anaerobic Digesters: Cost Structures and Policy Implications

Treating animal wastes through anaerobic digestion (AD) yields methane-rich biogas that can be used for power generation or heating, and a nutrient-rich digestate that can be land-applied as fertilizer. Furthermore, AD reduces odors from stored and land-applied manures. Despite these benefits, AD deployment rates in the U.S. are only 5% for dairy farms identified as suitable for AD by the U.S. Environmental Protection Agency. The objective of this study was to analyze the economic and technical limitations of farm-scale anaerobic digesters using a simple model permitting insight into the fundamental constraints on the technology. A model was developed to determine the cost of methane produced via AD based on operation size. Dairy plug-flow systems were modeled because of their well-documented economic performance, and model validation used data from AgSTAR\u27s FarmWare program. The analysis shows that farm size is critical to make digestion-derived methane cost-competitive with natural gas. At low herd sizes (\u3c400 \u3eanimals), carbon credits and odor reductions alone appear insufficient to overcome the low commercial energy rates in the U.S. However, moderate reductions in digester cost and interest rate, coupled with moderate increases in amortization period and/or natural gas prices, could make AD more competitive with commercial energy in the U.S. even at relatively small herd sizes (approx. 400 animals)

Detecting Insect Flight Sounds in the Field: Implications for Acoustical Counting of Mosquitoes

A prototype field-deployable acoustic insect flight detector was constructed from a noise-canceling microphone coupled to an off-the-shelf digital sound recorder capable of 10 h recordings. The system was placed in an urban forest setting 25 times over the course of the summer of 2004, collecting 250 h of ambient sound recordings that were downloaded to a personal computer and used to develop detection routines. These detection routines operated on short segments of sound (0.093 s, corresponding to 4096 samples at 44100 Hz). A variety of approaches were implemented to detect insect flight tones. Simple approaches, involving sensing the fundamental frequency (1st harmonic) and 2nd harmonic, were capable of detecting insects, but generated large numbers of false positives because of other ambient sounds including human voices, birds, frogs, automobiles, aircraft, sirens, and trains. In contrast, combining information from the first four harmonics, from the interharmonic regions, and from the sound envelope, reduced false positives greatly. Specifically, in the 250 h of recordings, 726 clear insect buzzes were detected by the final algorithm, with only 52 false positives (6.5%). Running the final algorithm with all criteria liberalized by 20% increased the number of clear insect buzzes by 8%, to 784, but increased false positives to 471 (28% of total detections). The potential of using this approach for detecting mosquito activity using low-cost sensors is discussed