Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 223-241).

Master of Agribusiness / Department of Agricultural Economics / Jason S. Bergtold / Cover crops can be used as forage for cattle and other grazing animals. This research investigated the net returns of using cover crops for forage or grazing under four scenarios. These scenarios were: 1) a mixed crop and livestock producer who owns a herd of cattle and has both dry or pregnant cows and weaned calves available to graze corn stover and cover crops; 2) a crop farmer who purchases stocker cattle for the purpose of grazing the cover crop and corn stover; 3) a crop farmer who leases out a corn stover and cover crop field to a livestock producer (and who provides value-added services to the livestock producer for a fee); and 4) an integrated operation with crops and cattle where cover crops are not grown and hay is fed to cattle during the winter months. Each of these scenarios had different budgets, risks, and profit potentials. The research aimed to address the risks and profit potentials for each scenario. The stocking density was initially set at three cows and 31 steers for a period of 90 days, and alternatively, three cows and 25 steers for a period of 120 days. Two sets of cattle pricing data were used: the average historical prices from 1992 to 2011 and reported prices from a regional stockyard for the period of November 2016 to March 2017. The results showed that the initial stocking densities used for scenarios one and two were too low to provide profitable net returns regardless of pricing data used. Net returns for scenario three were also not profitable based on the services rendered and the management fee charged. Scenario four was profitable on one occasion. November steers with a 500 lb. average starting weight fed hay and concentrate for 120 days resulted in a positive net return of $375. A second analysis was done using stocking rates of 50, 75, or 100 steers to determine if increasing stocking density would result in a positive net return using only the 2016/2017 pricing data and only evaluating net returns on 2.0 and 2.5 lbs. of average daily gain. Positive net returns were achieved at various start weights and average daily gain rates at stocking rates of 75 and 100 animals. No positive net returns were realized at the stocking rate of 50 animals/100 acre field. The management fee charged for providing management services under scenario three was adjusted based on stocking densities to determine if a positive net return could be achieved at the set fee rate of $0.875/head/day. At that rate, no stocking rate resulted in a positive net return. Using the cost data, less the $900 field lease income, a breakeven pricing point for the management fee was determined for each stocking density and grazing duration within the scenario. Management of cost factors to achieve greater chances of profitability and additional research needs are discussed.

The amount of available biomass feedstock and associated cost components were analyzed to determine the potential increase in energy capacity of two existing combined heat and power plants in Mississippi. The amount of corn stover and forest logging residue within a 10-mile radius can satisfy the existing requirements of CHP plants in Scott (1 MW) and Washington counties (5 MW). Transporting feedstock within a smaller source area had lower transportation costs, but higher total unit cost than the two other source buffer scenarios. However, capital costs associated with higher plant capacities were significantly higher and plant expansion may not be economically advantageous. Increasing the CHP capacity from 1 MW to 2 MW in Scott county and 5 MW to 10 MW in Washington county might be a sustainable approach by drawing feedstock from a smaller area and at lower utilization rates, while keeping transportation costs low.

<p dir="ltr">Biorefineries rely on compression feed screws to transport biomass for biofuel production in chemical reactors. However, flowability issues within these feedscrews often lead to production downtime, impacting profitability. Modeling biomass flow within the feedscrews is crucial to optimize processing parameters like torque and speed, reducing downtime. Biomass is a non-uniform granular material which faces flowability issues. The problems in flowability is influenced by factors such as particle size, moisture content, material composition, and processing methods. Identifying key parameters that can influence the material behavior is vital to minimize production downtimes. Feedscrews operate under high pressures which makes obtaining accurate material parameters at these high pressures challenging. Many methods used within the pharmaceutical industry to obtain material parameters are unable to reach the larger pressures that the material experiences within the feedscrew. However, Triaxial testing can be used to test the material at the high pressure of interest. Triaxial testing has been used within the civil engineering field to test granular materials such as soils, sand, and rocks. The Finite Element Method (FEM) using a continuum model is used for modeling systems with a large number of particles. The modified Drucker-Prager Cap (mDPC) continuum model is often used to capture complex material behavior, including densification and shear yielding in granular materials. This model seems well suited to capture the behaviors of biomass material. The focus of the thesis is to obtain the shear failure properties of corn stover using triaxial testing and the Drucker-Prager Cap continuum model. Simulations and experimental data are utilized to establish a criterion for identifying shear failure. While simulations depict ideal behavior of a DPC material with frictionless and frictional platens, experimental data shows trends of real-life corn stover. Simulation results effectively predict the material’s friction angle but show larger errors in estimating cohesion, potentially due to extrapolation or cohesion’s sensitivity to volumetric plastic strain. Further simulations at smaller hydrostatic unloading pressures are recommended to reduce this error. Experimental trends for shear failure seem to align with simulation trends for shear failure identification. However, the densification trends in experiments lack the clarity observed in the trends from the simulations. More triaxial experiments should be run to determine if the trends are consistent at other hydrostatic loading and unloading pressures. More than two experiments at the same hydrostatic loading pressure should also be run to estimate the shear failure line to obtain a better estimation. Experimentally there are a number of other factors that could contribute to errors such as the estimated material diameter used to calculate Mises stress, if corrections were made for items such as the moving piston, latex membrane, and more, and how far the shear failure line is extrapolated to the vertical axis.</p>

Doctor of Philosophy / Department of Grain Science and Industry / Praveen V. Vadlani / Lactic acid is an important platform chemical that has long history and wide applications in food, polymer, pharmaceutics and cosmetic industries. Lactic acid has two optical isomers; namely D-lactic acid and L-lactic acid. Racemic mixture of lactic acid are usually used as preservatives and ingredients in solvents, or as precursors for different chemicals. Currently there is an increasing demand of optical pure lactic acid as a feedstock for the production of poly-lactic acid (PLA). PLA is a biodegradable, biocompatible and environmental friendly alternative to plastics derived from petroleum based chemicals. Optically pure D or L-lactic acid is used for the synthesis of poly D or L- lactic acid (PDLA, PLLA). Blend of PDLA with PLLA results in a heat-resistant stereocomplex PLA with excellent properties. As a consequence, large quantity of cost effective D-lactic acid is required to meet the demand of stereocomplex PLA. Lignocellulosic biomass is a promising feedstock for lactic acid production because of its availability, sustainability and cost effectiveness compared to refined sugars and cereal grain-based sugars. Commercial use of lignocellulosic biomass for economic production of lactic acid requires microorganisms that are capable of using all sugars derived from lignocellulosic biomass. Therefore, the objectives of this study were: 1) to produce high level of optically pure D-lactic acid from lignocellulosic biomass-derived sugars using a homofermentative strain L. delbrueckii via simultaneous saccharification and fermentation (SSF); 2) to develop a co-culture fermentation system to produce lactic acid from both pentose and hexose sugars derived from lignocellulosic biomass; 3) to produce D-lactic acid by genetically engineered L. plantarum NCIMB 8826 ∆ldhL1 and its derivatives; 4) to construct recombinant L. plantarum by introduction of a plasmid (pLEM415-xylAB) used for xylose assimilation and evaluate its ability to produce D-lactic acid from biomass sugars; and 5) to perform metabolic flux analysis of carbon flow in Lactobacillus strains used in our study. Our results showed that D-lactic acid yield from alkali-treated corn stover by L. delbrueckii and L. plantarum NCIMB 8826 ∆ldhL1 via SSF were 0.50 g g[superscript]-1 and 0.53 g g[superscript]-1 respectively; however, these two D-lactic acid producing strains cannot use xylose from hemicellulose. Complete sugar utilization was achieved by co-cultivation of L. plantarum ATCC 21028 and L. brevis ATCC 367, and lactic acid yield increased to 0.78 g g[superscript]-1 from alkali-treated corn stover, but this co-cultivation system produced racemic mixture of D and L lactic acid. Simultaneous utilization of hexose and pentose sugars derived from biomass was achieved by introduction of two plasmids pCU-PxylAB and pLEM415-xylAB carrying xylose assimilation genes into L. plantarum NCIMB 8826 ∆ldhL1, respectively; the resulting recombinant strains ∆ldhL1-pCU-PxylAB and ∆ldhL1-pLEM415-xylAB used xylose and glucose simultaneously and produced high yield of optically pure D-lactic acid. Metabolic flux analysis verified the pathways used in these Lactobacillus strains and provided critical information to judiciously select the desired Lactobacillus strain to produce lactic acid catering to the composition of raw material and the optical purity requirement. This innovative study demonstrated strategies for low-cost biotechnological production of tailor-made lactic acid from specific lignocellulosic biomass, and thereby provides a foundational manufacturing route for a flexible and sustainable biorefinery to cater to the fuel and chemical industry.

Call number: LD2668 .T4 1984 D93 / Master of Science

The use of ethanol produced from lignocellulosic biomass for transportation fuel offers solutions in reducing environmental emission and the use of non-renewable fuels. However, lignocellulosic ethanol production is still hampered by economic and technical obstacles. For instance, the inhibitory effect of toxic compounds produced during biomass pretreatment was reported to inhibit the fermenting microorganisms, hence there was a decrease in ethanol yield and productivity. Thus, there is a need to improve the bioconversion of lignocellulosic biomass to ethanol in order to promote its commercialization. The research reported here investigated the use of poultry litter biochar to improve the ethanol production from steam-exploded poplar and corn stover. The effect of poultry litter biochar was first studied on Saccharomyces cerevisiae ATCC 204508/S288C growth, and second on the enzyme hydrolysis and fermentation of two steam-exploded biomasses: (poplar and corn stover). The third part of the study investigated optimal process parameters (biochar loading, biomass loading, and enzyme loading) on the reducing sugars production, and ethanol yield from steam-exploded corn stover. In this study, it has been shown that poultry litter biochar improved the S. cerevisiae growth and ethanol productivity; therefore poultry litter biochar could potentially be used to improve the ethanol production from steam-exploded lignocellulosic biomass.

The present study investigated the feasibility of production of sophorolipids (SLs) using yeast Candida bombicola grown on hydrolysates derived lignocellulosic feedstock either with or without supplementing oil as extra carbon source. Several researchers have reported using pure sugars and various oil sources for producing SLs which makes them expensive for scale-up and commercial production. In order to make the production process truly sustainable and renewable, we used feedstocks such as sweet sorghum bagasse, corn fiber and corn stover. Without oil supplementation, the cell densities at the end of day-8 was recorded as 9.2, 9.8 and 10.8 g/L for hydrolysate derived from sorghum bagasse, corn fiber, and corn fiber with the addition of yeast extract (YE) during fermentation, respectively. At the end of fermentation, the SL concentration was 3.6 g/L for bagasse and 1.0 g/L for corn fiber hydrolysate. Among the three major sugars utilized by C. bombicola in the bagasse cultures, glucose was consumed at a rate of 9.1 g/L-day; xylose at 1.8 g/L-day; and arabinose at 0.98 g/L-day. With the addition of soybean oil at 100 g/L, cultures with bagasse hydrolysates, corn fiber hydrolysates and standard medium had a cell content of 7.7 g/L; 7.9 g/L; and 8.9 g/L, respectively after 10 days. The yield of SLs from bagasse hydrolysate was 84.6 g/L and corn fiber hydrolysate was15.6 g/L. In the same order, the residual oil in cultures with these two hydrolysates was 52.3 g/L and 41.0 g/L. For this set of experiment; in the cultures with bagasse hydrolysate; utilization rates for glucose, xylose and arabinose was recorded as 9.5, 1.04 and 0.08 g/L-day respectively. Surprisingly, C. bombicola consumed all monomeric sugars and non-sugar compounds in the hydrolysates and cultures with bagasse hydrolysates had higher yield of SLs than those from a standard medium which contained pure glucose at the same concentration. Based on the SL concentrations and considering all sugars consumed, the yield of SLs was 0.55 g/g carbon (sugars plus oil) for cultures with bagasse hydrolysates. Further, SL production was investigated using sweet sorghum bagasse and corn stover hydrolysates derived from different pretreatment conditions. For the former and latter sugar sources, yellow grease or soybean oil was supplemented at different doses to enhance sophorolipid yield. 14-day batch fermentation on bagasse hydrolysates with 10, 40 and 60 g/L of yellow grease had cell densities of 5.7 g/L, 6.4 g/L and 7.8 g/L, respectively. The study also revealed that the yield of SLs on bagasse hydrolysate decreased from 0.67 to 0.61 and to 0.44 g/g carbon when yellow grease was dosed at 10, 40 and 60 g/L. With aforementioned increasing yellow grease concentration, the residual oil left after 14 days was recorded as 3.2 g/L, 8.5 g/L and 19.9 g/L. For similar experimental conditions, the cell densities observed for corn stover hydrolysate combined with soybean oil at 10, 20 and 40 g/L concentration were 6.1 g/L, 5.9 g/L, and 5.4 g/L respectively. Also, in the same order of oil dose supplemented, the residual oil recovered after 14-day was 8.5 g/L, 8.9 g/L, and 26.9 g/L. Corn stover hydrolysate mixed with the 10, 20 and 40 g/L soybean oil, the SL yield was 0.19, 0.11 and 0.09 g/g carbon. Overall, both hydrolysates supported cell growth and sophorolipid production. The results from this research show that hydrolysates derived from the different lignocellulosic biomass feedstocks can be utilized by C. bombicola to achieve substantial yields of SLs. Based upon the results revealed by several batch-stage experiments, it can be stated that there is great potential for scaling up and industrial scale production of these high value products in future.

No description available.

<p>  </p> <p>The potential of lignocellulose for producing fermentable sugars as feedstock to manufacture fuels, chemicals, and materials for decarbonization remains untapped due to costly logistics and conversion processes. Pelleting technology offers a solution by addressing logistical issues and impacting downstream conversion, though it comes with its own costs. An overview of recent advances in pelleting technologies and their impact on bioconversion highlights the importance of understanding variables and product attributes. The interplay between pelleting and pretreatment processes, considering various feedstocks, is crucial for future design. Practical considerations such as energy consumption, costs, and environmental impacts must not be overlooked, along with exploration of cutting-edge technologies and strategies in this field. This work further presents a comprehensive investigation into the recalcitrance of pelleted corn stover to enzymatic digestion prior to any pretreatment.</p> <p>The potential of lignocellulose for producing fermentable sugars as feedstock to manufacture fuels, chemicals, and materials for decarbonization remains untapped due to costly logistics and conversion processes. Pelleting technology offers a solution by addressing logistical issues and impacting downstream conversion, though it comes with its own costs. An overview of recent advances in pelleting technologies and their impact on bioconversion highlights the importance of understanding variables and product attributes. The interplay between pelleting and pretreatment processes, considering various feedstocks, is crucial for future design. Practical considerations such as energy consumption, costs, and environmental impacts must not be overlooked, along with exploration of cutting-edge technologies and strategies in this field. </p> <p>This dissertation further presents a comprehensive investigation into the recalcitrance of pelleted corn stover to enzymatic digestion prior to any pretreatment. One aspect focuses on the role of high moisture pelleting in enhancing the enzymatic digestibility of corn stover before pretreatment, along with the relevant substrate characteristics. The pelleting process increases the digestibility of unpretreated corn stover, resulting in a glucan conversion increase from 8.2% to 15.5% at a 5% solid loading using 1 FPU Cellic® CTec2 per gram of solids. Under the same enzymatic hydrolysis conditions, the conversion of glucan remains higher for pelleted corn stover compared to its non-pelleted counterpart, even though both samples underwent identical milling processes and passed through the same screen to minimize particle impact. Compositional analysis reveals that loose and pelleted corn stover have similar non-dissolvable compositions, albeit with differences in their extractives. Using microcrystalline cellulose (Avicel) as a substrate, the presence of corn stover extractives results in a lower sugar yield compared to using citrate buffer instead, particularly for extractives from pelleted corn stover. This indicates a more negative impact of pelleted corn stover extractives on the activity of employed enzyme, CTec2. However, pelleted corn stover still shows increased overall glucan conversion compared to loose corn stover, suggesting improved digestibility of non-dissolvable components after milling and washing. The improvement in digestibility of pelleted material can be attributed to factors such as reduced particle size, enhanced substrate accessibility, and hydrolysis of cross-linking structures induced by the pelleting process. These findings offer valuable insights for the development of processing strategies aimed at sustainable and efficient utilization of lignocellulose.</p> <p>Furthermore, this dissertation delves into the profound impact of extractives on enzymatic hydrolysis, prompting a thorough examination of the composition and characteristics of extractives derived from pelleted corn stover, as well as their effects on enzymatic conversion. In contrast to previous reports, it is discovered that water extractable materials actually enhance the enzymatic hydrolysis of extractive-free stover, while the enzyme activities diminish when using microcrystalline cellulose as a substrate. This divergent behavior of extractives is attributed to the presence of lignin, which may interact with inhibitory compounds like phenolics, thereby mitigating the detrimental effects of soluble inhibitors or insoluble lignin, or both. These findings significantly advance our fundamental understanding of the intrinsic behavior of extractives and contribute to the optimization of schemes for efficient and cost-competitive enzymatic conversion of lignocellulose. </p>