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A cost effective and sustainable supply of biomass feedstocks is a cribical component of a viable biorefinery industry that is capable of making a credible impact on petroleum displacement. Feedstock costs can amount to a very significant fraction of the cost of the final biorefinery product. Thus, the reduction of the costs of feedstock production, harvest, collection, transportation, storage, and preprocessing can have a direct and positive effect on the overall viability of a given biorefinery. In addition, the feedstock and technology choices that are made for maintaining a sustainable biomass supply will have important implications not only for the biorefinery industry, but also for society as a whole. This session focused on feedstock supply, logistics, processing and composition, all of which are important elements of the feedstock supply chain.

The lack of understanding the mechanical characteristics of cellulosic feedstocks is a limiting factor in economically collecting and processing crop residues, primarily wheat and barley stems and corn stover. Several testing methods—compression, tension, and bend—were investigated to increase the understanding of the biomechanical behavior of cellulosic feedstocks. Biomechanical data from these tests can provide required input to numerical models and help advance harvesting, handling, and processing techniques. In addition, integrating the models with the complete data set from this study can identify potential tools for manipulating the biomechanical properties of plant varieties in such a manner as to optimize their physical characteristics to produce higher-value biomass and more energy-efficient harvesting practices.

Crop residues collected during or after grain harvest are available once per year and must be stored for extended periods. The combination of air, high moisture, and high microbial loads leads to shrinkage during storage and risk of spontaneous ignition. Ensiling is a wet preservation method that could be used to store these residues stably. To economically adapt ensiling to biomass that is harvested after it has senesced, the need for nutrient, moisture, and microbial additions must be determined. We tested the ensiling of senesced wheat straw in sealed columns for 83 d. The straw was inoculated with and amended with several levels of water and free sugars. The ability to stabilize the straw polysaccharides was strongly influenced by both moisture and free sugars. Without the addition of sugar, the pH increased from 5.2 to as much as 9.1, depending on moisture level, and losses of 22% of the cellulose and 21% of the hemicellulose were observed. By contrast, when sufficient sugars were added and interstitial water was maintained, a final pH of 4.0 was attainable, with correspondingly low (<5%) losses of cellulose and hemicellulose. The results show that ensiling should be considered a promising method for stable storage of wet biorefinery feedstocks.

Issues of traffic congestion and community acceptance limit the size of biomass-processing plants based on truck delivery to about 2 million (M) dry t/yr or less. In this study, the cost of ethanol from an ethanol fermentation plant processing 2 M dry t/yr of corn stover supplied by truck is compared with that of larger plants in the range of 4–38 M dry t/yr supplied by a combination of trucks plus pipelines. For corn stover, a biomass source with a low yield per gross hectare, the cost of ethanol from larger plants is always higher. For wood chips from the boreal forest, a biomass source with a relatively high yield per gross hectare, a plant processing 14–38 M dry t/yr produces ethanol at a 13% reduction in cost compared with a plant producing 2 M dry t/yr supplied by truck. Processing of value-added products, such as chemicals from lignin, would be enabled by larger-scale plants.

Brazil is one of the world’s largest producers of alcohol from biomass at low cost and is responsible for more than 1 million direct jobs. In 1973, the Brazilian Program of Alcohol (Proalcool) stimulated the creation of a bioethanol industry that has led to large economic, social, and scientific improvements. In the year 1984, 94.5% of Brazil’s cars used bioethanol as fuel. In 2003/2004, 350.3 million of sugarcane produced 24.2 million t of sugar and 14.4 billion L of ethanol for an average 4.3 million cars using ethanol. Since its inception, cumulative investment in Proalcool totals US$11 billion, and Brazil has saved US$27 billion in oil imports. The ethanol production industry from sugarcane generates 152 times more jobs than would have been the case if the same amount of fuel was produced from petroleum, and the use of ethanol as a fuel is advantageous for environmental reasons. In 2003, one of the biggest Brazilian ethanol industries started consuming 50% of the residual sugarcane bagasse to produce electrical energy (60 MW), a new alternative use of bioenergy for the Brazilian market. Other technologies for commercial uses of bagasse are in development, such as in the production of natural fibers, sweeteners (glucose and xylitol), single-cell proteins, lactic acid, microbial enzymes, and many other products based on fermentations (submerged and semisolid). Furthermore, studies aimed at the increase in the biosynthesis of sucrose and, consequently, ethanol productivity are being conducted to understand the genetics of sugarcane. Although, at present, there remain technical obstacles to the economic use of some ethanol industry residues, several research projects have been carried out and useful data generated. Efficient utilization of ethanol industry residues has created new opportunities for new value-added products, especially in Brazil, where they are produced in high quantities.

Design and development of improved harvesting, preprocessing, and bulk handling systems for biomass requires knowledge of the biomechanical properties and structural characteristics of crop residue. Structural analysis of wheat stem cross-sections was performed using the theory of composites and finite element analysis techniques. Representative geometries of the stem’s structural components including the hypoderm, ground tissue, and vascular bundles were established using microscopy techniques. Material property data for the analysis was obtained from measured results. Results from the isotropic structural analysis model were compared with experimental data. Future work includes structural analysis and comparison with experimental results for additional wheat stem models and loading configurations.

The focuses of this Session were identification, modification, development, and cost-effective production and use of enzymes to achieve numerous biological and chemical transformations.

Urease has been immobilized and layered onto the walls of manufactured silicon microchannels. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged poly-electrolytes, with enzyme layers “encased” between them, were deposited onto the walls of the silicon microchannels. The polycations used were polyethylenimine (PEI), polydiallyldimethylammonium (PDDA), and polyallylamine (PAH). The polyanions used were polystyrenesulf onate (PSS) and polyvinylsulfate (PVS). The activity of the immobilized enzyme was tested by pumping a 1 g/L urea solution through the microchannels at various flow rates. Effluent concentration was measured using an ultraviolet/visible spectrometer by monitoring the absorbance of a pH sensitive dye. The architecture of PEI/PSS/PEI/urease/PEI with single and multiple layers of enzyme demonstrated superior performance over the PDDA and PAH architectures. The precursor layer of PEI/PSS demonstrably improved the performance of the reactor. Conversion rates of 70% were achieved at a residence time of 26 s, on d 1 of operation, and >50% at 51 s, on d 15 with a six-layer PEI/urease architecture.

A cellulase production process was developed by growing the fungi and on dairy manure. produced a high total cellulase titer (1.7 filter paper units [FPU]/mL, filter paper activity) in medium containing 10 g/L of manure (dry basis [w/w]), 2 g/L KHPO, 2 mL/L of Tween-80, and 2mg/L of CoCl. However, β-glucosidase activity in the -enzyme system was very low. was then cocultured with to enhance the β-glucosidase level. The mixed culture resulted in a relatively high level of total cellulase (1.54 FPU/mL) and β-glucosidase (0.64 IU/mL). The ratio of β-glucosidase activity to filter paper activity was 0.41, suitable for hydrolyzing manure cellulose. The crude enzyme broth from the mixed culture was used for hydrolyzing the manure cellulose, and the produced glucose was significantly ( < 0.01) higher than levels obtained by using the commercial enzyme or the enzyme broth of the pure culture .

The production of lipase by in solid-state fermentation was studied using babassu cake as the basal medium. Tray-type and packed-bed bioreactors were employed. In the former, the influence of temperature; content of the medium, and medium supplementation with olive oil, sugarcane molasses, corn steep liquor, and yeast hydrolysate was studied. For all combinations of supplements, a temperature of 30°C, a moisture content of 70%, and a concentration of carbon source of 6.25% (m/m, dry basis) provided optimum conditions for lipase production. When used as single supplements olive oil and molasses also were able to provide high lipase activities (20 U/g). Using packed-bed bioreactors and molasses-supplemented medium, optimum conditions for enzyme production were air superficial velocities above 55 cm/min and temperatures below 28°C. The lower temperature optimum found for these reactors is probably related to radial heat gradient formation inside the packed bed. Maximum lipase activities obtained in these bioreactors (26.4 U/g) were 30% higher than in tray-type reactors.