The Integrated Biomass Supply Analysis and Logistics (IBSAL) model was used to cal­culate cost and energy inputs for the supply chain of biomass (Sokhansanj et al. 2006) . IBSAL consists of different sub-modules for harvesting, processing, preprocessing (grind­ing), storage, and transportation. Model input data include local weather data, average net yield of biomass, crop harvest progress data (including start and end dates of harvest), dry matter loss with time in storage, moisture content of plant at the time of harvest, operating parameters of equipment, and $/hour cost of machinery. The model is built on the EXTEND™ (Imaginethat, Inc., San Jose, CA) platform (http://www. imaginethatinc. com). Main outputs of the model include delivered cost of biomass ($/t), carbon emission (kg of C per t), and energy consumption (GJ/t). IBSAL also calculates dry matter losses of biomass using limited data available for storing switchgrass bales (Sanderson et al. 1997) and handling hay (Rees 1982) . Details of the model can be found in Sokhansanj et al. )2006, 2008) .

The choice of particular size and operating conditions are based on three objectives: (1) the latest model of equipment that are commercially available for forage harvest; (2) the typical operational performance data that are available given by the American Society of Agricultural Engineering (ASAE, which is now the American Society of Agricultural and Biological Engineering [ASABE]) standard on Agricultural Machinery Management Data, ASAE D497 (ASAE 2004) or from manufacturer’s literature; and (3) limited equip­ment performance data published for switchgrass elsewhere. Hourly costs are calculated using the procedure and data described in Sokhansanj and Turhollow (2002). The rates represent the sum of fixed and variable costs. The hourly rates for the pull-type equipment (e. g., baler) are the sum of the hourly rate for the implement and the power equipment (e. g., tractor).

Collection Cost

Square baling cost is the highest at $23.72/t followed by loafing at $19.21/t (Sokhansanj and Turhollow 2002). The low collection cost using loafer is because of its reduced number of operations and the size of the loaf. The higher cost for dry chopping and piling ($35.17/t) and for ensiling ($35.75/t) is because of the higher cost of the forage chopper. Mowing and raking operations are eliminated in silaging operation but the extra cost of pit and packing the silage offsets the lower cost of harvest. The input data for silaging also includes the cost of silage pit at $4757 per year.

The energy inputs range from 0.319 GJ/dry t for loafing to 0.590 GJ/dry t for the dry chop system. The energy inputs are dependent on the size of power used to operate the equipment. Forage choppers require large amounts of power—more than 200kW. Using 16 GJ/dry t as the energy content of dry switchgrass, the energy input to the system ranges from roughly 2% for loafing to less than 4% for dry chopping. The energy expenditure for silaging is slightly less than for dry chopping. Conrado et al. (2005) analyzed switchgrass collection and handling with various types of equipment and concluded that once optimized for switchgrass loafing can become the most cost-effective option.

In the last century, innovation in various disciplines, such as plant breeding, crop protec­tion, soil fertility, and plant nutrition have supported an enormous increase in agricultural productivity (Sambamurty 2002; Tilman et al. 2002; Jauhar 2006; Wenzel 2006). As a result, the United States has large amounts of (1) crop residues, (2) agricultural processing residues, (3) animal manures and other wastes, and (4) grasses. Feedstock compositions directly affect product yield and tech-economical feasibility of ethanol conversion process and vary significantly among different kinds of agricultural residues (Table 9.1) (Wyman 2007). As shown in the second through eighth columns of Table 9.1, the high carbohydrate content (i. e., cellulose and hemicellulose) of many crop residues, such as corn stover, result in high theoretical ethanol yields, making them attractive candidates for fuel ethanol production. Among these, corn production residues, such as corncobs and corn stover, cotton processing residues, and sugarcane bagasse contain relatively high fractions of carbohydrates and relatively low lignin, making them particularly amenable for making fermentable sugars. On the other hand, nutshells are not promising feedstocks for bio­conversion to fuel ethanol due to their high lignin content and resulting low amounts of carbohydrates.

Competition for feedstocks and harvesting and transport costs are critical, particu­larly for initial commercial ventures. For example, because the stalks left after extrac­tion of sugar from sugarcane are already at a central location, no additional costs are incurred for collection and transport. However, these materials have value as a fuel for generating process heat and possibly electricity, which still must be taken into consid­eration. Corn fiber is also attractive because of its availability at a processing facility, but it has value as a binder and source of protein for cattle feed. Because residues such as corn stover or just the stalks are left on the field after harvesting the kernels, additional costs are incurred to gather and transport these materials compared to bagasse or corn fiber, and such residues frequently have value as a soil stabilizer and nutrient source, with the result that some must be left in the field (Karlen et al. 1984, Randall et al. 2006; Hoskinson et al. 2007). Other feedstocks such as rice straw are of interest because they are burned following rice harvest to prevent spread of plant diseases, making them potentially available. However, additional costs are incurred to harvest and transport such materials to a central processing site, and the high amounts of silica have a large impact on sugar and resulting ethanol yields and complicate processing to ethanol.

Table 9.2 summarizes the production of various categories of agricultural residues potentially available for conversion to ethanol and other products by 2030. Figure 9.1 breaks these totals down to show the current and predicted availability of those feedstocks with greatest potential impact in the United States (Perlack et al. 2005) . The amount of available feedstock is the residue that can be sustainably removed from the field, which is less than the total produced. The sustainably removable amounts depend on various factors, such as the annual crop residue collection technology, equipment used, soil type, climate, and crop tillage practices (Blanco-Canqui et al. 2006; Hoskinson et al. 2007). The predicted feedstock availabilities listed are based on two different scenarios: a rela­tively conservative assumption of moderate crop yield increases without land use changes to accommodate perennial crops (energy crops) and a high-end assumption that crop yields increase significantly with land use change to accommodate energy crops. As the data show, corn stover ranks first by a large margin in terms of availability in all sce­narios. Yet various crop residues can play an important role for fuel ethanol production, particularly when they are combined with others. As crop yields increase with land use change, the availability of some feedstocks, such as soybean straw and sorghum, could increase significantly.

42.4

oe

Table 9.1. Continued. Feedstock Arabinan Xylan Mannan Galactan Glucan Cellulose Hemicellulose Extractives Lignin Ash Reference Processing residues Corncobs 45 35 5 15 Koch 2006 Corn fiber 10.0 19.0 4.0 30.0 35.3 8 Allen et al. 2001a Corn husk 43.2 21.8 10.9 Kurakake et al. 2001 Cotton linter, 85-90 1-3 0.7-1.6 0.8-2 Han 1998 seed hull Sugarcane 1.6 23.11 0.3 0.45 43.39 43.39 25.46 1.52 24.09 2.84 bagasse Rice hull 1.9 14.4 0 1.1 31.2 30.9 16.8 35.9 Laser et al. 2002 Oat hull 1.2 15.5 0 0.0 48.9 48.4 16.1 16.2 Antal et al. 2000 Almond shells 0 26.1 0 1.8 25.0 24.7 27 27.2 Antal et al. 2000 Walnut shell 0 17.2 0 2.2 21.2 21.0 18.8 32.7 Antal et al. 2000 Pecan shell 0 2.8 0 1.1 5.6 5.6 3.8 70 Antal et al. 2000 Carrot peelings 39.49 9.71 Li et al. 2007 Coconut fiber 0.1 17 0.1 0.4 34.9 34.9 17.5 33.5 Han 1998 Coconut shell 0 25.5 0 0.0 24.5 24.2 24.7 34.9 Antal et al. 2000 Oil-palm empty 35.71 5.67 21.97 6.82 Minowa et al. 1998 fruit bunch Olive husk 24 23.6 9.4 48.4 Demirbas 1997 Orange peel 9.91 8.7 3.45 Grohmann et al. 1995 Manure Cow manure 32.6 23.8 26.8 43.7 Stiller et al. 1996 Horse manure 37.8 32.4 19.6 11.2 Stiller et al. 1996 Broiler litter 18.1 18.05 2.82 Rasool et al. 1996

Hans P Blaschek, Thaddeus C. Ezeji, and Jtirgen Scheffran

Around one-tenth of global primary energy use is based on bioenergy sources, of which about 10% are produced from modern bioenergy in the form of power, heat, and fuel. Biofuels for transportation account for 2.2% of all bioenergy, with a strong increase over the last decade. The total sustainable technical potential of bioenergy is estimated to be around a quarter of current global energy use.

Different from biomass specifically cultivated for energy purposes, residues and wastes are available as a byproduct of other processes. A significant amount of renewable energy is being generated from biogenic wastes and residues that do not require additional land and/or greenhouse gas emissions. Using their energy content would avoid methane emis­sions from slurry or landfills. Wastes and residues are quite heterogeneous: They arise in different sectors (agriculture and forestry, manufacturing, municipal enterprises, and private households) and at different stages of the value chain (biomass production and harvesting, processing, consumption, and disposal).

The technical potential of biogenic wastes and residues worldwide is estimated to be around 80 exajoules (EJ) per year. Research is needed in order to determine how much of this technical potential can be utilized in a sustainable and cost-effective way. A Department of Energy study has calculated in 2006 that over 1.3 billion dry tons per year of biomass from forestland and agricultural land alone are potentially available in the United States, a large fraction of which is from wastes and residues. This amount is sufficient to meet more than one-third of the current demand for transportation fuels while still meeting food, feed, and export demands. This biomass resource potential can be produced with relatively modest changes in land use, or agricultural and forestry practices.

Global production of biofuels in 2007 amounted to 16.4 billion gallons per year. Ethanol is currently the most important renewable liquid biofuel in the United States, which produces about half of the world’s ethanol, compared with 38% in Brazil and 4.3% in the European Union. As the worldwide demand for fuels and chemicals surges and petroleum deposits are depleted, producers of ethanol fuel are increasingly looking beyond corn, potatoes, and other starchy crops as substrates for ethanol fuel production. Especially promising is cellulosic ethanol that can capitalize on microbial engineering and biotechnology to reduce costs.

Biofuels from Agricultural Wastes and Byproducts Edited by Hans P. Blaschek, Thaddeus C. Ezeji and Ju rgen Scheffran 3

© 2010 Blackwell Publishing. ISBN: 978-0-813-80252-7

Derived from low-cost and plentiful feedstocks, it can achieve high yields, has high octane, and other desirable fuel properties. Lignocellulosic feedstocks, such as switchgrass, woody plants, mixture of prairie grass, agricultural residues, and municipal waste, have been pro­posed to offer environmental and economic benefits. Compared to current biofuel sources, these biomass feedstocks require fewer agricultural inputs than annual crops and can be grown on agriculturally marginal lands.

After crop harvesting, the residues usually represent relatively large amounts of cellulosic material that could be returned to the soil for its future enrichment in carbon and nutrients or could be made available for further conversion to biofuels. Similarly, animal wastes are high in cellulose content and can also be converted to liquid biofuels. Such agricultural byproducts can play an important role in triggering the transition to sustainable biofuels.

Increasing demand for bioenergy has generated a strong interest in the bioconversion of agricultural wastes and coproducts into fuels and chemical feedstocks. To reduce the impact on land resources available for the production of food crops, a further increase in ethanol production will require the use of agricultural materials not directly tied to food, especially lignocellulosic biomass such as corn stover and corn fiber, wheat straw and rice straw, paper and wood processing waste, landscape waste and sugarcane waste. Some of the technologies to be utilized also generate coproducts such as electricity, hydrogen, ammonia, and methanol.

The chapters in this book cover a wide range of topics and demonstrate the potential for production of biofuels and chemicals from agricultural wastes and byproducts.

The chapter by Nasib Qureshi, Stephen Hughes, and Thaddeus Ezeji describes recent progress in emerging technologies to produce ethanol from lignocellulosic substrates, over­coming inhibitors generated during pretreatment, development of genetically improved cul­tures, simultaneous product recovery, and process integration. It addresses problems associated with inhibitor generation and detoxification, fermentation of both hexose and pentose sugars to ethanol, and the development of efficient microbial strains. Simultaneous product recovery, process consolidation, and integration will further improve the economics of production of biofuels from biomass. Coproducts serve as additional sources for generating revenue.

Fermentation of lignocellulosic biomass to ethanol requires additional processing steps for hydrolysis of biomass to simple sugars before these sugars can be fermented. These extra processing steps add to the overall cost of the substrate. Generally, the chemicals that are used to pretreat lignocellulosic substrates include dilute acid or alkali, and their use results in higher sugar yields when compared to pretreatments such as hot water or ammonia. These pretreatments generate products that inhibit cell growth and/or the fermentation process or both. Another challenging problem with respect to fermentation of biomass involves the inability of some fermentation microorganisms to use pentose sugars for growth and produc­tion of biofuels. Lignocellulosic biomass contains up to 30% pentose sugars, which are not utilized by the traditional ethanol-producing cultures such as Saccharomyces cerevisiae. Although recombinant cultures of S. cerevisiae have been developed, the overall productivity and ethanol concentration that can be achieved by these strains are not optimal.

Next-generation alternative renewable liquid biofuels are under development. Butanol can be used in internal combustion engines. It has higher energy content, is more miscible with diesel, is less corrosive, and has a lower vapor pressure and flash point than ethanol. Butanol can also be used at higher blend levels with gasoline or even at 100% concentra­tion in car engines with little or no engine modification. Because of the solubility charac­teristics of butanol, it can be transported in existing fuel pipelines and tanks. Butanol can be produced by the fermentation route using renewable biomass. The low vapor pressure of butanol facilitates its use in existing gasoline supply lines. As opposed to ethanol — producing cultures, butanol-producing cultures (e. g., Clostridium acetobutylicum or Clostridium beijerinckii) can use both hexose and pentose sugars released during hydrolysis of lignocellulosic biomass. During World War I and World War II, butanol plants existed worldwide, including those in the United States, the former Soviet Union (Russia), Canada, China, Japan, Australia, India, Brazil, Egypt, and Taiwan. As a result of various technologi­cal developments, attempts are being made to revive commercial production of butanol from agricultural residues for both chemical and biofuel use.

One of the major problems associated with bioproduction of butanol is the cost of substrate, which has led to recent interest in the production of butanol from alternative, inexpensive materials. However, much of the proposed alternative substrates, such as corn stover and fiber, wheat and rice straw, or dedicated energy crops such as switchgrass and Miscanthus, present challenges that need to be overcome before they can be used as commercial substrates for butanol production. The chapter by Thaddeus Ezeji and Hans Blaschek details the butanol pathway, including pretreatment and hydrolysis; generation of lignocellulosic degradation products; effects of degradation products on growth and butanol production by fermenting microorganisms; and strategies for improved utilization of lignocellulosic hydrolysates.

Most bacteria use glucose as a preferred carbon source for growth, and only when glucose is limiting are the pentose sugars utilized, making fermentation of complex mixture of sugars in lignocellulosic hydrolysates challenging. The solventogenic acetone-butanol-ethanol (ABE)-producing clostridia have an added advantage over many other cultures in that they can utilize both hexose and pentose sugars, which are released from wood and agricultural residues upon hydrolysis in order to produce ABE. Pretreatment can result in the formation of a complex mixture of microbial inhibitors that are detrimental to growth of fermenting microorganisms. Options for the reduction or elimination of lignocellulosic degradation products during pretreatment include the removal of inhibitors prior to fermentation, develop­ment of inhibitor-tolerant mutants, or a combination of the above approaches. The develop­ment of inhibitor-tolerant mutants via culture adaptation appears to be the most viable approach from an economic standpoint, a research area in which the authors are currently involved.

Largus T. Angenent and Norman R. Scott discuss practical aspects and future directions for methane production from agricultural wastes. Anaerobic digestion is a proven technol­ogy for bioconversion of agricultural waste that is high in organic material to gaseous biofuel. It provides an efficient energy recovery system because methane and carbon dioxide are automatically and constantly removed from the process by degassing (bubble formation). Intermediate products in the food chain are converted into methane with very low concen­trations of carboxylic acids in the digester effluent and hydrogen in the off gas. While methane formation is a remarkable conversion process that circumvents product inhibition, it is susceptible to instabilities. This chapter discusses the anaerobic digestion of mixed cultures in which the waste material can be complex and variable in composition over the operating period. Practical studies assess the performance, stability, and limitations of methane fermentation, and the economic or environmental benefits in the conversion of agricultural residues.

In addition, upgrading the energy carrier methane to more valuable products may be neces­sary to guarantee economical viability. With the need for co-digestion, an opportunity exists to link agriculture, rural communities, and industry for sustainable rural community develop­ment, providing a number of specific case studies. A U. S. example for this system approach is BioTown in Richmond, Indiana, where the goal is to create an energy self-sufficient community using an anaerobic digester as an integrated technology to create biogas from animal manures, food wastes, organic municipal wastes, and crop residues. Communities such as these illustrate that anaerobic digestion is a significant and working technology with relatively high-energy efficiencies and that agricultural wastes play an essential role in such systems. Anaerobic digestion of agricultural wastes is a mature technology with numerous full-scale digesters all over the world. Even though the level of maturity is high, research on reactor stability is necessary. More powerful techniques, such as metagenomics and stable — isotope probing, are starting to shed light on our understanding of anaerobic digestion. For wastes from agriculture with complex nutrient and water cycles, anaerobic digestion should be seen in the larger context of an integrated system in which nutrients and water from digester effluent are continuously recycled.

The chapter by Edward A. Bayer, Raphael Lamed, Bryan A. White, Shi-You Ding, and Michael E. Himmel addresses the current status of knowledge regarding the function of cel — lulases and cellulosomes, and how they might be used in biomass conversion to biofuels. This includes a description of various types of cellulosic biomass in agricultural wastes and the pretreatment strategies required to enhance enzymatic hydrolysis and to avoid toxic by­products that would interfere with enzyme action and fermentation. The search for novel enzymes, and strategies for mutation and modification of cellulases and cellulosomes for future application to bioenergy initiatives are considered as well. Some of the bottlenecks and pitfalls in providing efficient processes for conversion of cellulosic biomass to ferment­able sugars for biofuels production are addressed. To develop successful future bioconversion processes, it is promising to mimic the concerted action of the cellulolytic microbes, the bacteria, and fungi that have evolved to produce cellulases and cellulosomes.

Structural biomass is a rich and renewable source of fermentable sugars for industrial production of biofuels. In attempting to utilize polysaccharides in lignocellulosic carbohy­drates at the commodity scale, one must consider a key principle set forth in the evolutionary development of the cell wall of terrestrial plants, namely essential recalcitrance to deconstruc­tion. The major bottleneck in this process is the deconstruction of the plant cell wall, liberating both C6 and C5 sugars. Nature has evolved microbes and their enzymes to deal primarily with damaged and decaying vegetation. Progress is being made in this endeavor, although the key cost challenges remain the subject of considerable international research focus today. New and improved enzyme systems closely coupled to related process technologies, such as biomass pretreatment, are required to provide cost — effective and large — scale quantities of liquid fuels from biomass.

Syed Shams Yazdani, Anu Jose Mattam, and Ramon Gonzalez describe the production of fuel and chemicals from glycerin (or glycerol) that is generated as an inevitable byproduct during the biodiesel production process, as well as at oleochemical and bioethanol production plants. Due to the tremendous growth in the biofuels industry, glycerin is now regarded as a waste product that needs to be disposed at a cost. Glycerol is not only abundant and inex­pensive, but also offers the opportunity to produce fuels and reduced chemicals at yields higher than those obtained with the use of common sugars. Anaerobic fermentation converts abundant and low-priced glycerol streams generated in the production of biodiesel into higher-value products and represents a promising route to achieving economic viability in the biofuel industry. A number of organisms are able to ferment glycerol and synthesize products with a wide range of functionalities. There are many advantages for the use of glycerol over sugars, which together translate into lower capital and operational costs.

As the chapter shows, there are few organisms that are able to utilize glycerol in the absence of external electron acceptors and that produce high-value chemicals such as 1,3-propanediol, succinic acid, propionic acid, and biosurfactant. In their recent studies, the authors have discovered that Escherichia coli can fermentatively metabolize glycerol and have established the pathways, mechanisms, and conditions enabling this metabolic process. The knowledge base created by the authors has opened up a new platform to engineer E. coli for the produc­tion of several fuels and chemicals, including the production of ethanol along with coproducts hydrogen and formate at high yields and productivities.

Commercial scale utilization of lignocellulosic biomass is not a trivial task and is quite different from the use of grain. As Klein E. Ileleji, Shahab A. Sokhansanj, and John S. Cundiff show, farm-gate to plant-gate delivery of lignocellulosic feedstocks from plant biomass for biofuel production is a key cost factor. The logistics and handling cost of feedstock can be very expensive and is one of the major reasons for the high cost of producing liquid fuels and power from lignocellulosic feedstocks. While diverse types of biomass may be chemi­cally similar, they are quite different with respect to their times of harvest/collection and physical characteristics. This means the unique differences of these feedstocks need to be considered when designing an effective biomass logistics system. Harvest is followed by transportation to on-farm storage, preprocessing, or biorefinery plants. Sustainable supply of feedstock from on — farm storage must be delivered to the biorefinery plant year round. To minimize costs, the design, operation, and coordination of efficient feedstock delivery systems is vital.

The chapter compares three herbaceous biomass logistic systems (cotton, sugarcane, and grain) with a woody biomass system (fuel chips) and explores the linkage between harvesting, in-field hauling, and over-fhe-road hauling. In all short-haul systems, truck productivity is maximized when the load time and unload time is minimized. Given the variability of field conditions, logistic systems must provide for efficient flow of material into and out of at-plant storage, which is critically important for any plant that has a high cost penalty for shutdown. Typically, the feedstock cost constitutes one-third to one-half of the total production cost of ethanol or power, where the actual percentage depends upon biomass species, yield, location, climate, local economy, and the type of systems used for harvesting, gathering and packaging, processing, storing, and transporting of biomass as a feedstock.

A logistic system for forage chopping has basically the same challenges as the sugarcane system, but as the authors note, it is not practical in the United States to have several hundred farmers chopping biomass and delivering on their own schedule to the bioenergy plant. Baling provides a disconnect between the harvest and in — field operations, which is a significant advantage. One operator can bale an entire field with no requirement to coordinate with any other operation. A systems integration approach is increasingly important to design systems and analyze pathways along the whole supply chain, including harvest, storage, and transport. A systems approach examines the complete system to see what processes can be combined for synergy of resources, reduction in waste, and cost reduction. An integrated approach seeks to combine multiple tasks, for instance, by harvesting grain and fiber together and subse­quently separating them. Systems integration also helps to overcome bottlenecks and lack of close collaboration, which allows everyone to see the bigger picture of how everything fits in place and harness the optimal strengths of the complex production chain as a whole.

Numerous opportunities exist to make ethanol plants more productive by reducing waste and expanding the diversity of both inputs and outputs. According to Timothy C. Lindsey’s assessment, byproducts and wastes from other industries such as food processing, landscap­ing, paper, and municipal solid waste facilities could be substituted for crops as feedstocks and processed into ethanol and other high-value products, thereby reducing the strain on food resources. A wide variety of cellulose — based biomass wastes and byproducts is available for conversion to biofuels, including agricultural residues (corn stalks and cobs, straws, cotton gin trash, and palm oil wastes); paper (paper mill sludge, recycled newspaper, and sorted municipal solid waste); wood waste (sawdust, wood chips, and prunings); and landscape waste (leaves, grass clippings, and vegetable and fruit wastes). Most of these materials are available at very low cost and some even command tipping fees associated with their disposal as wastes. This chapter points out that the United States currently converts approximately 15 million tons of agricultural products into ethanol and biodiesel, and discards approximately 270 million tons of agriculturally derived residues in the form of harvestable crop residues, animal manure, forest residues, and the organic fraction of municipal solid wastes.

This contribution describes two incremental opportunities and modifications for imple­menting existing technology that would enable expansion of existing dry-mill ethanol opera­tions to biorefineries with respect to feedstocks and products. Modification of existing processes to incorporate cellulosic feedstocks into existing operations could greatly improve the diversity and flexibility of feedstock options. Recovery of oil from byproducts such as germ, thin stillage syrup, or dried distillers’ grains and solubles (DDGS) could expand greatly the quantities and value of products produced from dry-mill plants and also provide valuable feedstock options for biodiesel producers. The DDGS could be further fractionated to separate and pelletize high-protein/high-value components from lower-value materials.

Furthermore, cogeneration systems could be implemented to burn lignin and other coproducts to simultaneously produce steam and electricity, thereby reducing requirements from external sources and providing electrical power for additional biorefining operations. Ethanol is an important industrial ingredient and has widespread use as a base chemical for other organic compounds (e. g., ethyl halides, ethyl esters, diethyl ether, acetic acid, buta­diene, and ethyl amines) that could provide unique opportunities for expanding operations in the future.

Emphasizing that cellulosic biomass is an inexpensive and abundant resource to collect and store large-scale solar energy, Bin Yang, Yanpin Lu, and Charles E. Wyman demonstrate that agricultural residues are particularly promising for initial commercial applications because of their potential low cost and near-term availability. Because feedstock costs are dominant in processing economics, it is critical to seek those for first applications that are low cost and sufficiently abundant. High product yields and ease of processing are also vital to minimizing costs, while sufficient amounts must be available to achieve reasonable econo­mies of scale. Agricultural residues are expected to serve as a major biofuels feedstock, and their potential low cost and current availability can be particularly important in the near term.

The rapidly evolving tools of biotechnology can significantly lower conversion costs and enhance yields, making biological processing a particularly promising approach to converting these solids into liquid fuels and chemicals and providing environmental, economic, and strategic benefits. The most expensive processing step is the breakdown of cellulosic materials into cellulose and hemicellulose to release fermentable sugars, while pretreatment has per­vasive impacts on all other major operations.

This chapter summarizes estimated amounts of major agricultural residues and their poten­tial for making ethanol, including environmental factors that determine their availability, composition, and reported yields. Emphasis is given to approaches, needs, and costs for harvesting, transporting, and storing agricultural residues with only little degradation of the feedstock. The economics of processing residues to ethanol demonstrates the importance of feedstock composition, availability, and cost to good returns on capital. Finally, opportunities and strategies for advanced technologies to lower the cost of biological processing to ethanol and other products are outlined. In estimating the potential for large-scale fuel production, consideration must be given to how much can be removed without negative environmental consequences such as depletion of soil carbon and soil erosion.

Selection of low-cost residues can be particularly important for overcoming the many obstacles to implementation of cellulosic ethanol technology. According to the authors, these include perceived risks and the associated high rates of return on capital, overdesign to com­pensate for risk, suboptimal facility sizes that keep investment costs lower but fail to capital­ize on economies of scale, and other disadvantageous burdens. Taking advantage of other economic levers such as integration of production of valuable coproducts from lignin, miner­als, or other components into an existing fermentation or power facility to reduce capital costs, and use of low-cost debt financing through partnerships with municipalities or others can have a tremendous impact on commercial success. Government assistance could prevent the private sector from bearing huge investments and make sure that projects are economi­cally viable. Once in place, significant learning curve improvements and technology advances would lower costs to make them competitive without government support.

Yuanhui Zhang analyzes thermochemical conversion (TCC) processes of biomass, includ­ing gasification (e. g., Fischer-Tropsch process), direct liquefaction, hydrothermal process, and pyrolysis. TCC is a chemical reforming process of biomass in a heated and usually pres­surized, oxygen — deprived enclosure, where long — chain organic compounds (solid biomass) break into short-chain hydrocarbons such as syngas or oil. Gasification of biomass produces syngas, a mixture of hydrogen and carbon monoxide that is then reformed into liquid oil with the presence of a catalyst. Pyrolysis is a heating process for converting dried biomass to syngas and oil in the absence of oxygen.

Hydrothermal processes (HTP) of various biomass feedstocks, including biowaste (manure and food processing waste), lignocellulose (crop residue), and algae, involves direct liquefac­tion of biomass, with the presence of water and perhaps some catalysts, to directly convert biomass into liquid oil. HTP mimics the natural process of fossil fuel formation from biomass feedstocks and holds great promise as a renewable energy technology, especially for liquid fuel. Converting biowaste materials into liquid fuel through HTP holds several unique advan­tages. Using biowaste has a net-zero carbon emission and provides a negative-cost feedstock that does not compete with the food supply.

During the deconstruction process, the natural protection mechanisms of biological systems to foreign intrusions have created tremendous obstacles for the economical production of biofuels. It is precisely for this reason why a large-scale production of biofuel from renew­able sources represented by biomass is still a challenge to the scientific and engineering communities. As Bin Wang and Hao Feng describe, among the restrictive factors is the generation of inhibitory chemicals during the deconstruction process, with either a chemical, enzymatic, or biological process. Inhibitory compounds will reduce the solvent production ability of a fermenting organism, or even totally block the growth and metabolism of the cells. A detoxification step may be used to remove the inhibitors or mitigate their negative effect before fermentation, based on chemical, physical, or biological methods. In this chapter, the technical aspects of the detoxification approaches are discussed with a focus on alternative detoxification methods as well as their potential applications in biomass—o-fuel production.

When on day 23 of the operating period the mixing duration was changed from intermittent to continuous mixing, continuous mixing resulted in a higher biomass level in the effluent (12gVS/L) compared with an effluent biomass level of 8 gVS/L for the control reactor (Figure 4.5B) due to an increase in the SVI of the washed out biomass from 27 to 37 mL/gTS (the SVI of the biomass in the reactor increased from 15 to 19 mL/gTS; Angenent et al. 2001). Even though some biomass loss became apparent, the biomass concentration in the reactor stabilized to a level of 22gVS/L compared with 29gVS/L (Figure 4.5B) and stable reactor conditions prevailed with similar soluble COD and total volatile fatty acid (VFA) concentra­tions compared with the control reactor. After a steady- -tate biomass concentration was achieved in the bioreactors, the VMPR was slightly lower for the continuously mixed biore­actor compared with the intermittently mixed control (1.7 vs. 1.9 L/L/day; Figure 4.5A) due to a slightly lower VS removal efficiency in the continuously mixed bioreactor (related to a higher VS level in the effluent). In addition, the relative 16S rRNA levels for the predominant acetoclastic methanogens Methanosaeta concilii and the predominant hydrogenotrophic methanogens from the order Methanomicrobiales had only decreased somewhat in the con­tinuously mixed digester (but had stabilized) compared with the control reactor (Figure 4.5C, D). Thus, the change in mixing duration for the ASBR deteriorated the performance slightly with lower VS removal efficiencies, but did not jeopardize the methanogenic com­munity structure or the stability. This result shows that intermittent gentle mixing is advanta­geous, and indicates that continuous mixing is not required for efficient conversion in high-rate anaerobic digesters, and, in fact, reduced the methane yield. Noteworthy is that during the gentle mixing period the concentrations of the methanogenic populations were much lower in the effluent biomass compared with the reactor biomass (Figure 4.5C, D). This is another advantage of high-rate anaerobic digester systems.

During the 24-hour feeding cycle (ASBRs were fed instantly at t = 0), the shape of the cumulative biogas production curves were similar between the intermittently and continuously mixed bioreactors at gentle mixing conditions with a lower slope at the end of the cycle (Figure 4.6A). This confirms the previous conclusion that reactor stability was not

jeopardized during continuous/gentle mixing. The shapes of the cumulative production in both bioreactors show a lag period with a relatively low biogas production rate just after feeding and then a maximum rate (i. e., slope) between 1 and 3 hours after feeding, corre­sponding to a higher acetate concentration in the mixed liquor between 600 and 1000mg/L (Figure 4.6B, C). The lowest biogas production rates were observed at the end of the 24-hour cycle when the acetate concentration was ~100mg/L in both systems (Figure 4.6B, C). Some differences were noticed between the cumulative curves of the two bioreactors (no difference was observed when both reactors were intermittently and gently mixed), because the rate of biogas production was faster ~1 hour after feeding for the continuously mixed bioreactor versus the control bioreactor (Figure 4.6A), indicating minor diffusion limitations in the intermittently mixed reactor. After 4 hours in the cycle, however, the cumulative biogas production in the intermittently mixed bioreactor had caught up with the continuously mixed bioreactor due to a higher maximum rate between 1 and 3 hours after feeding swine waste (Figure 4.6A). The maximum biogas production rates (slope) matched the location of the maximum acetate concentration, which occurred for the continuously mixed reactor after ~1 hour (660 mg/L) and for the intermittently mixed control reactor after ~2 hours (1015mg/L; Figure 4.6B, C). This result shows that mixing duration affects the function of the anaerobic food web for high-rate anaerobic digestion.

Glycerol can be converted into higher value products by either biological or chemical trans­formations. Biological conversions are generally preferred to chemical conversions because biological conversions have higher reaction specificities, lower reaction temperatures and pressure, and fewer chemical contaminants than chemical conversions. Crude glycerol gener­ated via biotransformations can be used as a carbon source for other microbial fermentations. The carbon atoms in glycerol molecules are highly reduced, and the conversion of glycerol to glycolytic intermediates generates twice the amount of reducing equivalents generated by glucose or xylose metabolism. For example, conversion of 1 mol of glycerol (a three-carbon molecule) to phosphoenol pyruvate (PEP) or pyruvate generates 2 mol of NADH, while conversion of 0.5 mol of glucose (a six-carbon molecule) or 0.6 mol of xylose (a five-carbon molecule) to PEP or pyruvate generates only 1 mol of NADH. As a result, yields of fuels and chemicals are higher when synthesized from glycerol than monosaccharides.

Uptake of glycerol across the cytoplasmic membrane by cells can occur via facilitated diffusion and active transport. In E. coli, the uptake of glycerol is through facilitated diffu­sion, mediated by an integral membrane protein, the glycerol facilitator GlpF (Heller et al. 1980; Voegele et al. 1993) . This intracellular glycerol is phosphorylated by the glycerol kinase and the glycerol-3-phosphate formed remains trapped inside the cell. In S. cerevisiae, the uptake of glycerol is mediated by either facilitated diffusion or active transport (Wang et al. 2001).

Although glycerol is commonly used by many microorganisms under aerobic condition, the highly reduced nature of glycerol can be exploited for the production of numerous bio­products. Few members of the Enterobacteriaceae family such as Citrobacter freundii (Homann et al. 1990) and Klebsiella pneumoniae (Forage and Foster 1982; Biebl et al. 1998) have been reported to ferment glycerol in a 1,3-propanediol (1,3-PDO)-dependent manner. Species such as Clostridium pasteurianum (Luers et al. 1997) Biebl 2001), Clostridium butyricum (Biebl 1991), Enterobacter agglomerans (Barbirato et al. 1996), Enterobacter aerogenes (Ito et al. 2005), and Lactobacillus reuteri (Talarico et al. 1990) have also been reported to ferment glycerol. A brief summary of the fermentation products of crude glycerol is given in Figure

Having enough storage space to maintain the minimum level of inventory (10 days) is vital to how much a facility can store on site. The quality of space and level of automation of the handling systems can greatly affect feedstock logistics. While some advocate that outdoor storage is adequate for biomass, this statement cannot be generalized as a rule of thumb, as

(b)

was earlier pointed out for the outdoor storage of corn cobs. Poorly stored feedstocks in outdoor storage will biodegrade more rapidly than indoor storage. Biodegradation of feed­stock could result in nutrient variability in the feedstock that will negatively affect conversion, handling challenges in conveying and processing, and potential fire and health hazards because of spontaneous combustion and inhalation of mold spores from deteriorating biomass. In general, woody feedstocks are more favorable to outdoor storage than herbaceous biomass. Figure 7.9a, b provides a good pictorial comparison of indoor stored bales of plant biomass and outdoor pile subject to deterioration by inclement weather.

HTL is similar to the geological processes that produced the fossil fuels used today, except that the technological process occurs in a time frame measured in minutes instead of geo­logical time. HTL is a chemical reforming process of biomass in a heated and usually pres­surized, oxygen deprived enclosure, where long-chain organic compounds (solid biomass) break into short — chain hydrocarbons. All fossil fuels found in nature—petroleum, natural gas, and coal, based on biogenic hypothesis—are formed through HTLs from biomass buried beneath the ground and subjected to high temperature and pressure. Simple heating without water (pyrolysis or anhydrous pyrolysis) has long been considered to take place naturally during the catagenesis of kerogens to form fossil fuels. In recent decades, it has been found that water under pressure causes more efficient breakdown of kerogens at lower temperatures than without it (Siskin and Katritzky 1991; Pennisi 1993). The carbon isotope ratio of natural gas also suggests that hydrogen from water has been added during creation of the gas, in addition to the formation of oil. The state of fossil fuels (solids, liquid, or gaseous) depends
on the composition of feedstocks and environmental conditions, including temperature, pres­sure, retention time, and presence of particular catalysts.

The exact pathways of HTL to produce crude oil from biomass remain unclear, and addi­tional research is needed. The following examples may give some hints of possible pathways of HTL of bio-waste feedstock. In a study by Appell et al. (1975) , one of the mechanisms for the conversion of carbohydrates into oil that was consistent with the results they obtained was as follows:

Sodium carbonate reacts with carbon monoxide and water to yield sodium formate:

Na2CO3 + 2CO + H2O ^ 2HCO2Na + CO2

Vicinal hydroxy groups in the carbohydrates undergo dehydration to form an enol followed by isomerization to a ketone:

H H H H H H

II I I II

—C_C_ * _C_C_ * _C_

O O O HO

H H H

The newly formed carbonyl group is reduced to the corresponding alcohol with formate ion and water:

The hydroxyl ion then reacts with additional carbon monoxide to regenerate the formate ion.

OH — + CO ^ HCO2-

A variety of side reactions may occur and the final product is a complex mixture of com­pounds. One of the beneficial side reactions occurs in alkaline conditions. Carbonyl groups tend to migrate along the carbon backbone. When two carbonyl groups become vicinal, a benzylic type of rearrangement occurs, yielding a hydroxy acid. The hydroxy acid readily decarboxyl — ates causing a net effect of reducing the remainder of the carbohydrate derived molecule.

This type of reaction is beneficial to HTL because it leads to the formation of paraffin-type structures, which has less oxygen than the original compounds. In addition, the reaction happens by disproportionation and does not require any additional reducing agent.

Aldol condensation may also be part of the reaction process. Aldol condensation occurs between a carbonyl group on one molecule and two hydrogens on another molecule with the elimination of water. The condensation product is a high-molecular weight compound typi­cally with high viscosity. Condensation reactions become a major pathway in the absence of reducing agents such as carbon monoxide and hydrogen. Reducing agents keep the carbonyl content of the reactant system sufficiently low so that liquid instead of solid products are formed.

In a study by Appell et al. (1980), the authors believed that the free hydrogen radical (H), not the hydrogen molecule (H2), participates in the chemical conversion reactions. Thus, they concluded that the addition of carbon monoxide (CO) to the process was more efficient than the addition of hydrogen gas. Based on the water-gas shift reaction, carbon monoxide reacts with water to form carbon dioxide and two hydrogen radicals.

C=O + H-O — H O=C=O + 2H •

In the presence of the hydrogen radicals, the oxygen is removed from the compounds containing carbonyl and hydroxyl groups, then form paraffin and water. A possible pathway is described in the following four reactions (He 2000).

O

I II II

— C—C— + 2H — — ► —C = C— + H2O

Hydroxyl group

The complexity of the chemical reactions involved in HTL can be attributed to the complex composition of feedstocks. According to Chornet and Overend (1985) and Vasilakos and Austgen (1985), some of the reactions that may be involved in the liquefaction of carbonaceous materials are cracking and reduction of polymers such as lignin and lipids, hydrolysis of cellulose and hemicellulose to glucose and other simple sugars, hydroge — nolysis in the presence of hydrogen, reduction of amino acids, reformation reactions via dehydration, decarboxylation, C-O and C-C bond ruptures, and hydrogenation of functional groups.

Noting that water goes into a gaseous phase at 100°C, hot water pretreatment is a process in which pressure is used to maintain water in a liquid state at high temperatures (140-230°C) as water comes into contact with biomass. The major objective of hot water pretreatment is to wet and solubilize lignocellulosic biomass components especially hemicellulose and make the cellulose component accessible to hydrolytic enzymes. About 40%-60% of the total biomass is solubilized during hot water pretreatment, with 4%-22% of the cellulose, 35%- 60% of lignin, and all of the hemicellulose being removed (Mosier et al. 2005). LHW pre­treatment enhances the cleavage of o-acetyl and uronic acid from hemicellulose to generate acetic, ferulic, glucuronic, and other organic acids, which decreases the pH of lignocellulosic biomass hydrolysates. The structural and chemical changes that occur in lignocellulosic biomass during hot water pretreatment are aided by the presence of these acids in solution. These acids catalyze the formation of monomeric sugars from xylan, arabinan, galactan, mannan polymers as well as aldehydes such as furfural from xylose and 5-HMF from glucose (Ezeji et al. 2007b).

Edward A. Bayer, Raphael Lamed, Bryan A. White, Shi-You Ding, and Michael E. Himmel

Abstract

Some forms of agricultural residues represent an attractive resource for lignocellulosic biomass in our quest to reduce the dependence of the Western World on fossil fuels. After crops have been harvested, the residues usually represent relatively large amounts of cellu — losic material that could be returned to the soil for its future enrichment in carbon and nutri­ents. However, today, many believe that a substantial portion of these residues could be made available for further conversion to biofuels. Likewise, animal wastes, particularly from her­bivores and notably from ruminants, are high in cellulose content and can also be converted to liquid biofuels. Although such agricultural byproducts cannot compensate completely for the large volumes of liquid fuels required to sustain our transportation energy requirements, they can play a decisive local and regional role to fill these needs.

However, in this case, nature and mankind have different agendas. The challenge regarding cellulosic biomass is that cellulose plays a critical structural role in the terrestrial plant cell wall. Glucose, the most desirable plant sugar for fermentation, is incorporated within the cellulose microfibrils that make up the complex plant cell wall. The most successful future bioconversion processes for the production of biofuels from lignocellulose may indeed ulti­mately mimic the concerted action of the cellulolytic microbes, the bacteria, and fungi that have evolved to produce cellulases and cellulosomes. It is now very clear that the major bottleneck in this process—both from a biochemical and economical point of view—is the deconstruction of the plant cell wall, liberating both C6 and C5 sugars. Nature has evolved microbes and their enzymes to deal primarily with damaged and decaying vegetation. Ultimately, much of this plant matter is again converted to a form that can be incorporated into living plant tissue. Nature thus has the time needed to manage the plant biosphere with low-energy consuming processes that can be less than ideal. We, on the other hand, must deploy rapid, efficient, and most importantly, cost-effective conversion processes that will meet our future energy needs.

The present chapter deals with the current status of our knowledge regarding the function of cellulases and cellulosomes, and how we might use them in processes for biomass

Biofuels from Agricultural Wastes and Byproducts Edited by Hans P. Blaschek, Thaddeus C. Ezeji and Ju rgen Scheffran 67 © 2010 Blackwell Publishing. ISBN: 978-0-813-80252-7

conversion to biofuels. This includes a description of various types of cellulosic biomass in agricultural wastes and the pretreatment strategies required to enhance enzymatic attack and to avoid toxic byproducts that would interfere with enzyme action and fermentation. The effects of treatment with free cellulases versus treatment with cellulosomes are also detailed. The natural cellulases and cellulosomes, their various families, modular, and subunit archi­tectures, are all documented. The search for novel enzymes, and strategies for mutation and modification of cellulases and cellulosomes for future application to bioenergy initiatives are considered as well. We address some of the bottlenecks and pitfalls that await us in our current and future efforts to provide efficient processes for conversion of cellulosic biomass to usable sugars for biofuel production.

Introduction

Lignocellulosic biomass has long been recognized as a potential low-cost renewable source of mixed sugars for fermentation to fuel ethanol (Lynd et al. 1991; Wheals et al. 1999; Lynd et al. 2002; Dien et al. 2003; Demain et al. 2005 ; Ragauskas et al. 2006; Schubert 2006; Himmel et al. 2007; Wall et al. 2008). One approach would be to degrade plant cell wall cellulose and hemicellulose to soluble sugars using severe chemistries, prior to conversion to ethanol, but economic and environmental issues preclude such strategies. The more accepted alternative is to employ microbial cellulases and related enzymes to cell walls that have been conditioned thermally and chemically in a milder process, known as “pretreatment.”

Several technologies have been developed over the past century that allow this conversion process to occur (Figure 5.1) , yet the clear objective now is to make this process cost- competitive in today’s markets (Bayer et al. 2007). Perhaps the major bottleneck for

Agricultural

Residues

Figure 5.1. Major steps in conversion of plant cell wall biomass to biofuels. Following growth and harvesting of crops, the agricultural wastes are collected and transferred to a central processing facility. The pretreated plant cell wall material is used to grow cellulolytic fungal or bacterial cell cultures to produce large amounts of free sugars. Cellulolytic enzymes are also produced from the cells and are used to hydrolyze the pretreated biomass directly. Ethanogenic microbes (e. g., yeast or appropriate bacterium) are grown on the resultant sugars (glucose and other simple sugars), which results in the production of ethanol (or other fuels). The enzymatic breakdown of cellulose is the major bottleneck in the design of a cost-effective process.

conversion of biomass to ethanol is the high cost and low efficiency of the enzymes, the cellulases, and other glycoside hydrolases, which are capable of degrading crystalline cel­lulose and related plant cell wall polysaccharides. Efficient hydrolysis is impeded by limited accessibility of the enzymes and the recalcitrance of cellulose, owing to its extremely stable “microcrystalline” arrangement of the cellulose chains in the cell wall microfibrils.

The rate — l imiting step in the hydrolysis of cellulose is not the catalytic cleavage of the P-1,4 bond, but the disruption of a single chain of the substrate from its native crystalline matrix, thereby rendering it accessible to the active site of the enzyme. Single cellulolytic enzymes alone are generally incapable of efficient cellulose hydrolysis. The mode of action of the various cellulases is different, and they are known now to act synergistically. Consequently, the secret to potent enzymatic degradation of the recalcitrant substrate is embedded in the knowledge of how these different types of enzymes work together.

This chapter describes the status of cellulases and cellulosomes en route to the efficient degradation of cellulosic biomass for the production of biofuels. We discuss the nature of cellulosic biomass in agricultural residues, various pretreatment strategies, and their effects on the microorganisms. We also discuss cellulolytic microorganisms, the various enzyme systems for biomass deconstruction, and future approaches for agricultural biomass decon­struction, while focusing on the production of soluble sugars. In doing so, we deem other topics as beyond the scope of the present chapter, notably microbial fermentation of soluble sugars to biofuels (Jeffries 2006; Hahn-Hagerdal et al. 2007a), metabolic engineering of bacteria, fungi, or yeast (Zhang et al. 1995; Hahn-Hagerdal et al. 2007b), and consolidated bioprocessing of cellulosic biomass directly to biofuels (Lynd et al. 2005; van Zyl et al. 2007; Lynd et al. 2008).

Klein E. Ileleji, Shahab Sokhansanj, and John S. Cundiff

Abstract

This chapter presents the logistics of delivering cellulosic biomass feedstock from the farm gate to the plant gate. Unlike the more familiar starchy feedstock and oilseed such as corn and soybean, which can be cost-effectively delivered to the plant gate for processing at the commercial scale, cellulosic biomass presents unique handling challenges at the commercial scale, which make them expensive to utilize. In the Introduction section of this chapter we discuss the essential components of the logistics chain and the unique logistical needs of lignocellulosic biomass as compared with starchy grain feedstocks. Then we discuss on-farm logistics of biomass harvest and delivery, which include biomass availability and distribution, harvest and collection, preprocessing operations, transport, economic, energy inputs, and carbon emissions. After that we discuss the logistics of handling feedstock at the plant gate, we examine the operations used in grain elevators, and we discuss the envisaged parallel operations that would occur in a biorefinery processing lignocellulosic biomass. Next we discuss related agricultural logistics operations (cotton harvest logistics, sugarcane harvest logistics, and fuel chip harvest logistics) and their application to biomass. A comparison of herbaceous fiber and grain logistics chain is also presented. The last section briefly presents a systems approach to feedstock logistics, discussing some unique opportunities to save cost and energy by integrating unit operations throughout the logistics chain.

Introduction

Lignocellulosic feedstocks from plant biomass such as grain plant residues (corn stover, wheat straw, rice straw, etc.), energy crops (switchgrass, canary reed grass, miscanthus, etc.), and wood (residues, wood chips, hybrid poplars and willows, etc.) are currently being inves­tigated for use in the production of second- generation advanced fuels (cellulose ethanol, FT-diesel, etc.) and for biopower either fired alone or co-fired with coal. As compared to

Biofuels from Agricultural Wastes and Byproducts Edited by Hans P. Blaschek, Thaddeus C. Ezeji and Ju rgen Scheffran 117 © 2010 Blackwell Publishing. ISBN: 978-0-813-80252-7

corn-grain-for-ethanol, their utilization for energy production does not compete with the demand for agricultural feedstocks such as grain for food and feed production. The increased production of corn ethanol in the United States has raised a number of concerns in recent times, the major one being the moral and social consciousness of using a food crop for fuel that could potentially drive up world food prices and create a hunger crisis in poor regions of the world. Another obvious reason for the use of lignocellulosics is because it would be practically impossible to produce the mandated fuel ethanol volumes with grain crops alone, even if the entire grain crop produced in the United States were converted to ethanol. Additionally, the Energy Independence and Security Act of2007 (WhiteHouse News Releases 2007) sets a mandatory Renewable Fuels Standard (RFS) for the production of 36 billion gallons of fuel ethanol by 2022, of which 15 billion must be produced from cellulose. While there is no commercial scale cellulose ethanol plant, there are commercial power plants in North America, Europe, and Asia that have some experience using biomass on a large scale.

Commercial scale utilization of lignocellulosic biomass is not a trivial task and is quite different from the use of grain. The logistics and handling cost of feedstock can be very expensive and is one of the major reasons for the high cost of producing liquid fuels and power from lignocellulosic feedstocks. In corn stover to ethanol production, feedstock and handling cost together can make up as much as 36% of the production cost (Ruth et al. 2002). The three diverse types of biomass mentioned previously, while chemically the same, are quite different in their times of harvest/collection, method, and physical characteristics. This means that the unique differences of these feedstocks need to be considered when designing an effective biomass logistics system. Once the feedstock is ready for harvest and collection, field machinery must be scheduled for harvesting the feedstock within a narrow window of opportunity usually from a few weeks to 3 months. Harvest is followed by transportation to on-farm storage, preprocessing, or biorefinery plants. Sustainable supply of feedstock from on farm storage must be delivered to the biorefinery year round to meet about 350 days of production schedule while maintaining an average of at least 10 days inventory at the biore­finery. The logistics of all these operations must be coordinated with the goal of delivering the least cost feedstock of the specified quality at the plant gate.

The design and operation of efficient feedstock delivery systems are vital to reducing the cost of feedstock/handling for commercial bioenergy production from lignocellulosics. Feedstock handling involves field harvest and collection, storage, preprocessing, transporta­tion and handling/delivery at the biorefinery. In the next two sections, we will discuss these operations in two segments: (1) field harvest/collection, preprocessing, and transport to the biorefinery and (2) handling/delivery of inbound feedstocks at the biorefinery. The third section will present the principles required for an efficient logistic system for biomass, illus­trated by several commercial operations making use of existing systems in U. S. agriculture. Finally, a systems integration approach will be presented as a way of approaching feedstock delivery by integrating it within the production system of the bioenergy conversion process.