BackgroundWhen producing biofuels from dedicated feedstock, agronomic factors such as harvest time and location can impact the downstream production. Thus, this paper studies the effectiveness of ammonia fibre expansion (AFEX) pretreatment on two harvest times (July and October) and ecotypes/locations (Cave-in-Rock (CIR) harvested in Michigan and Alamo harvested in Alabama) for switchgrass (Panicum virgatum).ResultsBoth harvest date and ecotype/location determine the pretreatment conditions that produce maximum sugar yields. There was a high degree of correlation between glucose and xylose released regardless of the harvest, pretreatment conditions, or enzyme formulation. Enzyme formulation that produced maximum sugar yields was the same across all harvests except for the CIR October harvest. The least mature sample, the July harvest of CIR switchgrass, released the most sugars (520 g/kg biomass) during enzymatic hydrolysis while requiring the least severe pretreatment conditions. In contrast, the most mature harvest released the least amount of sugars (410 g/kg biomass). All hydrolysates were highly fermentable, although xylose utilisation in the July CIR hydrolysate was poor.ConclusionsEach harvest type and location responded differently to AFEX pretreatment, although all harvests successfully produced fermentable sugars. Thus, it is necessary to consider an integrated approach between agricultural production and biochemical processing in order to insure optimal productivity.

Although cellulose is the most abundant organic molecule, its susceptibility to hydrolysis is restricted due to the rigid lignin and hemicellulose protection surrounding the cellulose micro fibrils. Therefore, an effective pretreatment is necessary to liberate the cellulose from the lignin-hemicellulose seal and also reduce cellulosic crystallinity. Some of the available pretreatment techniques include acid hydrolysis, steam explosion, ammonia fiber expansion (AFEX), alkaline wet oxidation, and hot water pretreatment. Besides reducing lignocellulosic recalcitrance, an ideal pretreatment must also minimize formation of degradation products that inhibit subsequent hydrolysis and fermentation. AFEX is an important pretreatment technology that utilizes both physical (high temperature and pressure) and chemical (ammonia) processes to achieve effective pretreatment. Besides increasing the surface accessibility for hydrolysis, AFEX promotes cellulose decrystallization and partial hemicellulose depolymerization and reduces the lignin recalcitrance in the treated biomass. Theoretical glucose yield upon optimal enzymatic hydrolysis on AFEX-treated corn stover is approximately 98%. Furthermore, AFEX offers several unique advantages over other pretreatments, which include near complete recovery of the pretreatment chemical (ammonia), nutrient addition for microbial growth through the remaining ammonia on pretreated biomass, and not requiring a washing step during the process which facilitates high solid loading hydrolysis. This chapter provides a detailed practical procedure to perform AFEX, design the reactor, determine the mass balances, and conduct the process safely.

Decentralized biomass processing facilities, known as biomass depots, may be necessary to achieve feedstock cost, quantity, and quality required to grow the future U.S. bioeconomy. In this paper, we assess three distinct depot configurations for technical difference and economic performance. The depot designs were chosen to compare and contrast a suite of capabilities that a depot could perform ranging from conventional pelleting to sophisticated pretreatment technologies. Our economic analyses indicate that depot processing costs are likely to range from ∼US$30 to US$63 per dry metric tonne (Mg), depending upon the specific technology implemented and the energy consumption for processing equipment such as grinders and dryers. We conclude that the benefits of integrating depots into the overall biomass feedstock supply chain will outweigh depot processing costs and that incorporation of this technology should be aggressively pursued.

Interest in commercially viable cellulosic biofuel production has greatly increased due to concerns regarding the sustainability of petroleum fuels. While research into solving the technical issues surrounding cellulosic biofuels is ongoing, much less attention has been paid to solving supply chain challenges such as low bulk density of cellulosic biomass, compositional variability and seasonality of the feedstock, food vs fuel issues, and local environmental concerns. To address these supply chain problems, we explore the concept of Regional Biomass Processing Depots (RBPDs), strategically distributed facilities that procure, pre-process /pre-treat and densify biomass into stable intermediate products that are compatible with existing bulk commodity logistical systems. In this perspective, we discuss the fundamental concept of RBPDs, their functionality, advantages, and potential challenges. We then extend the analysis of depots to include enhanced confi gurations and discuss some technologies that might be deployed in RBPD networks and the valuable coproducts that might be produced via synergies among these technologies. Current biomass supply system: problems and some prospective solutionsB iofuels are a near-term opportunity for the United States and the rest of the world to reduce or eliminate our reliance on petroleum for transportation. Currently, grain ethanol and oilseed biodiesel represent only a small fraction of US transportation use, but the addition of cellulosic biofuels could greatly increase this fraction. Th e Energy Independence and Security Act of 2007, for example, mandates the production of 16 billion gallons of cellulosic ethanol by 2022. A shift from petroleum-based fuels to biofuels would be a tremendous undertaking, requiring hundreds of billions in investment and large shift s in land use. Such a shift , however, would produce substantial benefi ts in 622

Miscanthus x giganteus is a tall perennial grass whose suitability as an energy crop is presently being appraised. There is very little information on the effect of pretreatment and enzymatic saccharification of Miscanthus to produce fermentable sugars. This paper reports sugar yields during enzymatic hydrolysis from ammonia fiber expansion (AFEX) pretreated Miscanthus. Pretreatment conditions including temperature, moisture, ammonia loading, residence time, and enzyme loadings are varied to maximize hydrolysis yields. In addition, further treatments such as soaking the biomass prior to AFEX as well as washing the pretreated material were also attempted to improve sugar yields. The optimal AFEX conditions determined were 160 degrees C, 2:1 (w/w) ammonia to biomass loading, 233% moisture (dry weight basis), and 5 min reaction time for water-soaked Miscanthus. Approximately 96% glucan and 81% xylan conversions were achieved after 168 h enzymatic hydrolysis at 1% glucan loading using 15 FPU/(g of glucan) of cellulase and 64 p-NPGU/(g of glucan) of beta-glucosidase along with xylanase and tween-80 supplementation. A mass balance for the AFEX pretreatment and enzymatic hydrolysis process is presented.

There is an intense ongoing debate regarding the potential scale of biofuel production without creating adverse effects on food supply. We explore the possibility of three land-efficient technologies for producing food (actually animal feed), including leaf protein concentrates, pretreated forages, and double crops to increase the total amount of plant biomass available for biofuels. Using less than 30% of total U.S. cropland, pasture, and range, 400 billion liters of ethanol can be produced annually without decreasing domestic food production or agricultural exports. This approach also reduces U.S. greenhouse gas emissions by 670 Tg CO 2 -equivalent per year, or over 10% of total U.S. annual emissions, while increasing soil fertility and promoting biodiversity. Thus we can replace a large fraction of U.S. petroleum consumption without indirect land use change.

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