How should the logistic system for a bioenergy plant be organized? It is appropriate to apply all that has been learned about the operation of existing biomass systems and develop a plan for a logistic system that can supply herbaceous biomass to a bioenergy plant operating 24/7, 47 weeks per year. A woody biomass system, the fuel chip system, is a commercial reality and has already been described.

For the sample calculations we assume that the bioenergy plant will process 25t/hour. Weekly demand is then

25 t/hours x 24 hours/day x 7 day/week = 42001.

Annual demand is

42001 week x 47 week/year = 197,4001

A truckload of fuel chips at 45% moisture content is about 12.4 dry t, thus it will require

4200 dryt week

= 339 trucks week

12.4 dry t/truck

If the receiving facility is open 5 days per week for 12 hours/day, the average operation will be 60 hours per week:

339 trucks week, ,

= 5 to 6 trucks hour

60 hours week

Average unload time will need to be around 10 minutes.

A truckload of sugarcane at 80% moisture content is about 4.9 dry t, thus it will require

4200 dry t week = 857 „ucks week

4.9 dry t/truck

If the receiving facility is open seven days per week for 12 hours/day, the average opera­tion will be

857 trucks week ^ , ,

= 10 trucks hour

84 hours week

Average unload time will need to be about 6 minutes if the plant operates with only one unload station. Note that this comparison does not use the four-bin-load with two bins on the truck trailer and two on a second trailer.

As a physicochemical process, adsorption involves the mass transfer of a solute (adsorbate) from a fluid phase to an adsorbent surface through weak atomic and molecular forces (physi­cal adsorption) or through weak chemical bonds (chemical adsorption). For a chemical adsorption, the adsorbate forms a monolayer on the surface of the adsorbent. Chemical adsorption methods for detoxification include the use of zeolite (Eken-Saragoglu and Arslan 2000), eartomaceous earth (Ribeiro et al. 2001), activated charcoal (Silva and Roberto. 2001), wood charcoal (Miyafuji et al. 2003), diatomacenous earth (Ribeiro et al. 2001), polymeric adsorbents (Weil et al. 2002), mixed bed resin (Tran and Chambers 1986), and ion-exchange resins (Sarvari Horvath et al. 2004; Chandel et al. 2007).

Zeolites are widely used as ion-exchange beds in domestic and commercial water purifica­tion, softening, and other applications. Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+, and others, which are loosely held and can readily be exchanged in a contact solution. Eken-Saragoglu and Arslan (2000) conducted detoxification tests with CaO and combinations with zeolite during ethanol production from corn cob hemicellulose hydrolysate by Pichia stipitis and Candida shehatae. They found that the single neutralization method did not support high ethanol production (2.8 g/L) during fermentation of hydrolysates by C. shehatae with only 2.8 g/L ethanol obtained. However, neutralization + zeolite treatments significantly increased final ethanol concentration to approximately 6.0 g/L.

In the study of Maddox and Murray (1983) , fermentation of crude hydrolysate of Pinus radiata by Clostridium acetobutylicum was not successful. After a decolorization or a steam­stripping detoxification treatment, the n-butanol fermentation was still not successful. However, a combination of the two gave a butanol concentration of up to 1.6 g/L. When activated carbon (150 g/L) was added to the hydrolysate, about 30% sugar was removed from the hydrolysates. Maddox and Murray also used anion and cation exchange resins to remove inhibitory compounds. They observed a butanol concentration of 5.7 g/L after the fermenta­tion, which represented a yield of 17% based on sugar utilized. Wood charcoals were also tested for removal of inhibitors such as furan and phenolic compounds in wood hydrolysates (Miyafuji et al. 2003). Wood charcoals prepared at various temperatures were found to selectively remove only the inhibitors without reducing the levels of fermentable sugars. A wood charcoal treatment with a wood charcoal weight to hydrolysates ratio of 0.07 could enhance the fermentation of wood hydrolysates (Miyafuji et al. 2003). The wood charcoals prepared at higher temperatures had enhanced ability to remove inhibitors, compared with wood charcoals prepared at lower temperatures (Miyafuji et al. 2003).

Polymeric adsorbents can also be used to remove aldehydes, such as furfural, that inhibit fermentation. Weil et al. (2002) investigated the removal of furfural from a biomass hydro­lysate using XAD-4 and XAD-7. The XAD-4 showed higher specificity for furfural removal than XAD — 7, and it also had little interaction with glucose. The fermentation of XAD-4- treated hydrolysate with E. coli K011 was nearly as rapid as the control medium that was formulated with sugars of the same concentration. Liquid chromatographic analysis showed that furfural concentrations were less than 0.01 g/L compared with the initial concentrations that were in the range of 1-5 g/L. The fermentation of the resulting biomass hydrolysate also confirmed that the concentration of furfural in the hydrolysate caused negligible inhibition (Weil et al. 2002).

Tran and Chambers (1986) compared a molecular sieve detoxification treatment with a mixed bed ion resin treatment. The molecular sieve method decreased the concentration of xylose, acetic acid, and furfural by 10%, 40%, and 82%, respectively. The mixed bed ion resin treatment, to a lesser extent, removed 7% of xylose, 20% of acetic acid, and 20% of furfural. Molecular sieve treatment produced higher ethanol (9.9 g/L) upon fermentation than mixed bed resin treatment of lignocellulosic hydrolysates (8.0g/L).

Ion exchange resin treatment is one of most efficient methods for lignocellulosic hydro­lysates detoxification (Larsson et al. 1999) . Wooley et al. ( 1999) used weak base resins (Amberlyst A20, Rohm & Haas, Paris, France) to treat dilute — acid- pretreated poplar and reported 88% removal of acetic acid and a 100% sugar recovery. Nilvebrant et al. (2001) tested the effects of an anion exchanger (AG1-X8, BioRad Laboratories, Richmond, CA), a cation exchanger (AG50 W-X8, BioRad Laboratories), and plain resins (XAD-X8, BioRad Laboratories) on detoxification of dilute-acid-pretreated spruce and fermentation by baker’s yeast. For ethanol productivity, the performance of the resins was in the sequence of AG1-X8 > XAD-X8 > AG50-X8. Sarvari Horvath et al. (2004) compared six different anion-exchange resins with different properties for detoxification of a hydrolysate from dilute-acid-pretreated spruce. The resins tested were featured by styrene-, phenol-, and acrylic-based matrices and strong as well as weak functional groups. Fractions of the hydrolysate were collected and analyzed for fermentable sugars and inhibitors, and the effect on the fermentability was evaluated using S. cerevisiae. An initial adsorption of glucose was found to occur in the strong alkaline environment, leading to glucose accu­mulation in the resin at a later stage. The fractions collected from strong anion-exchange resins with styrene-based matrices displayed the best fermentability: a sevenfold increase in ethanol productivity compared with untreated hydrolysate. The fractions from a strong anion exchanger with acrylic-based matrix and a weak exchange with phenol-based resin displayed an intermediate improvement in fermentability, a four — to fivefold increase in ethanol productivity. The fractions from two weak exchangers with styrene — and acrylic — based matrices displayed a twofold increase in the productivity. Phenolic compounds were more efficiently removed by resins with styrene — and phenol-based matrices than by resins with acrylic-based matrices. Volumetric productivity and ethanol yield increased after treatment with all six resins. The volumetric productivity in the reference fermentation, 2.2g/L/h, was eight times higher than in the untreated hydrolysates. The volumetric pro­ductivity in the anion-exchange-treated samples was two to seven times higher than in the untreated hydrolysate. For all adsorption-based detoxification methods, the reuse or recovery of the adsorbate will determine the economics and viability of the process.

Largus T. Angenent and Norman R. Scott

Abstract

Anaerobic digestion is a proven technology for bioconversion of agricultural wastes that are high in organic material. This engineered process with an undefined mixed microbial culture is based on the carboxylate platform (i. e., intermediates are channeled through short-chain fatty acids). The advantage of a mixed culture is that the waste material can be complex and variable in composition over the operating period, while sterilization is not necessary. The anaerobic food web is very efficient in transforming complex organic compounds into methane for stable digesters, because almost all intermediate products in the food chain are converted into methane with very low concentrations of carboxylates in the digester effluent and hydrogen in the off gas. The reason for such a high conversion is that the final products (methane and carbon dioxide) freely bubble out of the solution, which results in the cir­cumvention of product inhibition and separation costs. However, methane formation is sensi­tive to instabilities. Thus, practical studies are still being performed to answer the following questions: How do mixed substrates, such as agricultural residues and manures, affect methane fermentation during co-digestion? How can performance and stability be improved? What are the limitations of methane fermentation? What are the economic and environmental benefits of conversion of agricultural residues to methane? What are the future directions for improved methane fermentation? In this chapter we will address these questions for anaerobic digestion of slurries and solid wastes.

Some cellulases exhibit a higher level of complexity whereby more than one catalytic module and/or CBM is included in the same protein. Examples of such enzymes are the very similar cellulases from Anaerocellum thermophilum (Zverlov et al. 1998) and Caldocellum saccharolyticum (Te’o et al. 1995), both of which contain a GH9 and a GH48 catalytic module. Other paired catalytic modules include those from GH44 and either GH5 or GH9. Such an arrangement presumably indicates close cooperation between two particular catalytic domains, which may lead to synergistic action on the cellulosic substrate.

Some xylanases also exhibit such a multi-modular structure. GH10 and GH11 xylanases may be linked in the same polypeptide chain either to each other, to GH5, GH16, and GH43 catalytic modules or to ferulic, coumaric, or xylan acetic acid esterases from different families of carbohydrate esterase. One particularly interesting combination of multifunctional catalytic modules that appear in the same polypeptide chain is a typical GH10 xylanase together with a CE1 feruloyl esterase, which presumably allows enhanced cleavage of the xylan-lignin linkage in the plant cell wall (Grepinet et al. 1988; Fontes et al. 1995).

It is striking to note that many of the multifunctional enzymes in nature occur in bacteria that inhabit extreme environments, for example, growing at 60°C-90°C. One exception is evident in the rumen bacterium, Ruminococcus flavefaciens, which produces some very intriguing multifunctional xylanases (Flint et al. 1993; Laurie et al. 1997). One could argue, however, that the rumen environment is indeed a very specialized environment (Flint et al. 2008). Why this bacterium “chooses” to produce such complicated enzymes remains a mystery.

Pelletization is the only preprocessing step considered in the biomass supply system. The base case pellet plant has a production capacity of 6t/hour with the annual production of

45,0 t (Sokhansanj et al. 1999). The plant operates 24 hours for 310 days annually (annual utilization period 85%). Table 7.4 summarizes the cost of pellet production including variable costs using the system. For the base case, wood shavings at 10% (w. b.) moisture content was considered as a burner fuel with a fuel cost of $40/t delivered to the pelleting plant. Cost of wood shavings is considerably high because of the high demand for animal bedding materials and as a fuel for the pulp mills. The capital and operating cost of producing biomass pellets are $5.64 and $25.18/t of pellet production, respectively. The cost of producing pellets ($30.83/t) may be further reduced if the plant capacity is increased. Sokhansanj and Turhollow (2004) calculated a cost for cubing of corn stover at $26.17/t using corn stover as source of heat in the biomass dryer.

For the energy inputs to produce pellets, a sum of 0.821 GJ/t is calculated for the entire process. The sum is roughly 5% of the 16 GJ energy content in a ton of dry switchgrass. The most energy-consuming operation is the dryer (assumed drying from 50% to 10% moisture content), which constitutes more than 40% of the entire energy used for pelleting. Next in the list is the pelleting process followed by the grinder.

There are a number of means of lowering pellet costs and energy consumption. It is pos­sible to move the grinding operation to the field and grind to a bulk density as high as 128 kg/ m3. This change in the process sequence would reduce the cost of transporting loose stover and give almost the same density as a bale without the baling cost. Costs might be lowered by as much as $10/t. Operating the pelleting facility 300 days instead of 240 days/year will reduce costs. Achieving a higher density cube and higher pellet mill throughput, as with alfalfa, would also contribute to lowering costs. Other additional opportunities to reduce costs

would include having multiple feedstocks that are available as a fresh supply for as much as 180 to 240 days of the year.

Numerous studies have reported conversion of various agricultural residues and processing wastes to sugars and to ethanol using a variety of pretreatment and fermentation technologies. As shown in Table 9.3, high overall yields of xylose, glucose, and other sugars have been realized through pretreatment followed by enzymatic hydrolysis for the following feedstocks: corn stover, barley straw, and corn fiber. On the other hand, much lower yields have been reported for flatpea hay, wheat straw, and sugarcane bagasse. Unfortunately, it is challenging to compare many of these results accurately due to changes in methods, enzyme formulations, analytical approaches, and data reporting. However, one team did systematically investigate bioconversion of corn stover, which has the highest availability in the United States (see Figure 9.1), for different pretreatment operations in combination with the same enzymes and using the same methods (Wyman et al. 2005a). In this case, these leading pretreatments that spanned pH values from about 1.2-11 realized over 90% overall yields of xylose and glucose. Some work has also been conducted in determining the fermentability of the sugars released to ethanol as it is vital to obtain high ethanol yields in the fermentation step (Wyman et al. 2005b). In this case, inhibitory effects of compounds produced or released during up-stream processing by operations such as pretreatment must be avoided or overcome. In addition, high ethanol yields must be realized from all pentose and hexose sugars that tend to be preva­lent in agricultural residues. Furthermore, some pretreatments such as controlled pH produce substantial amounts of oligomeric sugars that many organisms cannot ferment to ethanol directly, and steps must be introduced to either hydrolyze these to monomers and possibly dimmers, or organisms must be employed that can fully utilize these soluble polymers (Yang and Wyman 2008).

Nasib Qureshi, Stephen Hughes, and Thaddeus C. Ezeji

Abstract

This is an overview of the emerging technologies that have been developed recently or are in the process of development for ethanol (biofuel) production from agricultural residues. In this direction numerous advances have been made. Problems associated with inhibitor generation and detoxification, fermentation of both hexoses and pentoses to ethanol, and development of efficient microbial strains have partially been addressed. Simultaneous product recovery and process consolidation and/or integration will further improve the economics of production of biofuels from biomass. It is emphasized that numerous domestic and international companies have initiated their programs to commer­cialize conversion of biomass (agricultural residues) to biofuels. Separation and use of byproducts as additional sources of generating revenues can strengthen this fermentation further.

Introduction

Traditional substrates that have been used to produce biofuels such as ethanol and butanol include molasses, corn, and whey permeate. Molasses is a byproduct of the sugarcane­processing industry and contains approximately 50% sugar. This substrate (molasses) has been used to produce ethanol in countries such as Australia, Brazil, and India. Corn has been used in the United States, while whey permeate has been used in New Zealand. The use of these substrates affects the economics of biofuel production (Qureshi and Manderson 1995) and is becoming more challenging due to these subtrates’ use for food and feed. Currently about 140 billion gallons of gasoline is used in the United States annually, of which 15% can be supplemented by corn ethanol (Qureshi and Ezeji 2008). In order to reach a higher level of supplementation, lignocellulosic biomass such as corn stover, wheat straw, barley straw, switchgrass, and reed canary grass has to be used.

Biofuels from Agricultural Wastes and Byproducts Edited by Hans P. Blaschek, Thaddeus C. Ezeji and Ju rgen Scheffran 11 © 2010 U. S. Government. ISBN: 978-0-813-80252-7

Fermentation of lignocellulosic biomass to ethanol requires additional processing steps for the 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 (H2SO4), or alkali (NaOH), and their use results in higher sugar yields when compared with pretreatments such as hot water or ammonia. These pretreatments (acid/alkali) generate products that inhibit cell growth and/ or the fermentation process or both. Another challenging problem with respect to fermentation of biomass involves the difficulty by various fermentation microbes for using pentose sugars. Lignocellulosic biomass contains up to 30% pentose sugars, which are not utilized by the traditional ethanol-producing cultures, such as Saccharomyces cerevisae. During the last two to three decades new cultures of Saccharomyces cerevisiae that can utilize both hexose and pentose sugars released from lignocellulosic hydrolysates have been developed (Hahn — Hagerdal and Pamment 2004; Sedlak and Ho 2o04; Hughes et al. 2009a, b). Although such cultures have been developed, the overall productivity and ethanol concentration that can be achieved by these strains are not optimal. This chapter describes recent progress with respect to the development of emerging technologies that have been developed to produce ethanol from lignocellulosic substrates. These challenging technologies include use of lignocellulosic biomass substrates, overcoming (at least partially) inhibitors generated during the pretreat­ment process, development of genetically improved cultures, simultaneous product recovery technologies, and process integration.

Butanol can be used in internal combustion engines. This biofuel can be produced by the fermentation route using renewable biomass (Ezeji et al. 2007a, b). Compared with ethanol, butanol is less volatile, less sensitive to water, less flammable, and has a slightly higher octane number. Its low vapor pressure facilitates its use in existing gasoline supply lines. As opposed to ethanol — producing cultures, butanol — producing cultures (Clostridium acetobutylicum or Clostridium beijerinckii) can use both hexose and pentose sugars released during hydrolysis of cellulosic biomass. During World War I and II there were plants worldwide including those in 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. Details of this fermentation are presented in Chapter 3.

The change (on day 40 of the operating period) from gentle continuous mixing by biogas recirculation to vigorous continuous mixing by liquid recirculation with a peristaltic pump showed a very different outcome. The vigorously mixed bioreactor showed an immediate and steady decline in the VMPRs (Figure 4.5A). Feeding had to be terminated on day 53 to prevent complete digester failure because the VFA levels in the effluent had increased from an average of 256.3 mg acetate/L on day 40 to 2846 mg acetate/L on day 52. Biomass washout was partly to blame, because biomass levels in the effluent had increased from 10 gVS/L on day 40 to 12gVS/L on day 41, resulting in a steady loss in VS biomass in the vigorously mixed bioreactor (the data for the control bioreactor remained constant; Figure 4.5B). In addition, slot-blot hybridization techniques showed that a severe loss in the concentration of the predominant methanogens was the result of the change in mixing intensity. That is, the relative 16S rRNA levels for M. concilii and for the order Methanomicrobiales decreased to levels lower than 1% on day 52 of the operating period (Figure 4.5C, D). This result supports the hypothesis postulated by Stroot et al. (2001) and McMahon et al. (2001) that vigorous, continuous mixing inhibited relationships between syntrophs and their methanogenic partners by destroying their juxtaposed position. In addition, it is also in agreement with Hoffmann et al. (2008) , who found that the filamentous concentrations of M. concilii was negatively affected by increased mixing intensities. Thus, vigorous mixing decreased the concentration of methanogens, which had been slowly built up during the long start-up periods (described in the ASBRs section). With the loss of methanogenic activity, the high-rate system became severely overloaded, and combined with a declining biomass concentration, unstable condi­tions emerged within weeks.

1.3- Propanediol is a valuable feedstock chemical that is commonly used as a monomer for the synthesis of polyethers, polyesters, and polyurethanes. It can also be used for the produc­tion of cosmetics, lubricants, foods, medicines, composites, adhesives, laminates, powder and UV- cured coatings, moldings, and anti — freeze. Glycerol is metabolized via oxidative and reductive pathways in Klebsiella, Citrobacter, Clostridium, and Enterobacter species. In the oxidative pathway, the nicotinamide adenine dinucleotide (NAD)-dependent glycerol dehy­drogenase (GldA) catalyzes the conversion of glycerol to dihydroxyacetone (DHA) with subsequent phosphorylation by dihydroxyacetone phosphate (DHAP) kinase to produce DHAP (Daniel et al. 1995) after which DHAP enters the glycolytic pathway. The reductive pathway is catalyzed by coenzyme B 12-dependent glycerol dehydratase, which converts glycerol to 3-hydroxypropionaldehyde (3-HPA). 3-HPA is reduced to 1,3-PDO by NADH — dependent enzyme 1,3-propanediol dehydrogenase (1,3-PDODH). As the conversion of glyc­erol to 1,3-PDO results in the net consumption of reducing equivalents, this pathway provides a mechanism for achieving redox balance in the absence of electron acceptors such as oxygen, nitrate, and fumarate.

Glycerol fermentation by Klebsiella results in the accumulation of two main products,

1.3- PDO and acetate, whereas Clostridium species produce butyrate and 1,3-PDO. Although high levels of 1,3-PDO are produced by Klebsiella species, their use on an industrial scale is limited because they are opportunistic pathogens capable of causing urinary tract and abdominal infections, and pneumonia. Therefore, Clostridia are preferred because many Clostridium species of biotechnological importance are not pathogenic and certain species do not require the presence of vitamin B12.

When batch fermentations with C. butyricum were performed using crude glycerol at a concentration of 112 g/L, the maximum amount of 1,3-PDO obtained was about 63.4 g/L with a specific yield of 0.69 mol/mol glycerol (Table 6.1; Barbirato et al. 1998). A newly isolated strain of C. butyricum was found to produce up to 46 g/L of 1,3-PDO a with a high volumetric productivity of 3.4 g/L/h (Papanikolaou et al. 2000). In another report, continuous fermenta­tion with K. pneumoniae yielded 35.2-48.5 g/L of 1,3-PDO. In that report, a low concentra­tion of glycerol was used initially and the concentration was gradually increased to prevent accumulation of substrate in the bioreactor (Menzel et al. 1997). The final volumetric pro­ductivity was in the range of 4.9-8.8 g/L/h. The addition of fumarate to the cultures of K. pneumoniae enhanced the utilization of glycerol and led to increased 1,3-PDO formation. Although the net 1,3-PDO yield of 0.57mol/mol glycerol was obtained with or without the addition of fumarate, the volumetric productivity increased up to 17mmol/L/h, an increase of almost 36% when compared to the corresponding control where glucose was used as substrate (Lin et al. 2005). This increase was attributed to two main factors. First, the addition of fumarate increased the activities of major enzymes involved in glycerol utilization and

1.3- PDO synthesis, that is, GldA, glycerol dehydratase, and 1,3-PDODH, which increased the metabolic flux toward 1,3-PDO production. Second, higher levels of fumarate led to a decrease in the NAD+/NADH ratio, which resulted in a greater concentration of reducing equivalents and hence a greater conversion of 3-HPA to 1,3-PDO.

The inbound logistics of delivering biomass from the field to a biorefinery has been investigated by the autors (Mukunda et al. 2006; Mukunda 2007). A model named, Biomass Feedstock Logistic Simulator (BmFLS) using discrete event simulation was developed on EXTEND™ . The model consisted of four blocks that simulated the following: (1) feed­stock generation from the field at harvest; (2) feedstock storage and loading at the field; (3) transportation to the biorefinery; and (4) inbound logistics operations at the biorefinery.

The analysis discussed here would only pertain to the feedstock inbound logistics. In developing a scenario for the analysis, an existing 102 MMGY corn ethanol fuel plant located in Indiana was assumed to be supplied corn stover feedstock. The inventory to be maintained was for 10 days of production. A conversion rate of 72gallons/dry ton of corn stover was used and 900 lbs of 8’x4′ x 3′ was assumed at the bale weight delivered to the plant from seven different farms that were categorized based on their sizes. These farms ranged from 10 to 80 miles of supply radius to the biorefinery and corn acreage data were taken from the National Agricultural Statistics Service (NASS) to compute the feedstocks collected from these radii mileage. Figure 7.10 (Mukunda 2007) shows the percentage of feedstock at various distances from the plant. It is important to observe that feedstock will be delivered from farms located at a range of mileage. This needs to be factored in when analyzing the travel times and arrival distances of trucks to the plant.

One of the first goals to tackle in analyzing the inbound logistics is to determine the fre­quency of feedstock delivery needed for maintaining the inventory level at the biorefinery. Feedstock delivery will have some restrictions based on the working hours of the plant deliv­ery schedule, the number of trucks that can be processed through, and the plant sampling, and unloading stations. The simulation tracked inventory at the plant and truck queuing inside the plant (Mukunda 2007) and the following statistics were collected: average feedstock inventory, total trip time, total service time, waiting time and utilization of the weighing, sampling, and unloading stations.

As mentioned before, the number of delivery trucks needs to match the sampling and unloading station capacity at the plant for trucks to be serviced within the limit of service hours (8-16 hours/day). Station utilization (sampling, weighing, and unloading) must be optimized to reduce redundancy. The number of stations needed is dictated by the numbers of inbound truck deliveries to the biorefinery and there is a trade-off between the number of trucks and unloading station capacity (Figure 7.11; Mukunda 2007) . The total trip time, service time, and waiting time all depends on the size of the biorefinery. On average, all these times increase with increasing plant sizes as shown by the analyses of plants capacities from 40 to 200 (Figure 7.11; Mukunda 2007). Reducing these times will reduce the cost of feedstock delivered.

As mentioned previously, the trucking cost is by far the most expensive of all the logistics components. Analysis conducted for 100MMGY showed that the trucking cost to the plant over 10 years can be 30 to 40 times more than the handling cost at the plant (Mukunda 2007). This means more emphasis should be placed in optimizing transportation tonnage in order to have a real impact on the logistics of handling bulky plant biomass feedstocks.