It is now clear that forestry carbon offsets are resilient features of Australian climate change policies. To partic­ipate in such markets, farmers must be able to adequately measure, and verify the mitigation achieved (The CRC for Greenhouse Accounting & Tony Beck Consulting Services Pty Ltd, 2003). Forestry plantations that include some rotational harvesting for biochar or bioenergy will require more sophisticated carbon accounting than a simple revegetation project (Indepen­dent Pricing and Regulatory Tribunal, 2008). The estab­lishment of tree fodder plantations has long offered a significant productivity option for some farmers (Sanford et al., 2003). Deferring the early grazing of annual pastures and reduce dry season hand-feeding has long generated interest (Patabendige et al., 1992; Cleugh et al., 2002), and perennial fodder tree planta­tions offer another source to supplement stock feed in the summer/autumn period (Sanford et al., 2003). Deep-rooted perennials are well known to use available water when annual pastures are dead, recover nutrients from deeper soils, reduce soil acidification, minimize erosion, and some leguminous species also fix nitrogen (Patabendige et al., 1992; Cransberg and McFarlane, 1994; Hatton and Nulsen, 1999; Wise and Cacho, 1999; Valzano et al., 2005). Adding value to these conventional applications in such regions is the use of tree woody wastes to produce biochar as a feed additive which may improve ruminant growth when fed on the trees (which may be of lower grade and/or be a "high tannin" content), and in the process sequester carbon in the soil (McHenry, 2010). The mechanism for this improvement is generally known as "detannification", and may enable the use of potentially large resources of high-tannin fod­der species (such as Acacia sp.) by increasing the avail­ability of leaf protein (Van et al., 2006; Blackwell et al.,

2009) . Acacia sp. fodder plantations require annual prun­ing of the higher branches to provide fodder for grazing animals. Animals eat the leaves from the branches on the ground, leaving the inedible woody waste components in the paddock to dry and be collected as a potential source of biomass for biochar manufacture. The improved digestibility of some high-tannin fodder trees with biochar feed additives may expand their utility within agricultural production systems (McHenry,

2010) . In particular, if an Acacia sp. biochar feed additive is effective in Australian semiarid production systems (such as the West Midlands), this might provide a further incentive to revegetate semiarid sandy soils suit­able to many native Acacia sp. to attain a combination of positive benefits (Graetz and Skjemstad, 2003; Antle et al., 2007). These options are currently based on a

12- week experiment by Van et al. (2006) comparing goat growth rates fed on tannin-rich Acacia sp. fodder. The goats were either fed biochar (produced from bamboo) at a feed rate of <1 g per day per kilo of live weight, or no biochar for the control group. The experi­mental group exhibited notably higher growth rates (~ 20%) than the control goats that received no biochar feed additive on the same feed regime. Over the 12 weeks the experimental goats fed biochar weighed 5.2% heavier than their controls (Van et al., 2006). This may be a sufficient commercial incentive to drive de­mand and subsequent biomass conversion technology investment without a carbon price (McHenry, 2010). The work by Van et al. (2006) also presents a mechanism (via animal excreta) that may be assessed for efficacy when avoiding relatively expensive biochar soil applica­tion options such as deep banding, broadcasting, seeding application, topdressing, aerial delivery, or pre­cision application to ailing plants (Blackwell et al., 2009). In addition to researching the efficacy of small biochar additions to the diet of grazing animals, the opportunity arises to simultaneously investigate the reported capacity and magnitude of numerous other biochar benefits (McHenry, 2010), including the ecologi­cally delivered biochar to biosequester C; biologically immobilize inorganic N; retain soil N; increase soil pH; adsorb dissolved ammonium, nitrates, phosphate, as well as hydrophobic organic soil pollutants such as polycyclic aromatic hydrocarbons (Beaton et al., 1960; Gustafsson et al., 1997; Accardi-Dey and Gschwend, 2002; Lehmann et al., 2003). The remaining levels of bio­char in the animal excreta would also determine the car­bon fractions that survive the digestive system to determine the maximum available long-lived carbon species fractions to be sequestered in soils via the ecolog­ical delivery method (McHenry, 2010). Long-term soil testing may also be able to detect the stable fraction of the ecologically delivered biochar after being exposed to the soil environment. However, there is clearly
much research required to verify a number of assertions and assumptions to provide a level of certainty accept­able to farmers and investors who collectively command much of Australia’s productive capacity (Intergovern­mental Panel on Climate Change, 2000; Barker et al., 2007).

Ionic liquids are strong solvents. They are able to dissolve the components of LB at ambient to moderate temperatures. Furthermore, ionic liquids are highly tunable through the selection of anion and cation. Beyond toxicity and corrosivity, other considerations affecting the selection of an ionic liquid include price, availability, water tolerance, biodegradability, and phys­ical properties such as viscosity, melting point, dipolar­ity and hydrogen bond basicity. An effective wood dissolution is possible when both the ionic liquid and conditions are properly identified and employed.

The most significant consideration for practical large-scale operations is the toxicity of the ionic liquid to be used. For example, 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) is a good solvent to use on cellulose as it is only moderately toxic compared to that of 1-ethyl-3-methylimidazolium chloride ([EMIM] [Cl]) (Swatloski et al., 2004; Wu et al., 2004).

Corrosivity of the selected ionic liquid is also impor­tant. It plays a large role in the economics of a commercial operation. One can minimize corrosivity by selecting an ionic liquid that is halogen free. Good choices include

1- ethyl-3-methylimidazolium acetate ([EMIM][OAc]) (Liebert, 2010) and 1,3-dimethylimidazolium-dimethyl- phosphate ([MMIM][(MeO)2PO2]) (Zavrel et al., 2009).

Balancing the physical properties and operational conditions is important to obtaining the most ideal disso­lution of LB. For example, if the viscosity of an ionic liquid is high, it may be necessary to operate the pretreat­ment at a high temperature to obtain a practical dissolu­tion. As a result, the reactions may become unstable and may give rise to undesirable reactions and by-products. A solution to this problem is to reduce the viscosity of the ionic liquid by combining it with a cosolvent. A good viscosity-reducing cosolvent is polyethylene glycol (Willauer et al., 2000).

The dissolution rate is inversely proportional to wood chip sizes. For example, ball-milled wood powder produces a higher dissolution rate than does sawdust. The dissolution rate for TMP fibers is higher than that for sawdust, which is much greater than that of wood chips (Kilpelainen et al., 2007; Sun et al., 2009; Zavrel et al., 2009).

In addition to particle size, dissolution efficiency is also highly sensitive to the water content. Water attenu­ates the dissolution effectiveness of an ionic liquid. Studies have shown that storing wood chips at warm temperatures, e. g. 50°C or 90°C, reduces the water con­tent of the wood and thus improves the pretreatment effectiveness (Kilpelainen et al., 2007; Sun et al., 2009). Reducing the water content improves the dissolution power of an ionic liquid regardless of the type of wood being treated. However, if the wood becomes too dry, the wood composition may change unfavorably. Determining the precise water content of LB is quite difficult and is complicated due to the diversity of envi­ronmental conditions of the regions from which the wood studied grew. Variables such as humidity and var­iances in species present a challenge when comparing literature on the subject (Wang et al., 2012).

The type of LB, dissolution time, temperature and ionic liquid to wood ratio, are all factors that contribute to the dissolution power of an ionic liquid. That said, those ionic liquids that were effective at dissolving both lignin and cellulose were also excellent at overall LB dissolution. One of the best solvents for wood chips is the combination of 1-allyl-3-methylimidazolium chlo­ride ([AMIM][Cl]) and [EMIM][OAc]. Ionic liquids derived from polycyclic amidine bases have been shown to dissolve aspen wood chips completely (D’Andola et al., 2008). The ionic liquids used in this study were 1,8-diazabicyclo[5,4,0] undec-7-enium salt, and 1,8-diazabicyclo[5,4,0] undec-7-enium chloride [HDBU] [Cl] (D’Andola et al., 2008). It has been observed that [AMIM][Cl] can effectively dissolve both hardwood and softwood wood chips. However, the same solvent only partially dissolved Norway spruce (Kilpelainen et al., 2007). The efficiency of [AMIM][Cl] in dissolution of wood is due to the presence of p-electrons both in the alkenyl chain as well as in the imidazolium ring. Possible p—p interactions may occur between the aro­matic part of lignin and the ionic liquid (Hunter and Sanders, 1990; Kilpelainen et al., 2007). The highest sol­ubility of maple wood powder was achieved using [AMIM][Cl] and [BMIM][Cl] (Lee et al., 2009).

[EMIM][OAc] can completely treat three types of wood chips. It is used to treat spruce, beech and chestnut. However, it only partially dissolves silver fir (Abies alba) wood chips (Zavrel et al., 2009). A plausible explanation for this difference is that silver fir contains more cellulose (50.3%) and lignin (27.7%) than the other wood species (Kuznetsov et al., 2002). When comparing the dissolution effectiveness of [EMIM][OAc] to [BMIM][Cl] and control­ling for species, wood chip size, and temperature one can obtain a 3.6-fold increase in dissolution effectiveness us­ing [EMIM][OAc] vs [BMIM][Cl]. In this case, southern yellow pine wood chips were treated at 110 °C. This

3.6- fold increase in dissolution effectiveness is

attributable to the basicity of the acetate anion, higher than that of the chloride anion. Thus, [EMIM][OAc] is stronger at breaking the intramolecular hydrogen bonds (Fort et al., 2007; Sun et al., 2009).

An opportunity for improvement in using ionic liq­uids is better recovery of solubilized cellulosic materials and lignin. A significant drawback is that much of the hemicellulose is washed away during the recovery pro­cess. Figure 27.5 illustrates the process.

Following pretreatment with an ionic liquid, an enzy­matic hydrolysis pretreatment is applied to produce the sugars for downstream fermentation. This pretreatment can recover as much as 90% of the cellulose for enzy­matic hydrolysis. While cellulose is recovered at a high rate, the hemicelluloses are not as they are washed away. As Figure 27.5 illustrates, the ionic liquids are recovered and recycled for reuse. Even so, the problems of price, toxicity, and the lost hemicellulose persist, which inhibit wide adoption in industrial scale operations.

Water Filtration

While considerable research has been conducted on soil remediation through adsorption of pollutants following biochar application, relatively little data have been published on the sorption of pollutants by biochars preceding biochar application to soil. Most of the few studies that have been published on this subject

use biochar to filter substances from surface waters that are not suitable for application to agricultural soil, such as arsenic (As), Cd, Cu, fluoride (F_), phenol (C6H5OH), uranium (U), and Zn (Table 25.2). Considering that these substances are better suited to be contained in a secure landfill than be applied on productive agricul­tural soil, further research should be conducted to deter­mine if these biochars could be as effective at reducing CH4 emissions from soil as demonstrated by Yaghoubi

(2011) .

Direct conversion of LB to biofuels is liquefaction. Typical products include biodiesel and heavy oils that are typically very viscous. Adding an alkali to the con­version will enhance the liquefaction process (Itoh et al., 1994; Demirbas, 2005). Hydrothermal liquefaction is an application where thermal depolymerization, or hydrous pyrolysis, is accomplished using superheated water under pressure.

Drying feedstock in unnecessary when using hydro­thermal liquefaction. Consequently, it is suitable for con­verting any biomass regardless of its moisture content. Aquatic biomass, garbage, organic sludge as well as LB are all good feedstock candidates for hydrothermal liquefaction.

At the boiling point of water, 100 °C, extraction of aqueous soluble components is possible. At tempera­tures above 150 °C hydrolysis begins and biomass polymers, such as cellulose, hemicellulose, proteins, and so on, degrade into monomers. Then at 200 °C and 1 MPa solidlike biomass changes into a slurry, a process called liquidization. At higher temperatures below the critical point of water, around 300 °C and 10 MPa, liquefaction takes place and oily product is obtained. If one changes the reaction conditions such as reaction time or the catalyst, the main product can be changed to char, a process referred to as hydrother­mal carbonization. Finally, at a temperature around the critical point and in the presence of a catalyst, the biomass will gasify.

CONCLUSION

Utilizing LB for energy and fuel production is as old as mankind. However, modern sources of fuel are more cost-effective and convenient to drive and meet our contemporary energy demands. Liberating carbon that has accumulated over millennia in such an unnatu­rally condensed period of time threatens to alter current climate conditions. Our economic engine has created de­pendencies on fossil fuels and has encouraged unhealthy relationships between highly industrialized societies like the United States and China and some energy suppliers around the world. The cycle of growing and using LB for fuel and energy is a closed and therefore, sustainable sys­tem that consumes as much carbon dioxide as is liber­ated. Finding technologies that can return modernized societies around the globe to more sustainable and self-reliant sources of energy is critical to reduce the envi­ronmental impact and improve national security and sovereignty. To that end, this chapter has presented and reviewed a wide array of biochemical and thermo­chemical LB conversion options. These methods have developed into capable methods of converting LB into fermentable intermediates such as sugars or products. Much development has already taken place and there is still much more needed until utilizing LB for energy and fuel can compete with and replace more convenient and less expensive sources of fuel.

Industrializing the process of converting LB into valuable materials is the function of a biorefinery and it employs a complex and diverse set of conversion tech­nologies to accomplish its tasks. There are several pre­treatment options available that either exploit thermal, mechanical and chemical mechanisms or use biological and chemical mechanisms. Ultimately the treatments chosen will depend on the desired product and desired specifications. These products may include liquid bio­fuels, biochemicals as well as steam, heat and electricity. Regardless, the objectives of the pretreatment are the same: to break down the strong crystalline lignin and cellulosic structures such that the biomass becomes vulnerable to conversion processes, such as hydrolysis treatment that yields fermentable sugars that are free from microbial growth inhibitors, or a thermochemical conversion such as gasification or liquefaction. No treat­ment option is ideal. There are often trade-offs between competing features and liabilities such as high yield and long retention time, low concentration of inhibitors and high cost, significant environmental and safety concerns and high efficacy.

The biochemical and thermochemical pretreatments and conversions have developed and improved over time independently and in conjunction with a series of pretreatment methods. The goal of the development of these pretreatments is to improve the quantity and qual­ity of materials available to conversion, whether it is bioconversion or thermochemical conversion. In order to compete with contemporary and convenient sources of energy it is important to maximize the pretreatment and conversion processes as well as to eliminate and recycle waste and energy.

The biorefinery holds great promise to enable the us­age of biomass as a sustainable and reliable source of en­ergy and fuel. The biochemical and thermochemical conversion options described here are by no means an exhaustive representation of all the studied methods. Many more exist in the literature and maybe the best methods are yet to come.

[1] Strengths, Weaknesses, Opportunities, and Threats

Source: Reproduced with the permission oflEA Bioenergy Task Leader, Dr. Ed de Jong.

[2]These requirements are in addition to the major research projects underway regarding the influence of various biochar feedstocks and conversion technologies on the characteristics of the final biochar product.

A simple analysis of potential value per unit of dry biomass associated with various potential production systems may help identify suitable uses of agricultural biomass (Table 26.8.) These theoretical comparative financial values are exclusive of costs, which are extremely variable according to the application and scale of operation. These basic scenarios seem to indicate that the highest values of agricultural residues are ani­mal husbandry or cropping applications—only if the biochar can increase conventional yields. This demon­strates that a key focus for the development of a sustain­able biochar industry is the value of the product to an industry, rather than the cost of production per se. This also illuminates the aspects of supplying biochar with appropriate characteristics for the specific applica­tion, as it is likely that biochar applications will mature,
and standards for biochars will be sought by users assessing cost-effective product suppliers. In any case, it seems reasonable that small-scale waste-to-energy suppliers will be established at some point near rural settlements with the assistance of government subsidies in Australia. It also seems reasonable that various agri­cultural wastes will be co-fired, as well as potential adjustments installed to increase clean biochar produc­tion options. These projects can be a sound foundation to understand biomass-to-biochar technology by supplying sufficient volumes of relatively cheap and consistent biochars suitable for numerous medium — to large-scale research trials. It is further likely that bioenergy and biochar cogeneration at a regional level may be more cost-effective when agricultural wastes are leveraged by municipal solid waste resources, if quality control of municipal wastes is maintained. However, this will also require much evaluation and research for processing technology and downstream application suitability.

CONCLUSION

Taken in isolation, the cost and benefits of using biochar for only farm soil carbon sequestration may

not be a profitable activity. Yet, the net sum over the agri­cultural system in terms of biochars increasing conventional productivity may prove to be a more cost-effective option than existing operations in some areas (Antle et al., 2007). Notwithstanding economic issues, the greater scientific challenge is determining the efficacy of biochar carbon species in a range of specific agricultural production systems over both the long and the short term (McHenry, 2009, 2011). Inte­grated agricultural production systems require suitably high-resolution data to determine the agricultural sys­tems and regions that may be able to implement options cost-effectively and sustainably (McHenry, 2010). Thus, a coordinated and cross-disciplinary research approach will likely be the most effective means of utilizing exist­ing biomass/bioenergy activities for new agricultural applications (Nabuurs et al., 2007). Providing greater scientific rigor and certainty to farmers, environmental­ists, governments and the broader community require undertaking biochar research alongside their impacts on upstream and downstream activities (McHenry,

2011) . Once this research becomes available, it may pro­vide a form of indemnity to farmers before prematurely applying new systems and technologies that may be only cost-effective in highly specific situations. Conversely, if biochar feed additives prove effective, even in localized regions, a major source of biochar will be required, and as Acacia sp. are native to Australia, and also most major continents, this may have extensive global implications in arid, semiarid, and even some temperate regions (McHenry, 2010). Nonetheless, complex biological and agroecological production sys­tems require high-resolution information to determine where the best opportunities are to integrate these new diversification options into their existing production systems. In conclusion, the author offers a selection of key biochar-related knowledge deficiencies for Australian agriculture in bullet points,[2] and also numbered suggestions for groups in the West Midlands of WA:

• Key sensitivities of biochars in major West Australian agricultural operations (grains and livestock);

• Key sensitivities of biochar carbon sequestration in major agricultural operations;

• Energy, material, and cost flows of various biochar/ bioenergy conversion systems;

• Major feedstock availability in different regions, costs, and transportation logistics;

• Efficacy and cost of various biochar application technologies for West Australian conditions;

• The sensitivity of biochar industry to policy change and administrative changes;

• Development of biochar research that aims to create major benefits to agricultural productivity.

1. Proceed with caution

2. Understand carbon credit ownership in biomass provided to regional power stations

3. Test cropping benefits with affordable biochar

4. Using appropriate safety precautions, experiment with on-farm production and application of biochar on a small scale

5. Encourage research into effects of biochar on crops, animal nutrition, and animal health

6. Monitor technical developments of small scale (2—20 MW) gasifier power units

7. Consider relationships with local waste-to-energy projects using landfill

DISCLAIMERS

This material has been written for Western Australian conditions, and many conclusions do not imply suit­ability to other areas. The inclusion of biochar/bio — energy products or trade names do not imply recommendation, the comparisons are simply for a gen­eral audience, and are not sufficiently detailed for com­mercial comparisons or technical appropriateness for any one or range of applications. The omission of any locally available technology is unintentional.

Acknowledgments

This chapter would not have been written without the considerable experience and expertise of Dr Paul Blackwell, Department of Agri­culture and Food, Western Australia’s (DAFWA) Geraldton Regional Office. Dr Blackwell’s long-time contribution to this field of research in WA under particularly limiting funding and time allocations is an example to those of us following in his notable footsteps.

Sulfites are found to be efficient agents for pretreating LB, in both hardwoods and softwoods (Zhu et al., 2009). In sulfite pretreatment to overcome recalcitrance of lig — nocelluloses (SPORL), the sulfite refers to any sulfite, bisulfate or combination. A combination may contain any two of the following three reagents: sulfite (SO§_), bisulfite (HSOL), and sulfur dioxide (SO2, or H2SO3). The specific combination to use depends on the pH of
the pretreatment liquor and the temperature (Zhu et al., 2009).

The first step in the process is to treat wood chips or another LB feedstock with a sulfite salt solution where the salt may be sodium, magnesium or calcium. This first step usually operates at a temperature between 160 °C and 190 °C and at a pH between two and four for 10—30 min. The second step is to fiberize the resul­tant biomass using a disk mill. This yields a fine fibrous substrate suitable for robust saccharification and fermentation (Shuai et al., 2010).

The typical acid charge on oven-dried wood is 0.5—1% for hardwood and 1—2% for softwood. The typical bisulfite charge is 1—3% for hardwood and

4— 8% for softwood (Zhu et al., 2010b). More than 90% of the cellulose was converted from SPORL-treated spruce chips. In this case the oven-dried wood chips were treated with an 8—10% bisulfate and 1.8—3.7% sul­furic acid combination at 180 °C for 30 min. The resul­tant material was treated with enzyme hydrolysis for 48 h using 14.6 cellulase and 22.5 b-glucosidase per gram of substrate. Shuai et al., and Zhu et al., have per­formed comparative SPORL studies using dilute-acid pretreatments for both softwoods and hardwoods (Shuai et al., 2010; Zhu et al., 2010b). In these studies, it was observed that SPORL is better at saccharification of hexoses and pentoses than was a dilute acid (DA) treatment. In one case, where oven-dried spruce was treated at 180 °C for 30 min with 1% H2SO4 at a 5:1 liquor-to-wood ratio, 87.9% of the hexoses and pentoses were recovered using SPORL versus a similar DA treat­ment where 56.7% of the saccharides were recovered.

About 92.5% of the cellulose was recovered in an SPORL process utilizing a 9% sodium sulfite (w/w of wood) and 77.7% for the DA (Shuai et al., 2010). In another study of aspen, or Populus tremuloides, a comparison was made between an SPORL pretreatment using a combination of sulfuric acid and sodium bisulfite and a dilute sulfuric acid (DA) pretreatment. It was observed that nearly 60% more ethanol was produced from the SPORL-treated wood than from the DA-treated wood. In both cases enzymatic hydrolysis was conducted using 10 FPU cellulase per gram glucan for 120 h (Zhu et al., 2010b).

Table 27.4 highlights a handful of comparisons between treatment methods and their effectiveness where the pretreatment conditions were L/W = 3, disk-milling solids loading = 30% (the solid contents of pretreated wood chips), and disk plate gap = 0.76 mm. Sodium bisulfite charge was 8% on oven-dried wood for the two SPORL runs; sulfuric acid charge was 2.21 (w/w) on oven-dried wood for the DA and low pH SPORL runs, and 0 for the hot water and high pH SPORL runs.

SPORL is an attractive pretreatment method due to several features. SPORL generates much less furfural and hydroxymethylfurfural (HMF) than does a simple DA pretreatment. SPORL significantly enhances fermentation yields by weakening the hydrophobic rela­tionship between lignin and enzymes and enhancing saccharification of cellulose. One of the products of SPORL is a sulfonified lignin, which has potential eco­nomic value as a directly marketable coproduct within existing markets and for opening new markets. The energy consumption in the size reduction process is reduced by an order of magnitude. Lastly, SPORL has demonstrated commercial scalability with low techno­logical and environmental risks (Zhu et al., 2010b).

While some substances, such as heavy metals, pesti­cides, and hormones, are not desirable in soil amend­ments, other substances, such as N and P, are regarded as pollutants in surface waters, yet are essential plant nutrients within agroecosystems. If biochar is used to fil­ter N and P from surface waters before in is incorporated into agricultural soil (Figure 25.3(b)), the process could reclaim a portion of the nutrients that are lost from agro­ecosystems to surface waters, and benefit both crop yield and surface water quality. If effective designer bio­chars are created for the purpose of N and P retention, it is feasible that those biochars, once saturated with N and P, could supply a crop area of some size with an adequate supply of runoff-derived nutrients to replace N and P fertilizer inputs entirely, and becoming effec­tively nutrient-neutral. Furthermore, it is feasible that if an analogous relocation of nutrients is performed where the deposition site is an area that would other­wise not receive fertilizer, and not be a likely source of runoff, such as a well-managed silvicultural system, then a nutrient-negative system could be created (Figure 25.4).

Runoff and water-induced erosion occur when pre­cipitation exceeds the infiltration capacity of a soil, and
gravity carries it downhill over the soil surface into a drainage ditch or natural waterway. Common practices employed to reduce erosion caused by runoff and retain eroded soil particles by slowing the velocity of water flow within drainage ditches are well established. These practices include lining the sides of channels with either large angular rocks or rectangular wire mesh containers filled with smaller rocks, lining the bottom of the chan­nel with grass sod, various bioengineering techniques involving the establishment of trees along the channel edge, and fixing straw bales in order to intercept eroded soil particles (Brady and Weil, 2008). Biochar contained within either reusable synthetic or single use biodegrad­able mesh containers could be used to simultaneously slow and filter overland flow (Figure 25.5). This may be complementary or even preferable to the aforemen­tioned runoff and erosion control methods due to the added benefits of nutrient-saturated biochar application to soil (Figure 25.6). In areas where runoff currently flows directly into natural waterways, an enclosed bio­char overland flow filter (Figure 25.7) fitted with mesh containers of biochar may be an effective option for reducing nutrient losses to surface water, allowing those nutrients to be relocated to soil and ultimately into plant biomass. Similarly, tile drain effluent may be filtered us­ing mesh containers of biochar. Like the biochar over­land flow filter discussed above, end caps on the tile drain with drain holes only in the upper half will in­crease the residence time of nutrient-laden water with the biochar and may increase filtration efficiency (Figure 25.8).

Michael P. Garver, Shijie Liu*

Department of Paper and Bioprocess Engineering, College of Environmental Science and Forestry,
State University of New York, Syracuse, NY, USA
*Corresponding author email: sliu@esf. edu

OUTLINE

Introduction 457

Characteristics of Lignocellulosic Biomass 458

An Overview on Biomass Conversion 461

Pretreatment—Biomass Size Reduction by Physical or Mechanical Methods 462

Mechanical Pretreatment—Chipping, Grinding,

Milling, Refining 463

Irradiation Pretreatment by Electron Beam, Gamma Ray, or Microwave 465

Ammonia Recycle Percolation Pretreatment 465

Ozonolysis Pretreatment 465

Organosolv Pretreatment 466

Oxidation Pretreatment 466

Ionic Liquid Pretreatment 467

Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses 468

Hot Water 469

Steam Explosion 470

Ammonia Fiber Explosion 473

Supercritical Carbon Dioxide Explosion 473

Biological Pretreatment 474

Acid Hydrolysis 474

Alkaline Hydrolysis 475

Hydrolysis 476

Bioconversion—Converting Sugars to Products 477

Thermochemical Conversion 478

Combustion 478

Gasification 478

Pyrolysis 481

Direct Liquefaction 481

Conclusion 482

References 482

INTRODUCTION

A biorefinery is a complex industrial system to convert raw biologically derived materials into usable and valuable products. The actual design of a bio­refinery depends on the desired product, the raw mate­rials available, and the method of conversion desired.

For the purposes of this chapter, the raw material considered is woody biomass or more generally,
lignocellulosic biomass (LB). LB may originate from for­est, herbaceous plants or organic waste streams such as sewage, food processing waste, or animal manure.

LB is a source of energy that can reduce the consump­tion of fossil fuels. Energy independence is an important economic and political goal. Renewable sources of energy are also critical for a balanced ecological policy.

Biorefineries may be designed to output a specific set of products and by-products. These products include

Bioenergy Research: Advances and Applications http://dx. doi. org/10.1016/B978-0-444-59561-4.00027-9

biofuels, adhesives, surfactants, biochemicals, biopoly­mers, food and medicine. This chapter will focus on some common products such as acetic acid, ethanol, butanol, acetone, hydrogen, and polyhydroxyalka — noates. These products stem from the fermentation of sugars derived from LB or they may be derived from thermochemical conversion processes.

The first objective in any conversion is to reduce the size and increase the surface area of the raw material. This enables subsequent treatment methods to attack and exploit specific properties of LB more effectively to obtain sugars for bioconversion or obtain products from thermochemical conversion.

Secondary treatment or conversion methodologies include some form of hydrolysis, fermentation or any of a variety of thermochemical conversion treatments. The objective of these methods is to break lignin and complex carbohydrates into either simple sugars or intermediate products or even down to CO and H2 (syn­gas) for further fermentation (bioconversion) or thermo­chemical conversion. Fermentation is usually followed by separations or filtrations as final steps in the acquisi­tion of a desired product in a bioconversion.

Utilizing liquid water by itself, as the only pretreat­ment reagent, is an option of interest as it is environmen­tally friendly and inexpensive compared to other
pretreatment methods (Amidon et al., 2008; Liu, 2010; Mosier et al., 2005). High pressure is applied to keep the water in a liquid state while it is at elevated temper­atures (Hendriks and Zeeman, 2009). This enables the water to penetrate the cell structure of the biomass and thus hydrate the cellulose and remove the hemicellu — loses. Another feature of water is that it has a high dielectric constant. This facilitates ionic substances to disassociate and allows for the dissolution of hemicellu — loses and a portion of the lignin.

When the water temperature exceeds 150 °C, the hemicellulose begins to solubilize. The degree to which this occurs is determined by thermal, acid and alkali stability of the hemicellulose, which is dependent on the composition of the hemicellulose backbone and the branching groups. Temperature of the water can selec­tively solubilize hemicelluloses. A 75% maximum xylan solubilization in the hot water extract of sugar maple was obtained at 175 °C after 2 h, whereas only 30% of the initial xylan was removed from a 2 h treatment at 152 °C (Mittal et al., 2009). When the water temperature exceeds 180 °C an exothermal reaction begins. It is most likely related to the solubilization of the hemicelluloses (Brasch and Free, 1965).

Another result of the thermal process is that the pH of the extract decreases to 3—4 (Gregg and Saddler, 1996a). Portions of the hemicelluloses are hydrolyzed, which form acids such as acetic acid. These are released from acetylated polysaccharides in the wood. These acids lower the pH and catalyze the additional hydrolysis of hemicellulose (Liu and Wyman, 2003; Liu, 2008; Tunc and van Heiningen, 2008; Zhu et al., 2005).

Depending on the intensity of the hot water extraction, sugars may dehydrate. When hexose sugar dehydrates HMF, also known as HFM or 5-hydroxymethyl-

2- furaldehyde, is formed. When pentose sugar dehy­drates, furfural is formed. In addition to solubilizing hemicellulose, hot water treatment can lead to solubiliza­tion of portions of lignin (Ramos, 2003). Regardless, the produced compounds are usually phenolic heterocyclic compounds such as vanillin, vanillin alcohol, furfural and HMF. This is especially true in strong acidic
conditions. Additionally, these compounds tend to inhibit or toxify bacteria, yeast, methanogens and archae. This is a significant disadvantage in using hot water to extract cellulose and hemicellulose (Brownell et al., 1986).

Hot water extracts can be converted to desired products as well, i. e. via separation and fermentation (Liu et al., 2009; Shupe and Liu, 2009). Fermentation is also strongly inhibited when a hydrolysate is produced from a treatment containing 3% or more of solids or the treatment temperature exceeded 220 °C for 2 min. These conditions likely yield furfural or soluble lignin com­pounds. At temperatures in excess of 250 °C pyrolysis begins to take place (Laser et al., 2002). Therefore, one should avoid these high temperatures. Another undesir­able effect of thermal pretreatment is that it may increase the crystallinity index (CrI) of cellulose (Weimer et al., 1995). It is important to remove the soluble lignin com­pounds quickly. Since lignin is highly reactive, the disengaged lignin will recondense and precipitate onto the biomass (Liu and Wyman, 2003). This seems to be more prevalent in cases where severe pretreatment con­ditions are used. In these cases, more condensation and precipitation of lignin compounds takes place and sometimes, soluble hemicellulosic compounds such as furfural and HMF are also produced (Mittal et al., 2009) and polymerized (condensed) and deposited onto the extracted biomass.

Despite the undesirable effects above, when compared to other pretreatment methods, liquid hot water wood extraction still has a major advantage. Since a large vol­ume of water is used the solubilized hemicelluloses and lignin compounds appear in lower concentrations. As a result, the risk of undesirable degradation products is reduced. The substances in the extract can be separated and converted to desired products.

Figure 27.6 illustrates the three methods of liquid hot water reactors. They are differentiated by their configu­rations. One is cocurrent, another is countercurrent and the third is a flow-through reactor.

Briefly, in cocurrent pretreatment, the biomass and water are heated and held at the desired conditions for a specific residence time prior to allowing it to cool. In the countercurrent design, water and lignocel — lulosic material flow in opposite directions through the reactor. The flow-through reactor is designed such that hot water is passed over a stationary bed of LB and carries the hydrolysate and dissolved lignocellulosic components out of the reactor (Hendriks and Zeeman, 2009).

Biochar has been reported to have the potential to be used as an amendment in plant nurseries.

FIGURE 25.4 Nutrient-positive, nutrient-neutral, and nutrient-negative agricultural and silvicultural systems.

For example, when 25% biochar was mixed with 75% peat, enhanced hydraulic conductivity and water retention were observed (Dumroese et al., 2011). Addi­tionally, this study showed that the expansion of pelletized biochar (biochar that has been compressed with a binding agent in order to increase particle size), when wetted nearly offset the shrinkage typi­cally exhibited by peat over time. A coconut fiber and tuff growing medium was shown to induce improved resistance of tomatoes to the necrotrophic
fungus Botrytis cinerea when mixed with biochar at rates as low as 0.5% w/w (Elad et al., 2011). In another study, coconut fiber and tuff growing medium was shown to increase leaf size, plant height, flower devel­opment, and crop yield in pepper plants across all application rates from 1% to 5% w/w (Graber et al., 2010). In addition to container growth media, research is currently being conducted into the effects of plant containers constructed from molded biochar (Pulver,

2013) .

CONCLUSIONS, KNOWLEDGE GAPS,
AND RESEARCH NEEDS

It is critical to understand that biochar is not a single material, but rather an entire class of materials (Spokas et al., 2012a) with a broad spectrum of chemical,
physical, and biological properties that are drawn from both the diversity of feedstocks, production methods, and postproduction intermediary uses. It is also equally important to recognize the environmentally beneficial functions that biochar can perform after production and before application to soil and that there may be

desirable uses for biochars that are not suited to soil amelioration (Figure 25.9). Long-term field trial data related to biochar functions and properties as they change over time are extremely limited (Verheijen et al., 2010). Glasshouse projects that may display poten­tial field scale benefits of biochar should be conducted, and continually monitored in order to measure, rather than project, what may be achievable for agriculture and the environment using biochar. It will be essential moving forward to be able to predict the sorption longevity and saturation point of biochars for pesticides and other pollutants. It is unknown if over time biochar in soil will lose or retain its ability to deactivate herbicides (Kookana et al., 2011). Similar temporal uncertainties exist in relation to most other biochar char­acteristics, aside from C stability. The understanding of both the short — and long-term effects of biochar on soil microbial communities remains limited (Sohi et al.,

2008) , yet is of critical importance due to the important role of microbes in many nutrient cycles and pollutant degradation pathways. Biochar uses that precede its incorporation into soil remain largely uninvestigated. Research related to the potential suitability of biochar for intermediate uses before application to soil, such as surface water filtration, enteric mitigation of methane production in ruminants, container media, and landfill cover is almost nonexistent. However, biochar itself has only recently expanded to become the focus of scientific research worldwide, so perhaps research into indirect biochar uses will progress accordingly.

Acknowledgments

The authors would like to thank Christian Pulver at Cornell University for his comments on the chapter.