Depending on the goal and scope of the LCA, choices regarding system definition and boundaries are more or less accurate. The goal may be process design-, operation-, or policy-oriented. While the definition of the system is more detailed in case of design or oper­ation improvement, the flowchart of biofuel pathways is simplified for policy-related LCA. In that latter case, the system boundaries are adapted to the purpose. For instance, if the intent is the comparison of various pathways of the same biofuel (e. g., bioethanol), a WtT LCA is appropriate because the pathways do not affect the performance of the fuel combustion in the vehicle’s engine. The situation changes dramatically if the LCA intends to compare selected biofuels with their fossil substitutes, for example, bioethanol blends versus gasoline or more generally when different kinds of fuels and blends are compared. In these cases, the utilization stage plays a crucial role as the energy need in the vehicle tank for a given ser­vice (e. g., 100 veh. km) depends on the combustion performances that in turn vary from one blend to the other. Ignoring this important factor even for simplicity will lead to implicit assumptions on the combustion performances and therefore may induce inconsistency.

However, several authors used WtT boundaries while comparing GHG emissions of biofuels and fossil fuels (e. g., ADEME-DIREM-PWC, 2002; Elsayed et al., 2003). In other stud­ies, the WtT was only a step for a complete WtWs assessment (e. g., Beer and Grant, 2007; CONCAWE-EUCAR-JRC, 2008; EMPA, 2007a; GM-LBST, 2002; Gnansounou and Dauriat, 2004; VIEWLS, 2005). Other aspects concerning the system definition and boundaries are the inclusion or not of land-use change and coproducts as part of the system. These two issues are addressed later on.

Biomass such as woody waste and food waste can be converted to a renewable energy source by means of carbonization processes. Carbonization processes for biomass is one of several technologies concerned with producing renewable energy sources and effectively reducing greenhouse gas production. Carbonization is done to obtain charcoal by heating solid biomass in the absence of air or oxygen. Carbonization is the term for the conversion of an organic substance into carbon or a carbon-containing residue through pyrolysis or destructive distillation. When biomaterial is exposed to sudden searing heat, it can be carbonized extremely quickly, turning it into solid carbon. From the point of view of waste, woody waste, food waste, and sewage sludge can be considered to contribute to biomass. The basic characteristics of woody waste and food waste, such as proximate analysis and heating value, are evaluated before carrying out carbonization tests. Medium-sized and small enterprises have been using carbonization technology for biomass, but the method is not used in large-scale operations because the production of carbonization residue by conventional technology is inefficient and uneconomical.

1.2 Definition of the System Under Study

The comparative analysis presented in this chapter is based on a reference case defined as follows: bioethanol is produced from wheat in a facility with a capacity of 40,000 t/yr (i. e.,

134,0 t/yr of wheat). The corresponding agricultural area is of the order of 20,900 ha located in the region surrounding the ethanol plant. Beside fuel ethanol, the plant also produces about 48,600 t/yr of DDGS. Fuel ethanol is distributed over an average distance of 250 km (100 km by lorry and 150 km by train). The cultivation of wheat is carried out under the usual practice in Switzerland, with an average yield of 6.425 t/ha of grains (fresh matter at 15% wt. moisture) and 3.915 t/ha of straw (fresh matter at 15% wt. mois­ture). The grains are sent to the plant over a distance of 50 km (10 km by tractor and 40 km by lorry).

A simplified flow diagram of bioethanol production is presented in Figure 4. The stages common to both bioethanol and DDGS are shown in block A and include grinding,

liquefaction, saccharification, fermentation, and distillation. Block B represents the stillage treatment, specific to DDGS. Block C is the dehydration stage, specific to bioethanol. When applicable, the allocation of impacts between bioethanol and DDGS is performed at the point of separation, after the distillation stage in this case (i. e., between hydrated ethanol and stillage). Allocation therefore applies to block A only (incl. production and delivery of wheat). The impacts associated to blocks B and C are fully allocated to DDGS and bioethanol, respectively.

Regarding the utilization phase, various blends are considered in this chapter. Each of these fuel blends has a specific performance (expressed in terms of fuel consumption per 100 km). The vehicle considered is a standard EURO 3 light-duty vehicle.

Lignocellulosic biomass mainly consists of three components, namely, cellulose, hemi — cellulose, and lignin. Cellulose (major component) 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. Pretreatment methods are subject to ongoing and intense research worldwide. Possible pretreatment methods can be classified as follows, although not all of them have been developed yet enough to be feasible for applications in large-scale processes (Taherzadeh and Karimi, 2008):

i. Physical pretreatments: milling (ball milling, two-roll milling, hammer milling, colloid milling, vibroenergy milling), irradiation (gamma ray, electron beam, microwave), others (hydrothermal, high-pressure steaming, expansion, extrusion, pyrolysis)

ii. Chemical and physicochemical pretreatment methods: explosion (steam explosion, ammonia fiber explosion, CO2 explosion, SO2 explosion),alkali treatment (treatment with sodium hydroxide, ammonia or ammonium sulfite), acid treatment (sulfuric acid, hydrochloric acid, phosphoric acid), gas treatment (chlorine dioxide, nitrogen dioxide, sulfur dioxide), addition of oxidizing agents (hydrogen peroxide, wet oxidation, ozone), solvent extraction of lignin (ethanol-water extraction, benzene-water extraction, ethylene glycol extraction, butanol-water extraction, swelling agents)

iii. Biological pretreatments (fungi and actinomycetes)

Mechanical comminuting reduces cellulose crystallinity, but power consumption is usu­ally higher than inherent biomass energy. Steam explosion causes hemicellulose degradation and lignin transformation and is cost effective but destroys a portion of the xylan fraction, causes incomplete disruption of the lignin-carbohydrate matrix, and generates compounds inhibitory to microorganism. 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. This process is not efficient for biomass with high lignin content. CO2 explosion increases accessible surface area; are cost effective and do not cause formation of inhibitory compounds but does not modify lignin or hemicelluloses. Ozonolysis reduces lignin content and do not produce toxic residues, but a large requirement of ozone makes it very expensive. Acid hydrolysis hydrolyzes hemicellulose to xylose and other sugars and alters lignin structure. Its disadvantages are high cost, equipment corrosion, and formation of toxic substances. Alkaline hydrolysis removes hemicelluloses and lignin and increases accessible surface area but long residence times are required, irre­coverable salts are formed and incorporated into biomass. Organosolv hydrolyzes lignin and hemicelluloses but solvents need to be drained from the reactor, evaporated, condensed, and recycled; hence, the process cost becomes high. Pulsed electrical field process is carried out in ambient conditions which disrupts plant cells and is simple equipment, but this pro­cess needs more research. Biological process involves degradation of lignin and hemi- celluloses and has low-energy requirements, but the rate of hydrolysis is very low (Kumar et al., 2009b).

Lignocellulosic biomass has lignin, cellulose, and hemicelluloses with the complex structures with high molecular weight. The selective and effective lignocellulosic biomass conversion methods are highly desirable to produce the wide range of usable hydrocarbons as fuels, chemicals, and other products. The decomposition of complex structure can be performed by using biochemical and thermochemical methods using conventional and nonconventional energy sources.

When comparing biofuels with fossil fuels, it is of utmost importance to consider the same relevant service from the various systems. In case of motor fuels, as long as mobility is concerned, this service must be related to mechanical energy, in other words, to the distance travelled. Most studies however choose 1 MJth of fuel (in the tank) as the functional unit, regardless of the type of fuel (ADEME-DIREM-PWC, 2002; Elsayed et al., 2003; EMPA, 2007a; GM-LBST, 2002; Malca and Freire, 2006; Shapouri et al., 2002). This choice is not rele­vant as the mechanical efficiency can vary from one fuel or engine to the other.

For example, several tests (AEAT, 2002; EMPA, 2007b; IDIADA, 2003) have shown that the consumption of E5 (fuel blend consisting of 5% vol. bioethanol and 95% vol. gasoline) in liters is slightly less than the consumption of gasoline for the same service, that is, 100 km. In this specific case, it means that 1 MJth gasoline should be compared with less than 1 MJth E5. For simplicity, if one considers that the consumption of gasoline (in liters per 100 km) equals that of E5, then, 1 liter of fuel (gasoline or ethanol) should be a good functional unit for comparing ethanol with gasoline when the blend is E5. Using (even for simplicity) 1 MJth of fuel as the functional unit, when comparing gasoline to ethanol, means that one makes the implicit choice that 1 liter of gasoline should be compared with 1.5 liter of ethanol (given as the ratio of the LHV of gasoline, i. e., 31.9 MJth/l, to the LHV of bioethanol, i. e., 21.2 MJth/l). This choice between liter and MJth would be relevant however if ethanol were used as pure fuel (or at least as the main component of the fuel blend, e. g., E85) or in the case of heat applications.

ADEME (2010) has considered the effect of biofuels incorporation rate on the vehicle/fuel performance (in terms of liters per 100 km or MJfuei/km).

HTC is a thermochemical conversion process for biomass to yield a solid, coal-like product. It has been used for almost a century in different sciences, mainly to simulate natural coalifi — cation in the laboratory. Due to the need for efficient biomass conversion technologies, HTC has attracted some interest as a possible application for biomass in recent years, and R&D projects have been launched to assess its feasibility and discover additional possibilities for applications. HTC has been in use as a method for simulating natural coalification in coal petrology for nearly a century, and many experimental results have been published. It was introduced to this research field by Bergius as early as 1913 and was discussed controversially from then on. HTC is an exothermic process that lowers both the oxygen and hydrogen content of the feed (described by the molecular O/C and H/C ratio) by mainly dehydration and decarboxylation to raise its carbon content with the aim of achieving a higher calorific value. This is achieved by applying temperatures of 180-200 °C in a suspension of biomass and water at saturated pressure for several hours. With this conversion process, a lignite-like, easy-to-handle fuel with well-defined properties can be created from biomass residues, even with high moisture content. Thus, it may contribute to a wider application of biomass for energetic purposes (Behar and Hatcher, 1995; Funke and Ziegle, 2009; Mukherjee et al., 1996; Payne and Ortoleva, 2001; Ross et al., 1991; Siskin and Katritzky, 1991; Wolfs et al., 1960).

Many chemical reactions that might appear during HTC have been mentioned throughout the literature, but just few have been the focus of detailed investigations, for example, the hydrolysis of cellulose. It has been realized that the process is governed in sum by dehy­dration and decarboxylation, which means that it is exothermal. Simultaneously, functional groups are being eliminated to some extent. But the complex reaction network is not known in detail. So, for the time being, only a separate discussion of general reaction mechanisms that have been identified can provide useful information about possibilities of manipulating the reaction. These mechanisms include hydrolysis, dehydration, decarboxylation, conden­sation polymerization, and aromatization. They do not represent consecutive reaction steps but rather form a parallel network of different reaction paths. It is understood that the detailed nature of these mechanisms, as well as their relative significance during the course of reaction, primarily depends on the type of feed.

Although HTC has been known for nearly a century, it has received little attention in current biomass conversion research. Although it received great attention for biomass lique­faction and gasification, a technical implementation of HTC has only been developed with comparably low effort. This may be due to the fact that coal as an energy carrier is inferior to liquid or gaseous fuels. On the other hand, process requirements of HTC are comparably low while producing a fuel that is easier to handle and store because it is stable and nontoxic. Due to these facts, HTC may provide some advantages when considering small-scale, decentralized applications. Moreover, it might become a viable option for the production of functional carbonaceous materials.

The mildest reaction conditions in terms of temperature and pressure are employed in HTC. Lignocellulosic substrates have been extensively examined (Titirici et al., 2007) as reactants at temperatures from 170 to 250 °C over a period of a few hours to a day (Heilmann et al., 2010). Latest research on HTC focused on the preparation of functional carbonaceous materials and achieved interesting results for a future application to produce even more value-added materials. Low-value and widely available biomass can be converted into interesting carbon nanostructures using environment-friendly steps. These low-cost nanostructured carbon materials can then be designed for applications in crucial fields such as separation, energy conversion, and catalysis. Besides controlling the chemistry of carboni­zation (i. e., C—C linkage), two other important prerequisites for the achievement of useful properties are the control over morphology both at nano — and macroscale and the control over functionality by chemical means in HTC (Titirici and Antonietti, 2010).

The effect of various methodological choices on the GHG and energy balance of bioethanol is evaluated, with an emphasis on allocation methods, land-use change, fuel blends, and vehicle/fuel performance. Each of these aspects is now explained in more detail.

1.2.1 Allocation Methods

Various allocation methods were investigated, including allocation by energy content, eco­nomic value, carbon content, dry mass, and substitution. The properties and prices of the coproducts are given in Table 4. Four various substitution scenarios are considered, namely: S-1) both straw and DDGS as animal feed, S-2) straw as animal feed and DDGS as fuel, S-3) straw as fuel and DDGS as animal feed, and S-4) both straw and DDGS as fuel. Each of these scenarios gives rise to a specific system definition (incl. the reference system). The "from" (reference) and "to" (studied) systems in the case of allocation (regardless of the method) and substitution (S-1) are illustrated in Figures 2 and 3, respectively.

Following pretreatment, woody biomass can be converted into simple sugars by enzymatic deconstruction via a cellulase treatment. This remains the second most expensive component in the bioconversion of wood to bioethanol, despite the fact that research studies over the past decade have decreased cellulase costs by greater than a 10-fold basis. Numerous publications and reviews have highlighted the use of (i) separate hydrolysis and fermentation (SHF) and

(ii) simultaneous saccharification and fermentation (SSF) to convert pretreated wood to ethanol (Wingren et al., 2003; Wyman, 1994). A process challenge in the conversion of wood to biofuels is the efficient conversion of all wood sugars (i. e., C5 and C6) to ethanol, especially for hardwoods which have greater amounts of pentoses.

One promising strategy has been to take a natural hexose ethanologen and add the pathways to convert other sugars (Helle et al., 2004; Lawford and Rousseau, 2002). An alter­native approach to minimize the cost of cellulose deconstruction and conversion to ethanol is consolidated bioprocessing (CBP). CBP involves (i) bioproduction of cellulolytic enzymes from thermophilic anaerobic microbes, (ii) hydrolysis of plant polysaccharides to simple sugars and (iii) their subsequent fermentation to ethanol all in one stage (Lynd et al.,

2005) . This bioprocess is projected to reduce the cost of bioethanol by a factor of four over SSF, and these reduced costs and simplicity of operation have heightened research in this field.

In practice, two LCA methods can be distinguished. The attributional LCA is concerned with evaluation of a given product without any consideration of the interactions with a more global system such as the socioeconomic system or the agricultural system. Furthermore, this type of LCA is not in a comparative framework. For example, its purpose could be to improve a given pathway. In that case, the reference system is a baseline of the pathway. However, the public debate on biofuels is rather related to their "renewability" and carbon neutrality. For that reason, a more open methodology is required closed to the consequential LCA. Finally, it is proposed to include these two methodologies into a more general one based on system analysis. In the proposed methodology, the performance indicators are defined by comparing the studies system with a reference or baseline system. In most studies, the reference system is implicitly limited to a fossil fuel pathway (e. g., gasoline or diesel). In various cases, however, this picture is not complete: for example, when coproducts from the biofuel pathway replace an existing product whose performances are significantly different. In this situation, a refer­ence substituted product should be defined. The same applies to the case when the produc­tion of feedstock for biofuels uses land that was previously storing carbon such as forests or grasslands. In this case, a "previous land-use" baseline should be included in order to deter­mine the carbon emissions from this change of land use. When the same feedstock or the land was previously used for another purpose, an "alternative biomass use" or "alternative land use," respectively, may be included in the baseline in order to estimate the effects due to indi­rect land-use changes. The choice to include or not an "alternative use" depends on the assumption made concerning the substitution versus the addition of products. For example, if biofuels substitute overproduced food crops, there is no requirement for additional resources for replacing the substituted products. Conversely, in case of underproduction due to biofuels, additional resources of land or imported products will be required.

In the past, the land-use baseline was included (in a simplified way) in a very limited num­ber of the LCA studies (e. g., ADEME, 2010; CONCAWE-EUCAR-JRC, 2008; GM-LBST, 2002; VIEWLS, 2005). In these three cases, the land used for growing energy crops was considered to be initially set aside (incl. extensive green crop cover with no farming inputs), and conse­quently no alternative use of land or biomass was assumed.

The process uses microwave heating at 200 °C in acidic aqueous media to carbonize pine sawdust (Pinus sp.) and a-cellulose (Solucell®) at three different reaction times. Elemental analysis showed that the lignocellulosic samples subjected to MAHC yielded carbon — enriched material 50% higher than raw materials. In order to qualitatively evaluate the carbonization process, H/C and O/C were plotted using the van Krevelen (1950) diagram, which provides information about the changes in chemical structure after carbonization. These results showed that microwave-assisted HTC is an innovative approach to obtain carbonized lignocellulosic materials (Guiotoku et al., 2009).