Biodiesel production costs are mainly made up of three components: feedstocks costs, capital costs and by-product credits (glycerol). Particularly, the refined production cost of biodiesel is very close to the price of the feedstock because capital costs for biodiesel production are minimum and by-product glycerol has currently a very low value. However, if glycerol is integrated into biofuel composition, the production efficiency of this novel biofuel can be increased over 10%. The last step of washing and cleaning of the biodiesel in the conventional synthetic process [to clean the biodiesel and remove the traces of glycerol up to 0.02% glycerol (EN 14214)] can also be removed, reducing costs and generation of waste water.28 High glycerol concentrations in the fuel cause various problems, including coking, viscosity increase and a potential dehydration to acrolein that can be further polymerized. Coking can also generate deposits of carbonaceous compounds on the injector nozzles, pistons and valves in standard engines, reducing the efficiency of the engines (Fig. 7.1).29,30

Recent investigations have also shown that minor components of biodiesel, usually considered contaminants under the biodiesel standard EN 14214, including FFAs and monoacyl glycerols or MGs, are essentially responsible for the lubricity of low-level blends of biodiesel and diesel fossil. Pure FAMEs exhibit a reduced lubricity compared to the biodiesel containing these

CH2OH-CHOH-CH2OH ________________ ^

Glycerin

2 CH2=CH-CHO + 02 —————————— ►

Acrolein

n [CH2=CH-COOH] ————————— ►

Acrylic acid

Acrylic resin

7.1 Dehydration (1), oxidation (2) and polymerization (3) reactions experienced by the residual glycerine in biodiesel into diesel engines.

compounds.31-36 The presence of greater quantities of MGs and/or FFAs enhances the lubricity of biodiesel, which is another key feature of these novel biofuels that incorporates high amounts of MG, since their presence improves performance and preserves the life of the engines.

Three types of reported biofuels integrating glycerol (Ecodiesel®, DMC — Biod®, Gliperol®) and the respective technologies to produce them will be the subject of the following sections.

The ABE fermentation of sugars and starch meanwhile is a mature process. The simplest method is batch fermentation combined with distillation (see below) to separate the solvents from the culture. Depending on the choice of substrate, it takes from around 30 hours up to six days to complete a run. Using this method, cell concentrations of up to 4 g/l and maximal solvent concentrations of 16-20 g/l (with a productivity of up to 0.5 g/l/h) could be reached, before solvent toxicity (see Section 10.5) inhibits further growth.

Higher yields could be achieved in fed-batch or continuous fermentations, but it is essential to have a proper product removal process in place (see below; Eckert and Schugerl, 1987; Ezeji et al, 2004). However, during prolonged or continuous cultivation, cells show a tendency to lose the ability to produce solvents. In C. acetobutylicum, this effect could be traced back to loss of the megaplasmid pSOL1 (Bahl, Andersch, and Gottschalk, 1982; Cornillot et al., 1997), which contains most of the genes required for solvent production (see Section 10.3). However, strain degeneration can also occur in C. beijerinckii (Kashket and Cao, 1993), which does not harbor any plasmids at all. Two systems were developed to monitor strain degeneration, using infrared spectrometry (Schuster et al., 2001) or real-time PCR (Lee et al., 2010) methods, respectively. However, it is possible to prevent strain degeneration in C. acetobutylicum cultures by limiting phosphate (Ezeji et al., 2005) and in C. beijerinckii cultures by addition of 20 mM sodium acetate (Chen and Blaschek, 1999a, 1999b). Another problem is the biphasic nature of the clostridial metabolism (see Section 10.2), which is not well suited for continuous fermentations. To overcome this issue, butyrate feeding was applied (Bahl, Andersch, Braun, et al. 1982; Qureshi et al., 2004; Tashiro et al., 2004) and two-stage (Bahl, Andersch, and Gottschalk, 1982; Godin and Engasser, 1990; Mutschlechner et al, 2000) or multi-stage (Ni and Sun, 2009; Zverlov et al., 2006) fermentations were designed.

The use of immobilized bioreactors proved to be advantageous as well, not only to increase the length of fermentation but also to increase cell concentrations and reaction rates (Qureshi, Annous, et al., 2005). Immobilized cell techniques have already been applied for ABE fermentation since the 1980s (Krouwel et al, 1983), and various supports and reactor configurations (Table 10.4) have meanwhile been tested with great success. In a plug-flow reactor using clay brick as a support, a reactor productivity of 16.2 g/l/h could be achieved with C. beijerinckii (Lienhardt et al, 2002), while cell concentrations of 74 g/l were reported for C. acetobutylicum in a packed bed reactor with bone charcoal as support (Qureshi et al., 1988). Another possibility to achieve high cell concentrations is the use of cell recycle reactors (Yang and Tsao, 1995). However, fouling of membranes is often a problem with such processes.

Regardless of the fermentation method, attention should be paid to some general factors. It is important to maintain a redox potential of -250 mV or less (Kim et al, 1988), since the pyruvate:ferredoxin-oxidoreductase (one of the key enzymes of the clostridial metabolism; see Section 10.2) transfers electrons at a very low potential (Meinecke et al, 1989). Another critical point is the pH value (see Section 10.2). Although low amounts of butanol can be produced at a neutral pH (Fontaine et al., 2002; Holt et al., 1984), in general, a low pH value is required for solvent production. However, if the pH decreases too fast (e. g. in poorly buffered media), a sudden termination of solventogenesis (known as ‘acid crash’) may occur (Maddox et al., 2000).

10.3.2 Downstream processing

The traditional product recovery process is distillation carried out at the end of growth. The separation is a result of the different boiling points of water (100°C at standard pressure), acetone (56°C), butanol (117°C) and ethanol (78°C). High energy and disposal costs notwithstanding this technique is still used for batch fermentations. However, continuous fermentations require integrated recovery techniques, since high butanol concentrations in the fermentation broth are growth limiting (see Section 10.5).

Adsorption is an attractive alternative, which can be used in situ and has a low energy requirement (Qureshi, Hughes, et al., 2005). On the other hand, this technique offers only a low selectivity and nutrients are often removed from the media as well. Moreover, the prices of the resins are (still) too high.

A relatively inexpensive and simple method is gas stripping (Ennis et al., 1986; Ezeji et al., 2004; Groot et al., 1989). During the ABE fermentation, high amounts of CO2 and H2 gases are generated, which could be used to capture the solvents from the fermentation broth. The gases are sparged through the fermentation broth, cooled down in a condenser to strip off the solvents, and then recycled back into the fermenter to recover more solvents. However, this technique is not capable of a complete solvent removal from the fermentation broth and also has a low selectivity.

A method that offers higher selectivity is liquid-liquid extraction, in which a water insoluble organic extractant is mixed with the fermentation broth (Ezeji et al., 2007). Since butanol is more soluble in organic than in aqueous solutions, it selectively accumulates in the organic phase of the extractant. However, only few non-toxic extractants such as oleyl alcohol are known.

To overcome this issue, perstraction was developed (Qureshi and Maddox, 2005), a technique by which a membrane separates the fermentation broth from the extractant. Unfortunately, membranes are generally expensive and often suffer from clogging and fouling problems.

This is also true for other recovery processes such as pervaporation (Friedl et al., 1991; Geng and Park, 1994; Groot et al., 1984; Izak et al., 2008; Jitesh et al., 2000; Larrayoz and Puigjaner, 1987; Matsumura et al., 1992; Qureshi and Blaschek, 1999, 2000) and reverse osmosis (Garcia III et al., 1985), which are based on selective semi-permeable membranes. Separation of the solvents is accomplished by vaporation and high pressures, respectively.

Hydrogen can also be produced through a microbial electrolysis cells (MEC) which is a modified microbial fuel cell (MFC) converting directly biodegradable material into hydrogen instead of electricity (Call and Logan, 2008). In a typical MF C, protons released by the oxidation of the organic substrate in the anode, migrate through an external load to the cathode to combine with oxygen and form water. A MEC operates under anaerobic conditions (no oxygen in the cathode) and a small external voltage is applied to the cell, so that protons and electrons produced by the anodic reaction are combined at the cathode to form hydrogen. The power supply is required since hydrogen generation from the protons and the electrons is thermodynamically unfavorable (Liu et al., 2005) and with external potential application, the cathode potential increases overcoming the thermodynamic barrier. The required external potential for a MEC is theoretically 110 mV. In practice, the minimum applied voltage to produce hydrogen from the bioelectrolysis of a pure substrate such as acetate, has been found to be more than 250 mV due to ohmic resistances and electrode overpotentials. This value is still much lower than the respective one required for direct electrolysis of water, which is 1210 mV (Liu et al., 2005).

MEC can potentially produce about 8-9 mol H2/mol of glucose consumed, which is double, compared to the typical 4 mol H2/mol glucose, achieved in a conventional fermentation process (see Section 13.3.2). The MEC compared to the MFC, has the advantage that there is no need for oxygen in the cathodic chamber affecting in the better performance of the system (Das and Veziroglu, 2008) and leading to improved efficiencies from an economic point of view.

Under certain conditions, methane which is competitive to hydrogen can also be generated in a MFC. Strategies to control and suppress methanogenesis have been proposed (Call and Logan, 2008), resulting in more complex and expensive systems, with significantly increased operation requirements. Up to now, the majority of researchers on MECs systems have investigated the use of pure compounds (primarily acetate) as the substrate. However, alternative substrates such as domestic or animal wastewaters can be used (Ditzig et al., 2007; Wagner et al., 2009) but the performance of such systems is limited in terms of hydrogen yields due to the appreciable methane gas production.

Different reactor configurations have been proposed for hydrogen production through MECs. Two-chamber (Liu et al., 2005; Cheng and Logan, 2007) or one-chamber (Call and Logan, 2008) systems, with membrane (Rozendal et al., 2007) or without membrane (Call and Logan, 2008) are some of the characteristics of the MECs developed in laboratories. One of the challenges in scaling up MECs is the cost of the cathode and the cathode catalysts since most MECs use platinum applied on carbon cloth (Ditzig et al., 2007; Call and Logan, 2008) or carbon paper (Liu et al., 2008). In order to improve the performance and economic feasibility of MECs, platinum needs to be replaced by alternative low-cost cathode materials such as stainless steel (Selembo et al., 2009) or microbial biocathodes (Jeremiasse et al., in press). In addition to these limitations, securing viable continuous operation, operation under carbon limited conditions, ways of increasing the microorganisms tolerance to impurities, and the possible use of alternative feedstocks, are all issues that need to be investigated. Although promising, this is still an experimental method for hydrogen production which has not been evolved beyond the laboratory since certain microbiological, technological and economic challenges need to be resolved before full-scale implementation.

R. LUQUE AND J. M. CAMPELO, Universidad de Cordoba, Spain and J. H. CLARK, University of York, UK

1.1 Introduction

The urgency to identify a more sustainable way forward for society has become clear with alarming trends in global energy demand, the finite nature of fossil fuel reserves, the need to dramatically curb emissions of greenhouse gases (GHG) to mitigate the devastating consequences of climate change, the damaging volatility of oil prices (in particular for the transport sector) and the geopolitical instability in supplier regions. Currently, energy and the environment are two key hot topics present in all European challenges for the future. With oil prices fluctuating month after month, a cost-competitive and stable solution is needed, especially with an expected 60% increase in the demand of energy for transport by 2030 (the sector expanding in the US A and Europe and specially developing in the newly industrialised and emerging economies of China and India).1 Transport has also shown the highest rates of growth in GHG emissions in any sector over the last ten years (20% global CO2 emissions, 25% UK emissions), with a predicted 80% increase in energy use and carbon emissions by 2030.2

In order to avoid this dependence on oil and to meet the sustainability goals with regard to GHG emissions originally proposed in the 1997 Kyoto Protocol (confirmed by the European Union (EU) in 2002), clean, secure and affordable supplies of transportation fuels that involve low-carbon technologies are essential.3

In this regard, biofuels can make a significant contribution in the short-to-medium term,4 contributing to energy independence, mitigation of climate change and rural development, being reported as one of the most promising solutions (but not the only one) to help meet targets on the use of renewables and reduced emissions.5 However, thoughtful analyses of some first-generation biofuels (conventionally produced from ‘food’ crops, including wheat, maize, corn, sugar cane, rapeseed, sunflower seeds and palm oil) have been recently showing that such alternatives may be little better than traditional fossil fuels, at least, in terms of overall carbon footprint and environmental damage, despite some very promising figures reported in terms of CO2 emission savings from sugar cane bioethanol use in Brazil.6

In contrast, preliminary figures on second-generation biofuels (defined as those produced from non-food sources and including dedicated energy crops such as perennial grasses, short-rotation coppice willow and other lignocellulosic plants as well as waste biomass from agricultural, forestry, municipal solid waste, etc.) in terms of GHG emissions savings, carbon footprint and environmental damage (e. g. deforestation, biodiversity threat, food vs. fuel, etc.) are showing that these can significantly improve on first-generation biofuels. Nevertheless, most technologies for the production of second-generation biofuels from biomass/ waste are still in their infancy and those under development require pre-treatment of the feedstock in many ways (to reduce acidity, floating solids, etc.). So they are far away from being optimised, requiring more research efforts in the future.

In this book, we aim to provide an overview of the different processes and technologies available and those under development for the production of biofuels, with special emphasis on second-generation biofuels produced from biomass. The various biofuels currently produced and/or under development can be grouped according to the processes and technologies employed for their preparation. These include chemical, biological and thermo-chemical conversion.7

In the first introductory chapters, details on policies, and socio-economic and environmental implications of the implementation of biofuels (Chapter 2) as well as on life cycle analysis (LCA) (Chapter 3) and the different biofuel feedstocks (Chapter 4) will be presented. The rest of the book is aimed to give a balanced overview on key technologies and processes for the production of biofuels, from first to later generation, as outlined in the next few sections.

Peanut is an annual crop grown predominantly in the Mediterranean region (Aydin, 2007). Arachis hypogaea L., of the Fabaceae family, develops in an underground pod containing two seeds (Fig. 4.4). It is widely cultivated in warm climates and has short yellow flowers. Most peanuts grown in the world

are used for oil production, peanut butter, confections and snack products (Yu et al., 2007). Peanut oil is a pale yellow oil with a distinctive nutty taste and odour obtained from the processing of peanut kernel (Oyinlola et al., 2004; Aydin, 2007).

Studies about biodiesel production from peanut oil have been carried (Kaya et al., 2009) out and minimisation of the concentration of long-chain saturated fatty acids has been suggested, either through processing or breeding efforts, to improve cold weather properties (Davis et al., 2009). Even Rudolf Diesel (1900) used straight peanut oil to run the diesel engine. In 1911, he wrote ‘The diesel engine can be fed with vegetable oils and would help considerably in the development of agriculture of countries which will use it’ (Kaya et al., 2009).

Pre-treatment of the feedstocks and the reaction conditions for the transesterification are influencing a number of biodiesel parameters such as ester content, acid number, glycerides content, glycerol content, total contaminations, metal content, ash and phosphorus.

The ester content is decreased by the presence of water in the feedstock, reactor and/or catalyst causing deactivation of the catalyst. Presence of FFAs can give rise to soap formation resulting in inadequate transesterification and poor layer separation due to emulsion formation. Poor catalyst neutralization after the reaction is causing hydrolysis and soap formation. The ester yields can be upgraded by: (1) drying of the feedstocks for water removal and (2) removal of FFAs via neutralization, stripping, alcohol extraction, combined esterification and transesterification, and (3) post-purification by distillation, filtration or adsorption.

The acid number of the biodiesel is too high due to non-removal of FFAs by refining or acid esterification, hydrolysis of methy esters during washing due to the presence of catalyst, hydrolysis during storage, presence of mineral acids due to the poor layer separation in work-up and washing.

Too high concentrations of mono-, di — and triglycerides arise from inefficient transesterification due to deactivation of the catalyst due to the presence of water or FFA. Another reason is a back reaction in which the glycerol anion is reacting with the FAMEs at low methanol concentration, especially during evaporation of the methanol in alkaline conditions. The presence of monoglycerides gives various problems. Monoglycerides are excellent emulsifiers leading to poor layer separation that results in high water, glycerol concentration, high total ash and contaminants and higher viscosity. In addition monoglycerides are easily precipitated leading to high CP and cold soak test.

Metal/mineral/ash content can be high due to poor layer separation, washing with hard water or due to the inappropriate pre-treatment of the feedstocks. However, post-treatment (adsorption and distillation) can solve these problems. Phosphorus and sulfur content of biodiesel can also be too high due to the nature of the feedstocks or the lack of efficient refining or pre-treatment and needs to be controlled.

The oxidative stability can be maintained by the exclusion of air during processing and storage by adding synthetic anti-oxidants and by post-treatment by adsorption.

Biodiesel in accordance with the standards will be dependent upon used feedstocks (especially for the physical parameters), used technology/processing/ reaction conditions (particularly for the chemical parameters and purity) and post­treatment (which is leading to an improvement of the biodiesel quality but also to additional costs and adequate combination of feedstock processing).

5.5 Conclusions and future trends

Biodiesel is a renewable alternative to substitute petrodiesel. It was expected that by 2010, 5.75% biofuels should be used of which the majority will be biodiesel. Petrodiesel can be substituted by maximum 20% biodiesel without modifications of the engine. In the EU, the majority of blending is in the range four to seven per cent. In order to reach the biodiesel standards, refined oils and fats are the most suitable feedstocks. However, this is creating a competition with the food and feed applications.

Therefore, there is an increase in attention for other resources which are not creating ethical problems. Biodiesel can be prepared from waste or used oils and fats and from resources which are not competing with the food applications. Non-edible feedstocks such as jatropha and other seed oils can be converted into biodiesel using conventional processes. Algae oil has also a great potential to be a widespread feedstock in the future.

At this moment, biodiesel is mainly produced on industrial scale by homo­geneous catalyzed transesterification. The use of heterogeneous catalysis is however looking promising with the advantage of easier post-treatment of glycerol. However, only two plants are now in operation using alkaline heterogeneous catalysts.

Many trials have been performed on laboratory scale using enzymatic production of biodiesel, we refer the readers to Chapter 6 in which this topic has been covered in detail.

The advantage of this technique is that simultaneously FFAs and TAGs are converted into FAAE. However, no industrial applications using enzymes are available until now.

Various other modifications have been proposed either to facilitate the reaction or to avoid pre — and/or post-treatment. Processes using solvents, microwave techniques, microreactors and others are proposed but these are not operating at large scale. The majority of methanol utilized for biodiesel transesterification is produced via petrochemistry. In order to be completely renewable, ethanol can be used. Bio-butanol produced by fermentation is also looking very promising in order to produce a complete green and renewable biofuel (see Chapter 9 for more details).

At this moment, the boom in biodiesel production is stopped and the capacity is used only for 50% due to the high price for the feedstocks and the cut-in-tax directives. However, if 20% of the fuel should be renewable for 2020, biodiesel is one of the most promising options to fulfill this goal.

The conversion rate of TAGs to FAMEs, changes in the composition of biodiesel during transesterification and analysis of biodiesel characteristics are the main aspects that are investigated in most studies about biodiesel production from vegetable oils (Darnoko and Cheryan, 2000; Dorado et al., 2004; Vicente et al., 2005; Arzamendi et al., 2006). The above parameters are related to the FAME concentration resulting during transesterification and characterize biodiesel yield or purity (Vicente et al., 2007). Contrary to biodiesel production from vegetable oils, there are limited publications investigating the optimum conditions (e. g. reaction duration, reaction temperature, agitation, type and amount of catalyst, ratio of alcohol to SCO) for biodiesel production from SCO.

SCO derived from various yeast and fungi should be thoroughly compared with vegetable oils in order to justify the possibility to substitute for the current raw materials used for biodiesel production. SCO-derived biodiesel should be characterized according to biodiesel standards ASTMD 6751 (USA), DIN 51606 (Germany) and EN 14214 (European Organization). Preliminary results indicate that SCO could be regarded as a potential raw material for biodiesel production. Li et al. (2007) claimed that the fatty acid distribution of the SCO produced during fed-batch fermentations by Rhodosporidium toruloides could be converted into biodiesel with a cetane number (CN) higher than 51, which meet the minimal CN standards (47, 49 and 51) set by ASTMD 6751, DIN 51606 and EN 14214. Zhu et al. (2008) reported that the SCO produced by T. fermentans contained an unsaturated fatty acid content of 64% which is similar to that of vegetable oils but a relatively high acid value of 5.6 mg KOH/g. After pretreatment of SCO, transesterification via methanolysis resulted in a methyl ester yield of 92% (Zhu et al., 2008).

Transesterification of SCO could be carried out either directly without extraction of SCO from the microbial biomass or indirectly after extraction of SCO from microbial cells. Extraction of SCO from cellular biomass components by solvent extraction or other means will increase production cost and capital investment. It is therefore evident that future research should investigate more thoroughly the direct transesterification of SCO without extraction from microbial cells. The processing steps of direct transesterification involves separation of cellular biomass by centrifugation after the end of fermentation, washing the cells with water, drying the cells to constant weight and finally mix the dry cells with a mineral acid solution (HCL or H2SO4) and methanol (Liu and Zhao, 2007). Liu and Zhao (2007) reported that direct acid-catalyzed transesterification of SCO — rich microbial biomass from two yeast (Lipomyces. starkeyi and R. toruloides) and one fungal strain (M. isabellina) resulted in FAMEs with CN of 59.9, 63.5 and 56.4 respectively and lipid to FAME yields higher than 90% (w/w). The optimum reaction conditions applied by Liu and Zhao (2007) were 0.2 mol/L H2SO4 at 70 °C for 20 h with a biomass-to-methanol ratio of 1:20 (w/v). Vicente et al. (2009) compared the efficiency of direct transesterification with indirect transesterification (lipid extraction was carried out by 3 solvent systems including chloroform:methanol, chloroform:methanol:water and n-hexane) for biodiesel production from SCO produced by the fungal strain Mucor circinelloides. The direct transesterification method produced FAMEs with higher purities (>99%) than those from the indirect process (91.4-98.0%) and a significantly higher yield due to a more efficient lipid extraction when the acid catalyst was present (Vicente et al., 2009). The reaction conditions applied by Vicente et al. (2009) were 8% (w/w relatively to the microbial oil) BF3, H2SO4 or HCl for 8 h at 65 °C with a methanol to oil molar ratio of 60:1.

Ethylene glycol is similar in structure to glycerol. Glycerol is a C3 triol and ethylene glycol is also a polyol, but a C2 diol. Although ethylene glycol has two alcohol groups, its main application is as the main ingredient in antifreeze and not

for fuel purposes. Although it can be used, similar to glycerol, as a fuel for a fuel cell.1316 Ethylene glycol is normally produced from ethylene which is produced from fossil resources rather than biomass. However, ethylene glycol can be produced from biomass. Ethylene can be produced from sugars via microorganisms like Pseudomonas syringae and Penicillium digitatum. The bio-ethylene produced can then be used to produce ethylene glycol. However, ethylene glycol can also be produced by pyrolysis of biomass.17 Although ethylene glycol is toxic, it is easy to work with due to its low volatility and other solvent properties, so it is easy to reform and quite high in energy density. It has also been proposed that ethylene glycol can be produced from biomass like cellulose and xylan by periodate oxidation followed by reductive hydrolysis. This was shown to be successful for producing bio-ethylene glycol directly from corn residue without any isolation or purification processes.18

Agricultural practices are becoming increasingly essential for climate change because of their influential role in carbon sequestration. For example in cultivated lands carbon remains captured within the soil; if afforestation or reforestation practices are in place, carbon becomes subject of long-term sequestration as well as in the case of land or forestry rotation practices. When land is converted for fuel crops, the amount of GHG reductions depends on the net effects that the biofuels feedstock production releases on the yields (see also Section 2.3). The occurrence of positive benefits for climate change mitigation from agricultural biofuels practices is mostly not recognised by the society. On the contrary, various projects aiming at improving energy efficiency or reducing emissions generated by the industrial sector receive emission permits under the requirements of the Kyoto Protocol. Furthermore, even though the Protocol addresses carbon permits for bioenergy production, current practices to account for these mechanisms are similar to those of energy generation from grids. This leaves developing countries, where technology level is limited, incapable of contributing to GHG emission reductions and generating income from bioenergy credits. Similarly, afforestation and reforestation accounting practices for carbon payments in developing countries still remain too complex to be implemented. On the other hand, these practices have not yet been incorporated into the existing European Union Emission Trading System (ETS).

The Kyoto Protocol established three main mechanisms for carbon reductions: (1) International Emission Trading System; (2) Joint Implementation (JI) allowing carbon trading projects between developed countries and economies in transition; and (3) Clean Development Mechanism (CDM) allowing the trading of carbon reductions between developed and developing countries. The latter is an essential tool for developing countries to generate carbon credits. However, while most of current projects consist in reducing GHGs from energy efficiency, wind and solar or biomass energy projects, agricultural land-use change (including biofuels feedstock production) and afforestation and reforestation activities are not yet eligible for certified emissions in CDM. Future scenarios may be possible under post-Kyoto negotiations after 2012. These should include land-use changes (as well as afforestation and reforestation policies) to compensate countries for the carbon credits gained under land conversion for biofuels feedstock and biomass production.

Similarly, the possibility to develop a carbon trading system for bioenergy activities is under scrutiny. Brazil is moving toward the establishment of a domestic carbon market based on a cap-and-trade system for ethanol. The sugar cane industry believes that numerous advantages for the country exist (Brazil Institute, 2009). Firstly, the system would grant the industry to trade on sugar cane by-products and therefore providing opportunities to capture carbon emissions. Secondly, it would also support value-added creation encouraging the international market to purchase differentiated agricultural products and increase the supply chain worldwide. Brazil is also pushing toward an afforestation trading system to allow land-use change and forestry management to account for carbon reductions. This argument is based on Brazilian commitment to reduce deforestation by 75% by 2017 and the possibility that the United States could soon adopt a voluntary cap-and-trade mechanism on bioenergy and afforestation. The consequent realisation of a bilateral trade between Brazil and United States on these new carbon markets would decrease carbon emissions and distribute the benefits of carbon credits from bioenergy sources across farmers.

Manihot esculenta, a perennial woody shrub with an edible root used in feed formulations, is also known as cassava and tapioca (Fig. 4.11). It grows in many parts of tropical and subtropical areas, specially in places where the soil is relatively poor and other crop yields are low (Mojovic et al., 2006).

Ethanol production from cassava can be accomplished using either the whole cassava tuber or the starch extracted from it (Lopez-Ulibarri and Hall, 1997; Zhang et al, 2003). Starch extraction can be carried out through a high-yield, large-volume

industrialised process such as the Alfa Laval extraction method (FAO, 2004) or by a traditional process for small — and mid-scale plants. This process can be considered as the equivalent of the wet milling process for ethanol production from corn, while fuel ethanol production from whole cassava is equivalent to ethanol production from corn by dry milling technology. Due to its high moisture content, cassava should be transported as soon as possible from cropping areas considering its rapid deterioration (Sanchez and Cardona, 2008). Authors have found that to make ethanol competitive to gasoline, the combination of increasing crop yield and decreasing farming costs is required (Nguyen et al., 2008).