Microbial fermentation production of valuable phytochemicals may be colocated (onsite, integral use of materials or energy streams) with starch — or lignocellulose-based bioenergy processes, to benefit from locally produced, inexpensive fermentable sugars (intermediates or by-products of bioenergy processes) (Thomsen et al., 2006). In principle, all microbial fermen­tations for biochemicals production may be run on sugars converted from starch, sugarcane or lignocellu — lose in various bioenergy processes, to yield chemicals like surfactants, polyols or organic acids (Choi et al., 2007; Aalford and Morel, 2006; Mapari et al., 2005). For instance, X. dendrorhous can be grown on cellulases- digested pine and produce carotenoids (Chattopadhyay et al., 2008), and Serratia marcescens can be grown on processed cassava waste to produce prodigiosin (Casullo de Araujo et al., 2010).

Utilization of Phytochemical Production By-Products for Bioenergy

Production of valuable phytochemicals (such as those for therapeutic, cosmetic, dietary or agricultural uses) from either wild-type or transgenic plants generates lignocellulosic by-products. Such materials might serve as feedstocks for (onsite) bioenergy production. This might add value, reduce waste, and enhance raw mate­rial or energy use efficiency. For instance, the woody residues from vinblastine or vincristine production in C. roseus (Braz-Filho, 1999) or other natural products production (Simard et al., 2012), or the citrus peel resi­dues from furanocoumarins, flavonoid glycosides, poly- methoxylated flavones, triterpenoids, limonoids or peel oil extraction (Manthey, 2012), have potential as bio­energy feedstocks.

Phytochemical production has focused mainly on therapeutic, dietary or cosmetic agents from specific fruits, flowers, nuts, vegetables, or other plant sources. In comparison, less attention has been paid on phyto­chemicals coproduction in current or future bioenergy processes. Integral coproductions of biofuels, biochem­icals, phytochemicals and other valuable materials are imperative for highly efficient and viable bioenergy and biorefinery processes (Huang and Ramaswamy, 2012). In some cases, relatively simple combinations or colocations of existing bioenergy and phytochemi­cals processes may suffice to coproduce biofuels, biochemicals and phytochemicals. In other cases, new production technology or process engineering may need to be developed. To maximize the economy of raw materials and energy utilization and minimize the carbon footprint, bioenergy processes will evolve into more comprehensive biorefineries in which the coproduction of industrial phytochemicals plays an important role.

There exist several approaches proposing sustain­ability criteria for bioenergy (e. g. Cramer et al., 2007; EU, 2009; IEA, 2010; RSB, 2011; GEF et al., 2013, where the last two are very detailed). They usually cover some goal for GHG emission reductions, e. g. a 35% reduction of aggregate emissions over some time period with respect to the baseline as suggested in EU regula­tions (50% from 2017 to 60% from 2018 onwards, EU, 2009). While this seems a clear criterion, its assessment is complex. The choice of different default values, soil carbon stock data and land use change definitions, for example, is behind the huge differences in GHG bal­ances between two GHG calculation tools as assessed in Hennecke et al. (2013), one of them being the tool used by the Roundtable of Sustainable Biomaterials (RSB) whose sustainability criteria are discussed below. Other aspects are decisive as well. The choice of the time horizon over which aggregate reductions have to be achieved and the choice of the social discount rate, which influences the relative importance of current and future emissions, also greatly influence the outcome (De Gorter and Tsur, 2009).

The sustainability criteria proposed for biofuel pro­duction that relate to agricultural production and the food system, address land competition, biodiversity, environmental impacts on soil, water and air, and social aspects. Land competition, resp. absence thereof and the related food security are by far the most prominent criteria in the discussion (HLPE, 2013). Potential drivers for land competition are many. First, there is the fact that bioenergy crops need fertile land to achieve economi­cally interesting yields. Biofuels on marginal lands are some option in smallholder and community — self-sufficiency contexts, but for commercial supply of biofuels in significant shares of total global energy de­mand, production on fertile land that potentially is used for food production is necessary (cf. Section Bio­energy Potential on Farm Level). Similarly, bioenergy crop production depends on water availability and nutrient inputs as any other agricultural production sys­tem. Thus, a second potential competition is not only on fertile lands, but also on land with sufficient water avail­ability (Lysen and van Egmond, 2008), in particular in the context of climate change, where water scarcity will become a prevalent problem in many regions (Meehl et al., 2007). Third, relative price differences be­tween bioenergy and food production will be and have been a key driver behind land competition as without further regulation, land will be allocated to the most profitable production. Stated differently, an increasing demand for biofuels leads to higher prices, which trig­gers an increasing supply for it, with corresponding land use (HLPE, 2013). It has to be emphasized that land competition between food and other uses is not new and relative profitability has always been a key driver behind this. As Nhantumbo and Salomao (2010) state, "Competition for higher-value resources existed well before the biofuels campaign was initiated. In this sense, biofuels production per se cannot be blamed for land use conflicts, as the same types of conflicts have occurred in other economic activities. But, in conjunc­tion with other activities like mining, forestry and tourism, biofuels projects further exacerbate competi­tion for land, water and other resources" (p. 4). The key point is thus that biofuel expansion increases the pressure on the already scarce resource of fertile land. In principle, policy measures can be used to mitigate these adverse effects. However, their implementation is often riddled with difficulties and land-use rights pro­tection, enforcement of laws and regulations, etc. have to be carefully considered when establishing potentially promising institutions for sustainable land use. Nhan — tumbo and Salomao (2010) illustrate these challenges for the case of Mozambique and draw a rather pessi­mistic picture.

The land use debate is further complicated by ILUCs (Wicke et al., 2012). Those arise, for example, if biofuel expansion in one region (e. g. sugar cane in southern Brazil) leads to land use change in another region (in this case, deforestation for livestock production in north­ern Brazil). The rationale behind this example is the fact that expanding sugarcane in the South is at the expense of already existing pastures in this region, that then themselves relocate at the expense of other uses such as natural forests (Andrade De Sa et al., 2013). Such ef­fects are very difficult to clearly identify and assess (Wicke et al., 2012). This is also the case in the detailed analysis in Andrade De Sa et al. (2013) who find only very weak significant statistical effects. Nevertheless, there is evidence from many descriptive studies that the potential presence of such mechanisms must not be neglected (PBL, 2010). ILUC is not only relevant for the competition between different land uses but also for the GHG balances of biofuels, as it can have consider­able negative effects on those (PBL, 2010; Faist Emmenegger et al., 2012).

Biodiversity criteria mainly refer to the ban of using forests or protected areas for bioenergy production (e. g. Cramer et al., 2007; EU, 2009) or to being attentive not to use invasive species as bioenergy crops (UNEP, 2010). The use of protected areas can also be seen as a particular aspect of land competition from biofuel pro­duction. As mentioned above, biofuel production com­petes not only with food for land but also with other uses, such as biodiversity protection and also with fiber and biomaterial production that all depend on land availability. Invasive species are seen as a potential danger, due to already existing cases but also due to gen­eral characteristics of biofuel crops that also correlate with invasiveness (e. g. fast growth or tolerance to wide range of soil and climate conditions, UNEP, 2010). Much less prominent in this discussion are the adverse effects of current agricultural production on biodiversity (mainly due to overfertilization with nitro­gen and pesticide use), albeit those are a key driver behind biodiversity losses (Galloway et al. 2008). This is mentioned in Bindraban et al. (2009) and adoption of agricultural practices with low negative effects on biodiversity is a criterion in GEF (2013), but not in EU (2009) or RSB (2011).

Other environmental impacts largely remain rather unspecific in the criteria suggested, although the range of adverse environmental effects of current agricultural production as described above will also realize in bio­energy cropping systems. EU (2009) for example only posits that the production has to meet the Community environmental requirements and in GEF et al. (2013), water contamination is assumed to be no issue if legal requirements are met. The size of the adverse environ­mental effects depends on the types of crops. Grassland or wood products usually perform better than annual crops, for example, WBGU (2009). Somewhat more detailed criteria are usually given in reference to soil — related aspects such as soil fertility and soil organic car­bon contents (see e. g. Cramer et al., 2007; EU, 2009; RSB, 2011; GEF et al., 2013). Regarding soil organic carbon, some sustainability criteria explicitly exclude bioenergy cropping on peatlands and other carbon-rich soils (EU, 2009). On the other hand, some bioenergy crops are judged to be advantageous for soil carbon levels, mainly grassland and forest-based bioenergy. The effect on soil carbon is not that clear for some perennial crops and rather negative for annual crops (WBGU, 2009).

Social sustainability criteria, finally, sometimes tend to be formulated on a very general level. EU (2009), for example, only requires that source countries for bio­energy have "ratified and implemented" (p. 97) a range of conventions referring to labor rights, gender aspects, etc. RSB (2011) and GEF et al. (2013), on the other hand, are quite detailed on the social aspects that cover a range of important criteria for social sustainability in agricul­tural production. RSB (2011) and GEF et al. (2013) also make long-term economic viability of bioenergy projects a criterion for their sustainability assessment. It is not mentioned as a criterion, but bioenergy crops can have some risk-spreading characteristics as they can increase production diversity of a farm and as their demand and price dynamics likely follows different patterns than food or fiber crop demand and prices. Some types of bio­energy crops can also be used for direct on-farm energy provision without much investment needs, such as Jatropha, for example. These energy crops thus have the potential to increase energy access and reduce work­load of women considerable in case they have to collect fuel-wood from far away, which is a common situation in many poor regions in developing countries. Energy crops can also provide specific income sources for women, as many case-studies show (Karlsson and Banda, 2009). However, there is similar evidence of problematic situations from case-studies, and whether a bioenergy project is advantageous for single farmers, the community and women in particular strongly de­pends on the concrete design and institutional context. Further example of positive cases are given in Practical Action Consulting (2009), and some negative cases for example in Ribeiro and Matavel (2009), focusing on Jatropha in Mozambique.

The choice of sustainability criteria for bioenergy thus reflects the classical topics of sustainability criteria, with a focus on environmental aspects and climate change in particular. An additional aspect is land competition, which is covered extensively in the discussion. The focus on environmental criteria is understandable as bioenergy is a climate change mitigation strategy and prime impacts of agricultural production are in the envi­ronment. However, besides GHG emissions and, partly, biodiversity, the assessment of environmental criteria remains rather weak. For a comprehensive sustainability assessment, the topical breadth and depth in analysis must be improved. Generally, bioenergy production has the same impacts as any agricultural production and sustainability in bioenergy production largely links to sustainable agricultural production.

Biomass Use

The assessment of proposed sustainability criteria for bioenergy production shows that the competition for biomass between bioenergy use and for fertilizing sus­tainable agricultural production systems is no topic. It is covered marginally in some other publications on sus­tainable bioenergy, e. g. in Bindraban et al. (2009) or Blonz et al. (2008), although it is of key relevance for sustainable agricultural production. Some publications address this topic as a caveat of agricultural or forestry residues use, as exporting too much of them causes soil carbon losses and soil degradation (e. g. WBGU, 2009). Only Muller (2009) takes up this topic in depth. The export of biomass from the fields for bioenergy use also exports nutrients that have to be replaced by other fertilizers, i. e. mineral fertilizers. The overuse of mineral fertilizers is however a key driver behind many environmental problems of current agricultural production. Sustainable agricultural production systems are based on closed nutrient cycles and organic fertilizers (compost from crop residues, roots and residues that remain on and in the fields, and manure from livestock operations). Those are keys for soil fertility and increased soil organic carbon levels (Lal, 2008; Gat — tinger et al., 2012). The nutrient export becomes particu­larly relevant for second-generation biofuels, where basically the whole plant can be used and no unused res­idues remain, resp. where cellulosic residues from any crops can be utilized (IEA, 2010). This is even suggested as a strategy to mitigate land use competition, as residues come without additional land requirements and feed­stock for second-generation biofuel is claimed to often grow on marginal lands (IEA, 2010, 2011). On marginal lands in particular, high organic matter inputs are key to improve soil fertility, though. Also for bioenergy crops, yields tend to be lower and erratic on marginal lands and economic viability of bioenergy projects is often given on fertile land only (Bindraban et al., 2009). Thus, regarding the biomass competition, the most promising options to avoid land use competition seem particularly problematic.

The finite nature of fossil fuels and the emission of greenhouse gases as result of the consumption, these resources provide the impetus to seek alternative sour­ces of clean energy, which can be produced in a sustain­able manner. This important quest underpins the essential requirement for research and development on various types of bioenergy. Bioethanol production has been the focus of considerable research in the context of liquid fuels for transportation. The use of starch — based (first-generation) agricultural products as substrates as bioethanol feedstocks is possible but raises some concerns because of potential competition with food production. Although numerous investigations on bioenergy have been performed over the past decades to clarify the potential of, and to develop processes for the use of agricultural crops and biomass as feedstock for fuel and energy, the recent period has seen a renewed intensity of research on biomass to bio­energy conversion technologies and processes, with the aim of developing economical and sustainable solutions at commercial scale. To support economic sustainability, biorefinery systems have been implemented to convert renewable materials, such as wood or agricultural crops, into additional valuable products such as platform and feedstock chemicals, and pharma compounds. It is envisaged that the biorefinery concept should enable a transition from the traditional fossil fuel-based plat­forms for production of commodity products to more environmentally favorable and sustainable bio-based processes. For researchers and industrialists alike, the biorefinery approach brings both significant scientific and technical challenges and much opportunity for tech­nological innovation.

Second-generation bioenergy uses the lignocellulose present in woody biomass, forestry residue, agricul­tural residues, food wastes, agricultural wastes and animal wastes. Agricultural residues include the straw from wheat and rice, sugar cane bagasse, stem and roots from food crops, the top ends of trees like euca­lyptus not used in paper manufacture, and fast devel­oping tall grasses (e. g. Miscanthus spp., coastal grasses, etc.). A detailed understanding of the compo­sition of the lignocellulosic waste is essential to develop and optimize mechanistic models for its conversion. Inclusion of pretreatment processes to aid the integration of waste streams into the raw materials for ethanol plants in such models is essential to increase both fuel (ethanol)/bioenergy yields, recover valuable coproducts and biorefinery feedstocks, as well as to reduce process costs. Hydrolysis of lignocel — lulosic materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. Hydro­lysis using enzymes (generally derived from microbial sources) is the preferred option as enzymes can be used to selectively convert carbohydrate-rich biopoly­mers in biomass to fermentable sugars, without forma­tion of by-products that inhibit downstream bioenergy and biorefinery conversion processes. However, pretreatment of the lignocellulose to reduce its recalci­trance to enzymatic and microbial conversion is essen­tial. Pretreatment by physical, chemical or biological means is an essential process for ethanol production from lignocellulosic materials. Pretreatment also enhances the biodegradability of the wastes for ethanol and biogas production and increases accessibility of the enzymes to the biopolymers present in the biomass/waste feedstocks. Research is necessary to improve process efficiencies in the areas of pretreat­ment and bioconversion, and to explore new technolo­gies for conversion of lignocellulose to bioenergy. Similarly, the major challenge for microalgal biodiesel production is the high cost of producing microalgal biomass, and the current significant environmental, safety and sustainability concerns surrounding the recovery and extraction of lipid fractions used for bio­diesel production. In this sector, the key issues to be solved are the costs for harvesting the algae, protection of the high-oil microalgae from the contamination by other algae, and the development of environmentally and operationally more benign extraction processes. Another important issue for both lignocellulosic ethanol and microalgal biodiesel processes involves the development of technologies for the utilization of coproducts and residues formed through primary bioconversion processes which should increase overall process economics. Utilization of each fraction in biomass agricultural wastes provides an effective way to minimize environmental pollution, address food security problems and improve agricultural waste management approaches.

This book focuses on current innovative methods and technological developments which are aimed at over­coming the bottlenecks in biofuel and bioenergy processes. Reviews of the potential of lignocellulosics for the production of (bio)chemicals are also included. Chapters on biorefining routes resulting in a product with higher market value than ethanol have been included. It is envisaged that once such approaches have reached viable commercial scale, global depen­dence on petroleum for a host of products used in day-to-day applications will be reduced, and a more sustainable global bioeconomy will result.

Editors

Foreword

Our present industrial civilization relies on the consumption of enormous amounts of energy and much of today’s economic wealth is based on a petro­leum-based economy. Petroleum not only is used as energy in transport but also is the starting material of many other products of our daily life including such diverse products as plastics, pharmaceuticals, solvents, fertilizers, pesticides and clothing up to the tarmac, which we use for the transport of these products. However, our continued reliance on fossil fuels will make it impossible to reduce greenhouse gas emissions to stop environmental problems such as global warm­ing. Without decisive actions, the global usage of energy and energy-related emissions of carbon dioxide is pre­dicted to double by 2050. Although there is an active debate when the demand for oil will exceed its supply (Peak Oil), it is clear that our present economic system will need a major shift to develop effective alternatives including a more sustainable economy. This sustainable development will be based on renewable energy and biomass sources as well as more efficient ways to use these.

Traditionally, biomass has been used to produce food, feed and wood fiber. But biomass can also provide energy in the form of (bio)fuels and it can be used as a source of feedstock chemicals replacing the petro­leum-based products. The development of such a bio­based economy is occurring already at a relatively rapid pace and some of its products are already on the market including first-generation biofuels. The commercial viability of this approach will depend largely on the availability of cost-competitive technologies capable of converting (waste) biomass within a holistic concept of a biorefinery to biofuels and other bio-based products. Biorefining—the sustainable processing of biomass into food/feed ingredients, chemicals, materials and bioenergy—aims to use the available biomass resources as efficient as possible. At the moment, a wide range of biomass conversion technologies are under develop­ment to improve efficiencies, lower costs along the whole supply chain and improve the environmental performance. But there is also a need for further techno­logical innovation leading to more efficient and cleaner conversion of a more diverse range of feedstocks. These include not only existing lignocellulosic waste residues from forestry, agriculture and urban communities but also the generation of new feedstocks from energy crops or microalgae. A first wave of cellulosic biofuels demon­stration plants is now reaching completion producing transportation fuels from agro-, forestry and process residues. To make the overall process more market competitive, these plants co-produce added-value bio­based products thereby supplying processes that are less energy or chemically intensive compared to their petroleum-based counterparts.

Increasing deployment of biomass will include also other challenges for our society including an increasing competition for land, questions of biodiversity and soil quality or the availability of water resources. But biomass will be an important part of the future energy mix thereby contributing to a low CO2 future. Excluding biomass from the energy mix would significantly increase the cost of decarbonizing our energy system.

This book has been initiated to describe the current stage of knowledge on bioenergy research from various perspectives, thereby outlining also those areas where further progress is needed.

Dr. Bernhard Seiboth

Professor, Head of Molecular Biotechnology, Vienna University of Technology, Vienna, Austria

Nicotiana tabacum, commonly referred as tobacco, is a commercial shrub with pink flowers and green capsules containing abundant small seeds grown in a large num­ber of countries around the world. The foliage of the plant is the commercial product and used in the prepa­ration of cigarettes and other tobacco-containing prod­ucts. The oil content of the seeds, a by-product from tobacco, ranges from 36 wt% to 41 wt% (Usta, 2005). This tobacco seed oil contains more than 17 wt% FFAs (Veljkovic et al., 2006) and is high in linoleic acid (69.5 wt%), along with oleic (14.5 wt%) and palmitic (11.0 wt%) acid in significant amounts. Due to high lino — leic acid content of tobacco seed oil, the corresponding methyl esters display relatively low kinematic viscosity (3.5 mm2/s) in comparison to most other biodiesel fuels (Usta, 2005).

Biodiesel from Animal Fat Wastes

The feedstock issues are very critical, which affect the economic potential of biodiesel production, since feed­stock accounts around 75% of the biodiesel total cost (Figure 1.7). Recently, alternative lipid residues such as waste frying oil and nonedible animal fats have also received substantial attention from the biofuel sector. To take benefit of these low-cost and low-quality resources, a suitable act would be to reuse residues in

order to integrate sustainable energy supply and waste management in food processing facilities. Animal fats are typically considered as waste by-products and less expensive than commodity vegetable oils, which make them attractive as feedstock for biodiesel production. These animal wastes are collected from chicken, cow, pork lard, and other animals such as fish and insects.

Naveen Kumar Mekala1, Ravichandra Potumarthi2’*,

1 3

Rama Raju Baadhe 1, Vijai K. Gupta 3

^Department of Biotechnology, National Institute of Technology, Warangal, Andhra Pradesh, India,
^Department of Chemical Engineering, Monash University, Clayton, Victoria, Australia, 3Molecular Glycobiotechnology
Group, Department of Biochemistry, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland
*Corresponding author email: ravichandra. potumarthi@monash. edu; pravichandra@gmail. com

OUTLINE

Introduction 1

Different Forms of Bioenergy 3

Biopellets 3

Bioethanol 3

Feedstock for Bioethanol 3

Pretreatment of Lignocelluloses 4

Biological Pretreatment 5

Physical Pretreatment 6

Chemical

Pretreatment 6

Bioethanol Fermentation 7

Molecular Biology Trends in Bioethanol

Production Development 8

Bioreactors in Ethanol

Production 8

Immobilization of Cells for Ethanol

Production 9

Biodiesel 9

Feedstocks for Biodiesel 10

Biodiesel from Pure Vegetable Oil 10

Biodiesel from Animal Fat Wastes 11

Other Waste Cooking Oils 12

Algae as a Biodiesel Source 12

Bioreactors for Biodiesel Production 13

Biogas 14

Biogas Feedstock 15

Household Digesters for Biogas 15

Fixed Dome Digesters 15

Floating Drum Digesters 16

Social and Environmental Aspects of Biogas Digesters 17

Conclusion 17

References 18

INTRODUCTION

Modern world is facing two vital challenges, energy crisis and environmental pollution. Energy is a key component for all sectors of modern economy and plays an elementary role in improving the quality of life (US DOE, 2010). In current situations, approxi­mately 80% of world energy supplies rely on rapidly exhausting nonrenewable fossil fuels. At the current
rate of consumption, crude oil reserves, natural gas and liquid fuels were expected to last for around 60 and 120 years, respectively (British Petroleum Statisti­cal Review, 2011). An additional challenge with fossil fuel consumption is emission of greenhouse gases (GHGs). In 2010, an average of 450 g of CO2 was emitted by production of 1 kWh of electricity from the coal (Figure 1.1) (International Energy Agency Statis­tics, 2012). It is also clear that coal’s share of the global

Bioenergy Research: Advances and Applications http://dx. doi. org/10.1016/B978-0-444-59561-4.00001-2

energy continues to rise, and by 2017 coal will come close to surpassing oil as the world’s top energy source. China and India lead the growth in coal consumption over the next 5 years. Research says China will surpass the rest of the world in coal demand during the outlook period, while India will become the largest seaborne coal importer and second largest consumer, surpassing the United States (IEA, 2012).

Growing global energy needs, release of environ­mental pollutants from fossil fuels and national security have finally tuned the attention in clean liquid fuel as a suitable alternative source of energy. The alternative bio­energy sources, not only cut the dependence on oil trade and reduce the doubts caused by the fluctuations in oil price, but also secure reductions in environmental pollu­tion due to their high oxygen content (Huang et al., 2008; Boer et al., 2000).

In this context, the availability of bioenergy in its two main appearances, wood and agro energy can offer cleaner energy services to meet basic energy require­ments. This century could see a remarkable switchover from fossil fuel-based energy to bioenergy-based econ­omy, with agriculture and forestry as the main sources of feedstock for biofuels such as wood pellets, fuel — wood, charcoal, bioethanol, and biodiesel (Agarwal,

2007) . Moreover, energy crops can be part of highly specialized and various agricultural production chains and biorefineries, where a variety of bioproducts could be obtained besides bioenergy, which are important for their economic competitiveness (United Nations Envi­ronment Program, 2006).

The exploitation of currently unused by-products and growing energy crops can address other existing environmental concerns. Perennial energy crops and plantations are generally characterized by higher biodi­versity compared with conventional annual crops. By providing more continuous soil cover, they reduce the impact of rainfall and sediment transport, thereby pre­venting soil erosion. The introduction of annual energy crops into crop systems allows for diversification and expansion of crop rotations, replacing less favorable monocropping systems (Kheshgi et al., 1996). Defor­ested, degraded and marginal land can be rehabilitated with bioenergy plantations, thus helping to combat desertification and hopefully reducing market and geo­social pressures on high-quality arable land.

Biofuels can be obtained in bulk when they are derived from agricultural crops, crop residues and processing wastes from agroindustries, forests, etc. Despite this immense potential, existing biofuel policies have been very costly; they produce slight reductions in fossil fuel use and increase, rather than decrease, in GHG emissions (Wuebbles and Jain, 2001). However, recent volatility and rise in international fossil fuel prices, make biomass increasingly competitive as energy feedstock.

Current bioenergy research around the globe should direct us toward reduced production cost, higher energy conversion efficiency and greater cost- effectiveness of biofuels. After all we are aware of a fact "use of biomass as a potentially large source of energy in the 21st century will have a significant impact in rural, agricultural and forestry development" (UNEP, 2006).

Animal fats like beef tallow and chicken fat are by­products from the meat industry and stand for cheap feedstock for biodiesel production. The key fatty acids found in beef tallow were oleic (47.2 wt%), palmitic (23.8 wt%), and stearic (12.7 wt%) acids. The prime fatty acids contained in chicken fat include oleic (40.9 wt%), palmitic (20.9 wt%), and linoleic (20.5 wt%) acids (Wyatt et al., 2005). Due to very low concentration of polyunsat­urated fatty acid in beef tallow, the corresponding methyl esters illustrate excellent oxidative stability, as evidenced by an oil stability index (OSI) value of 69 h at 110 °C. In addition, other physical properties of beef tallow methyl esters include kinematic viscosity (40 °C) of 5.0 mm2/s, a flash point (FP) of 150 °C, and CP, PP and cold filter plugging point (CFPP) values of 11, 13, and 8 °C respectively (Moser, 2009). In chicken fat, due to high polyunsaturated fatty acid content, the corresponding methyl esters display poor oxidative sta­bility, as evidenced by an OSI value of 3.5 h at 110 °C. Burning the B20 blends of beef tallow and chicken fat methyl esters results in NOx exhaust emissions of only 2.4% versus 6.2% of B20 blend of soybean methyl esters (SME) (Wyatt et al., 2005).

PORK LARD

Pork lard is a by-product of the food industry and symbolizes a low-cost feedstock for biodiesel produc­tion. The main fatty acids in pork lard includes stearic (121 wt%), linoleic (127 wt%), oleic (44.7 wt%), and pal­mitic (26.4 wt%) acids (Jeong et al., 2009). Due to high saturated fatty acid content in pork lard, the correspond­ing methyl esters exhibit quite high CFPP value of 8 °C and a relatively low iodine value (IV) of 72, along with a typical kinematic viscosity (40 °C) of 4.2 mm2/s. Another study determined that pork lard methyl esters have a kinematic viscosity (40 °C) of 4.8 mm2/s, FP of 160 °C, OSI value of 18.4 h at 110 °C, and CP, PP, and CFPP values of 11, 13, and 8 °C, respectively (Wyatt et al., 2005). Furthermore, combustion of B20 blends of pork lard methyl esters results in NOx exhaust emis­sions of only 3.0% versus 6.2% for a B20 blend of SME.

Other Waste Cooking Oils

Waste oils may include a variety of low-worth mate­rials such as used cooking or frying oils, acid oils, tall oil, vegetable oil soapstocks, and other waste materials.

Waste oils are usually characterized by relatively high FFA and water contents and potentially contain a variety of solid materials that must be removed by filtration prior to conversion to biodiesel (Moser, 2009). In the case of used cooking or frying oils, hydrogenation to in­crease the useful cooking lifetime of the oil may result in the introduction of relatively high-melting trans constit­uents, which influence the physical properties of the resulting biodiesel. Used frying or cooking oil is mainly acquired from restaurants and may cost between free to 50% less expensive than commodity vegetable oils, depending on the source and the availability (Predo — jevic, 2008). The physical properties of methyl esters pre­pared from used cooking or frying oils include kinematic viscosities (40 °C) of 4.23 (Meng et al., 2008), 4.79, and 4.89 mm2/s; FP of 171 °C; cetane number of 55, IV of 125, CFPP values of 1 and —6 °C (Cetinkaya and Karaosmanoglu, 2004), CP values of 9 and 3 °C, and PP values of —3 and 0 °C (Phan and Phan, 2008). The disparities in the physical property data among the various studies may be a result of feedstock origin or due to differences in product purity.

Organic matter holding bioenergy sources in side is known as biomass. We can utilize this biomass in many different ways, through something as simple as burning wood for heat, or as complex as growing genet­ically modified microbes to produce cellulosic ethanol (Adler et al., 2009). Since nearly entire bioenergy can be traced back to energy from sunlight, bioenergy has the key advantage of being a renewable energy source. Here, in this chapter we will discuss various forms of bioenergy and their application in detail.

BIOPELLETS

Today, wood pellets are an imperative and well — accepted fuel in lots of different countries and the according markets are likely to rise even further in future. For these reasons, it is feared that the inadequate avail­ability of cheap wood as a feedstock for pellets will limit this market increase (Marina et al., 2011; Larsson et al.,

2008) . As alternative, autumn leaves from urban areas, as a seasonal available waste material, are the possible substitutes for or additives to wood. In lot of Western countries, wood pellets become a more and more signif­icant fuel for the use in small furnaces for household buildings or in industries as a climate-neutral alternative to crude oil or natural gas (Verma et al., 2012; Nielsen et al., 2009). This pelletized biomass has a number of advantages like tolerance against microbial degradation, high transport and storage density of bioenergy, and the process of pelletization is quite simpler (Figure 1.2).

BIOETHANOL

Bioethanol is the most common biofuel worldwide. It is produced by simple fermentation of sugars derived from wheat, corn, sugar beets, sugarcane, molasses and
any sugar or starch sources that alcoholic beverages can be made from (Cara et al., 2008). Bioethanol can be used in petrol engines as a substitute for gasoline. Bioconver­sion of lignocellulosics into fermentable sugars is a bio­refining area in which enormous research labors have been invested, as it is a prerequisite for the subsequent bioethanol production (Broder et al., 1992). Although extensive research has been carried out to meet the potential challenges of bioenergy generation, there is no self-sufficient process or technology available today to convert the lignocellulosic biomass to bioethanol (Tu et al., 2007).

Use of bioethanol-blended fossil fuel for automobiles can significantly cut the petroleum use and exhaust GHG emission. Bioethanol can be produced from different kinds of raw materials and these raw materials are classified into three categories of agricultural raw materials: simple sugars, starch and lignocelluloses (Mustafa and Havva, 2009). Bioethanol from sugarcane, under proper conditions, is essentially a clean fuel and has several advantages over petroleum-derived gasoline in reducing GHG emissions and improving air quality in metropolitan cities. Conversion technologies for produc­ing bioethanol from cellulosic biomass resources such as forest materials, agricultural residues and urban wastes are under development and have not yet been estab­lished commercially (Demirbas, 2008).

Algae can also be used to produce energy in a number of ways. One of the most competent ways is through exploitation of the algal oils to produce biodiesel. Algal biomass contains three major components: carbohy­drates, proteins, and lipids/natural oils (Dunahay et al., 1996). Because the natural oil made by microalgae is in the form of triacylglycerol molecule, which is the right kind of oil for producing biodiesel, microalgae are the exclusive focus in the algae to biofuel arena. Actual biodiesel yield per hectare is about 80% of the yield of the parent crop oil given in Table 1.5.

In view of Table 1.5, microalgae emerged to be the only source of biodiesel that has the potential to completely replace petroleum diesel. Unlike other oil crops, microalgae grow extremely rapidly and many are exceedingly rich in oil. Microalgae commonly dou­ble their biomass within 24 h. Biomass doubling times during exponential growth are commonly as short as

3— 4 h. Oil content in microalgae can exceed 70% by weight of dry biomass (Metting, 1996; Spolaore et al.,

2006) . Oil levels up to 50% are quite common. Oil pro­ductivity, the mass of oil produced per unit volume of the microalgal broth per day, depends on the algal growth rate and the oil content of the biomass. Microal­gae with high oil productivities are desired for produc­ing biodiesel.

CHEMICAL TRANSESTERIFICATION PROCESS FOR BIODIESEL PRODUCTION

The source oil used in making biodiesel consists of tri­glycerides (Figure 1.7), in which three fatty acid

molecules are esterified with a molecule of glycerol. In biodiesel production, triglycerides are reacted with methanol in a reaction known as transesterification or alcoholysis. Transesterification produces methyl esters of fatty acids that are biodiesel and glycerol (Figure 1.7). The reaction occurs stepwise: triglycerides are first con­verted to diglycerides, then to monoglycerides and finally to glycerol.

At equilibrium, transesterification needs 3 mol of alcohol for every mole of triglyceride to produce 1 mol of glycerol and 3 mol of methyl esters (Figure 1.8). In­dustrial processes use 6 mol of methanol for each mole of triglyceride (Fukuda et al., 2001). This large excess of methanol ensures that the reaction is driven in the di­rection of methyl esters, i. e. toward biodiesel. Yield of methyl esters exceeds 98% on a weight basis.

Transesterification is catalyzed by acids and alkalis (Fukuda et al., 2001). Alkali-catalyzed transesterification is about 4000 times quicker than the acid-catalyzed reac­tion. Thus, alkalis such as sodium and potassium hy­droxide are frequently used as commercial catalysts at a concentration of about 1% by weight of oil. Alkoxides such as sodium methoxide (CH3ONa) act like better cat­alysts than sodium hydroxide and are being increas­ingly used. Use of lipases offers significant advantages, but it is currently not feasible because of the relatively high cost of the catalyst (Chisti, 2007). Alkali-catalyzed transesterification is carried out at about 60 °C under one atmospheric pressure, as methanol boils off at 65 °C at atmospheric pressure. Under these conditions, reaction takes about 90 min to complete (Meher et al.,

CH2-COO-R CH-COO-R’ + ЗСН3ОН CH2-COO-R" Methanol |Triglyceridi|

FIGURE 1.8 Transesterification of oil to biodiesel.

2006) . A higher temperature can be used in combination with higher pressure, but the process becomes expen­sive. During reaction, methanol and oil do not mix; hence, the reaction mixture shows two liquid phases. Other alcohols can be used, but methanol is the least expensive. To stop yield loss due to saponification reac­tions (soap formation), the oil and alcohol must be dry and the oil should have a least of FFAs. Biodiesel is recovered by repeated washing with water to remove glycerol and methanol.

Across the globe, there is a rising need to find out new and cheap carbohydrate sources for bioethanol produc­tion (Mohanty et al., 2009). Presently, a serious focus is on biofuels made from renewable energy crops such as sugarcane, corn, wheat, soybeans, etc. In a given produc­tion line, the comparison of the biomass includes several issues: (1) cultivation practices, (2) chemical composi­tion of the biomass, (3) use of resources, (4) emission of GHGs, (5) availability of land and land use practices, (6) soil erosion, (7) energy balance, (8) price of the

biomass, (9) contribution to biodiversity and landscape value losses, (10) direct economic value of the feedstock, (11) water requirements and water availability, (12) cre­ation or maintain of employment, and (13) logistic cost (transport and storage of the biomass) (Gnansounou et al., 2005).

Bioethanol feedstock can be divided into three major groups: (1) sugar-based feedstock (e. g. sugarcane, beet sugar, sorghum and fruits), (2) starchy feedstock (e. g. corn, sweet potato, rice, potatoes, cassava, wheat and barley), and (3) lignocellulosic feedstock (e. g. wood, straw, grasses, and corncob). In short term, production of bioethanol as a fuel is almost entirely dependent on starch and sugars from existing food crops (Smith, 2008; Potumarthi et al., 2012). The negative part in pro­ducing bioethanol from starch and sugar is that the feed­stock tends to be costly and demanded by other applications as well (Enguidanos et al., 2002). Lignocel — lulosic biomass is envisaged to provide a major portion of the raw materials for bioethanol production in the long term due to its low cost and high availability (Gnansounou et al., 2005).

Up to 2003, about 60% of global bioethanol was ob­tained from sugarcane and 40% from all other crops (Dufey, 2006). Brazil utilizes sugarcane for bioethanol production, while the United States and other western countries mainly use starch from corn, wheat and barley (Linde et al., 2008). Brazil is the largest producer of sug­arcane with about 672,157,000 tons of global production followed by India, second largest producer with

285,029,0 ton production (Food & Agricultural Orga­nization of United Nations, 2013).

Bioethanol production in Brazil is less expensive than in the United States from corn or in Europe from sugar beet, because of lower labor costs, shorter processing
time, lower transport costs, and other input costs. After sugarcane, starch is the high-yield feedstock for bio­ethanol production, but pretreatment is necessary to produce bioethanol by fermentation (Pongsawatmanit et al., 2007). Starch is a homopolymer consisting mono­mers of D-glucose and for bioethanol production it is necessary to break down this carbohydrate for obtaining glucose syrup, which can be further transformed into bioethanol by yeasts. Starch-based feedstock are the most utilized for bioethanol production in America and Europe.

Biomass from agricultural waste (wheat straw, sugar­cane bagasse, etc.), wood, and energy crops are attrac­tive materials for bioethanol production since it is the most abundant reproducible assets on earth (Figure 1.3). The existing biomass from crops could produce up to 442 American billion liters per year of bioethanol (Bohlmann, 2006). Thus, the total possible bioethanol production from crop residues and wasted crops is 491 American billion liters per year, about 16 times higher than the existing world bioethanol production. Advantages of biofuels are as follows: (1) biofuels are easily available from common biomass sources, (2) bio­fuels have a considerable environmentally friendly po­tential, and (3) they are biodegradable and contribute to sustainability (Balat, 2007; Mekala et al., 2008). Although lignocellulosic biomass is the best alternative source, initial pretreatment is a must to attain simple sugars for simultaneous ethanol fermentation.

Lipases (triacylglycerol hydrolase, EC 3.1.1.3.) are en­zymes that catalyze the breakdown of carboxylic ester link in the triacylglycerol molecule to form FFAs, di — and monoglycerides and glycerol. Although their pur­pose is to catalyze hydrolysis of ester links, they can also catalyze the esterification, the conception of this link between alcohol hydroxyl groups and carboxyl groups of carboxylic acids. Therefore, they can catalyze hydrolysis, alcoholysis, esterification and transesterifi­cation and they have a wide spectrum of biotechnolog­ical applications (Kirk et al., 2002). Lipases are also highly specific as regio, chemo and enantioselective cat­alysts. Thanks to protein engineering, it is possible to enhance catalytic potential of lipases and "tailor" them to exact application and process situation, enabling further expansion of their industrial applications (B van Beilen and Li, 2002). Among lipases from animal, plant and microbial origins, the most commonly used are microbial lipases. They have abundant advantages over lipases from animal and plant sources. Using mi­crobes it is possible to achieve a higher yield of enzymes, and to genetically control the strain in obtaining a low — cost lipase with preferred properties for the conversion of fats and oils into biodiesel. In addition, the enzymatic yield is independent of potential seasonal variations and it is possible to achieve rapid growth of microbes in low — cost media (Gupta et al., 2004).