Biomass Energy Scenario in Southeast Asia

The rapid economic growth and industrialization in Southeast Asian region is characterized by a significant gap between energy supply and demand. The energy demand in the region is expected to grow rapidly in the coming years which will have a profound impact on the global energy market. In addition, the region has many locations with high population density, which makes public health vulnerable to the pollution caused by fossil fuels.

Another important rationale for transition from fossil-fuel-based energy systems to renewable ones arises out of observed and projected impacts of climate change. Due to the rising share of greenhouse gas emissions from Asia, it is imperative on all Asian countries to promote sustainable energy to significantly reduce GHGs emissions and foster sustainable energy trends. Rising proportion of greenhouse gas emissions is causing large-scale ecological degradation, particularly in coastal and forest ecosystems, which may further deteriorate environmental sustainability in the region.

The reliance on conventional energy sources can be substantially reduced as the Southeast Asian region is one of the leading producers of biomass resources in the world. Southeast Asia, with its abundant biomass resources, holds a strategic position in the global biomass energy atlas.

There is immense potential of biomass energy in ASEAN countries due to plentiful supply of diverse forms of wastes such as agricultural residues, agro-industrial wastes, woody biomass, animal wastes, municipal solid waste, etc. Southeast Asia is a big producer of wood and agricultural products which, when processed in industries, produces large amounts of biomass residues.

palm-kernel-shell-uses

Palm kernel shells is an abundant biomass resource in Southeast Asia

According to conservative estimates, the amount of biomass residues generated from sugar, rice and palm oil mills is more than 200-230 million tons per year which corresponds to cogeneration potential of 16-19 GW. Woody biomass is a good energy resource due to presence of large number of forests and wood processing industries in the region.

The prospects of biogas power generation are also high in the region due to the presence of well-established food processing, agricultural and dairy industries. Another important biomass resource is contributed by municipal solid wastes in heavily populated urban areas.

In addition, there are increasing efforts from the public and private sectors to develop biomass energy systems for efficient biofuel production, e.g. biodiesel and bioethanol. The rapid economic growth and industrialization in Southeast Asia has accelerated the drive to implement the latest biomass energy technologies in order to tap the unharnessed potential of biomass resources, thereby making a significant contribution to the regional energy mix.

Biodiesel Program in India – An Analysis

The Government of India approved the National Policy on Biofuels in December 2009. The biofuel policy encouraged the use of renewable energy resources as alternate fuels to supplement transport fuels (petrol and diesel for vehicles) and proposed a target of 20 percent biofuel blending (both biodiesel and bioethanol) by 2017. The government launched the National Biodiesel Mission (NBM) identifying Jatropha curcas as the most suitable tree-borne oilseed for biodiesel production.

The Planning Commission of India had set an ambitious target covering 11.2 to 13.4 million hectares of land under Jatropha cultivation by the end of the 11th Five-Year Plan. The central government and several state governments are providing fiscal incentives for supporting plantations of Jatropha and other non-edible oilseeds. Several public institutions, state biofuel boards, state agricultural universities and cooperative sectors are also supporting the biofuel mission in different capacities.

State of the Affairs

The biodiesel industry in India is still in infancy despite the fact that demand for diesel is five times higher than that for petrol. The government’s ambitious plan of producing sufficient biodiesel to meet its mandate of 20 percent diesel blending by 2012 was not realized due to a lack of sufficient Jatropha seeds to produce biodiesel.

Currently, Jatropha occupies only around 0.5 million hectares of low-quality wastelands across the country, of which 65-70 percent are new plantations of less than three years. Several corporations, petroleum companies and private companies have entered into a memorandum of understanding with state governments to establish and promote Jatropha plantations on government-owned wastelands or contract farming with small and medium farmers. However, only a few states have been able to actively promote Jatropha plantations despite government incentives.

Key Hurdles

The unavailability of sufficient feedstock and lack of R&D to evolve high-yielding drought tolerant Jatropha seeds have been major stumbling blocks. In addition, smaller land holdings, ownership issues with government or community-owned wastelands, lackluster progress by state governments and negligible commercial production of biodiesel have hampered the efforts and investments made by both private and public sector companies.

The non-availability of sufficient feedstock and lack of R&D to evolve high-yielding drought tolerant Jatropha seeds have been major stumbling blocks in biodiesel program in India. In addition, smaller land holdings, ownership issues with government or community-owned wastelands, lackluster progress by state governments and negligible commercial production of biodiesel have hampered the efforts and investments made by both private and public sector companies.

Another major obstacle in implementing the biodiesel programme has been the difficulty in initiating large-scale cultivation of Jatropha. The Jatropha production program was started without any planned varietal improvement program, and use of low-yielding cultivars made things difficult for smallholders. The higher gestation period of biodiesel crops (3–5 years for Jatropha and 6–8 years for Pongamia) results in a longer payback period and creates additional problems for farmers where state support is not readily available.

The Jatropha seed distribution channels are currently underdeveloped as sufficient numbers of processing industries are not operating. There are no specific markets for Jatropha seed supply and hence the middlemen play a major role in taking the seeds to the processing centres and this inflates the marketing margin.

Biodiesel distribution channels are virtually non-existent as most of the biofuel produced is used either by the producing companies for self-use or by certain transport companies on a trial basis. Further, the cost of biodiesel depends substantially on the cost of seeds and the economy of scale at which the processing plant is operating.

The lack of assured supplies of feedstock supply has hampered efforts by the private sector to set up biodiesel plants in India. In the absence of seed collection and oil extraction infrastructure, it becomes difficult to persuade entrepreneurs to install trans-esterification plants.

Energy Potential of Bagasse

Sugarcane is one of the most promising agricultural sources of biomass energy in the world. Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk while bagasse is the fibrous residue left over after milling of the Cane, with 45-50% moisture content and consisting of a mixture of hard fibre, with soft and smooth parenchymatous (pith) tissue with high hygroscopic property. Bagasse contains mainly cellulose, hemi cellulose, pentosans, lignin, Sugars, wax, and minerals. The quantity obtained varies from 22 to 36% on Cane and is mainly due to the fibre portion in Cane and the cleanliness of Cane supplied, which, in turn, depends on harvesting practices.

The composition of Bagasse depends on the variety and maturity of Sugarcane as well as harvesting methods applied and efficiency of the Sugar processing. Bagasse is usually combusted in furnaces to produce steam for power generation. Bagasse is also emerging as an attractive feedstock for bioethanol production. It is also utilized as the raw material for production of paper and as feedstock for cattle. The value of Bagasse as a fuel depends largely on its calorific value, which in turn is affected by its composition, especially with respect to its water content and to the calorific value of the Sugarcane crop, which depends mainly on its sucrose content.

Moisture contents is the main determinant of calorific value i.e. the lower the moisture content, the higher the calorific value. A good milling process will result in low moisture of 45% whereas 52% moisture would indicate poor milling efficiency. Most mills produce Bagasse of 48% moisture content, and most boilers are designed to burn Bagasse at around 50% moisture. Bagasse also contains approximately equal proportion of fibre (cellulose), the components of which are carbon, hydrogen and oxygen, some sucrose (1-2 %), and ash originating from extraneous matter. Extraneous matter content is higher with mechanical harvesting and subsequently results in lower calorific value.

For every 100 tons of Sugarcane crushed, a Sugar factory produces nearly 30 tons of wet Bagasse. Bagasse is often used as a primary fuel source for Sugar mills; when burned in quantity, it produces sufficient heat and electrical energy to supply all the needs of a typical Sugar mill, with energy to spare. The resulting CO2 emissions are equal to the amount of CO2 that the Sugarcane plant absorbed from the atmosphere during its growing phase, which makes the process of cogeneration greenhouse gas-neutral.

35MW Bagasse and Coal CHP Plant in Mauritius

Cogeneration of Bagasse is one of the most attractive and successful energy projects that have already been demonstrated in many Sugarcane producing countries such as Mauritius, Reunion Island, India and Brazil. Combined heat and power from Sugarcane in the form of power generation offers renewable energy options that promote sustainable development, take advantage of domestic resources, increase profitability and competitiveness in the industry, and cost-effectively address climate mitigation and other environmental goals.

Biochemical Conversion of Biomass

Biochemical conversion of biomass involves use of bacteria, microorganisms and enzymes to breakdown biomass into gaseous or liquid fuels, such as biogas or bioethanol. The most popular biochemical technologies are anaerobic digestion (or biomethanation) and fermentation. Anaerobic digestion is a series of chemical reactions during which organic material is decomposed through the metabolic pathways of naturally occurring microorganisms in an oxygen depleted environment. Biomass wastes can also yield liquid fuels, such as cellulosic ethanol, which can be used to replace petroleum-based fuels.

Anaerobic Digestion

Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.  Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat. Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as municipal solid waste, animal manure, poultry litter, food wastes, sewage and industrial wastes.

An anaerobic digestion plant produces two outputs, biogas and digestate, both can be further processed or utilized to produce secondary outputs. Biogas can be used for producing electricity and heat, as a natural gas substitute and also a transportation fuel. A combined heat and power plant system (CHP) not only generates power but also produces heat for in-house requirements to maintain desired temperature level in the digester during cold season. In Sweden, the compressed biogas is used as a transportation fuel for cars and buses. Biogas can also be upgraded and used in gas supply networks.

Working of Anaerobic Digestion Process

Digestate can be further processed to produce liquor and a fibrous material. The fiber, which can be processed into compost, is a bulky material with low levels of nutrients and can be used as a soil conditioner or a low level fertilizer. A high proportion of the nutrients remain in the liquor, which can be used as a liquid fertilizer.

Biofuel Production

A variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.

The largest potential feedstock for ethanol is lignocellulosic biomass wastes, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial). Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantly, lignocellulosic feedstocks do not interfere with food security.

Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

A Glance at Drop-in Biofuels

drop-in-biofuelsBiofuel commercialization has proved to be costly and lingering than expected due to its high production cost and modification to flexibility in engines. Drop-in fuels are alternatives to existing liquid fuels without any significant modification in engines and infrastructures. According to IEA, “Drop-in biofuels are liquid bio-hydrocarbons that are functionally equivalent to petroleum fuels and are fully compatible with existing petroleum infrastructure”.

What are Drop-in Biofuels

Drop-in biofuels are can be produced from oilseeds via trans-esterification, lignocellulosic biomass via thermochemical process, sugars and alcohol via biochemical conversion or by hybrids of the above methods. Drop-in fuels encompass high hydrogen to carbon ratio with no/low sulfur and oxygen content, low water solubility and high carbon bond saturation. In short drop-in fuel is a modified fuel with close functional resemblance to fossil fuel.

Existing biofuels – bioethanol and biodiesel – have wide variation from fossil fuels in their blend wall properties – high oxygen content, hydrophilicity, energy density and mainly compatibility in existing engines and infrastructures. Oxygenated groups in biofuel have a domino effect such as reduction in the energy density, production of impurities which are highly undesirable to transportation components, instability during storage etc.

Major advantages of drop-in fuels over existing fuels are as follows:

  • Reduced sulphur oxide emissions by ultra low sulphur content.
  • Reduced ignition delay by high cetane value
  • Reduced hydrocarbons and nitrogen oxides emissions
  • Low aromatic content
  • Low olefin content, presence of olefin compounds undergo auto-oxidation leading to surface depositions.
  • High saturates, therefore leaving minimum residues
  • Low particulate emissions
  • No oxygenates therefore has high stability.

Potential Biomass Feedstock

Drop-in biofuels can be produced from various biomass sources- lipids (vegetable oils, animal fats, greases, and algae) and lignocellulosic material (such as crop residues, woody biomass, and dedicated energy crops). The prominent technologies for biomass conversion to drop-in fuel are the thermochemical and the biochemical process.

The major factor playing role in selection of biomass for thermochemical methods is the energy content or heating value of the material, which is correlated with ash content. Wood, wood chips accounts for less than 1% ash content, which is favorable thermal processing than biochemical process, whereas straws, husks, and majority of the other biomass have ash content ranging up to 25% of dry mass.

Free sugar generating plants such as sugarcane and sweet sorghum, are desirable feedstock for Acetone-Butanol-Ethanol fermentation and have been widely implemented. Presently there is a focus to exploit lignocellulosic residues, rich in hydrocarbon, for fuel production. However, this biomass requires harsh pretreatment to remove lignin and to transform holocellulose (cellulose & hemicelluloses) into fermentable products.

The lignocellulose transformation technology must be circumspectly chosen by its life cycle assessment, as it resists any changes in their structural integrity owing to its complexity. Lignocellulosic biomass, when deoxygenated, has better flexibility to turn to drop-in fuels. This is because, in its native state of the feedstock, each oxygen atom consumes two hydrogen atoms during combustion which in turn reduces effective H: C ratio. Biomass feedstock is characterized with oxygen up to 40%, and higher the oxygen content higher it has to be deoxygenated.

Thermochemical Route

Thermochemical methods adopted for biomass are pyrolysis and gasification, on thermolysis of biomass produce intermediate gas (syngas) and liquid (bio crude) serving as precursors for drop-in fuel. Biomass when exposed to temperature of 500oC-600oC in absence of oxygen (pyrolysis) produce bio-oil, which constitutes a considerable percentage of oxygen. After down streaming by hydroprocessing (hydrotreating and hydrocracking) the rich hydrocarbon tar (bio-oil) can be converted to an efficient precursor for drop-in fuel.

At a higher temperature, above 700, under controlled oxygen, biomass can be converted to liquid fuel via gas phase by the process, gasification. Syngas produced is converted to liquid fuel by Fischer-Tropsch with the help of ‘water gas shift’ for hydroprocessing. Hydroprocessing after the thermochemical method is however costly and complex process in case of pyrolysis and inefficient biomass to fuel yield with gasification process.

Biochemical Pathway

The advanced biocatalytic processes can divert the conventional sugar-ethanol pathway and convert sugars to fatty acids. Modified microbial strain with engineered cellular machineries, can reroute the pathway to free fatty acid that can be transformed into butanol or drop-in fuel with necessary processing.

Schematic for the preparation of jet fuel from biomass

Schematic for the preparation of jet fuel from biomass

Biological processing requires operation under the stressful conditions on the organisms to reroute the pathways, in additional to lowering NADPH (hydrogen) consumption. Other value added products like carboxylic acid, polyols, and alcohol in the same biological routes with lower operational requirements have higher market demands and commercial success. Therefore little attention is given by chemical manufacturers to the biological pathways for drop-in fuel production.

The mechanisms of utilization of lignocellulosic biomass to fuel by biological pathway rely heavily on the availability of monomeric C5 and C6 sugars during fermentation. Ethanol is perhaps the best-known and commercially successful alcohol from ABE fermentation. However, butanol has various significant advantages over ethanol- in the perception of energy content, feasibility to existing infrastructures, zero blend wall, safety and clean aspects. Although butanol is a closer drop-in replacement, existing biofuel ethanol, is a major commercial competitor. Low yield from fermentation due to the toxicity of butanol and complexity in down streaming are the vital reasons that hamper successful large scale butanol production.

Challenges to Overcome

Zero oxygen and sulphur content mark major challenges for production of drop-in fuels from conventional biomass. This demands high hydrogen input on the conventional biomass, with H: C ratio below 0.5, like sugar, starch, cellulose, lignocellulose to meet the effective hydrogen to carbon ratio of 2 as in drop-in fuel. This characterizes most of the existing biomass feedstock as a low-quality input for drop-in fuels. However oleochemicals like fats, oils, and lipids have closer H: C ratio to diesel, gasoline and drop-in fuels, thus easier to conversion. Oleochemical feedstock has been commercially successful, but to prolong in the platform will be a major challenge. Lipid feedstock is generally availed from crop-based vegetable oil, which is used in food sectors. Therefore availability, food security concerns, and economics are the major constraints to sustaining the raw material. Consequently switching to lignocellulosic biomass feedstock for drop-in holds on.

Conclusions

Despite the hurdles on biomass characteristics and process technology for drop-in fuel, it is a vital requirement to switch to better replacement fuel for fossil fuel, considering environmental and economic benefits. Understanding its concepts and features, drop-in fuel, can solve existing greenhouse emission debate on current biofuels. Through crucial ambiguities existing on future of alternative fuels, drop-in fuel has a substantial potential to repute itself as an efficient sustainable eco-friendly fuel in the naear future.

References

  • Neal K Van Alfen: ENCYCLOPEDIA OF AGRICULTURE AND FOOD SYSTEMS, Elsevier, Academic Press.
  • Pablo Domínguez de María John: INDUSTRIAL BIORENEWABLES:A Practical Viewpoint: Wiley & Sons.
  • Ram Sarup Singh, Ashok Pandey, Edgard Gnansounou: BIOFUELS- PRODUCTION AND FUTURE PERSPECTIVES, CRC Press.
  • Satinder Kaur Brar, Saurabh Jyoti Sarma, Kannan Pakshirajan : PLATFORM CHEMICAL BIOREFINERY-FUTURE GREEN CHEMISTRY, Elsevier.
  • Sergios Karatzos, James D. McMillan, Jack N. Saddle: Summary of IEA BIOENERGY TASK 39 REPORT-THE POTENTIAL AND CHALLENGES OF DROP-IN BIOFUELS, IEA Bioenergy.
  • Vijai Kumar Gupta, Monika Schmoll, Minna Maki, Maria Tuohy, Marcio Antonio Mazutti: APPLICATIONS OF MICROBIAL ENGINEERING, CRC Press.

Bioethanol: Challenges in India

bioethanol-indiaGlobal demand for fuel efficiency, environmental quality and energy security have elicited global attention towards liquid biofuels, such as bioethanol and biodiesel. Around the world, governments have introduced various policy measurements, mandatory fuel blending programmes, incentives for flex-fuel vehicles and agricultural subsidies for the farmers. In India, the government launched Ethanol Blended Petrol (EBP) programme in January 2013 for 5% ethanol blended petrol. The policy had significant focus on India’s opportunity to agricultural and industrial sectors with motive of boosting biofuel (bioethanol and biodiesel) usage and reducing the existing dependency on fossil fuel.

The Government of India initiated significant investments in improving storage and blending infrastructure. The National Policy on Biofuels has set a target of 20% blending of biofuel by 2017. However, India has managed to achieve only 5% by September 2016 due to certain technical, market and regulatory hurdles.

In India, sugarcane molasses is the major resource for bioethanol production and inconsistency of raw material supply holds the major liability for sluggish response to blending targets.  Technically speaking, blend wall and transportation-storage are the major challenges towards the biofuel targets. Blending wall is the maximum percent of ethanol that can be blended to fuel without decreasing the fuel efficiency.

Various vehicles are adaptable to various blending ratio based on the flexibility of engines. The technology for the engine modification for flex fuel is not new but making the engines available in India along with the supply chain and calibrating the engine for Indian conditions is the halting phase. The commonly used motor vehicles in the country are not effectual with flex fuel.

Sugarcane molasses is the most common feedstock for bioethanol production in India

Sugarcane molasses is the most common feedstock for bioethanol production in India

Ethanol being a highly flammable liquid marks obligatory safety and risk assessment measures during all phases of production, storage and transportation. The non-uniform distribution of raw material throughout the country, demands a compulsory transportation and storage, especially inter-state movement, encountering diverse climatic and topographic conditions.

Major ethanol consumers in India are potable liquor sector (45%), alcohol based chemical industry (40%), the rest for blending and other purposes. The yearly profit elevation in major sectors is a dare to an economical ethanol supply for Ethanol Blending Programme. Drastic fluctuation in pricing of sugar cane farming and sugar milling resulted to huge debt to farmers by mill owners. Gradually the farmers shifted from sugarcane cultivation other crops.

Regulatory and policy approaches on excise duty on storage and transportation of ethanol and pricing strategy of ethanol compared to crude oil are to be revised and implemented effectively. Diversifying the feedstocks (especially use of lignocellulosic biomass) and advanced technology for domestic ethanol production in blending sectors are to be fetched out from research laboratories to commercial scale. Above all the knowledge of economic and environmental benefits of biofuel like reduction in pollutants and import bills and more R&D into drop-in biofuels, need to be amplified for the common man.

Biomass Resources from Sugar Industry

Sugarcane is one of the most promising agricultural sources of biomass energy in the world. It is the most appropriate agricultural energy crop in most sugarcane producing countries due to its resistance to cyclonic winds, drought, pests and diseases, and its geographically widespread cultivation. Due to its high energy-to-volume ratio, it is considered one of nature’s most effective storage devices for solar energy and the most economically significant energy crop. The climatic and physiological factors that limit its cultivation to tropical and sub-tropical regions have resulted in its concentration in developing countries, and this, in turn, gives these countries a particular role in the world’s transition to sustainable use of natural resources.

According to the International Sugar Organization (ISO), Sugarcane is a highly efficient converter of solar energy, and has the highest energy-to-volume ratio among energy crops. Indeed, it gives the highest annual yield of biomass of all species. Roughly, 1 ton of Sugarcane biomass-based on Bagasse, foliage and ethanol output – has an energy content equivalent to one barrel of crude oil.   Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk and Bagasse is the milling by-product which remains after extracting sugar from the stalk. The potential energy value of these residues has traditionally been ignored by policy-makers and masses in developing countries. However, with rising fossil fuel prices and dwindling firewood supplies, this material is increasingly viewed as a valuable renewable energy resource.

Sugar mills have been using Bagasse to generate steam and electricity for internal plant requirements while Cane Trash remains underutilized to a great extent. Cane Trash and Bagasse are produced during the harvesting and milling process of Sugarcane which normally lasts 6 to 7 months.

Around the world, a portion of the Cane Trash is collected for sale to feed mills, while freshly cut green tops are sometimes collected for farm animals. In most cases, however, the residues are burned or left in the fields to decompose. Cane Trash, consisting of Sugarcane tops and leaves can potentially be converted into around 1kWh/kg, but is mostly burned in the field due to its bulkiness and its related high cost for collection/transportation.

On the other hand, Bagasse has been traditionally used as a fuel in the Sugar mill itself, to produce steam for the process and electricity for its own use. In general, for every ton of Sugarcane processed in the mill, around 190 kg Bagasse is produced. Low pressure boilers and low efficiency steam turbines are commonly used in developing countries. It would be a good business proposition to upgrade the present cogeneration systems to highly efficient, high pressure systems with higher capacities to ensure utilization of surplus Bagasse.

Biofuels from Lignocellulosic Biomass

Lignocellulose is a generic term for describing the main constituents in most plants, namely cellulose, hemicelluloses, and lignin. Lignocellulose is a complex matrix, comprising many different polysaccharides, phenolic polymers and proteins. Cellulose, the major component of cell walls of land plants, is a glucan polysaccharide containing large reservoirs of energy that provide real potential for conversion into biofuels. Lignocellulosic biomass consists of a variety of materials with distinctive physical and chemical characteristics. It is the non-starch based fibrous part of plant material.

First-generation biofuels (produced primarily from food crops such as grains, sugar beet and oil seeds) are limited in their ability to achieve targets for oil-product substitution, climate change mitigation, and economic growth. Their sustainable production is under scanner, as is the possibility of creating undue competition for land and water used for food and fibre production.

The cumulative impacts of these concerns have increased the interest in developing biofuels produced from non-food biomass. Feedstocks from ligno-cellulosic materials include cereal straw, bagasse, forest residues, and purpose-grown energy crops such as vegetative grasses and short rotation forests. These second-generation biofuels could avoid many of the concerns facing first-generation biofuels and potentially offer greater cost reduction potential in the longer term.

The largest potential feedstock for ethanol is lignocellulosic biomass, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial). Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantlylignocellulosic feedstocks do not interfere with food security. Moreover, bioethanol is very important for both rural and urban areas in terms of energy security reason, environmental concern, employment opportunities, agricultural development, foreign exchange saving, socioeconomic issues etc.

Lignocellulosic biomass consists mainly of lignin and the polysaccharides cellulose and hemicellulose. Compared with the production of ethanol from first-generation feedstocks, the use of lignocellulosic biomass is more complicated because the polysaccharides are more stable and the pentose sugars are not readily fermentable by Saccharomyces cerevisiae. In order to convert lignocellulosic biomass to biofuels the polysaccharides must first be hydrolysed, or broken down, into simple sugars using either acid or enzymes. Several biotechnology-based approaches are being used to overcome such problems, including the development of strains of Saccharomyces cerevisiae that can ferment pentose sugars, the use of alternative yeast species that naturally ferment pentose sugars, and the engineering of enzymes that are able to break down cellulose and hemicellulose into simple sugars.

Lignocellulosic processing pilot plants have been established in the EU, in Denmark, Spain and Sweden. The world’s largest demonstration facility of lignocellulose ethanol (from wheat, barley straw and corn stover), with a capacity of 2.5 Ml, was first established by Iogen Corporation in Ottawa, Canada. Many other processing facilities are now in operation or planning throughout the world.

Economically, lignocellulosic biomass has an advantage over other agriculturally important biofuels feedstocks such as corn starch, soybeans, and sugar cane, because it can be produced quickly and at significantly lower cost than food crops. Lignocellulosic biomass is an important component of the major food crops; it is the non-edible portion of the plant, which is currently underutilized, but could be used for biofuel production. In short, lignocellulosic biomass holds the key to supplying society’s basic needs for sustainable production of liquid transportation fuels without impacting the nation’s food supply.

Ethanol Production via Biochemical Route

Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

Pretreated biomass can directly be converted to ethanol by using the process called simultaneous saccharification and cofermentation (SSCF). Pretreatment is a critical step which enhances the enzymatic hydrolysis of biomass. Basically, it alters the physical and chemical properties of biomass and improves the enzyme access and effectiveness which may also lead to a change in crystallinity and degree of polymerization of cellulose. The internal surface area and pore volume of pretreated biomass are increased which facilitates substantial improvement in accessibility of enzymes. The process also helps in enhancing the rate and yield of monomeric sugars during enzymatic hydrolysis steps.

Pretreatment methods can be broadly classified into four groups – physical, chemical, physio-chemical and biological. Physical pretreatment processes employ the mechanical comminution or irradiation processes to change only the physical characteristics of biomass. The physio-chemical process utilizes steam or steam and gases, like SO2 and CO2. The chemical processes employs acids (H2SO4, HCl, organic acids etc) or alkalis (NaOH, Na2CO3, Ca(OH)2, NH3 etc). The acid treatment typically shows the selectivity towards hydrolyzing the hemicelluloses components, whereas alkalis have better selectivity for the lignin. The fractionation of biomass components after such processes help in improving the enzymes accessibility which is also important to the efficient utilization of enzymes.

The pretreated biomass is subjected to enzymatic hydrolysis using cellulase enzymes to convert the cellulose to fermentable sugars. Cellulase refers to a class of enzymes produced chiefly by fungi and bacteria which catalyzes the hydrolysis of cellulose by attacking the glycosidic linkages. Cellulase is mixture of mainly three different functional protein groups: exo-glucanase (Exo-G), endo-glucanase(Endo-G) and ?-glucosidase (?-G). The functional proteins work synergistically in hydrolyzing the cellulose into the glucose. These sugars are further fermented using microorganism and are converted to ethanol. The microorganisms are selected based on their efficiency for ethanol productivity and higher product and inhibitors tolerance. Yeast Saccharomyces cerevisiae is used commercially to produce the ethanol from starch and sucrose.

Escherichia coli strain has also been developed recently for ethanol production by the first successful application of metabolic engineering. E. coli can consume variety of sugars and does not require the complex growth media but has very narrow operable range of pH. E. coli has higher optimal temperature than other known strains of bacteria.

Lower GHG emissions and empowerment of rural economy are major benefits associated with bioethanol

The major cost components in bioethanol production from lignocellulosic biomass are the pretreatment and the enzymatic hydrolysis steps. In fact, these two process are someway interrelated too where an efficient pretreatment strategy can save substantial enzyme consumption. Pretreatment step can also affect the cost of other operations such as size reduction prior to pretreatment. Therefore, optimization of these two important steps, which collectively contributes about 70% of the total processing cost, are the major challenges in the commercialization of bioethanol from 2nd generation feedstock.

Enzyme cost is the prime concern in full scale commercialization. The trend in enzyme cost is encouraging because of enormous research focus in this area and the cost is expected to go downward in future, which will make bioethanol an attractive option considering the benefits derived its lower greenhouse gas emissions and the empowerment of rural economy.

A Primer on Biofuels

The term ‘Biofuel’ refers to liquid or gaseous fuels for the transport sector that are predominantly produced from biomass. A variety of fuels can be produced from biomass resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The biomass resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues.

The agricultural resources include grains used for biofuels production, animal manures and residues, and crop residues derived primarily from corn and small grains (e.g., wheat straw). A variety of regionally significant crops, such as cotton, sugarcane, rice, and fruit and nut orchards can also be a source of crop residues. The forest resources include residues produced during the harvesting of forest products, fuelwood extracted from forestlands, residues generated at primary forest product processing mills, and forest resources that could become available through initiatives to reduce fire hazards and improve forest health. Municipal and urban wood residues are widely available and include a variety of materials — yard and tree trimmings, land-clearing wood residues, wooden pallets, organic wastes, packaging materials, and construction and demolition debris.

Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking. Biofuel industries are expanding in Europe, Asia and the Americas. Biofuels are generally considered as offering many priorities, including sustainability, reduction of greenhouse gas emissions, regional development, social structure and agriculture, and security of supply.

First-generation biofuels are made from sugar, starch, vegetable oil, or animal fats using conventional technology. The basic feedstocks for the production of first-generation biofuels come from agriculture and food processing. The most common first-generation biofuels are:

  • Biodiesel: extraction with or without esterification of vegetable oils from seeds of plants like soybean, oil palm, oilseed rape and sunflower or residues including animal fats derived from rendering applied as fuel in diesel engines
  • Bioethanol: fermentation of simple sugars from sugar crops like sugarcane or from starch crops like maize and wheat applied as fuel in petrol engines
  • Bio-oil: thermo-chemical conversion of biomass. A process still in the development phase
  • Biogas: anaerobic fermentation or organic waste, animal manures, crop residues an energy crops applied as fuel in engines suitable for compressed natural gas.

First-generation biofuels can be used in low-percentage blends with conventional fuels in most vehicles and can be distributed through existing infrastructure. Some diesel vehicles can run on 100 % biodiesel, and ‘flex-fuel’ vehicles are already available in many countries around the world.

Second-generation biofuels are derived from non-food feedstock including lignocellulosic biomass like crop residues or wood. Two transformative technologies are under development.

  • Biochemical: modification of the bio-ethanol fermentation process including a pre-treatment procedure
  • Thermochemical: modification of the bio-oil process to produce syngas and methanol, Fisher-Tropsch diesel or dimethyl ether (DME).

Advanced conversion technologies are needed for a second generation of biofuels. The second generation technologies use a wider range of biomass resources – agriculture, forestry and waste materials. One of the most promising second-generation biofuel technologies – ligno-cellulosic processing (e. g. from forest materials) – is already well advanced. Pilot plants have been established in the EU, in Denmark, Spain and Sweden.

Third-generation biofuels may include production of bio-based hydrogen for use in fuel cell vehicles, e.g. Algae fuel, also called oilgae. Algae are low-input, high-yield feedstocks to produce biofuels.