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A biofuel is a fuel that contains energy from geologically recent carbon fixation, such as plants. These fuels are produced from living organisms. Examples of this carbon fixation occur in plants and microalgae. These fuels are made by a biomass conversion (biomass refers to recently living organisms, most often referring to plants or plant-derived materials). This biomass can be converted to convenient energy containing substances in three different ways: thermal conversion, chemical conversion, and biochemical conversion. This biomass conversion can result in fuel in solid, liquid, or gas form. This new biomass can be used for biofuels. Biofuels have increased in popularity because of rising oil prices and the need for energy security.

Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or starch crops such as corn, sugarcane, or sweet sorghum. Cellulosic biomass, derived from non-food sources, such as trees and grasses, is also being developed as a feedstock for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. Bioethanol is widely used in the USA and in Brazil. Current plant design does not provide for converting the lignin portion of plant raw materials to fuel components by fermentation.

Biodiesel can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats using transesterification and is the most common biofuel in Europe.

In 2010, worldwide biofuel production reached 105 billion liters (28 billion gallons US), up 17% from 2009,^[1] and biofuels provided 2.7% of the world's fuels for road transport, a contribution largely made up of ethanol and biodiesel.^{[citation needed]} Global ethanol fuel production reached 86 billion liters (23 billion gallons US) in 2010, with the United States and Brazil as the world's top producers, accounting together for 90% of global production. The world's largest biodiesel producer is the European Union, accounting for 53% of all biodiesel production in 2010.^[1] As of 2011, mandates for blending biofuels exist in 31 countries at the national level and in 29 states or provinces.^[2] The International Energy Agency has a goal for biofuels to meet more than a quarter of world demand for transportation fuels by 2050 to reduce dependence on petroleum and coal.^[3]

There are various social, economic, environmental and technical issues relating to biofuels production and use, which have been debated in the popular media and scientific journals. These include: the effect of moderating oil prices, the "food vs fuel" debate, poverty reduction potential, carbon emissions levels, sustainable biofuel production, deforestation and soil erosion, loss of biodiversity, and impact on water resources.

Biofuel power stations

Liquid fuels for transportation

Most transportation fuels are liquids, because vehicles usually require high energy density. This occurs naturally in liquids and solids. High energy density can also be provided by an internal combustion engine. These engines require clean-burning fuels. The fuels that are easiest to burn cleanly are typically liquids and gases. Thus, liquids meet the requirements of being both energy-dense and clean-burning. In addition, liquids (and gases) can be pumped, which means handling is easily mechanized, and thus less laborious.

First-generation biofuels

'First-generation' or conventional biofuels are made from sugar, starch, or vegetable oil.

Ethanol

Biologically produced alcohols, most commonly ethanol, and less commonly propanol and butanol, are produced by the action of microorganisms and enzymes through the fermentation of sugars or starches (easiest), or cellulose (which is more difficult). Biobutanol (also called biogasoline) is often claimed to provide a direct replacement for gasoline, because it can be used directly in a gasoline engines.

Ethanol fuel is the most common biofuel worldwide, particularly in Brazil. Alcohol fuels are produced by fermentation of sugars derived from wheat, corn, sugar beets, sugar cane, molasses and any sugar or starch from which alcoholic beverages such as whiskey, can be made (such as potato and fruit waste, etc.). The ethanol production methods used are enzyme digestion (to release sugars from stored starches), fermentation of the sugars, distillation and drying. The distillation process requires significant energy input for heat (sometimes unsustainable natural gas fossil fuel, but cellulosic biomass such as bagasse, the waste left after sugar cane is pressed to extract its juice, is the most common fuel in Brazil, while pellets, wood chips and also waste heat are more common in Europe Waste steam fuels ethanol factory- where waste heat from the factories also is used in the district heating grid.

Ethanol can be used in petrol engines as a replacement for gasoline; it can be mixed with gasoline to any percentage. Most existing car petrol engines can run on blends of up to 15% bioethanol with petroleum/gasoline. Ethanol has a smaller energy density than that of gasoline; this means it takes more fuel (volume and mass) to produce the same amount of work. An advantage of ethanol (CH
₃CH
₂OH) is that it has a higher octane rating than ethanol-free gasoline available at roadside gas stations, which allows an increase of an engine's compression ratio for increased thermal efficiency. In high-altitude (thin air) locations, some states mandate a mix of gasoline and ethanol as a winter oxidizer to reduce atmospheric pollution emissions.

Ethanol is also used to fuel bioethanol fireplaces. As they do not require a chimney and are "flueless", bioethanol fires^[4] are extremely useful for newly built homes and apartments without a flue. The downsides to these fireplaces is that their heat output is slightly less than electric heat or gas fires, and precautions must be taken to avoid carbon monoxide poisoning.

In the current corn-to-ethanol production model in the United States, considering the total energy consumed by farm equipment, cultivation, planting, fertilizers, pesticides, herbicides, and fungicides made from petroleum, irrigation systems, harvesting, transport of feedstock to processing plants, fermentation, distillation, drying, transport to fuel terminals and retail pumps, the net energy content value added and delivered to consumers is about 1.3 - 2 times higher than the total energy input. The net climate benefit (all things considered) was in the early 2000s between 15 and 30% net savings,^[5] but have since improved and is now approaching the European wheat and corn-based ethanol with typical values of 65-67 % reduction of climate gasses. The best European production lines are however reducing climate emissions with 90-95 %.^[6]

Corn-to-ethanol and other food stocks has led to the development of cellulosic ethanol. According to a joint research agenda conducted through the US Department of Energy,^[7] the fossil energy ratios (FER) for cellulosic ethanol, corn ethanol, and gasoline are 10.3, 1.36, and 0.81, respectively.^[8]^[9]^[10]

Ethanol has roughly one-third lower energy content per unit of volume compared to gasoline. This is partly counteracted by the better efficiency when using ethanol (in a long-term test of more than 2,1 million km, the BEST project found FFV vehicles to be 1-26 % more energy efficient than petrol cars The BEST project), but the volumetric consumption increases by approximately 30%, so more fuel stops are required. For practical terms this has no big implications as the typical driver does not use up a full tank in one trip. (E.g. European citizens drive on average less than 20 km/day).

With current subsidies, ethanol fuel is slightly cheaper per distance traveled in the United States.^[11]

Biodiesel

Biodiesel is the most common biofuel in Europe. It is produced from oils or fats using transesterification and is a liquid similar in composition to fossil/mineral diesel. Chemically, it consists mostly of fatty acid methyl (or ethyl) esters (FAMEs). Feedstocks for biodiesel include animal fats, vegetable oils, soy, rapeseed, jatropha, mahua, mustard, flax, sunflower, palm oil, hemp, field pennycress, Pongamia pinnata and algae. Pure biodiesel (B100) currently reduces emissions with up to 60% compared to diesel Second generation B100.

Biodiesel can be used in any diesel engine when mixed with mineral diesel. In some countries, manufacturers cover their diesel engines under warranty for B100 use, although Volkswagen of Germany, for example, asks drivers to check by telephone with the VW environmental services department before switching to B100. B100 may become more viscous at lower temperatures, depending on the feedstock used. In most cases, biodiesel is compatible with diesel engines from 1994 onwards, which use 'Viton' (by DuPont) synthetic rubber in their mechanical fuel injection systems. Note however, that no vehicles are certified for using neat biodiesel before 2014, as there was no emission control protocol available for biodiesel before this date.

Electronically controlled 'common rail' and 'unit injector' type systems from the late 1990s onwards may only use biodiesel blended with conventional diesel fuel. These engines have finely metered and atomized multiple-stage injection systems that are very sensitive to the viscosity of the fuel. Many current-generation diesel engines are made so that they can run on B100 without altering the engine itself, although this depends on the fuel rail design. Since biodiesel is an effective solvent and cleans residues deposited by mineral diesel, engine filters may need to be replaced more often, as the biofuel dissolves old deposits in the fuel tank and pipes. It also effectively cleans the engine combustion chamber of carbon deposits, helping to maintain efficiency. In many European countries, a 5% biodiesel blend is widely used and is available at thousands of gas stations.^[12]^[13] Biodiesel is also an oxygenated fuel, meaning it contains a reduced amount of carbon and higher hydrogen and oxygen content than fossil diesel. This improves the combustion of biodiesel and reduces the particulate emissions from unburnt carbon. However, using neat biodiesel may increase NOx-emissions Nylund.N-O & Koponen.K. 2013. Fuel and Technology Alternatives for Buses. Overall Energy Efficiency and Emission Performance. IEA Bioenergy Task 46. Possibly the new emission standards Euro VI/EPA 10 will lead to reduced NOx-levels also when using B100.

Biodiesel is also safe to handle and transport because it is non-toxic and biodegradable, and has a high flash point of about 300 °F (148 °C) compared to petroleum diesel fuel, which has a flash point of 125 °F (52 °C).^[14]

In the USA, more than 80% of commercial trucks and city buses run on diesel. The emerging US biodiesel market is estimated to have grown 200% from 2004 to 2005. "By the end of 2006 biodiesel production was estimated to increase fourfold [from 2004] to more than" 1 billion US gallons (3,800,000 m³).^[15]

Other bioalcohols

Methanol is currently produced from natural gas, a nonrenewable fossil fuel. In the future it is hoped to be produced from biomass as biomethanol. This is technically feasible, but the economic viability is still pending^[16] The methanol economy is an alternative to the hydrogen economy, compared to today's hydrogen production from natural gas.

Butanol (C
₄H
₉OH) is formed by ABE fermentation (acetone, butanol, ethanol) and experimental modifications of the process show potentially high net energy gains with butanol as the only liquid product. Butanol will produce more energy and allegedly can be burned "straight" in existing gasoline engines (without modification to the engine or car),^[17] and is less corrosive and less water-soluble than ethanol, and could be distributed via existing infrastructures. DuPont and BP are working together to help develop butanol. E. coli strains have also been successfully engineered to produce butanol by modifying their amino acid metabolism.^[18]

Green diesel

Green diesel is produced through hydrocracking biological oil feedstocks, such as vegetable oils and animal fats.^[19]^[20] Hydrocracking is a refinery method that uses elevated temperatures and pressure in the presence of a catalyst to break down larger molecules, such as those found in vegetable oils, into shorter hydrocarbon chains used in diesel engines.^[21] It may also be called renewable diesel, hydrotreated vegetable oil^[21] or hydrogen-derived renewable diesel.^[20] Green diesel has the same chemical properties as petroleum-based diesel.^[21] It does not require new engines, pipelines or infrastructure to distribute and use, but has not been produced at a cost that is competitive with petroleum.^[20] Gasoline versions are also being developed.^[22] Green diesel is being developed in Louisiana and Singapore by ConocoPhillips, Neste Oil, Valero, Dynamic Fuels, and Honeywell UOP.^[20]^[23] and also by Preem in Gothenburg, Sweden Evolution Diesel

Biofuel gasoline

In 2013 UK researchers developed a genetically modified strain of Escherichia coli which could transform glucose into biofuel gasoline that does not need to be blended.^[24] Later in 2013 UCLA researchers engineered a new metabolic pathway to bypass glycolysis and increase the rate of conversion of sugars into biofuel,^[25] while KAIST researchers developed a strain capable of producing short-chain alkanes, free fatty acids, fatty esters and fatty alcohols through the fatty acyl (acyl carrier protein (ACP)) to fatty acid to fatty acyl-CoA pathway in vivo.^[26] It is believed that in the future it will be possible to "tweak" the genes to make gasoline from straw or animal manure.

Vegetable oil

Straight unmodified edible vegetable oil is generally not used as fuel, but lower-quality oil can and has been used for this purpose. Used vegetable oil is increasingly being processed into biodiesel, or (more rarely) cleaned of water and particulates and used as a fuel.

As with 100% biodiesel (B100), to ensure the fuel injectors atomize the vegetable oil in the correct pattern for efficient combustion, vegetable oil fuel must be heated to reduce its viscosity to that of diesel, either by electric coils or heat exchangers. This is easier in warm or temperate climates. Big corporations like MAN B&W Diesel, Wärtsilä, and Deutz AG, as well as a number of smaller companies, such as Elsbett, offer engines that are compatible with straight vegetable oil, without the need for after-market modifications.

Vegetable oil can also be used in many older diesel engines that do not use common rail or unit injection electronic diesel injection systems. Due to the design of the combustion chambers in indirect injection engines, these are the best engines for use with vegetable oil. This system allows the relatively larger oil molecules more time to burn. Some older engines, especially Mercedes, are driven experimentally by enthusiasts without any conversion, a handful of drivers have experienced limited success with earlier pre-"Pumpe Duse" VW TDI engines and other similar engines with direct injection. Several companies, such as Elsbett or Wolf, have developed professional conversion kits and successfully installed hundreds of them over the last decades.

Oils and fats can be hydrogenated to give a diesel substitute. The resulting product is a straight-chain hydrocarbon with a high cetane number, low in aromatics and sulfur and does not contain oxygen. Hydrogenated oils can be blended with diesel in all proportions. They have several advantages over biodiesel, including good performance at low temperatures, no storage stability problems and no susceptibility to microbial attack.^[29]

Bioethers

Bioethers (also referred to as fuel ethers or oxygenated fuels) are cost-effective compounds that act as octane rating enhancers."Bioethers are produced by the reaction of reactive iso-olefins, such as iso-butylene, with bioethanol."^[30] Bioethers are created by wheat or sugar beet.^[31] They also enhance engine performance, whilst significantly reducing engine wear and toxic exhaust emissions. Though bioethers are likely to replace petroethers in the UK, it is highly unlikely they will become a fuel in and of itself due to the low energy density.^[32] Greatly reducing the amount of ground-level ozone emissions, they contribute to air quality.^[33]^[34]

When it comes to transportation fuel there are six ether additives- 1. Dimethyl Ether (DME) 2. Diethyl Ether (DEE) 3. Methyl Teritiary-Butyl Ether (MTBE) 4. Ethyl ter-butyl ether (ETBE) 5. Ter-amyl methyl ether (TAME) 6. Ter-amyl ethyl Ether (TAEE)^[35]

The European Fuel Oxygenates Association (aka EFOA) credits Methyl Tertiary-Butyl Ether (MTBE) and Ethyl ter-butyl ether (ETBE) as the most commonly used ethers in fuel to replace lead. Ethers were brought into fuels in Europe in the 1970s to replace the highly toxic compound.^[36] Although Europeans still use Bio-ether additives, the US no longer has an oxygenate requirement therefore bio-ethers are no longer used as the main fuel additive.^[37]

Biogas

Biogas is methane produced by the process of anaerobic digestion of organic material by anaerobes.^[38] It can be produced either from biodegradable waste materials or by the use of energy crops fed into anaerobic digesters to supplement gas yields. The solid byproduct, digestate, can be used as a biofuel or a fertilizer.

Biogas can be recovered from mechanical biological treatment waste processing systems.

Note: Landfill gas, a less clean form of biogas, is produced in landfills through naturally occurring anaerobic digestion. If it escapes into the atmosphere, it is a potential greenhouse gas.

Farmers can produce biogas from manure from their cattle by using anaerobic digesters.^[39]

Syngas

Syngas, a mixture of carbon monoxide, hydrogen and other hydrocarbons, is produced by partial combustion of biomass, that is, combustion with an amount of oxygen that is not sufficient to convert the biomass completely to carbon dioxide and water.^[29] Before partial combustion, the biomass is dried, and sometimes pyrolysed. The resulting gas mixture, syngas, is more efficient than direct combustion of the original biofuel; more of the energy contained in the fuel is extracted.

Syngas may be burned directly in internal combustion engines, turbines or high-temperature fuel cells.^[40] The wood gas generator, a wood-fueled gasification reactor, can be connected to an internal combustion engine.
Syngas can be used to produce methanol, DME and hydrogen, or converted via the Fischer-Tropsch process to produce a diesel substitute, or a mixture of alcohols that can be blended into gasoline. Gasification normally relies on temperatures greater than 700 °C.
Lower-temperature gasification is desirable when co-producing biochar, but results in syngas polluted with tar.

Solid biofuels

Examples include wood, sawdust, grass trimmings, domestic refuse, charcoal, agricultural waste, nonfood energy crops, and dried manure.

When raw biomass is already in a suitable form (such as firewood), it can burn directly in a stove or furnace to provide heat or raise steam. When raw biomass is in an inconvenient form (such as sawdust, wood chips, grass, urban waste wood, agricultural residues), the typical process is to densify the biomass. This process includes grinding the raw biomass to an appropriate particulate size (known as hogfuel), which, depending on the densification type, can be from 1 to 3 cm (0 to 1 in), which is then concentrated into a fuel product. The current processes produce wood pellets, cubes, or pucks. The pellet process is most common in Europe, and is typically a pure wood product. The other types of densification are larger in size compared to a pellet, and are compatible with a broad range of input feedstocks. The resulting densified fuel is easier to transport and feed into thermal generation systems, such as boilers.

Industry has used sawdust, bark and chips for fuel for decades, primary in the pulp and paper industry, and also bagasse (spent sugar cane) fueled boilers in the sugar cane industry. Boilers in the range of 500,000 lb/hr of steam, and larger, are in routine operation, using grate, spreader stoker, suspension burning and fluid bed combustion. Utilities generate power, typically in the range of 5 to 50 MW, using locally available fuel. Other industries have also installed wood waste fueled boilers and dryers in areas with low cost fuel.^[41]

One of the advantages of biomass fuel is that it is often a byproduct, residue or waste-product of other processes, such as farming, animal husbandry and forestry.^[42] In theory, this means fuel and food production do not compete for resources, although this is not always the case.^[42]

A problem with the combustion of raw biomass is that it emits considerable amounts of pollutants, such as particulates and polycyclic aromatic hydrocarbons. Even modern pellet boilers generate much more pollutants than oil or natural gas boilers. Pellets made from agricultural residues are usually worse than wood pellets, producing much larger emissions of dioxins and chlorophenols.^[43]

In spite of the above noted study, numerous studies have shown biomass fuels have significantly less impact on the environment than fossil based fuels. Of note is the US Department of Energy Laboratory, operated by Midwest Research Institute Biomass Power and Conventional Fossil Systems with and without CO2 Sequestration – Comparing the Energy Balance, Greenhouse Gas Emissions and Economics Study. Power generation emits significant amounts of greenhouse gases (GHGs), mainly carbon dioxide (CO₂). Sequestering CO₂ from the power plant flue gas can significantly reduce the GHGs from the power plant itself, but this is not the total picture. CO₂ capture and sequestration consumes additional energy, thus lowering the plant's fuel-to-electricity efficiency. To compensate for this, more fossil fuel must be procured and consumed to make up for lost capacity.

Taking this into consideration, the global warming potential (GWP), which is a combination of CO₂, methane (CH₄), and nitrous oxide (N₂O) emissions, and energy balance of the system need to be examined using a life cycle assessment. This takes into account the upstream processes which remain constant after CO₂ sequestration, as well as the steps required for additional power generation. Firing biomass instead of coal led to a 148% reduction in GWP.

A derivative of solid biofuel is biochar, which is produced by biomass pyrolysis. Biochar made from agricultural waste can substitute for wood charcoal. As wood stock becomes scarce, this alternative is gaining ground. In eastern Democratic Republic of Congo, for example, biomass briquettes are being marketed as an alternative to charcoal to protect Virunga National Park from deforestation associated with charcoal production.^[44]

Second-generation (advanced) biofuels

Second generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of biomass. Biomass is a wide-ranging term meaning any source of organic carbon that is renewed rapidly as part of the carbon cycle. Biomass is derived from plant materials but can also include animal materials.

First generation biofuels are made from the sugars and vegetable oils found in arable crops, which can be easily extracted using conventional technology. In comparison, second generation biofuels are made from lignocellulosic biomass or woody crops, agricultural residues or waste, which makes it harder to extract the required fuel.

Sustainable biofuels

Biofuels in the form of liquid fuels derived from plant materials, are entering the market, driven mainly by the need to reduce climate gas emissions, but also by factors such as oil price spikes and the need for increased energy security. However, many of the biofuels that are currently being supplied have been criticised for their adverse impacts on the natural environment, food security, and land use.^[45]^[46]

The challenge is to support biofuel development, including the development of new cellulosic technologies, with responsible policies and economic instruments to help ensure that biofuel commercialization is sustainable. Responsible commercialization of biofuels represents an opportunity to enhance sustainable economic prospects in Africa, Latin America and Asia.^[45]^[46]^[47]

Biofuels by region

There are international organizations such as IEA Bioenergy,^[48] established in 1978 by the OECD International Energy Agency (IEA), with the aim of improving cooperation and information exchange between countries that have national programs in bioenergy research, development and deployment. The UN International Biofuels Forum is formed by Brazil, China, India, Pakistan, South Africa, the United States and the European Commission.^[49] The world leaders in biofuel development and use are Brazil, the United States, France, Sweden and Germany. Russia also has 22% of world's forest,^[50] and is a big biomass (solid biofuels) supplier. In 2010, Russian pulp and paper maker, Vyborgskaya Cellulose, said they would be producing pellets that can be used in heat and electricity generation from its plant in Vyborg by the end of the year.^[51] The plant will eventually produce about 900,000 tons of pellets per year, making it the largest in the world once operational.

Biofuels currently make up 3.1%^[52] of the total road transport fuel in the UK or 1,440 million litres. By 2020, 10% of the energy used in UK road and rail transport must come from renewable sources – this is the equivalent of replacing 4.3 million tonnes of fossil oil each year. Conventional biofuels are likely to produce between 3.7 and 6.6% of the energy needed in road and rail transport, while advanced biofuels could meet up to 4.3% of the UK’s renewable transport fuel target by 2020.^[53]

Debates regarding the production and use of biofuel

There are various social, economic, environmental and technical issues with biofuel production and use, which have been discussed in the popular media and scientific journals. These include: the effect of moderating oil prices, the "food vs fuel" debate, poverty reduction potential, carbon emissions levels, sustainable biofuel production, deforestation and soil erosion, loss of biodiversity,^[54] impact on water resources, the possible modifications necessary to run the engine on biofuel, as well as energy balance and efficiency. The International Resource Panel, which provides independent scientific assessments and expert advice on a variety of resource-related themes, assessed the issues relating to biofuel use in its first report Towards sustainable production and use of resources: Assessing Biofuels.^[55] "Assessing Biofuels" outlined the wider and interrelated factors that need to be considered when deciding on the relative merits of pursuing one biofuel over another. It concluded that not all biofuels perform equally in terms of their impact on climate, energy security and ecosystems, and suggested that environmental and social impacts need to be assessed throughout the entire life-cycle.

Another issue with biofuel use and production is the US has changed mandates many times because the production has been taking longer than expected. The Renewable Fuel Standard (RFS) set by congress for 2010 was pushed back to at best 2012 to produce 100 million gallons of pure ethanol (not blended with a fossil fuel).^[56]

Current research

Research is ongoing into finding more suitable biofuel crops and improving the oil yields of these crops. Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace fossil fuel usage. It would require twice the land area of the US to be devoted to soybean production, or two-thirds to be devoted to rapeseed production, to meet current US heating and transportation needs. ^{[citation needed]}

Specially bred mustard varieties can produce reasonably high oil yields and are very useful in crop rotation with cereals, and have the added benefit that the meal left over after the oil has been pressed out can act as an effective and biodegradable pesticide.^[57]

The NFESC, with Santa Barbara-based Biodiesel Industries, is working to develop biofuels technologies for the US navy and military, one of the largest diesel fuel users in the world.^[58] A group of Spanish developers working for a company called Ecofasa announced a new biofuel made from trash. The fuel is created from general urban waste which is treated by bacteria to produce fatty acids, which can be used to make biofuels.^[59]

Ethanol biofuels

As the primary source of biofuels in North America, many organizations are conducting research in the area of ethanol production. The National Corn-to-Ethanol Research Center (NCERC) is a research division of Southern Illinois University Edwardsville dedicated solely to ethanol-based biofuel research projects.^[60] On the federal level, the USDA conducts a large amount of research regarding ethanol production in the United States. Much of this research is targeted toward the effect of ethanol production on domestic food markets.^[61] A division of the U.S. Department of Energy, the National Renewable Energy Laboratory (NREL), has also conducted various ethanol research projects, mainly in the area of cellulosic ethanol.^[62]

Cellulosic ethanol commercialization is the process of building an industry out of methods of turning cellulose-containing organic matter into fuel. Companies, such as Iogen, POET, and Abengoa, are building refineries that can process biomass and turn it into bioethanol. Companies, such as Diversa, Novozymes, and Dyadic, are producing enzymes that could enable a cellulosic ethanol future. The shift from food crop feedstocks to waste residues and native grasses offers significant opportunities for a range of players, from farmers to biotechnology firms, and from project developers to investors.^[63]

As of 2013, the first commercial-scale plants to produce cellulosic biofuels have begun operating. Multiple pathways for the conversion of different biofuel feedstocks are being used. In the next few years, the cost data of these technologies operating at commercial scale, and their relative performance, will become available. Lessons learnt will lower the costs of the industrial processes involved.^[64]

In parts of Asia and Africa where drylands prevail, sweet sorghum is being investigated as a potential source of food, feed and fuel combined. The crop is particularly suitable for growing in arid conditions, as it only extracts one seventh of the water used by sugarcane. In India, and other places, sweet sorghum stalks are used to produce biofuel by squeezing the juice and then fermenting into ethanol.^[65]

A study by researchers at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) found that growing sweet sorghum instead of grain sorghum could increase farmers incomes by US$40 per hectare per crop because it can provide fuel in addition to food and animal feed. With grain sorghum currently grown on over 11 million hectares (ha) in Asia and on 23.4 million ha in Africa, a switch to sweet sorghum could have a considerable economic impact.^[66]

Algae biofuels

From 1978 to 1996, the US NREL experimented with using algae as a biofuels source in the "Aquatic Species Program".^[67] A self-published article by Michael Briggs, at the UNH Biofuels Group, offers estimates for the realistic replacement of all vehicular fuel with biofuels by using algae that have a natural oil content greater than 50%, which Briggs suggests can be grown on algae ponds at wastewater treatment plants.^[68] This oil-rich algae can then be extracted from the system and processed into biofuels, with the dried remainder further reprocessed to create ethanol. The production of algae to harvest oil for biofuels has not yet been undertaken on a commercial scale, but feasibility studies have been conducted to arrive at the above yield estimate. In addition to its projected high yield, algaculture — unlike crop-based biofuels — does not entail a decrease in food production, since it requires neither farmland nor fresh water. Many companies are pursuing algae bioreactors for various purposes, including scaling up biofuels production to commercial levels.^[69]^[70] Prof. Rodrigo E. Teixeira from the University of Alabama in Huntsville demonstrated the extraction of biofuels lipids from wet algae using a simple and economical reaction in ionic liquids.^[71]

Jatropha

Several groups in various sectors are conducting research on Jatropha curcas, a poisonous shrub-like tree that produces seeds considered by many to be a viable source of biofuels feedstock oil.^[72] Much of this research focuses on improving the overall per acre oil yield of Jatropha through advancements in genetics, soil science, and horticultural practices.

SG Biofuels, a San Diego-based jatropha developer, has used molecular breeding and biotechnology to produce elite hybrid seeds that show significant yield improvements over first-generation varieties.^[73] SG Biofuels also claims additional benefits have arisen from such strains, including improved flowering synchronicity, higher resistance to pests and diseases, and increased cold-weather tolerance.^[74]

Plant Research International, a department of the Wageningen University and Research Centre in the Netherlands, maintains an ongoing Jatropha Evaluation Project that examines the feasibility of large-scale jatropha cultivation through field and laboratory experiments.^[75] The Center for Sustainable Energy Farming (CfSEF) is a Los Angeles-based nonprofit research organization dedicated to jatropha research in the areas of plant science, agronomy, and horticulture. Successful exploration of these disciplines is projected to increase jatropha farm production yields by 200-300% in the next 10 years.^[76]

Fungi

A group at the Russian Academy of Sciences in Moscow, in a 2008 paper, stated they had isolated large amounts of lipids from single-celled fungi and turned it into biofuels in an economically efficient manner. More research on this fungal species, Cunninghamella japonica, and others, is likely to appear in the near future.^[77] The recent discovery of a variant of the fungus Gliocladium roseum points toward the production of so-called myco-diesel from cellulose. This organism was recently discovered in the rainforests of northern Patagonia, and has the unique capability of converting cellulose into medium-length hydrocarbons typically found in diesel fuel.^[78]

Animal Gut Bacteria

Microbial gastrointestinal flora in a variety of animals have shown potential for the production of biofuels. Recent research has shown that TU-103, a strain of Clostridium bacteria found in Zebra feces, can convert nearly any form of cellulose into butanol fuel.^[79] Microbes in panda waste are being investigated for their use in creating biofuels from bamboo and other plant materials.^[80]

Greenhouse gas emissions

Some scientists have expressed concerns about land-use change in response to greater demand for crops to use for biofuel and the subsequent carbon emissions.^[81] The payback period, that is, the time it will take biofuels to pay back the carbon debt they acquire due to land-use change, has been estimated to be between 100 and 1000 years, depending on the specific instance and location of land-use change. However, no-till practices combined with cover-crop practices can reduce the payback period to three years for grassland conversion and 14 years for forest conversion.^[82] Biofuels made from waste biomass or from biomass grown on abandoned agricultural lands incur little to no carbon debt.^[83]

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^ Farrell, A.E. et al. (2006) "Ethanol can Contribute to Energy and Environmental Goals", Science, 311, 506-8.
^ Hammerschlag, R. 2006. "Ethanol's Energy Return on Investment: A Survey of the Literature 1999-Present", Environ. Sci. Technol., 40, 1744-50.
^ http://www.e85prices.com/. {{cite web}}: Missing or empty |title= (help)
^ "ADM Biodiesel: Hamburg, Leer, Mainz". Biodiesel.de. Retrieved 14 July 2010.
^ RRI Limited for Biodiesel Filling Stations. "Welcome to Biodiesel Filling Stations". Biodieselfillingstations.co.uk. Retrieved 14 July 2010.
^ "Biofuels Facts". Hempcar.org. Retrieved 14 July 2010.
^ THE FUTURIST, Will Thurmond. July–August 2007
^ Börjesson.P. et al. 2013, REPORT f3 2013:13, p 170
^ "ButylFuel, LLC Main Page". Butanol.com. 15 August 2005. Retrieved 14 July 2010.
^ Evans, Jon (14 January 2008). "Biofuels aim higher". Biofuels, Bioproducts and Biorefining (BioFPR). Retrieved 3 December 2008.
^ Brown, Robert; Jennifer Holmgren. "Fast Pyrolysis and Bio-Oil Upgrading" (PDF). Retrieved 15 March 2012.
^ ^a ^b ^c ^d "Alternative & Advanced Fuels". US Department of Energy. Retrieved 7 March 2012.
^ ^a ^b ^c Knothe, Gerhard (2010). "Biodiesel and renewable diesel: A comparison". Progress in Energy and Combustion ScienceTemplate:Inconsistent citations {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: postscript (link)
^ Jessica, Ebert. "Breakthroughs in Green Gasoline Production". Biomass Magazine. Retrieved 14 August 2012.
^ Albrecht, KO; Hallen, RT (March 2011). "A Brief Literature Overview of Various Routes to Biorenewable Fuels from Lipids for the National Alliance of Advanced Biofuels and Bio-products NAAB Consortium" (PDF). Prepared by the US Department of EnergyTemplate:Inconsistent citations {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: postscript (link)
^ Summers, Rebecca (24 April 2013) Bacteria churn out first ever petrol-like biofuel New Scientist, Retrieved 27 April 2013
^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1038/nature12575, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1038/nature12575 instead.
^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1038/nature12536, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1038/nature12536 instead.
^ Nishimoto, Alex (10 March 2014). "Walmart Debuts Turbine-Powered WAVE Semi Truck Prototype". Motor Trend.
^ "Wal-Mart To Test Hybrid Trucks". Sustainable Business. 3 February 2009.
^ ^a ^b Evans, G. "Liquid Transport Biofuels - Technology Status Report", National Non-Food Crops Centre, 2008-04-14. Retrieved on 2009-05-11.
^ Rock, Kerry; Maurice Korpelshoek (2007). [<http://www.digitalrefining.com/article_1000210 "Bioethers Impact on the Gasoline Pool"]. Digital Refining. Retrieved 15 February 2014. {{cite web}}: Check |url= value (help)
^ beet.http://biofuel.org.uk/bioethers.html
^ http://biofuel.org.uk/bioethers.html
^ "Council Directive 85/536/EEC of 5 December 1985 on crude-oil savings through the use of substitute fuel components in petrol". Eur-lex.europa.eu. Retrieved 14 July 2010.
^ "Microsoft Word - IA 55 EN.doc" (PDF). Retrieved 14 July 2010.
^ Sukla, Mirtunjay Kumar. [<http://www.ascension-publishing./BIZ/DMEoverview.pdf> "Bio-Ethers as Transportation Fuel: A Review"]. Indian Institute of Petroleum Dehradun. Retrieved 15 February 2014. {{cite web}}: Check |url= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ [<http://www.petrochemistry.eu/ftp/pressroom/EFOA_2008_def.pdf> "What are Bio-Ethers?"]. . The European Fuel Oxygenates Association. {{cite web}}: Check |url= value (help)
^ [< http://www.epa.gov/mtbe/gas.htm> "Gasoline"]. Environmental Protection Agency. {{cite web}}: Check |url= value (help)
^ Redman, G., The Andersons Centre. "Assessment of on-farm AD in the UK", National Non-Food Crops Centre, 2008-06-09. Retrieved on 2009-05-11.
^ "BIOGAS: No bull, manure can power your farm." Farmers Guardian (25 September 2009): 12. General OneFile. Gale.
^ Electricity from wood through the combination of gasification and solid oxide fuel cells, Ph.D. Thesis by Florian Nagel, Swiss Federal Institute of Technology Zurich, 2008
^ Biomass and Alternate Energy Fuel Systems: An Engineering and Economic Guide
^ ^a ^b Frauke Urban and Tom Mitchell 2011. Climate change, disasters and electricity generation. London: Overseas Development Institute and Institute of Development Studies
^ Cedric Briens, Jan Piskorz and Franco Berruti, "Biomass Valorization for Fuel and Chemicals Production -- A Review," 2008. International Journal of Chemical Reactor Engineering, 6, R2
^ "Threat to Great Apes Highlighted at Virunga Meeting". America.gov. Retrieved 14 July 2010.
^ ^a ^b The Royal Society (January 2008). Sustainable biofuels: prospects and challenges, ISBN 978-0-85403-662-2, p. 61.
^ ^a ^b Gordon Quaiattini. Biofuels are part of the solution Canada.com, April 25, 2008. Retrieved December 23, 2009.
^ EPFL Energy Center (c2007). Roundtable on Sustainable Biofuels Retrieved December 23, 2009.
^ "IEA bioenergy". IEA bioenergy. Retrieved 14 July 2010.
^ "Press Conference Launching International Biofuels Forum". United Nations Department of Public Information. 2 March 2007. Retrieved 15 January 2008.
^ Greenpeace - The Russian Forests
^ "World's Largest Pellet Plant to Start by Year-End". Moscow Times
^ UK falls short of biofuel targets for 2010/2011
^ National Non-Food Crops Centre. "Advanced Biofuels: The Potential for a UK Industry, NNFCC 11-011", Retrieved on 2011-11-17
^ Fletcher Jr., Robert J.; Bruce A Robertson; Jason Evans; Patrick J Doran; Janaki RR Alavalapati; Douglas W Schemske (2011). "Biodiversity conservation in the era of biofuels: risks and opportunities". Frontiers in Ecology and the Environment. 9 (3): 161–168. doi:10.1890/090091. Retrieved 10 December 2013.
^ Towards sustainable production and use of resources: Assessing Biofuels, 2009, International Resource Panel, United Nations Environment Programme
^ Bracmort, Kelsi. "Meeting the Renewable Fuel Standard (RFS) Mandate for Cellulosic Biofuels:Questions and Answers" (PDF). Washington, DC: Congressional Research Service.
^ "Mustard Hybrids for Low-Cost Biofuels and Organic Pesticides" (PDF). Retrieved 15 March 2010.
^ Future Energies (30 October 2003). "PORT HUENEME, Calif: U.S. Navy to Produce its Own Biofuels :: Future Energies :: The future of energy". Future Energies. Retrieved 17 October 2009.
^ "Newsvine - Ecofasa turns waste to biofuels using bacteria". Lele.newsvine.com. 18 October 2008. Retrieved 17 October 2009.
^ Ethanol Research (2 April 2012). "National Corn-to-Ethanol Research Center (NCERC)". Ethanol Research. Retrieved 2 April 2012.
^ American Coalition for Ethanol (2 June 2008). "Responses to Questions from Senator Bingaman" (PDF). American Coalition for Ethanol. Retrieved 2 April 2012.
^ National Renewable Energy Laboratory (2 March 2007). "Research Advantages: Cellulosic Ethanol" (PDF). National Renewable Energy Laboratory. Retrieved 2 April 2012.
^ Pernick, Ron and Wilder, Clint (2007). The Clean Tech Revolution p. 96.
^ HLPE (2013). "Biofuels and food security" (PDF).
^ "Sweet Sorghum : A New "Smart Biofuel Crop"". Agriculture Business Week. 30 June 2008.
^ Sweet sorghum for food, feed and fuel New Agriculturalist, January 2008.
^ Sheehan, John; et al. (July 1998). "A Look Back at the U. S. Department of Energy's Aquatic Species Program: Biofuels from Algae" (PDF). National Renewable Energy Laboratory. Retrieved 16 June 2012. {{cite web}}: Explicit use of et al. in: |author2= (help)
^ Briggs, Michael (August 2004). "Widescale Biodiesel Production from Algae". UNH Biodiesel Group (University of New Hampshire). Archived from the original on 24 March 2006. Retrieved 2 January 2007.
^ "Valcent Products Inc. Develops "Clean Green" Vertical Bio-Reactor". Valcent Products. Retrieved 9 July 2008.
^ "Technology: High Yield Carbon Recycling". GreenFuel Technologies Corporation. Retrieved 9 July 2008.
^ R. E. Teixeira (2012). "Energy-efficient extraction of fuel and chemical feedstocks from algae". Green Chemistry. 14 (2): 419–427. doi:10.1039/C2GC16225C.
^ B.N. Divakara, H.D. Upadhyaya, S.P. Wani, C.L. Laxmipathi Gowda (2010). "Biology and genetic improvement of Jatropha curcas L.: A review". Applied Energy. 87 (3): 732–742. doi:10.1016/j.apenergy.2009.07.013.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Biofuels Digest (16 May 2011). "Jatropha blooms again: SG Biofuels secures 250K acres for hybrids". Biofuels Digest. Retrieved 8 March 2012.
^ SG Biofuels (8 March 2012). "Jmax Hybrid Seeds". SG Biofuels. Retrieved 8 March 2012.
^ Plant Research International (8 March 2012). "JATROPT (Jatropha curcas): Applied and technical research into plant properties". Plant Research International. Retrieved 8 March 2012.
^ Biofuels Magazine (11 April 2011). "Energy Farming Methods Mature, Improve". Biofuels Magazine. Retrieved 8 March 2012.
^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1134/S0003683808050128, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1134/S0003683808050128 instead.
^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1099/mic.0.2008/022186-0, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1099/mic.0.2008/022186-0 instead.
^ Kathryn Hobgood Ray (25 August 2011). "Cars Could Run on Recycled Newspaper, Tulane Scientists Say". Tulane University news webpage. Tulane University. Retrieved 14 March 2012.
^ USA (10 September 2013). "Panda Poop Might Help Turn Plants Into Fuel". News.nationalgeographic.com. Retrieved 2 October 2013.
^ Searchinger, Timothy (2011). "Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change". Science. pp. 1238–1240. doi:10.1126/science.1151861. Retrieved 8 November 2011. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Kim, Hyungtae; Seungdo Kim; Bruce E. Dale (2009). "Biofuels, Land Use Change, and Greenhouse Gas Emissions: Some Unexplored Variables". Environmental Science. pp. 961–967. doi:10.1021/es802681k. {{cite web}}: Missing or empty |url= (help)
^ fargione, Joseph; Jason Hill; David Tilman; Stephen Polasky; Peter Hawthorne (2008). "Land Clearing and the Biofuel Carbon Debt". Science. pp. 1235–1238. doi:10.1126/science.1152747. Retrieved 12 November 2011.

External links

EFOA
Alternative Fueling Station Locator (EERE)
Towards Sustainable Production and Use of Resources: Assessing Biofuels by the United Nations Environment Programme, October 2009.
Biofuels guidance for businesses, including permits and licences required on NetRegs.gov.uk
How Much Water Does It Take to Make Electricity?—Natural gas requires the least water to produce energy, some biofuels the most, according to a new study.
International Conference on Biofuels Standards - European Union Biofuels Standardization
International Energy Agency: Biofuels for Transport - An International Perspective
Biofuels from Biomass: Technology and Policy Considerations Thorough overview from MIT
The Guardian news on biofuels
The U.S. DOE Clean Cities Program - links to all of the Clean Cities coalitions that exist throughout the U.S. (there are 87 of them)
Biofuels Factsheet by the University of Michigan's Center for Sustainable Systems
Learn Biofuels - Educational Resource for Students

[Biofuels2010-1] "Biofuels Make a Comeback Despite Tough Economy". Worldwatch Institute. 31 August 2011. Retrieved 31 August 2011.

[ren212011-2] REN21 (2011). "Renewables 2011: Global Status Report" (PDF). pp. 13–14.{{cite web}}: CS1 maint: numeric names: authors list (link)^{[dead link‍]}

[3] "Technology Roadmap, Biofuels for Transport" (PDF). 2011.

[4] Bio ethanol fires information bio ethanol fireplace. (2009)

[5] Wang, Michael, May Wu and Hong Huo. Life-cycle energy and greenhouse gas emission impacts of different corn ethanol plant types. Environ. Res. Lett. 2007

[6] Energimyndigheten 2013. Hållbara biodrivmedel och flytande biobränslen 2013

[7] see "Breaking the Biological Barriers to Cellulosic Ethanol"

[8] Brinkman, N. et al., "Well-to-Wheels Analysis of Advanced/Vehicle Systems", 2005.

[9] Farrell, A.E. et al. (2006) "Ethanol can Contribute to Energy and Environmental Goals", Science, 311, 506-8.

[10] Hammerschlag, R. 2006. "Ethanol's Energy Return on Investment: A Survey of the Literature 1999-Present", Environ. Sci. Technol., 40, 1744-50.

[11] ttp://www.e85prices.com/. {{cite web}}: Missing or empty |title= (help)

[12] "ADM Biodiesel: Hamburg, Leer, Mainz". Biodiesel.de. Retrieved 14 July 2010.

[13] RRI Limited for Biodiesel Filling Stations. "Welcome to Biodiesel Filling Stations". Biodieselfillingstations.co.uk. Retrieved 14 July 2010.

[14] "Biofuels Facts". Hempcar.org. Retrieved 14 July 2010.

[15] THE FUTURIST, Will Thurmond. July–August 2007

[16] Börjesson.P. et al. 2013, REPORT f3 2013:13, p 170

[17] "ButylFuel, LLC Main Page". Butanol.com. 15 August 2005. Retrieved 14 July 2010.

[butanol-18] Evans, Jon (14 January 2008). "Biofuels aim higher". Biofuels, Bioproducts and Biorefining (BioFPR). Retrieved 3 December 2008.

[19] Brown, Robert; Jennifer Holmgren. "Fast Pyrolysis and Bio-Oil Upgrading" (PDF). Retrieved 15 March 2012.

[seven-20] "Alternative & Advanced Fuels". US Department of Energy. Retrieved 7 March 2012.

[alpha-21] Knothe, Gerhard (2010). "Biodiesel and renewable diesel: A comparison". Progress in Energy and Combustion ScienceTemplate:Inconsistent citations {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: postscript (link)

[22] Jessica, Ebert. "Breakthroughs in Green Gasoline Production". Biomass Magazine. Retrieved 14 August 2012.

[23] Albrecht, KO; Hallen, RT (March 2011). "A Brief Literature Overview of Various Routes to Biorenewable Fuels from Lipids for the National Alliance of Advanced Biofuels and Bio-products NAAB Consortium" (PDF). Prepared by the US Department of EnergyTemplate:Inconsistent citations {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: postscript (link)

[24] Summers, Rebecca (24 April 2013) Bacteria churn out first ever petrol-like biofuel New Scientist, Retrieved 27 April 2013

[25] Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1038/nature12575, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1038/nature12575 instead.

[26] Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1038/nature12536, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1038/nature12536 instead.

[27] Nishimoto, Alex (10 March 2014). "Walmart Debuts Turbine-Powered WAVE Semi Truck Prototype". Motor Trend.

[28] "Wal-Mart To Test Hybrid Trucks". Sustainable Business. 3 February 2009.

[evans-29] Evans, G. "Liquid Transport Biofuels - Technology Status Report", National Non-Food Crops Centre, 2008-04-14. Retrieved on 2009-05-11.

[30] Rock, Kerry; Maurice Korpelshoek (2007). [<http://www.digitalrefining.com/article_1000210 "Bioethers Impact on the Gasoline Pool"]. Digital Refining. Retrieved 15 February 2014. {{cite web}}: Check |url= value (help)

[31] t.http://biofuel.org.uk/bioethers.html

[32] ttp://biofuel.org.uk/bioethers.html

[33] "Council Directive 85/536/EEC of 5 December 1985 on crude-oil savings through the use of substitute fuel components in petrol". Eur-lex.europa.eu. Retrieved 14 July 2010.

[34] "Microsoft Word - IA 55 EN.doc" (PDF). Retrieved 14 July 2010.

[35] Sukla, Mirtunjay Kumar. [<http://www.ascension-publishing./BIZ/DMEoverview.pdf> "Bio-Ethers as Transportation Fuel: A Review"]. Indian Institute of Petroleum Dehradun. Retrieved 15 February 2014. {{cite web}}: Check |url= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

[36] [<http://www.petrochemistry.eu/ftp/pressroom/EFOA_2008_def.pdf> "What are Bio-Ethers?"]. . The European Fuel Oxygenates Association. {{cite web}}: Check |url= value (help)

[37] [< http://www.epa.gov/mtbe/gas.htm> "Gasoline"]. Environmental Protection Agency. {{cite web}}: Check |url= value (help)

[38] Redman, G., The Andersons Centre. "Assessment of on-farm AD in the UK", National Non-Food Crops Centre, 2008-06-09. Retrieved on 2009-05-11.

[39] "BIOGAS: No bull, manure can power your farm." Farmers Guardian (25 September 2009): 12. General OneFile. Gale.

[e-collection.ethbib.ethz.ch-40] Electricity from wood through the combination of gasification and solid oxide fuel cells, Ph.D. Thesis by Florian Nagel, Swiss Federal Institute of Technology Zurich, 2008

[41] Biomass and Alternate Energy Fuel Systems: An Engineering and Economic Guide

[ODI1-42] Frauke Urban and Tom Mitchell 2011. Climate change, disasters and electricity generation. London: Overseas Development Institute and Institute of Development Studies

[43] Cedric Briens, Jan Piskorz and Franco Berruti, "Biomass Valorization for Fuel and Chemicals Production -- A Review," 2008. International Journal of Chemical Reactor Engineering, 6, R2

[44] "Threat to Great Apes Highlighted at Virunga Meeting". America.gov. Retrieved 14 July 2010.

[roy-45] The Royal Society (January 2008). Sustainable biofuels: prospects and challenges, ISBN 978-0-85403-662-2, p. 61.

[sol-46] Gordon Quaiattini. Biofuels are part of the solution Canada.com, April 25, 2008. Retrieved December 23, 2009.

[47] EPFL Energy Center (c2007). Roundtable on Sustainable Biofuels Retrieved December 23, 2009.

[48] "IEA bioenergy". IEA bioenergy. Retrieved 14 July 2010.

[49] "Press Conference Launching International Biofuels Forum". United Nations Department of Public Information. 2 March 2007. Retrieved 15 January 2008.

[50] Greenpeace - The Russian Forests

[51] "World's Largest Pellet Plant to Start by Year-End". Moscow Times

[52] UK falls short of biofuel targets for 2010/2011

[nnfcc_adv-53] National Non-Food Crops Centre. "Advanced Biofuels: The Potential for a UK Industry, NNFCC 11-011", Retrieved on 2011-11-17

[54] Fletcher Jr., Robert J.; Bruce A Robertson; Jason Evans; Patrick J Doran; Janaki RR Alavalapati; Douglas W Schemske (2011). "Biodiversity conservation in the era of biofuels: risks and opportunities". Frontiers in Ecology and the Environment. 9 (3): 161–168. doi:10.1890/090091. Retrieved 10 December 2013.

[55] Towards sustainable production and use of resources: Assessing Biofuels, 2009, International Resource Panel, United Nations Environment Programme

[56] Bracmort, Kelsi. "Meeting the Renewable Fuel Standard (RFS) Mandate for Cellulosic Biofuels:Questions and Answers" (PDF). Washington, DC: Congressional Research Service.

[57] "Mustard Hybrids for Low-Cost Biofuels and Organic Pesticides" (PDF). Retrieved 15 March 2010.

[58] Future Energies (30 October 2003). "PORT HUENEME, Calif: U.S. Navy to Produce its Own Biofuels :: Future Energies :: The future of energy". Future Energies. Retrieved 17 October 2009.

[59] "Newsvine - Ecofasa turns waste to biofuels using bacteria". Lele.newsvine.com. 18 October 2008. Retrieved 17 October 2009.

[60] Ethanol Research (2 April 2012). "National Corn-to-Ethanol Research Center (NCERC)". Ethanol Research. Retrieved 2 April 2012.

[61] American Coalition for Ethanol (2 June 2008). "Responses to Questions from Senator Bingaman" (PDF). American Coalition for Ethanol. Retrieved 2 April 2012.

[62] National Renewable Energy Laboratory (2 March 2007). "Research Advantages: Cellulosic Ethanol" (PDF). National Renewable Energy Laboratory. Retrieved 2 April 2012.

[63] Pernick, Ron and Wilder, Clint (2007). The Clean Tech Revolution p. 96.

[64] HLPE (2013). "Biofuels and food security" (PDF).

[65] "Sweet Sorghum : A New "Smart Biofuel Crop"". Agriculture Business Week. 30 June 2008.

[66] Sweet sorghum for food, feed and fuel New Agriculturalist, January 2008.

[NREL_biofuels_algae-67] Sheehan, John; et al. (July 1998). "A Look Back at the U. S. Department of Energy's Aquatic Species Program: Biofuels from Algae" (PDF). National Renewable Energy Laboratory. Retrieved 16 June 2012. {{cite web}}: Explicit use of et al. in: |author2= (help)

[Briggs2004-68] Briggs, Michael (August 2004). "Widescale Biodiesel Production from Algae". UNH Biodiesel Group (University of New Hampshire). Archived from the original on 24 March 2006. Retrieved 2 January 2007.

[69] "Valcent Products Inc. Develops "Clean Green" Vertical Bio-Reactor". Valcent Products. Retrieved 9 July 2008.

[70] "Technology: High Yield Carbon Recycling". GreenFuel Technologies Corporation. Retrieved 9 July 2008.

[71] R. E. Teixeira (2012). "Energy-efficient extraction of fuel and chemical feedstocks from algae". Green Chemistry. 14 (2): 419–427. doi:10.1039/C2GC16225C.

[72] B.N. Divakara, H.D. Upadhyaya, S.P. Wani, C.L. Laxmipathi Gowda (2010). "Biology and genetic improvement of Jatropha curcas L.: A review". Applied Energy. 87 (3): 732–742. doi:10.1016/j.apenergy.2009.07.013.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[73] Biofuels Digest (16 May 2011). "Jatropha blooms again: SG Biofuels secures 250K acres for hybrids". Biofuels Digest. Retrieved 8 March 2012.

[74] SG Biofuels (8 March 2012). "Jmax Hybrid Seeds". SG Biofuels. Retrieved 8 March 2012.

[75] Plant Research International (8 March 2012). "JATROPT (Jatropha curcas): Applied and technical research into plant properties". Plant Research International. Retrieved 8 March 2012.

[76] Biofuels Magazine (11 April 2011). "Energy Farming Methods Mature, Improve". Biofuels Magazine. Retrieved 8 March 2012.

[77] Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1134/S0003683808050128, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1134/S0003683808050128 instead.

[78] Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1099/mic.0.2008/022186-0, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1099/mic.0.2008/022186-0 instead.

[79] Kathryn Hobgood Ray (25 August 2011). "Cars Could Run on Recycled Newspaper, Tulane Scientists Say". Tulane University news webpage. Tulane University. Retrieved 14 March 2012.

[80] USA (10 September 2013). "Panda Poop Might Help Turn Plants Into Fuel". News.nationalgeographic.com. Retrieved 2 October 2013.

[Science-81] Searchinger, Timothy (2011). "Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change". Science. pp. 1238–1240. doi:10.1126/science.1151861. Retrieved 8 November 2011. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[ES&T-82] Kim, Hyungtae; Seungdo Kim; Bruce E. Dale (2009). "Biofuels, Land Use Change, and Greenhouse Gas Emissions: Some Unexplored Variables". Environmental Science. pp. 961–967. doi:10.1021/es802681k. {{cite web}}: Missing or empty |url= (help)

[Science2-83] rgione, Joseph; Jason Hill; David Tilman; Stephen Polasky; Peter Hawthorne (2008). "Land Clearing and the Biofuel Carbon Debt". Science. pp. 1235–1238. doi:10.1126/science.1152747. Retrieved 12 November 2011.

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v t e Bioenergy
Biofuels	Alcohol Algae Babassu oil Bagasse Biobutanol Biodiesel Biogas Biogasoline Bioliquids Biomass Cooking oil vegetable oil Ethanol cellulosic mixtures Methanol Stover corn Straw Water hyacinth Wood gas
Energy from foodstock	Camelina sativa Cassava Coconut oil Grape Hemp Maize Oat Palm oil Potato Rapeseed Rice Sorghum Soybean Sugar beet Sugarcane Sunflower Wheat Yam
Non-food energy crops	Arundo Big bluestem Camelina Chinese tallow Duckweed Jatropha curcas Miscanthus × giganteus Pongamia pinnata Salicornia Switchgrass Wood
Technology	Bioconversion of biomass to mixed alcohol fuels Bioenergy with carbon capture and storage Biomass heating systems Biorefinery Fischer–Tropsch process Industrial biotechnology Pellet fuel mill stove Sabatier reaction Thermal depolymerization
Concepts	Agflation Cellulosic ethanol commercialization Energy content of biofuel Energy crop Energy forestry Energy return on investment Food vs. fuel Issues relating to biofuels Sustainable biofuel
Category

v t e Environmental technology
General	Appropriate technology Clean technology Climate smart agriculture Environmental design Environmental impact assessment Eco-innovation Ecotechnology Electric vehicle Energy recycling Environmental Design Environmental impact assessment Environmental impact design Green building Green vehicle Environmentally healthy community design Public interest design Sustainability Sustainability science Sustainable (agriculture architecture design development food systems industries procurement refurbishment technology transport)
Pollution	Air pollution (control dispersion modeling) Industrial ecology Solid waste treatment Waste management Water (agricultural wastewater treatment industrial wastewater treatment sewage treatment waste-water treatment technologies water purification)
Sustainable energy	Efficient energy use Electrification Energy development Energy recovery Fuel (alternative fuel biofuel carbon-neutral fuel hydrogen technologies) List of energy storage projects Renewable energy commercialization transition Sustainable lighting Transportation (electric vehicle hybrid vehicle)
Conservation	Building (green insulation natural sustainable architecture New Urbanism New Classical) Conservation biology Ecoforestry Efficient energy use Energy conservation Energy recovery Energy recycling Environmental movement Environmental remediation Glass in green buildings Green computing Heat recovery ventilation High-performance buildings Land rehabilitation Nature conservation Permaculture Recycling Water heat recycling

v t e Sustainability
Outline Index
Principles	Anthropocene Environmentalism Global governance Human impact on the environment Planetary boundaries Development
Consumption	Anthropization Anti-consumerism Circular economy Durable good Earth Overshoot Day Ecological footprint Ethical Green consumption Micro-sustainability Over-consumption Product stewardship Simple living Social return on investment Steady-state economy Sustainability Advertising Brand Marketing myopia Sustainable Consumer behaviour Market Systemic change resistance Tragedy of the commons
World population	Demographic transition Family planning Control Sustainable population
Technology	Appropriate Environmental technology Natural building Sustainable architecture Sustainable design Sustainable industries Sustainable packaging
Biodiversity	Biosecurity Biosphere Conservation biology Endangered species Holocene extinction Invasive species
Energy	Carbon footprint Renewable energy Sustainable energy
Food	Civic agriculture Climate-smart agriculture Community-supported agriculture Cultured meat Sustainable agriculture Sustainable diet Sustainable fishery
Water	Air well (condenser) Bioretention Bioswale Blue roof Catchwater Constructed wetland Detention basin Dew pond Footprint Hydroelectricity Hydropower Infiltration basin Irrigation tank Marine energy Micro hydro Ocean thermal energy conversion Pico hydro Rain garden Rainwater harvesting Rainwater tank Reclaimed water Retention basin Run-of-the-river hydroelectricity Scarcity Security Small hydro Sustainable drainage system Tidal power Tidal stream generator Tree box filter Water conservation Water heat recycling Water recycling shower Water-sensitive urban design
Accountability	Corporate environmental responsibility Corporate social responsibility Environmental accounting Environmental full-cost accounting Environmental planning Sustainability Accounting Measurement Metrics and indices Reporting Standards and certification Sustainable yield
Applications	Advertising Art Business City Climate finance Community Disinvestment Eco-capitalism Eco-cities Eco-investing Eco-socialism Ecovillage Environmental finance Green economy Construction Fashion Finance Gardening Geopark Green Development Infrastructure Marketing Green roof Greening Impact investing Landscape Livelihood Living Market Organic movement Organizations Procurement Refurbishment Socially responsible business Socially responsible marketing Sanitation Sourcing Space Sustainability organization Tourism Transport Urban drainage systems Urban infrastructure
Sustainable management	Environmental Fisheries Forest Humanistic capitalism Landscape Materials Natural resource Planetary Recycling Waste
Agreements and conferences	UN Conference on the Human Environment (Stockholm 1972) Brundtlandt Commission Report (1983) Our Common Future (1987) Earth Summit (1992) Rio Declaration on Environment and Development (1992) Agenda 21 (1992) Convention on Biological Diversity (1992) Lisbon Principles (1997) Earth Charter (2000) UN Millennium Declaration (2000) Earth Summit 2002 (Rio+10, Johannesburg) UN Conference on Sustainable Development (Rio+20, 2012) Sustainable Development Goals (2015)
Category Lists Science Studies Degrees