Biofuels are a wide range of fuels which are in some way derived from biomass. The term covers solid biomass, liquid fuels and various biogases. Biofuels are gaining increased public and scientific attention, driven by factors such as oil price spikes and the need for increased energy security.
Bioethanol is an alcohol made by fermenting the sugar components of plant materials and it is made mostly from sugar and starch crops. With advanced technology being developed, cellulosic biomass, such as trees and grasses, are also used as feedstocks 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.
Biodiesel is made from vegetable oils, animal fats or recycled greases. 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.
Biofuels provided 1.8% of the world's transport fuel in 2008. Investment into biofuels production capacity exceeded $4 billion worldwide in 2007 and is growing.
- 1 Liquid fuels for transportation
- 1.1 First generation biofuels
- 1.2 First Generation Biofuel Controversies
- 1.3 Second generation biofuels
- 1.4 Third generation biofuels
- 1.5 Green fuels
- 1.6 Ethanol from living algae
- 1.7 Helioculture
- 2 Biofuels by region
- 3 Issues with biofuel production and use
- 4 Further reading
- 5 External links
- 6 Related Links
- 7 References
Liquid fuels for transportation
Most transportation fuels are liquids, because vehicles usually require high energy density, as occurs in liquids and solids. High power density can be provided most inexpensively by an internal combustion engine; these engines require clean burning fuels, to keep the engine clean and minimize air pollution.
The fuels that are easiest to burn cleanly are typically liquids and gases. Thus liquids (and gases that can be stored in liquid form) meet the requirements of being both portable and clean burning. Also, liquids and gases can be pumped, which means handling is easily mechanized, and thus less laborious.
First generation biofuels
'First-generation biofuels' are biofuels made from sugar, starch, vegetable oil, or animal fats using conventional technology. The basic feedstocks for the production of first generation biofuels are often seeds or grains such as wheat, which yields starch that is fermented into bioethanol, or sunflower seeds, which are pressed to yield vegetable oil that can be used in biodiesel. These feedstocks could instead enter the animal or human food chain, and as the global population has risen their use in producing biofuels has been criticised for diverting food away from the human food chain, leading to food shortages and price rises.
The most common biofuels are listed below.
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 engine (in a similar way to biodiesel in diesel engines).
Ethanol fuel is the most common biofuel worldwide, particularly Ethanol fuel in Brazil. Alcohol fuels are produced by fermentation of sugars derived from wheat, corn, sugar beets, sugar cane, molasses and any sugar or starch that alcoholic beverages can be made from (like 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 (often unsustainable natural gas fossil fuel, but cellulosic biomass such as bagasse, the waste left after sugar cane is pressed to extract its juice, can also be used more sustainably).
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 gasoline, which means it takes more fuel (volume and mass) to produce the same amount of work. An advantage of ethanol (CH3CH2OH) is that is 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 bio ethanol fireplaces. As they do not require a chimney and are "flueless", bio ethanol fires  are extremely useful for new build homes and apartments without a flue. The downside to these fireplaces, is that the heat output is slightly less than electric and gas fires.
In the current alcohol-from-corn 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, and lower ethanol fuel energy content, the net energy content value added and delivered to consumers is very small. And, the net benefit (all things considered) does little to reduce un-sustainable imported oil and fossil fuels required to produce the ethanol.
Although ethanol-from-corn and other food stocks has implications both in terms of world food prices and limited, yet positive energy yield (in terms of energy delivered to customer/fossil fuels used), the technology has led to the development of cellulosic ethanol. According to a joint research agenda conducted through the U.S. Department of Energy, the fossil energy ratios (FER) for cellulosic ethanol, corn ethanol, and gasoline are 10.3, 1.36, and 0.81, respectively.
Many car manufacturers are now producing flexible-fuel vehicles (FFV's), which can safely run on any combination of bioethanol and petrol, up to 100% bioethanol. They dynamically sense exhaust oxygen content, and adjust the engine's computer systems, spark, and fuel injection accordingly. This adds initial cost and ongoing increased vehicle maintenance. As with all vehicles, efficiency falls and pollution emissions increase when FFV system maintenance is needed (regardless of the fuel mix being used), but is not performed. FFV internal combustion engines are becoming increasingly complex, as are multiple-propulsion-system FFV hybrid vehicles, which impacts cost, maintenance, reliability, and useful lifetime longevity.
Even dry ethanol has roughly one-third lower energy content per unit of volume compared to gasoline, so larger / heavier fuel tanks are required to travel the same distance, or more fuel stops are required. With large current un-sustainable, non-scalable subsidies, ethanol fuel still costs much more per distance traveled than current high gasoline prices in the United States.
Methanol is currently produced from natural gas, a non-renewable fossil fuel. It can also be produced from biomass as biomethanol. The methanol economy is an interesting alternative to the hydrogen economy, compared to today's hydrogen produced from natural gas, but not hydrogen production directly from water and state-of-the-art clean solar thermal energy processes.
Butanol 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), 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]] have also been successfully engineered to produce Butanol by hijacking their amino acid metabolism.
Green diesel, also known as renewable diesel, is a form of diesel fuel which is derived from renewable feedstock rather than the fossil feedstock used in most diesel fuels. Green diesel is not to be confused with biodiesel which is chemically quite different and processed using transesterification rather than the traditional fractional distillation used to process green diesel.
Green diesel feedstock can be sourced from a variety oils including canola, algae, jatropha and salicornia in addition to tallow.
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 (FAME). Oils are mixed with sodium hydroxide and methanol (or ethanol) and the chemical reaction produces biodiesel (FAME) and glycerol. One part glycerol is produced for every 10 parts biodiesel. 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) is by far the lowest emission diesel fuel. Although liquefied petroleum gas and hydrogen have cleaner combustion, they are used to fuel much less efficient petrol engines and are not as widely available.
Biodiesel can be used in any diesel engine when mixed with mineral diesel. The majority of vehicle manufacturers limit their recommendations to 15% biodiesel blended 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, requiring vehicles to have fuel line heaters. In most cases, biodiesel is compatible with diesel engines from 1994 onwards, which use 'Viton' (by DuPont) synthetic rubber in their mechanical injection systems. Electronically controlled 'common rail' and 'pump duse' type systems from the late 1990s onwards may only use biodiesel blended with conventional diesel fuel. These engines have finely metered and atomized multi-stage injection systems 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. NExBTL is suitable for all diesel engines in the world since it overperforms DIN EN 590 standards.
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. Biodiesel is also an oxygenated fuel, meaning that it contains a reduced amount of carbon and higher hydrogen and oxygen content than fossil diesel. This improves the combustion of fossil diesel and reduces the particulate emissions from un-burnt carbon.
Biodiesel is safe to handle and transport because it is as biodegradable as sugar, 10 times less toxic than table salt, and has a high flashpoint of about 300 F (148 C) compared to petroleum diesel fuel, which has a flash point of 125 F (52 C).
In 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 gallons".
Edible vegetable oil is generally not used as fuel, but lower quality oil can be 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. To ensure that the fuel injectors atomize the fuel 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, Wartsila 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 like 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, high in cetane, low in aromatics and sulphur and does not contain oxygen. Hydrogenated oils can be blended with diesel in all proportions Hydrogenated oils have several advantages over biodiesel, including good performance at low temperatures, no storage stability problems and no susceptibility to microbial attack.
Bio ethers (also referred to as fuel ethers or fuel oxygenates) are cost-effective compounds that act as octane rating enhancers. They also enhance engine performance, whilst significantly reducing engine wear and toxic exhaust emissions. Greatly reducing the amount of ground-level ozone, they contribute to the quality of the air we breathe.
Biogas is produced by the process of anaerobic digestion of organic material by anaerobes. 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. In the UK, the National Coal Board experimented with microorganisms that digested coal in situ converting it directly to gases such as methane.
Biogas contains methane and can be recovered from industrial anaerobic digesters and mechanical biological treatment systems. Landfill gas is a less clean form of biogas which is produced in landfills through naturally occurring anaerobic digestion. If it escapes into the atmosphere it is a potent greenhouse gas.
Oils and gases can be produced from various biological wastes:
- Thermal depolymerization of waste can extract methane and other oils similar to petroleum.
- GreenFuel Technologies Corporation developed a patented bioreactor system that uses nontoxic photosynthetic algae to take in smokestacks flue gases and produce biofuels such as biodiesel, biogas and a dry fuel comparable to coal.
Farmers can produce biogas from manure from their cows by getting a anaerobic digester (AD).
Syngas, a mixture of carbon monoxide and hydrogen, 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. Before partial combustion the biomass is dried, and sometimes pyrolysed.
The resulting gas mixture, syngas, is itself a fuel. Using the 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 or turbines. The wood gas generator is a wood-fueled gasification reactor mounted on an internal combustion engine. Syngas can be used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process to produce a synthetic diesel substitute, or a mixture of alcohols that can be blended into gasoline. Gasification normally relies on temperatures >700°C. Lower temperature gasification is desirable when co-producing biochar but results in a Syngas polluted with tar.
Examples include wood, sawdust, grass cuttings, domestic refuse, charcoal, agricultural waste, non-food 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 (1 in), which is then concentrated into a fuel product. The current types of processes are pellet, cube, or puck. 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 broadrange of input feedstocks. The resulting densified fuel is easier transport and feed into thermal generation systems such as boilers.
A problem with the combustion of raw biomass is that it emits considerable amounts of pollutants such as particulates and PAHs (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.
Notwithstanding the above noted study, numerous studies have shown that biomass fuels have significantly less impact on the environment than fossil based fuels. Of note is the U.S. 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 approach. 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. Bio-char 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 in order to protect Virunga National Park from deforestation associated with charcoal production.
First Generation Biofuel Controversies
There is controversy and political speculation surrounding first-generation biofuels due to the agricultural, economic, and social implications associated with the potential expansion of biofuel production.
Research has been done in China that indicates that the demand for bio-fuel feedstock such as maize, sugarcane, and cassava will significantly increase due to the expansion of biofuel production; the increased demand for feedstock will lead prices for such grain to significantly increase . A similar study done examining a potential increase in ethanol production capacity in the United States also predicts an upward trend in agricultural prices as a direct affect of expanding domestic biofuel production . Expanding biofuel production is also projected to have an effect on livestock prices. A study done in China predicted that increased maize prices, due to biofuel expansion, will indirectly cause the prices of livestock production to increase due to the heavy reliance on maize for animal feed . The increase in input prices would also lead to a decrease in livestock production and ultimately decrease in the income of livestock producers, affecting families globally.
Increased agricultural prices will also provide incentives for farmers to stray away from producing other less profitable grains, causing a shift in the crop production structure, leading to a decrease in agricultural diversity subsequently diverting food away from the human food chain. In order for the United States to meet the biofuel target introduced in the Energy Independence and Security Act 40% of the land that is currently devoted to corn production would have to be converted to biofuel feedstock production . Shifts in crop production and the changes in world price of agricultural commodities due to the expansion of the biofuel market are expected to have global impacts on consumers. Individuals who are food insecure will be more heavily impacted by the increase in world prices; food price volatility has the largest impact on the extremely poor, those who spend 55-75% of their income on food .
Second generation biofuels
Supporters of biofuels claim that a more viable solution is to increase political and industrial support for, and rapidity of, second-generation biofuel implementation from non-food crops. These include waste biomass, the stalks of wheat, corn, wood, and special-energy-or-biomass crops (e.g. Miscanthus). Second generation (2G) biofuels use biomass to liquid technology, including cellulosic biofuels. Many second generation biofuels are under development such as biohydrogen, biomethanol, 2,5-Dimethylfuran, Bio-DME, Fischer-Tropsch diesel, biohydrogen diesel, mixed alcohols and wood diesel.
Cellulosic ethanol production uses non-food crops or inedible waste products and does not divert food away from the animal or human food chain. Lignocellulose is the "woody" structural material of plants. This feedstock is abundant and diverse, and in some cases (like citrus peels or sawdust) it is in itself a significant disposal problem.
Producing ethanol from cellulose is a difficult technical problem to solve. In nature, ruminant livestock (like cattle) eat grass and then use slow enzymatic digestive processes to break it into glucose (sugar). In cellulosic ethanol laboratories, various experimental processes are being developed to do the same thing, and then the sugars released can be fermented to make ethanol fuel. In 2009 scientists reported developing, using "synthetic biology", "15 new highly stable fungal enzyme catalysts that efficiently break down cellulose into sugars at high temperatures", adding to the 10 previously known. In addition, research conducted at TU Delft by Jack Pronk has shown that elephant yeast, when slightly modified can also create ethanol from non-edible ground sources (e.g. straw).
The recent discovery 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.
Scientists also work on experimental recombinant DNA genetic engineering organisms that could increase biofuel potential.
Third generation biofuels
Algae fuel, also called oilgae or third generation biofuel, is a biofuel from algae. Algae are low-input, high-yield feedstocks to produce biofuels. Based on laboratory experiments, it is claimed that algae can produces up to 30 times more energy per acre than land crops such as soybeans, but these yields have yet to be produced commercially. With the higher prices of fossil fuels (petroleum), there is much interest in algaculture (farming algae). One advantage of many biofuels over most other fuel types is that they are biodegradable, and so relatively harmless to the environment if spilled. Algae fuel still has its difficulties though, for instance to produce algae fuels it must be mixed uniformly, which, if done by agitation, could affect biomass growth.
The United States Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require 15,000 square miles (38,849 square kilometers), which is roughly the size of Maryland, or less than one seventh the amount of land devoted to corn in 2000.
Second and third generation biofuels are also called advanced biofuels.
Algae, such as Botryococcus braunii and Chlorella vulgaris, are relatively easy to grow, but the algal oil is hard to extract. There are several approaches, some of which work better than others. Macroalgae (seaweed) also have a great potential for bioethanol and biogas production.
However, if biocatalytic cracking and traditional fractional distillation used to process properly prepared algal biomass i.e. biocrude, then as a result we receive the following distillates: jet fuel, gasoline, diesel, etc.. Hence, we may call them third generation or green fuels.
Ethanol from living algae
Most biofuel production comes from harvesting organic matter and then converting it to fuel but an alternative approach relies on the fact that some algae naturally produce ethanol and this can be collected without killing the algae. The ethanol evaporates and then can be condensed and collected. The company Algenol is trying to commercialize this process.
Helioculture is a newly developed technology which is claimed to be able to produce 20,000 gallons of fuel per acre per year, and which removes carbon dioxide from the air as a feedstock for the fuel.
Helioculture involves direct conversion of carbon dioxide into fuel using solar power. Helioculture can be used to develop many different fuels and petroleum-derived chemicals all while not using any fresh water or agriculture.
Biofuels by region
Recognizing the importance of implementing bioenergy, there are international organizations such as IEA Bioenergy, 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 United Nations International Biofuels Forum is formed by Brazil, China, India], South Africa, the United States and the European Commission. The world leaders in biofuel development and use are Brazil, United States, France, Sweden and Germany.
Issues with biofuel production and use
There are various current issues with biofuel production and use, which are presently being discussed in the popular media and scientific journals. These include: the effect of moderating oil prices, the "food vs fuel" debate, carbon emissions levels, sustainable biofuel production, deforestation and soil erosion, impact on water resources, human rights issues, poverty reduction potential, biofuel prices, energy balance and efficiency, and centralised versus decentralised production models.
- Nordic Energy Solutions Advanced Biofuel Solutions from the Nordic Region
- 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
- NGO Biofuelwatch
- Biofuels News
- Biotechnology For Biofuels
- Biofuels Center of North Carolina
- Outlook Big Oil Can't Get Past Petroleum - Washington Post, June 14, 2010, Questions & Answers - Daniel Sperling & Deborah Gordon
- "Political, economic and environmental impacts of biofuels: A review"
- (2009-10-16). "Towards Sustainable Production and Use of Resources: Assessing Biofuels"
- UN biofuels report
- Bio ethanol fires information bio ethanol fireplace. (2009)
- Andrew Bounds (2007-09-10). ""OECD warns against biofuels subsidies""
- see "Breaking the Biological Barriers to Cellulosic Ethanol"
- Brinkman, N. et al., "Well-to-Wheels Analysis of Advanced/Vehicle Systems", 2005.
- 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.
- (2007-04-27). "With only 2/3 the energy of gasoline, ethanol costs more per mile"
- Hydrogen Solar home
- ButylFuel, LLC Main Page
- (14 January 2008). Biofuels, Bioproducts and Biorefining (BioFPR). "Biofuels aim higher"
- ADM Biodiesel: Hamburg, Leer, Mainz
- Welcome to Biodiesel Filling Stations
- THE FUTURIST, Will Thurmond. July-August 2007
- Evans, G. "Liquid Transport Biofuels - Technology Status Report", National Non-Food Crops Centre, 2008-04-14. Retrieved on 2009-05-11.
- http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31985L0536:EN:HTML, Council Directive 85/536/EEC of 5 December 1985 on crude-oil savings through the use of substitute fuel components in petrol
- http://circa.europa.eu/Public/irc/env/fuel_quality/library?l=/stakeholder_october/presentations/copert_brusselsppt/_EN_1.0_&a=d COPERT Study: An assessment of the impact of ethanol-blended petrol
- http://www.europarl.europa.eu/registre/docs_autres_institutions/commission_europeenne/sec/2007/0055/COM_SEC(2007)0055_EN.pdf Fuel Quality Directive Impact Assessment
- 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 (Sept 25, 2009): 12. General OneFile. Gale.
- 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
- Qui, Huanguang, Jikun Huang, Michiel Keyzer, Wim van Veen*. (2008). Policy options for China’s bio-ethanol development and the implications for its agricultural economy. China & World Economy, 16(6), 112-124
- M.W. Rosegrant, S. Msangi, T.Sulser, and R.Valmonte-Santos, Biofuels and the Global Food Balance (Washington, DC: International Food Policy Research Institute, 2006)
- Qiu, H., Huang, J., Yang, J., Rozelle, S., Zhang, Y., Zhang, Y., et al. (2009). Bioethanol development in China and the potential impacts on its agricultural economy. Applied Energy, 87(1), 76-83. doi:10.1016/j.apenergy.2009.07.015.
- Thomas, V. M., Choi, D. G., Luo, D., Okwo, A., & Wang, J. H. (2009). Relation of biofuel to bioelectricity and agriculture: Food security, fuel security, and reducing greenhouse emissions. Chemical Engineering Research and Design, 87(9), 1140-1146
- Naylor, R., Liska, A., & Burke, M. (2007). The Ripple Effect: Biofuels, Food Security, and the Environment. Environment, 49(9), 30-43. Retrieved November 16, 2009, from General Science Full Text database
- Oliver R. Inderwildi, David A. King. "Quo Vadis Biofuels"
- Chris Somerville. ""Development of Cellulosic Biofuels""
- EurekAlert. (2009). 15 new highly stable fungal enzyme catalysts that efficiently break down cellulose into sugars at high temperatures.
- Jack Pronk's elephant yeast
- Straw to ethanol plant in Sas van Gent
- ""Fill her up please, and make it myco-diesel""
- *Fisher, Lawrence M. April 24th 2007. "Carbon gas is explored as a source of ethanol" New York Times.
- *Voegele, E. August 27th 2009. "LanzaTech develops waste gas to ethanol technology", Ethanol Producer Magazine
- Eviana Hartman (2008-01-06). ""A Promising Oil Alternative: Algae Energy""
- Globeco biodegradable bio-diesel
- Friends of Ethanol.com biodegradable ethanol
- Low Cost Algae Production System Introduced
- "New algal extraction techniques using helix bioreactor." Industrial Bioprocessing (April 3, 2009): NA. General OneFile. Gale.
- Nanofarming technology harvest biofuel oils without harming algae
- Propagation of Algae By Use of Covered Ponds,
- Prospects for the Biodiesel Industry
- Seaweed Biofuels: Production of Biogas and Bioethanol from Brown Macroalgae
- University of Oklahoma (2009, January 14). 'Green' Gasoline On The Horizon. ScienceDaily. Retrieved March 9, 2010, from http://www.sciencedaily.com/releases/2009/01/090113155902.htm
- Start-Up's Biofuel Recipe Mixes CO2, Slime and Sunshine, The New York Times, July 27, 2009
- Moon, Mariella. "Redefining solar energy.(GOODCLEANTECH)(Joules Biotechnologies)(Brief article)." PC Magazine 28.9 (Sept 2009): 10(1). Expanded Academic ASAP. Gale.
- Berry, David. "Biological solar: combining synthetic biology and solar technology could provide a way to trap carbon dioxide and produce fuel.(BIOFUELS)." Technology Review (Cambridge, Mass.) 112.5 (Sept-Oct 2009): 12(1). General OneFile. Gale.
- IEA bioenergy
- (2007-03-02). "Press Conference Launching International Biofuels Forum"