biogas biogas biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. it is a renewable energy source. pipes carrying biogas (foreground) and condensate part of a series onsustainable energy energy conservation arcology building insulation cogeneration eco hotel efficient energy use energy storage environmental planning environmental technology fossil fuel phase-out green building green building and wood green retrofit heat pump list of low-energy building techniques low-energy house microgeneration sustainable architecture sustainable city sustainable habitat thermal energy storage tropical green building zero-energy building zero heating building renewable energy biofuel biogas biomass carbon-neutral fuel geothermal hydroelectricity hydropower marine energy renewable energy transition renewable heat solar sustainable biofuel tidal power wave power wind sustainable transport bicycle cycle rickshaw electric bicycle electric vehicle green vehicle human–electric hybrid vehicle human-powered helicopter human-powered hydrofoil human-powered land vehicle human-powered transport human-powered watercraft hybrid vehicle kick scooter personal rapid transit personal transporter plug-in hybrid quadracycle rail transport rapid transit roller skating skateboarding solar vehicle tram twike velomobile walking wind-powered vehicle renewable energy portal category biogas is produced by anaerobic digestion with anaerobic organisms or methanogen inside an anaerobic digester, biodigester or a bioreactor. biogas is primarily methane (ch4) and carbon dioxide (co2) and may have small amounts of hydrogen sulfide (h2s), moisture and siloxanes. the gases methane, hydrogen, and carbon monoxide (co) can be combusted or oxidized with oxygen. this energy release allows biogas to be used as a fuel; it can be used in fuel cells and for any heating purpose, such as cooking. it can also be used in a gas engine to convert the energy in the gas into electricity and heat. biogas can be compressed after removal of carbon dioxide and hydrogen sulphide, the same way as natural gas is compressed to cng, and used to power motor vehicles. in the united kingdom, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. it qualifies for renewable energy subsidies in some parts of the world. biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide. as the organic material grows, it is converted and used. it then regrows in a continually repeating cycle. from a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released, when the material is ultimately converted to energy. production biogas is produced by microorganisms, such as methanogens and sulfate-reducing bacteria, performing anaerobic respiration. biogas can refer to gas produced naturally and industrially. natural in soil, methane is produced in anaerobic environments by methanogens, but is mostly consumed in aerobic zones by methanotrophs. methane emissions result when the balance favors methanogens. wetland soils are the main natural source of methane. other sources include oceans, forest soils, termites, and wild ruminants. industrial main article: anaerobic digestion the purpose of industrial biogas production is the collection of biomethane, usually for fuel. industrial biogas is produced either; as landfill gas (lfg), which is produced by the decomposition of biodegradable waste inside a landfill due to chemical reactions and microbes, or as digested gas, produced inside an anaerobic digester. biogas production in rural germany bio-gas plants a biogas plant is the name often given to an anaerobic digester that treats farm wastes or energy crops. it can be produced using anaerobic digesters (air-tight tanks with different configurations). these plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste. during the process, the micro-organisms transform biomass waste into biogas (mainly methane and carbon dioxide) and digestate. higher quantities of biogas can be produced when the wastewater is co-digested with other residuals from the dairy industry, sugar industry, or brewery industry. for example, while mixing 90% of wastewater from beer factory with 10% cow whey, the production of biogas was increased by 2.5 times compared to the biogas produced by wastewater from the brewery only. manufacturing of biogas from intentionally planted maize has been described as being unsustainable and harmful due to very concentrated, intense and soil eroding character of these plantations. key processes there are two key processes: mesophilic and thermophilic digestion which is dependent on temperature. in experimental work at university of alaska fairbanks, a 1000-litre digester using psychrophiles harvested from "mud from a frozen lake in alaska" has produced 200–300 liters of methane per day, about 20–30% of the output from digesters in warmer climates. dangers the air pollution produced by biogas is similar to that of natural gas as when methane (a major constituent of biogas) is ignited for its usage as an energy source, carbon dioxide is made as a product which is a greenhouse gas ( as described by this equation: ch4 + 2o2 → co2 + 2h2o ). the content of toxic hydrogen sulfide presents additional risks and has been responsible for serious accidents. leaks of unburned methane are an additional risk, because methane is a potent greenhouse gas. a facility may leak 2% of the methane. biogas can be explosive when mixed in the ratio of one part biogas to 8–20 parts air. special safety precautions have to be taken for entering an empty biogas digester for maintenance work. it is important that a biogas system never has negative pressure as this could cause an explosion. negative gas pressure can occur if too much gas is removed or leaked; because of this biogas should not be used at pressures below one column inch of water, measured by a pressure gauge. frequent smell checks must be performed on a biogas system. if biogas is smelled anywhere windows and doors should be opened immediately. if there is a fire the gas should be shut off at the gate valve of the biogas system. landfill gas landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a similar way to biogas. the waste is covered and mechanically compressed by the weight of the material that is deposited above. this material prevents oxygen exposure thus allowing anaerobic microbes to thrive. biogas builds up and is slowly released into the atmosphere if the site has not been engineered to capture the gas. landfill gas released in an uncontrolled way can be hazardous since it can become explosive when it escapes from the landfill and mixes with oxygen. the lower explosive limit is 5% methane and the upper is 15% methane. the methane in biogas is 28 times more potent a greenhouse gas than carbon dioxide. therefore, uncontained landfill gas, which escapes into the atmosphere may significantly contribute to the effects of global warming. in addition, volatile organic compounds (vocs) in landfill gas contribute to the formation of photochemical smog. technical biochemical oxygen demand (bod) is a measure of the amount of oxygen required by aerobic micro-organisms to decompose the organic matter in a sample of material being used in the biodigester as well as the bod for the liquid discharge allows for the calculation of the daily energy output from a biodigester. another term related to biodigesters is effluent dirtiness, which tells how much organic material there is per unit of biogas source. typical units for this measure are in mg bod/litre. as an example, effluent dirtiness can range between 800 and 1200 mg bod/litre in panama. from 1 kg of decommissioned kitchen bio-waste, 0.45 m3 of biogas can be obtained. the price for collecting biological waste from households is approximately €70 per ton. composition typical composition of biogas compound formula percentage by volume methane ch4 50–80 carbon dioxide co2 15–50 nitrogen n2 0–10 hydrogen h2 0–1 hydrogen sulfide h2s 0–0.5 oxygen o2 0–2.5 source: www.kolumbus.fi, 2007 the composition of biogas varies depending upon the substrate composition, as well as the conditions within the anaerobic reactor (temperature, ph, and substrate concentration). landfill gas typically has methane concentrations around 50%. advanced waste treatment technologies can produce biogas with 55–75% methane, which for reactors with free liquids can be increased to 80–90% methane using in-situ gas purification techniques. as produced, biogas contains water vapor. the fractional volume of water vapor is a function of biogas temperature; correction of measured gas volume for water vapour content and thermal expansion is easily done via simple mathematics which yields the standardized volume of dry biogas. for 1000 kg (wet weight) of input to a typical biodigester, total solids may be 30% of the wet weight while volatile suspended solids may be 90% of the total solids. protein would be 20% of the volatile solids, carbohydrates would be 70% of the volatile solids, and finally fats would be 10% of the volatile solids. sulfur compounds toxic and foul smelling hydrogen sulfide (h2s) is the most common contaminant in biogas, but other sulfur-containing compounds, such as thiols may be present. left in the biogas stream, hydrogen sulfide is corrosive and when combusted yields sulfur dioxide (so2) and sulfuric acid (h2so4), also corrosive and environmentally hazardous compounds. ammonia ammonia (nh3) is produced from organic compounds containing nitrogen, such as the amino acids in proteins. if not separated from the biogas, combustion results in nox emissions. siloxanes in some cases, biogas contains siloxanes. they are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. during combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or other elements in the combustion gas. deposits are formed containing mostly silica (sio2) or silicates (sixoy) and can contain calcium, sulfur, zinc, phosphorus. such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means. practical and cost-effective technologies to remove siloxanes and other biogas contaminants are available. benefits of manure derived biogas part of a series onrenewable energy biofuel biomass biogas carbon-neutral fuel geothermal energy geothermal heating geothermal power hydroelectricity hydropower marine current power marine energy osmotic power solar energy solar power sustainable biofuel tidal power wave power wind power nuclear power proposed as renewable energy topics by country marketing and policy trends high levels of methane are produced when manure is stored under anaerobic conditions. during storage and when manure has been applied to the land, nitrous oxide is also produced as a byproduct of the denitrification process. nitrous oxide (n2o) is 320 times more aggressive as a greenhouse gas than carbon dioxide and methane 25 times more than carbon dioxide by converting cow manure into methane biogas via anaerobic digestion, the millions of cattle in the united states would be able to produce 100 billion kilowatt hours of electricity, enough to power millions of homes across the united states. in fact, one cow can produce enough manure in one day to generate 3 kilowatt hours of electricity; only 2.4 kilowatt hours of electricity are needed to power a single 100-watt light bulb for one day. furthermore, by converting cattle manure into methane biogas instead of letting it decompose, global warming gases could be reduced by 99 million metric tons or 4%. applications a biogas bus in linköping, sweden biogas can be used for electricity production on sewage works, in a chp gas engine, where the waste heat from the engine is conveniently used for heating the digester; cooking; space heating; water heating; and process heating. if compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells and is a much more effective displacer of carbon dioxide than the normal use in on-site chp plants. biogas upgrading raw biogas produced from digestion is roughly 60% methane and 39% co2 with trace elements of h2s: inadequate for use in machinery. the corrosive nature of h2s alone is enough to destroy the mechanisms. methane in biogas can be concentrated via a biogas upgrader to the same standards as fossil natural gas, which itself has to go through a cleaning process, and becomes biomethane. if the local gas network allows, the producer of the biogas may use their distribution networks. gas must be very clean to reach pipeline quality and must be of the correct composition