for the distribution network to accept. carbon dioxide, water, hydrogen sulfide, and particulates must be removed if present. there are four main methods of upgrading: water washing, pressure swing absorption, selexol absorption, and amine gas treating. in addition to these, the use of membrane separation technology for biogas upgrading is increasing, and there are already several plants operating in europe and usa. the most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas. this arrangement could deliver 98% methane with manufacturers guaranteeing maximum 2% methane loss in the system. it takes roughly between 3% and 6% of the total energy output in gas to run a biogas upgrading system. biogas gas-grid injection gas-grid injection is the injection of biogas into the methane grid (natural gas grid). until the breakthrough of micro combined heat and power two-thirds of all the energy produced by biogas power plants was lost (as heat). using the grid to transport the gas to consumers, the energy can be used for on-site generation, resulting in a reduction of losses in the transportation of energy. typical energy losses in natural gas transmission systems range from 1% to 2%; in electricity transmission they range from 5% to 8%. before being injected in the gas grid, biogas passes a cleaning process, during which it is upgraded to natural gas quality. during the cleaning process trace components harmful to the gas grid and the final users are removed. biogas in transport "biogaståget amanda" ("amanda the biogas train") train near linköping station, sweden if concentrated and compressed, it can be used in vehicle transportation. compressed biogas is becoming widely used in sweden, switzerland, and germany. a biogas-powered train, named biogaståget amanda (the biogas train amanda), has been in service in sweden since 2005. biogas powers automobiles. in 1974, a british documentary film titled sweet as a nut detailed the biogas production process from pig manure and showed how it fueled a custom-adapted combustion engine. in 2007, an estimated 12,000 vehicles were being fueled with upgraded biogas worldwide, mostly in europe. biogas is part of the wet gas and condensing gas (or air) category that includes mist or fog in the gas stream. the mist or fog is predominately water vapor that condenses on the sides of pipes or stacks throughout the gas flow. biogas environments include wastewater digesters, landfills, and animal feeding operations (covered livestock lagoons). ultrasonic flow meters are one of the few devices capable of measuring in a biogas atmosphere. most of thermal flow meters are unable to provide reliable data because the moisture causes steady high flow readings and continuous flow spiking, although there are single-point insertion thermal mass flow meters capable of accurately monitoring biogas flows with minimal pressure drop. they can handle moisture variations that occur in the flow stream because of daily and seasonal temperature fluctuations, and account for the moisture in the flow stream to produce a dry gas value. biogas generated heat/electricity biogas can be used in different types of internal combustion engines, such as the jenbacher or caterpillar gas engines. other internal combustion engines such as gas turbines are suitable for the conversion of biogas into both electricity and heat. the digestate is the remaining inorganic matter that was not transformed into biogas. it can be used as an agricultural fertiliser. biogas can be used as the fuel in the system of producing biogas from agricultural wastes and co-generating heat and electricity in a combined heat and power (chp) plant. unlike the other green energy such as wind and solar, the biogas can be quickly accessed on demand. the global warming potential can also be greatly reduced when using biogas as the fuel instead of fossil fuel. however, the acidification and eutrophication potentials produced by biogas are 25 and 12 times higher respectively than fossil fuel alternatives. this impact can be reduced by using correct combination of feedstocks, covered storage for digesters and improved techniques for retrieving escaped material. overall, the results still suggest that using biogas can lead to significant reduction in most impacts compared to fossil fuel alternative. the balance between environmental damage and green house gas emission should still be considered while implicating the system. technological advancements projects such as nanoclean are nowadays developing new ways to produce biogas more efficiently, using iron oxide nanoparticles in the processes of organic waste treatment. this process can triple the production of biogas. biogas and sanitation faecal sludge is a product of onsite sanitation systems. post collection and transportation, faecal sludge can be treated with sewage in a conventional treatment plant, or otherwise it can be treated independently in a faecal sludge treatment plant. faecal sludge can also be co-treated with organic solid waste in composting or in an anaerobic digestion system. biogas can be generated through anaerobic digestion in the treatment of faecal sludge. the appropriate management of excreta and its valorisation through the production of biogas from faecal sludge helps mitigate the effects of poorly managed excreta such as waterborne diseases and water and environmental pollution. legislation european union the european union has legislation regarding waste management and landfill sites called the landfill directive. countries such as the united kingdom and germany now have legislation in force that provides farmers with long-term revenue and energy security. the eu mandates that internal combustion engines with biogas have ample gas pressure to optimize combustion, and within the european union atex centrifugal fan units built in accordance with the european directive 2014–34/eu (previously 94/9/eg) are obligatory. these centrifugal fan units, for example combimac, meidinger ag or witt & sohn ag are suitable for use in zone 1 and 2 . united states the united states legislates against landfill gas as it contains vocs. the united states clean air act and title 40 of the code of federal regulations (cfr) requires landfill owners to estimate the quantity of non-methane organic compounds (nmocs) emitted. if the estimated nmoc emissions exceeds 50 tonnes per year, the landfill owner is required to collect the gas and treat it to remove the entrained nmocs. that usually means burning it. because of the remoteness of landfill sites, it is sometimes not economically feasible to produce electricity from the gas. there are a variety of grants and loans the support the development of anaerobic digestor systems. the rural energy for american program provides loan financing and grant funding for biogas systems, as does the environmental quality incentives program, conservation stewardship program, and conservation loan program. global developments united states with the many benefits of biogas, it is starting to become a popular source of energy and is starting to be used in the united states more. in 2003, the united states consumed 43 twh (147 trillion btu) of energy from "landfill gas", about 0.6% of the total u.s. natural gas consumption. methane biogas derived from cow manure is being tested in the u.s. according to a 2008 study, collected by the science and children magazine, methane biogas from cow manure would be sufficient to produce 100 billion kilowatt hours enough to power millions of homes across america. furthermore, methane biogas has been tested to prove that it can reduce 99 million metric tons of greenhouse gas emissions or about 4% of the greenhouse gases produced by the united states. the number of farm-based digesters increased by 21% in 2021 according to the american biogas council. in vermont biogas generated on dairy farms was included in the cvps cow power program. the program was originally offered by central vermont public service corporation as a voluntary tariff and now with a recent merger with green mountain power is now the gmp cow power program. customers can elect to pay a premium on their electric bill, and that premium is passed directly to the farms in the program. in sheldon, vermont, green mountain dairy has provided renewable energy as part of the cow power program. it started when the brothers who own the farm, bill and brian rowell, wanted to address some of the manure management challenges faced by dairy farms, including manure odor, and nutrient availability for the crops they need to grow to feed the animals. they installed an anaerobic digester to process the cow and milking center waste from their 950 cows to produce renewable energy, a bedding to replace sawdust, and a plant-friendly fertilizer. the energy and environmental attributes are sold to the gmp cow power program. on average, the system run by the rowells produces enough electricity to power 300 to 350 other homes. the generator capacity is about 300 kilowatts. in hereford, texas, cow manure is being used to power an ethanol power plant. by switching to methane biogas, the ethanol power plant has saved 1000 barrels of oil a day. over all, the power plant has reduced transportation costs and will be opening many more jobs for future power plants that will rely on biogas. in oakley, kansas, an ethanol plant considered to be one of the largest biogas facilities in north america is using integrated manure utilization system (imus) to produce heat for its boilers by utilizing feedlot manure, municipal organics and ethanol plant waste. at full capacity the plant is expected to replace 90% of the fossil fuel used in the manufacturing process of ethanol and methanol. in california, the southern california gas company has advocated for mixing biogas into existing natural gas pipelines. however, california state officials have taken the position that biogas is "better used in hard-to-electrify sectors of the economy-- like aviation, heavy industry and long-haul trucking." europe biogas fueling station in mikkeli, finland the level of development varies greatly in europe. while countries such as germany, austria and sweden are fairly advanced in their use of biogas, there is a vast potential for this renewable energy source in the rest of the continent, especially in eastern europe. mt-energie is a german biogas technology company operating in the field of renewable energies. different legal frameworks, education schemes and the availability of technology are among the prime reasons behind this untapped potential. another challenge for the further progression of biogas has been negative public perception. in february 2009, the european biogas association (eba) was founded in brussels as a non-profit organisation to promote the deployment of sustainable biogas production and use in europe. eba's strategy defines three priorities: establish biogas as an important part of europe's energy mix, promote source separation of household waste to increase the gas potential, and support the production of biomethane as vehicle fuel. in july 2013, it had 60 members from 24 countries across europe. uk as of september 2013, there are about 130 non-sewage biogas plants in the uk. most are on-farm, and some larger facilities exist off-farm, which are taking food and consumer wastes. on 5 october 2010, biogas was injected into the uk gas grid for the first time. sewage from over 30,000 oxfordshire homes is sent to didcot sewage treatment works, where it is treated in an anaerobic digestor to produce biogas, which is then cleaned to provide gas for approximately 200 homes. in 2015 the green-energy company ecotricity announced their plans to build three grid-injecting digesters. italy in italy the biogas industry first started in 2008, thanks to the introduction of advantageous feed tariffs. they were later replaced by feed-in premiums and the preference was given to by products and farming waste and leading to stagnation in biogas production and derived heat and electricity since 2012.as of september 2018, in italy there are more than 200 biogas plants with a production of about 1.2 gw germany germany is europe's biggest biogas producer and the market leader in biogas technology. in 2010 there were 5,905 biogas plants operating throughout the country: lower saxony, bavaria, and the eastern federal states are the main regions. most of these plants are employed as power plants. usually the biogas plants are directly connected with a chp which produces electric power by burning the bio methane. the electrical power is then fed into the public power grid. in 2010, the total installed electrical capacity of these power plants was 2,291 mw. the electricity supply was approximately 12.8 twh, which is 12.6% of the total generated