Renewable natural gas

Most RNG is made from biogas produced via anaerobic digestion of organic waste. Biogas is produced as a byproduct of landfilling and wastewater treatment. At landfills, buried organic waste undergoes anaerobic digestion producing biogas that can be collected through a series of wells installed in the landfill.{{Cite web |last=US EPA |first=OAR |date=2016-04-15 |title=Basic Information about Landfill Gas |url=https://www.epa.gov/lmop/basic-information-about-landfill-gas |access-date=2025-03-19 |website=www.epa.gov |language=en}} Wastewater treatment facilities often use anaerobic digestion tanks to degrade sludge from settling tanks.{{Cite web |last=Bachmann |first=Nathalie |date=2015 |title=Sustainable Biogas Production in Municipal Wastewater Treatment Plants |url=https://www.ieabioenergy.com/wp-content/uploads/2015/11/Wastewater_biogas_grey_web-1.pdf |access-date=19 March 2019 |website=IEA Bioenergy}} Wastewater treatment plants with anaerobic digesters often use biogas for process heat and flare excess biogas. Landfills in some jurisdictions are required to capture biogas to minimize methane leakage into the atmosphere, the captured gas is either flared, combusted to produce electricity, or upgraded into RNG.{{Cite web |title=Landfill Gas Management Regulation |url=https://www.bclaws.gov.bc.ca/civix/document/id/complete/statreg/391_2008 |access-date=2025-03-19 |website=www.bclaws.gov.bc.ca}}

Anaerobic digesters can also be purpose-built facilities to produce RNG. Anaerobic digesters typically handle waste biomass from agricultural and municipal sources. Agricultural wastes include manure, spoiled products, and animal bedding. Municipal wastes include source separated organic wastes, fats, oils, and greases (FOG), and industrial byproducts.{{Cite web |date=2019 |title=Canadian Anaerobic Digester Guideline |url=https://biogasassociation.ca/resources/page/canadian_anaerobic_digestion_guideline/ |access-date=19 March 2025 |website=Canadian Biogas Association}} In some regions, non-waste feedstocks are also used. These feedstocks can be energy crops, such as maize and barley, or cover crops that are grown outside of the growing season to improve soil quality.{{Cite web |last=Braun |first=Rudolf |date=2010 |title=Biogas from Energy Crop Disgestion |url=https://www.ieabioenergy.com/wp-content/uploads/2010/01/energycrop_def_Low_Res.pdf |access-date=19 March 2025 |website=IEA Bioenergy}} In France, regulations limit the amount of energy crops that can be used for producing biogas, which has encouraged the use of cover crops.{{Cite journal |last1=Levavasseur |first1=Florent |last2=Martin |first2=Lucie |last3=Boros |first3=Léa |last4=Cadiou |first4=Jeanne |last5=Carozzi |first5=Marco |last6=Martin |first6=Philippe |last7=Houot |first7=Sabine |date=2023 |title=Land cover changes with the development of anaerobic digestion for biogas production in France |url=https://onlinelibrary.wiley.com/doi/full/10.1111/gcbb.13042 |journal=GCB Bioenergy |language=en |volume=15 |issue=5 |pages=630–641 |doi=10.1111/gcbb.13042 |bibcode=2023GCBBi..15..630L |issn=1757-1707|doi-access=free }} Depending on the availability of biomass feedstocks, the feedstock is processed in a dedicated facility or co-processes with other types of feedstock.

Commercial anaerobic digesters typically make money through a combination of selling RNG, selling digestate, and by charging tipping fees for waste disposal. Costs are minimized by maximizing production scale and by locating an anaerobic digestion plant next to transport links (e.g. a port or highway) for the chosen source of biomass. Selecting a site close the gas transmission or distribution grid is also important to reduce interconnection costs. Gas storage is often required to deal with periods of low gas demand during the summer, depending on the region.Energy Research Centre of the Netherlands [http://www.ecn.nl/docs/library/report/2005/rx05187.pdf 'Heat from Biomass via Synthetic Natural Gas']

RNG can also be produced via methanization of either carbon dioxide or syngas produced via thermal gasification.{{Cite web |last=Kramer |first=Andrew |date=February 2019 |title=Low Carbon Renewable Natural Gas (RNG) from Wood Wastes |url=https://www.gti.energy/wp-content/uploads/2019/02/Low-Carbon-Renewable-Natural-Gas-RNG-from-Wood-Wastes-Final-Report-Feb2019.pdf |access-date=19 March 2025 |website=GTI Energy}} Both approaches are still largely pre-commercial and do not represent a major source of RNG production globally.

Raw biogas is a mixture of primarily methane and carbon dioxide at a ratio of approximately 60:40. Biogas can also contain small amount of oxygen and nitrogen pulled in from air and is typically saturated with water. All biogas sources contain hydrogen sulphide and biogas produced from waste water treatment or landfills will often contain siloxanes and other volatile organic components.{{Cite journal |last1=Li |first1=Yin |last2=Alaimo |first2=Christopher P |last3=Kim |first3=Minji |last4=Kado |first4=Norman Y |last5=Peppers |first5=Joshua |last6=Xue |first6=Jian |last7=Wan |first7=Chao |last8=Green |first8=Peter G |last9=Zhang |first9=Ruihong |last10=Jenkins |first10=Bryan M |last11=Christoph F A Vogel |last12=Wuertz |first12=Stefan |last13=Young |first13=Thomas M |last14=Kleeman |first14=Michael J |date=2019-09-18 |title=Composition and Toxicity of Biogas Produced from Different Feedstocks in California |journal=Environmental Science & Technology |language=en |volume=53 |issue=19 |pages=11569–11579 |doi=10.1021/acs.est.9b03003 |pmid=31479247 |pmc=7608650 |bibcode=2019EnST...5311569L }}

Biogas upgrading refers to the removal of trace contaminants, water, and non-methane gases from biogas to produce a product that is interchangeable with natural gas. Biogas upgrading has two general steps - removal of contaminants and water, followed by gas separation. Contaminants and water a typically removed with sacrificial media beds containing activated carbon, activated alumina, and iron oxide.{{Cite journal |last1=Golmakani |first1=Ayub |last2=Ali Nabavi |first2=Seyed |last3=Wadi |first3=Basil |last4=Manovic |first4=Vasilije |date=2022-06-01 |title=Advances, challenges, and perspectives of biogas cleaning, upgrading, and utilisation |url=https://www.sciencedirect.com/science/article/abs/pii/S0016236121029458 |journal=Fuel |volume=317 |pages=123085 |doi=10.1016/j.fuel.2021.123085 |bibcode=2022Fuel..31723085G |hdl=1826/17561 |issn=0016-2361|hdl-access=free }} Contaminants can also be removed through biological scrubbing using sulphur oxidizing bacteria, chemical scrubbing with ammonia, or using regenerative process such as temperature swing adsorption.

After contaminants and water have been removed, biogas undergoes gas separation to concentrate methane. There are multiple methods of gas separation used in biogas upgrading:

• Membrane separation uses hollow fibres to separate gases using molecular size differences.{{Cite journal |last1=Gkotsis |first1=Petros |last2=Kougias |first2=Panagiotis |last3=Mitrakas |first3=Manassis |last4=Zouboulis |first4=Anastasios |date=2023-02-01 |title=Biogas upgrading technologies – Recent advances in membrane-based processes |url=https://www.sciencedirect.com/science/article/abs/pii/S0360319922050418 |journal=International Journal of Hydrogen Energy |volume=48 |issue=10 |pages=3965–3993 |doi=10.1016/j.ijhydene.2022.10.228 |bibcode=2023IJHE...48.3965G |issn=0360-3199|url-access=subscription }}
• Pressure swing adsorption separates gases based on their affinity for particular media such as zeolites or carbon molecular sieves. During the high pressure phase, one gas is trapped in the media and the product gas exits the vessel. The media is then regenerated with a vacuum to remove the other gas.{{Cite journal |last1=Lu |first1=Wei |last2=Xiao |first2=Gongkui |last3=Weh |first3=Roman |last4=May |first4=Eric F. |date=2020-09-01 |title=Rejecting N2 from natural gas by dual reflux pressure swing adsorption with activated carbon |url=https://www.sciencedirect.com/science/article/abs/pii/S1875510020303115 |journal=Journal of Natural Gas Science and Engineering |volume=81 |pages=103457 |doi=10.1016/j.jngse.2020.103457 |issn=1875-5100}}
• Chemical washing uses either ammonia or water to dissolve carbon dioxide. The chemical is then regenerate through flashing or heating.

RNG is generally considered to be interchangeable with natural gas. Many regions have minimum specifications for RNG quality that is deemed acceptable for local natural gas infrastructure.{{Cite web |last=Government of Canada |first=Canada Energy Regulator |date=2023-11-24 |title=CER – Market Snapshot: Two Decades of Growth in Renewable Natural Gas in Canada |url=https://www.cer-rec.gc.ca/en/data-analysis/energy-markets/market-snapshots/2023/market-snapshot-two-decades-growth-renewable-natural-gas-canada.html |access-date=2025-03-25 |website=www.cer-rec.gc.ca}} The major difference between RNG and natural gas is that RNG does not contain any hydrocarbons (such as propane) other than methane. This results in RNG having a lower heating value and wobbe index than natural gas.

As of 2023, more than 300 RNG facilities are currently operational in North America,{{Cite web |last=International |first=Bioenergy |date=2023-08-03 |title=300 RNG facilities operating in North America – RNG Coalition |url=https://bioenergyinternational.com/300-rng-facilities-operating-in-north-america-rng-coalition/ |access-date=2023-10-31 |website=Bioenergy International |language=en-US}} with more than 70% of supplies drawn from the MSW and landfill sectors, according to the U.S. trade group RNG Coalition.{{Cite web |title=Renewable Natural Gas Infographics: View at RNG Coalition |url=https://www.rngcoalition.com/infographic |access-date=2023-10-31 |website=The Coalition For Renewable Natural Gas |language=en-US}}

In North America, most RNG development has historically developed as a form of landfill gas utilization.{{Cite web |title=The story of RNG in America |url=https://www.linkedin.com/pulse/story-rng-america-ricardo-carmona |access-date=2023-10-31 |website=www.linkedin.com |language=en}} The first commercial RNG facility was launched at the Fresh Kills landfill near New York City in 1982. Landfill gas projects were the dominant type of RNG in the United States project up until 2021, when agricultural projects became the dominant type of RNG production. As of 2023, there are 102 landfill RNG projects in the United States.{{Cite web |last=US EPA |first=OAR |date=2018-12-06 |title=Renewable Natural Gas |url=https://www.epa.gov/lmop/renewable-natural-gas |access-date=2025-03-21 |website=www.epa.gov |language=en}}

Sludge settled during the processing of wastewater can be degraded in an anaerobic digester. The use of anaerobic digesters in a popular method of treating sludge because it produces biogas, which can be used to produce heat for wastewater treatment facility.{{Cite web |last=Lee |first=Uisung |date=September 2016 |title=LIFECYCLE ANALYSIS OF RENEWABLE NATURAL GAS AND HYDROCARBON FUELS FROM WASTEWATER TREATMENT PLANTS' SLUDGE |url=https://publications.anl.gov/anlpubs/2016/09/130493.pdf |access-date=21 March 2025 |website=Argonne National Laboratory}} Many wastewater treatment plants produce more biogas than they plant consumes. This gas is either flared to destroy methane, used in a combined heat and power engine, or upgraded to RNG.

Anaerobic digesters can be integrated into farming operations. Typically, the base feedstock for an agricultural anaerobic digester is manure. Manure provides a colony of micro-organisms for anaerobic digestion and a regular supply of liquid feedstock slurry.{{Cite web |last=DeBruyn |first=J |date=November 2022 |title=Anaerobic Digestion Basics |url=https://files.ontario.ca/omafra-anaerobic-digestion-basics-22-055-en-2023-02-09.pdf |access-date=25 March 2025 |website=Ontario Ministry of Agriculture, Food, and Agribusiness}} Farms will often add other wastes like spoiled produce or animal bedding. Depending on the region, agricultural projects may accept some off-farm feedstocks.{{Cite web |title=Organic Matter Recycling Regulation |url=https://www.bclaws.gov.bc.ca/civix/document/id/complete/statreg/18_2002 |access-date=2025-03-25 |website=www.bclaws.gov.bc.ca}} Anaerobic digesters on farms treat wastes, produce liquid digestate that can be used as fertilizer, and create an additional revenue stream for farmers.

Municipal anaerobic digesters refer to facilities where the main feedstock is source separated organics (SSO) collected through green bin programs. These digesters differ from agricultural digesters because SSO feedstocks tend to have a higher solids content than manure. Municipal anaerobic digesters often need pretreatment to remove contaminants such as plastic and glass containers.{{Cite web |date=March 2015 |title=Municipal Guide to Biogas |url=https://biogasassociation.ca/images/uploads/documents/2015/municipal_guide_to_biogas/Municipal-Guide-to-Biogas-2015March.pdf |access-date=27 March 2025 |website=Canadian Biogas Association}} Municipalities operate anaerobic digesters as a form of organic waste diversion from landfills to reduce methane emissions.

Syngas is a mixture of primarily methane, hydrogen, carbon dioxide and carbon monoxide. Similarly to biogas, syngas be can be combusted directly or reformed in to RNG or hydrogen. The process start with the production of syngas, typically woody biomass, through gasification or pyrolysis. Syngas is then cleaned of contaminants such as hydrogen sulfide and tar.{{Cite journal |last1=Ren |first1=Jie |last2=Liu |first2=Yi-Ling |last3=Zhao |first3=Xiao-Yan |last4=Cao |first4=Jing-Pei |date=2020-02-07 |title=Methanation of syngas from biomass gasification: An overview |url=https://www.sciencedirect.com/science/article/abs/pii/S0360319919345239 |journal=International Journal of Hydrogen Energy |volume=45 |issue=7 |pages=4223–4243 |doi=10.1016/j.ijhydene.2019.12.023 |bibcode=2020IJHE...45.4223R |issn=0360-3199|url-access=subscription }} To upgrade syngas, the ratio of hydrogen to carbon monoxide is increased using the water gas shift reaction.{{Cite web |title=7.4. Technology for SNG Production |url=https://netl.doe.gov/research/carbon-management/energy-systems/gasification/gasifipedia/coal-to-sng |access-date=2025-03-25 |website=netl.doe.gov |language=en}} With close to the stoichiometric ratio, the syngas is reformed into methane using the Sabatier reaction and then carbon dioxide is removed using similar techniques to biogas upgrading.

Renewable natural gas plants based on wood can be categorized into two main categories, one being allothermal, which has the energy provided by a source outside of the gasifier. One example is the double-chambered fluidized bed gasifiers consisting of a separate combustion and gasification chambers. Autothermal systems generate the heat within the gasifier, but require the use of pure oxygen to avoid nitrogen dilution.{{cite book |last=Van der Meijden |first=C.M. |url=http://www.ecn.nl/docs/library/report/2010/b10016.pdf |title=Development of the MILENA gasification technology for the production of Bio-SNG |publisher=ECN |year=2010 |location=Petten, Netherlands |access-date=21 October 2012}}

Core advantage of producing RNG from wood wastes is a higher efficiency that Fisher-Tropsch based liquid fuels production and smaller-production scale than other second generation biofuel production systems.{{cite journal |last=Åhman |first=Max |title=Biomethane in the transport sector—An appraisal of the forgotten option |journal=Energy Policy |year=2010 |volume=38 |issue=1 |pages=208–217 |doi=10.1016/j.enpol.2009.09.007|bibcode=2010EnPol..38..208A }} The Energy Research Centre of the Netherlands has conducted extensive research on large-scale RNG production from woody biomass, based on the importation of feedstocks from abroad.{{cite web |url=http://www.biosng.com/synthetic-natural-gas/ |title=BioSNG: Synthetic Natural Gas |access-date=27 December 2012}}

Renewable natural gas can be produced and distributed via the existing gas grid, making it an attractive means of supplying existing premises with renewable heat and renewable gas energy. Renewable natural gas can also be converted into liquefied natural gas (LNG) or compressed natural gas (CNG) for direct use as fuel in transport sector.

In the United States, projections of the ultimate supply potential for RNG vary. An analysis conducted in 2011 by the Gas Technology Institute determined that renewable gas from waste biomass including agricultural waste has the potential to add up to 2.5 quadrillion Btu annually, being enough to meet the natural gas needs of 50% of American homes.{{cite web |title=Natural Gas Can Come From Renewable Sources |url=https://www.socalgas.com/smart-energy/benefits-of-natural-gas/renewable |url-status=dead |archive-url=https://web.archive.org/web/20171017004604/https://www.socalgas.com/smart-energy/benefits-of-natural-gas/renewable |archive-date=17 October 2017 |access-date=3 May 2018 |website=www.socalgas.com |publisher=Sempre Energy}}{{cite web |last1=Minter |first1=George |title=SoCalGas's Minter on Renewable Natural Gas as a Foundational Fuel |url=https://www.planningreport.com/2017/10/25/socalgas-minter-renewable-natural-gas-foundational-fuel |access-date=3 May 2018 |website=www.planningreport.com |publisher=David Abel}} The Environmental and Energy Study Institute estimated that renewable natural gas could replace up to 10% of all natural gas used in the United States,{{Cite web |title=Fact Sheet {{!}} Biogas: Converting Waste to Energy {{!}} White Papers {{!}} EESI |url=https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy |access-date=2021-12-09 |website=www.eesi.org}} and a study by the National Association of Clean Water Agencies and the Water Environment Federation found that the quantity of biosolids removed from wastewater could be turned into enough biogas to potentially meet up to 12% of America's national electricity demand.{{Cite web |title=Alternative Fuels Data Center: Renewable Natural Gas Production |url=https://afdc.energy.gov/fuels/natural_gas_renewable.html |access-date=2021-12-09 |website=afdc.energy.gov}}

More recently, a study commissioned by the American Gas Foundation and executed by ICF in 2019 projected that between 1.6-3.78 trillion cubic feet of RNG could be produced annually for pipeline injection in the U.S. by 2030.{{Cite web |title=Renewable Sources of Natural Gas |url=https://www.aga.org/research-policy/resource-library/renewable-sources-of-natural-gas/ |access-date=2023-10-31 |website=American Gas Association |language=en-US}}

In combination with power-to-gas, whereby the carbon dioxide and carbon monoxide fraction of biogas are converted to methane using electrolyzed hydrogen, the renewable gas potential of raw biogas is approximately doubled.{{Cite journal |last1=Marija |first1=Saric |last2=Dijkstra |first2=Jan Wilco |last3=Haije |first3=Wim G. |date=July 2017 |title=Economic perspectives of Power-to-Gas technologies in bio-methane production |url=https://www.sciencedirect.com/science/article/abs/pii/S2212982016301767 |journal=Journal of CO2 Utilization |volume=20 |pages=81–90 |bibcode=2017JCOU...20...81S |doi=10.1016/j.jcou.2017.05.007}}

In the UK, using anaerobic digestion is growing as a means of producing renewable biogas, with nearly 90 biomethane injection sites built across the country.{{cite web |title=AD map – biomethane plants |url=http://adbioresources.org/map |website=ADBA |publisher=The Anaerobic Digestion & Bioresources Association |access-date=12 June 2018 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612232841/http://adbioresources.org/map |url-status=dead }} Ecotricity announced plans to supply green gas to UK consumers via the national grid.The Guardian [https://www.theguardian.com/environment/2009/nov/22/food-waste-green-biogas-tariff 'Food waste to provide green gas for carbon-conscious consumers'] Centrica also announced that it would begin injecting gas, manufactured from sewage, into the gas grid.The Guardian [https://www.theguardian.com/business/2010/oct/05/human-waste-turned-renewable-gas 'Human waste turned into renewable gas to power homes']

In Canada, FortisBC, a gas provider in British Columbia, injects renewably created natural gas into its existing gas distribution system.Kachan & Co.[https://web.archive.org/web/20110507072941/http://www.prweb.com/releases/2011/5/prweb8377459.htm 'New Bio Natural Gas May Assist In Adding Solar and Wind to Utility Renewable Power Generation, Study Finds']

A company called Divert, which also reduces food waste through donation, says it will use a $1 billion investment from Canadian pipeline operator Enbridge to scale its existing network of food waste anaerobic digesters to cover all major markets of North America.[https://www.environmentalleader.com/2023/03/divert-inc-announces-1-billion-infrastructure-deal-with-enbridge-inc/ Divert Inc. Announces $1B Infrastructure Deal with Enbridge Inc. to Tackle Food Waste and Combat Climate Change][https://www.reuters.com/business/sustainable-business/enbridge-commits-1-bln-company-turning-food-waste-energy-2023-03-01/ Enbridge commits $1 billion to company turning food waste to energy]

In Sweden, Göteborg Energi opened the first demonstration plant for large scale production of bio-synthetic natural gas (SNG) through gasification of forest residues in Gothenburg, Sweden within the GoBiGas project. The plant had the capacity to produce 20 megawatts-worth of bioSNG from about 30 MW-worth of biomass, aiming at a conversion efficiency of 65%. From December 2014 the bioSNG plant was fully operational and supplied gas to the Swedish natural gas grid, reaching the quality demands with a methane content of over 95%.{{Cite web |title=GoBiGas |url=https://gobigas.goteborgenergi.se/English_version/About_GoBiGas |access-date=10 November 2017 |website=www.gobigas.goteborgenergi.se}} The plant was permanently closed due to economic problems in April 2018. Göteborg Energi had invested 175 million euro in the plant and intensive attempts for a year to sell the plant to new investors had failed.{{Cite news |last1=Nyheter |first1=S. V. T. |last2=Youcefi |first2=Fouad |date=3 April 2018 |title=Investerade nästan två miljarder i Gobigas – nu läggs projektet ner |url=https://www.svt.se/nyheter/lokalt/vast/investerade-nastan-tva-miljarder-i-biogasanlaggning-nu-laggs-projektet-ner |access-date=25 April 2018 |newspaper=SVT Nyheter}}

Biogas creates similar environmental pollutants as ordinary natural gas fuel, such as carbon monoxide, sulfur dioxide, nitrogen oxide, hydrogen sulfide and particulates. Any unburned gas that escapes contains methane, a long lived greenhouse gas. The key difference from fossil natural gas is that it is often considered partly or fully carbon neutral,{{Cite web

| author = Dr. Ann C. Wilkie

| title = Biogas – Frequently Asked Questions (Biogas FAQ)

| url = https://biogas.ifas.ufl.edu/faq.asp

| date = 2019-12-16

| access-date = 2022-09-02

| website = University of Florida – Soil and Water Sciences Department

}} since the carbon dioxide contained in the biomass is naturally renewed in each generation of plants, rather than being released from fossil stores and increasing atmospheric carbon dioxide.

A major concern is that the potential biogas yield would only represent a small percentage of existing supplies of fossil gas (also called natural gas). This fact has led existing natural gas suppliers to push back against measures to increase the use of electricity as an energy supply - decreasing demand for gas. This reality prompted Southern California Gas Company (SoCalGas) to covertly support the creation of a nonprofit: Californians for Balanced Energy Solutions (C4Bes) which then went on to lobby for the gas sector and against the momentum in favor of electrification. The Sierra Club exposed the hand of SoCalGas in the formation of C4Bes (astroturfing) and so C4Bes curtailed its lobbying activities, although it continued to promote demand for gas.{{Cite web

| author = David Roberts

| title = The false promise of "renewable natural gas" - It's no substitute for shifting to clean electricity.

| url = https://www.vox.com/energy-and-environment/2020/2/14/21131109/california-natural-gas-renewable-socalgas

| website = Vox

| date = 2020-02-20

| access-date = 2022-09-02

}}{{Cite web

| author = Sammy Roth

| title = California's next frontier in fighting climate change: your kitchen stove

| url = https://www.latimes.com/business/la-fi-gas-stove-climate-change-southern-california-20190404-story.html

| website = Los Angeles Times

| date = 2019-04-04

| access-date = 2022-09-02

}}{{Cite web

| author = Susie Cagle

| title = US gas utility funds 'front' consumer group to fight natural gas bans

| url = https://www.theguardian.com/us-news/2019/jul/26/us-natural-gas-ban-socalgas-berkeley

| website = The Guardian

| date = 2019-07-26

| access-date = 2022-09-02

}}

{{Portal|Energy|Renewable energy}}

• Anaerobic digestion
• Biofuel
• Biogas
• Carbon-neutral fuel
• Issues relating to biofuels
• Landfill gas utilization
• Power-to-gas
• Renewable energy
• Sustainable energy

{{Reflist}}

• [https://arena.gov.au/blog/renewable-methane-southwest-queensland/ "Renewable carbon neutral methane to be produced in south-west Queensland" ARENA accessed 6 December 2020]
• National Grid U.S. – Vision for a Sustainable Gas Network [http://www.nationalgridus.com/non_html/NG_renewable_WP.pdf]
• American Gas Foundation Study: The Potential for Renewable Gas [http://www.aga.org/our-issues/renewable-gas/Pages/default.aspx]
• [http://www.sgc.se/rapporter/display.asp?ID=1182 SGC Rapport 187 Substitute natural gas from biomass gasification]
• [http://www.sgc.se/Rapporter/Resources/seminar_screen.pdf SGC Rapport on gasification and methanation]
• http://www.eee-info.net/cms/netautor/napro4/wrapper/media.php?
• Production of Synthetic Natural Gas (SNG) from Biomass- From Energy Research Centre of the Netherlands
• ECN SNG Website [http://www.biosng.com/fileadmin/biosng/user/documents/reports/e06018.pdf]
• [http://www.biosng.com/synthetic-natural-gas/id=%2C%2C%2C%2CZmlsZW5hbWU9YXJjaGl2ZSUzRCUyRjIwMDkuMDIuMTMlMkYxMjM0NTE1MDMxLnBkZiZybj1lbmdsJTIwU05HJTIwVGVjaG5vbG9neS5wZGY%3D SNG Platform in Güssing]{{Dead link|date=February 2025 |bot=InternetArchiveBot |fix-attempted=yes }}
• [http://www.nationalgrid.com/uk/Gas/SustainableGasGroup/ National Grid/UK Sustainable Gas Group]
• [https://sewaf.com/ Production of Biogas from organic waste Bioenergy]

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