# Introduction Use of fossil fuels such as natural gas, oil, and coal are responsible for about 75% of global greenhouse gas (GHG) emissions, and make up 98% of GHG emissions within the energy sector. Alternative energy sources exist with far fewer GHGs emissions, but technological, economic, and administrative barriers prevent and limit their development. Biogas is a renewable energy source that can be produced via several different pathways. One option is anaerobic digestion, where organic materials such as food waste, animal manure, and agricultural residues are broken down by microorganisms in an oxygen-free environment. Common uses of biogas include: * Injection: Purification of biogas to biomethane and directly injecting it into the gas network. * Cogeneration: Generation of electricity and heat by a biogas engine or turbine for a combined heat and power (CHP) system. * Heat only: Production of heat in a biogas boiler. * Transport: Compressed natural gas (BioCNG) and liquefied natural gas (BioLNG) The second output of anaerobic digestion, digestate, is a material rich in organic matter and nutrients that is spread on agricultural fields. [Numerous life cycle assessments (LCAs)](#user-content-fn-1)[^1] have confirmed that using biogas from anaerobic digestion rather than energy from fossil fuels leads to reduced GHG emissions. Yet, biogas makes up a small share of energy consumption: in 2022 in Europe, [20 times](#user-content-fn-2)[^2] more natural gas was used than biogas,. [^1]: * Hijazi, O., Munro, S., Zerhusen, B., Effenberger, M., 2016. Review of life cycle assessment for biogas production in Europe. Renewable and Sustainable Energy Reviews 54, 1291–1300. [URL](https://doi.org/10.1016/j.rser.2015.10.013) * Salvador, R., Barros, M.V., Rosário, J.G.D.P.D., Piekarski, C.M., da Luz, L.M., de Francisco, A.C., 2019. Life cycle assessment of electricity from biogas: A systematic literature review. Environmental Progress & Sustainable Energy 38, 13133.[ ](https://doi.org/10.1002/ep.13133)[URL](https://doi.org/10.1002/ep.13133) * Esteves, E.M.M., Herrera, A.M.N., Esteves, V.P.P., Morgado, C. do R.V., 2019. Life cycle assessment of manure biogas production: A review. Journal of Cleaner Production 219, 411–423. [URL](https://doi.org/10.1016/j.jclepro.2019.02.091) [^2]: * Eurostat 2024. Supply, transformation and consumption of renewables and wastes. DOI: . Accessed May 2024. - Eurostat 2024. Supply, transformation and consumption of gas. DOI: . Accessed May 2024. ↑ --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.rainbowstandard.io/methodologies/biogas-from-anaerobic-digestion/introduction.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.