--- title: Biogas, Landfill Gas and Digesters Explained url: https://www.sarveshanalytics.com/learn/biogas-landfill-gas-and-digesters-explained.html description: How anaerobic digesters and landfills make methane-rich gas, what raw biogas contains, how it is cleaned and upgraded to compressed biogas. updated: 2026-11-02 source: html --- Learn · Process primers # Biogas, landfill gas and digesters explained Biogas is a renewable fuel whose value rests on its composition. Measuring it turns a smelly gas stream into a managed energy source. Beginner 3 min read Lesson 6 of 13[Process primers](https://www.sarveshanalytics.com/learn/track-process-primers.html) Helpful first: [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html) Quick answer Anaerobic digestion converts organic waste into biogas: methane, CO2, water vapour and traces of H2S. Landfills produce a similar gas, with air drawn in at wells. Biogas is cleaned and sometimes upgraded to biomethane or compressed biogas by removing CO2 and contaminants. Analysers read methane, CO2 and oxygen at the digester, before the engine and at the upgrader outlet. Updated 2 November 2026 · Figures from Sarvesh datasheets **After this lesson you can** - Describe how biogas forms - List raw biogas components and impurities - Explain upgrading in outline - Choose measurement points ## How it forms Microorganisms break down organic matter without oxygen in a sealed digester or under a landfill cover. The gas they produce is mostly methane and CO2. Feedstocks include sewage sludge, cattle dung, food waste, distillery effluent and agricultural residue. ## What the gas contains | Component | Typical level in raw biogas | Why it matters | |---|---|---| | Methane | Around 50 to 70 % | The fuel value | | CO2 | Around 30 to 50 % | Dilutes the fuel; removed in upgrading | | Water vapour | Saturated | Condenses in lines; needs drying | | H2S | Tens to thousands of ppm | Corrosive and toxic; removed by scrubbing | | Oxygen and nitrogen | Small, from air | Show air ingress; hazard and quality issue | | Siloxanes | Traces in landfill and some wastes | Damage engines and sensors | Levels vary with feed, process and site. ## Cleaning and upgrading Raw biogas can fuel a gas engine after drying and removing H2S. To make biomethane or compressed biogas (CBG), CO2 is also removed, by water scrubbing, membranes, pressure swing adsorption or amine absorption, leaving gas with a methane content typically above 90 %. Many analysers are placed along the train to monitor each step. ## Where to measure - **Digester gas:** methane, CO2, oxygen. Shows process health. - **Before the engine or flare:** methane and CO2 for fuel quality. - **Upgrader outlet:** methane, CO2, oxygen for CBG quality. - **Landfill wells:** methane, CO2 and oxygen; oxygen shows air ingress and fire risk. NDIR does the methane and CO2 work: [Measuring methane and biogas composition online](https://www.sarveshanalytics.com/learn/measuring-methane-and-biogas.html). Wet and H2S-bearing streams need conditioning: [What samples an analyser cannot take: know the limits](https://www.sarveshanalytics.com/learn/what-samples-an-analyser-cannot-take.html). ## Safety Biogas is flammable and can carry toxic H2S. Gas handling and analysis locations need area classification and ventilation, and oxygen monitoring helps prevent air ingress near flammable gas: [Flammability, explosive limits and gas safety basics](https://www.sarveshanalytics.com/learn/flammability-explosive-limits-and-gas-safety-basics.html). ## Applications See the application pages for biogas and CBG, landfill gas wells and flares, and sewage, dairy and food-waste digesters: [Biogas and compressed biogas (CBG)](https://www.sarveshanalytics.com/applications/biogas-and-cbg-methane-co2-analysis.html), [Landfill gas wells and flares](https://www.sarveshanalytics.com/applications/landfill-gas-wells-and-flares.html), [Sewage-treatment-plant, dairy and food-waste digesters](https://www.sarveshanalytics.com/applications/sewage-treatment-plant-dairy-and-food-waste-digesters.html). **In short** - Biogas is mostly methane and CO2 from oxygen-free digestion. - Raw gas is wet and can carry H2S; upgrading removes CO2 and contaminants. - Measure methane, CO2 and oxygen at digester, engine and upgrader. - Oxygen shows air ingress, a quality and safety issue. ## Check your understanding Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading. **What are the two main components of biogas?** Methane and CO2. **Why is oxygen measured in landfill gas?** It shows air being drawn into the gas system, reducing quality and raising the fire risk. **What does upgrading remove?** CO2 and contaminants such as H2S and water, raising the methane content. ## Key terms - [CBG (compressed biogas)](https://www.sarveshanalytics.com/learn/glossary.html#t-cbg-compressed-biogas) - [NDIR](https://www.sarveshanalytics.com/learn/glossary.html#t-ndir) - [Condensate](https://www.sarveshanalytics.com/learn/glossary.html#t-condensate) ## Frequently asked questions **What is biogas made of?** Mostly methane and CO2, with water vapour and traces of H2S. **What is CBG?** Compressed biogas: biogas upgraded to high methane content and compressed for use as fuel. **Why is H2S a problem?** It is corrosive and toxic and damages sensors and engines. **Which analyser measures biogas methane?** ACCURRA-S 4030, by NDIR, on a conditioned sample. ## Related products [ ### ACCURRA-S Online analyser for trace, percent and purity O2, CO, CO2, CH4 and dew point; can measure two gases from one sample. View ACCURRA-S ](https://www.sarveshanalytics.com/safe-gas-analyser.html)[ ### i-Cons Smart Peltier sample conditioner with diagnostics, auto blowback and Modbus, in a compact 19 inch cabinet. View i-Cons ](https://www.sarveshanalytics.com/smart-systems-for-gas-analyser.html) ## Where this applies - [Biogas and compressed biogas (CBG)](https://www.sarveshanalytics.com/applications/biogas-and-cbg-methane-co2-analysis.html) - [Landfill gas wells and flares](https://www.sarveshanalytics.com/applications/landfill-gas-wells-and-flares.html)