What Is The Biogas To Biomethane Process? Steps & Standards

Biogas-to-biomethane is the process of turning raw biogas from anaerobic digestion into pipeline‑grade renewable natural gas (RNG). Raw biogas is mostly methane and carbon dioxide with traces of water, hydrogen sulphide and other contaminants. Upgrading simply means cleaning out the trace compounds and removing CO2 so the gas is almost pure methane. The result behaves like conventional natural gas for grid injection or as BioCNG/BioLNG fuel.

This article gives you a practical guide to the full journey: feedstocks and typical gas make‑up; pre‑treatment and upgrading stages; how the main technologies compare; polishing and quality control; a typical process flow and equipment layout; handling CO2 and off‑gas; grid and vehicle fuel specifications; safety, monitoring and compliance; performance metrics such as methane recovery and energy use; and how to size, scale and specify an integrated system. Here’s how it works, step by step.

Why upgrade biogas to biomethane

Upgrading biogas to biomethane turns a variable, wet, corrosive stream into a fungible, high‑value product. The biogas to biomethane process removes CO2 and impurities so the gas meets pipeline and vehicle fuel specs, enabling grid injection or BioCNG/BioLNG with no equipment changes. It improves project economics by raising the methane concentration and allowing use of existing gas networks, while cutting lifecycle emissions by capturing methane that would otherwise escape and isolating a pure biogenic CO2 co‑product for utilisation or storage. For sites from farms to landfills, upgrading aligns with decarbonisation policy, unlocks incentives, and makes waste management part of a dependable energy supply.

Feedstocks and typical biogas composition

Your feedstock and production pathway determine what leaves the digester—and how hard the upgrading will be. Across anaerobic digesters, landfill gas recovery and sewage plants, raw biogas typically contains 45–75% methane by volume, with most of the remainder CO2. Its lower heating value is about 16–28 MJ/m3. Trace compounds include hydrogen sulphide (H2S), moisture and volatile organic compounds (VOCs); small amounts of oxygen can also appear. These variations drive the choice of cleaning, upgrading and polishing steps.

• Common feedstocks: crop residues, animal manure, the organic fraction of municipal solid waste (including some industrial food‑processing waste), and wastewater sludge.

• Pathways: airtight biodigesters, landfill gas capture systems and wastewater treatment plants all produce biogas with different impurity profiles.

Knowing the starting composition frames the biogas to biomethane process you’ll specify next.

Step-by-step process: from raw biogas to biomethane

Think of the biogas to biomethane process as a clean, sequenced hand‑off: stabilise the raw stream, remove the troublemakers, separate CH4 from CO2, then polish and prove quality. Follow these steps to turn variable digester gas into grid‑ or vehicle‑grade RNG reliably.

1. Raw gas conditioning: Smooth flow and pressure from the digester or wellhead, cool and knock out condensate to protect downstream equipment.

2. Pre‑treatment (cleaning): Desulphurise (e.g., activated carbon) to remove H2S, strip VOCs/siloxanes where present, and dry the gas. This “purification” protects the upgrader and meets corrosion limits.

3. Compression: Raise pressure to what your chosen upgrader needs; membranes and scrubbers each have defined pressure windows.

4. Upgrading (CO2 removal): Separate methane from CO2 to create a near‑pure CH4 stream. Common routes include water scrubbing and membrane separation; all aim to maximise methane recovery.

5. Polishing and specification control: Final drying, trace H2S trim, and oxygen management to hit grid or vehicle fuel limits; odorisation and, where required, calorific value adjustment (e.g., small propane addition) before injection.

6. Measurement and interconnection: Verified metering, quality monitoring and pressure control at the grid tie‑in or BioCNG/BioLNG unit.

7. CO2/off‑gas handling: Manage the CO2‑rich stream for utilisation or capture; it’s a concentrated, biogenic co‑product.

This end‑to‑end sequence is the backbone of any robust biogas to biomethane process.

Upgrading technologies explained

At the heart of the biogas to biomethane process is the upgrader: a unit that separates methane from carbon dioxide by exploiting physical or chemical differences. In practice, you choose between a handful of proven routes that balance CAPEX, OPEX, footprint and methane recovery. Globally, water scrubbing and membrane separation dominate and account for almost 60% of biomethane production today, reflecting their maturity and reliability. Multi‑stage membrane systems can deliver very high methane purity, while scrubbing and adsorption routes remain dependable workhorses.

• Water scrubbing: CO2 dissolves into water under pressure. Robust and simple; requires water management and off‑gas handling.

• Membrane separation: Polymer membranes at elevated pressure, typically in two–three stages with recycle. Compact, chemical‑free, high purity with low slip when well‑staged.

• PSA (pressure swing adsorption): Solid adsorbents capture CO2 cyclically. Dry feed gas needed; flexible operation with established supply chain.

• Chemical solvents (amines): Selective CO2 absorption with thermal regeneration. High purity and deep CO2 removal; more heat duty and larger plant.

• Cryogenic separation: Low‑temperature separation of CO2/CH4; attractive where BioLNG or liquid CO2 recovery is planned, with higher power intensity.

Match technology to your feedstock, required specification and off‑gas strategy; that’s where upgrading performance is won or lost.

Contaminant removal and polishing stages

Cleaning and polishing turn raw, corrosive gas into a specification‑ready product. In the biogas to biomethane process, pre‑treatment removes the small but damaging compounds that foul equipment and breach limits, then final polishing dials in dryness, odour and calorific value so grid operators and vehicle systems accept the gas without modification.

• H2S control: Desulphurisation (often activated carbon) removes hydrogen sulphide to protect downstream units.

• Dehumidification: Cooling and drying prevent condensate; stable operation and correct dew point follow.

• VOC removal: Targeted filtration strips troublesome volatile organics from feedstocks like OFMSW.

• Oxygen management: Control and trim O2 to meet tight grid or fuel specs before injection or dispensing.

• Final polish: Trace H2S trim, fine drying and quality verification at the metering station.

• Odorisation and CV set: Add odourant and, where required, adjust calorific value (e.g., small propane addition) prior to export.

Process flow and typical equipment layout

A clean, compact layout keeps pressure drops low and maintenance simple. Most plants arrange the biogas to biomethane process as modular, skid‑mounted or containerised blocks in a straight run from the digester outlet to the grid or vehicle tie‑in. That gives clear piping, safe access, and reliable process control from start to finish.

• Knock‑out/chiller at digester outlet for condensate control.

• Booster/blower to deliver steady pressure and flow.

• Pre‑treatment skid: H2S, VOCs and moisture removal.

• Compressor to vendor setpoint (e.g., ~16 bar for membranes).

• Upgrader: water scrubber, membranes or PSA with recycle.

• Polishing/injection: final dry, odorise, CV adjust, meter.

• CO2/off‑gas tie‑in for utilisation or disposal.

Managing CO2 and off-gas

Upgrading yields two streams: a methane‑rich product and a CO2‑rich off‑gas. The priority is to minimise methane slip by recycling off‑gas back to the upgrader and only sending a final residual to a thermal oxidiser or flare under permit. The CO2 co‑product is concentrated and biogenic, so it can be monetised or permanently removed from the carbon cycle—an important lever in the biogas to biomethane process.

• Utilise CO2: Greenhouse enrichment and food & beverage applications are common uses.

• Liquefy for value: Modern systems capture and liquefy CO2 at roughly 12–66 bar to >99 mol% purity for sale or storage.

• Make more methane: Combine CO2 with hydrogen (methanation) to create additional biomethane.

• Store it: Geological storage turns biomethane into a CO2‑negative energy option.

• Control slip: Multi‑stage recycle and continuous CH4 monitoring on vents keep emissions and losses low.

Gas quality standards for grid injection

Grid operators accept biomethane when it behaves like pipeline natural gas. That means the biogas to biomethane process must deliver a near‑pure methane stream (biomethane is indistinguishable from natural gas, with an LHV around 36 MJ/m3), strip out corrosives, and meet the local grid code. In many jurisdictions you must add odourant before export and, if required, trim the calorific value/Wobbe index (often via small propane addition) so the gas sits within the network’s quality band.

• Methane content/purity: High CH4 to match network energy quality.

• CO2 limit: Very low residual CO2 after upgrading.

• H2S and sulphur: Trace only; desulphurisation is mandatory.

• Water/dew point: Dry gas to specified dew point to avoid condensation.

• Oxygen and inerts: Tight O2/N2/total inerts limits per grid code.

• Wobbe index/CV: Within local band; CV adjustment may be required.

• Siloxanes/VOCs/particulates: Effectively removed to protect assets.

• Odorisation: Added at injection where mandated.

• Measurement and monitoring: Calibrated metering and continuous quality verification at the interconnection.

Gas quality standards for vehicle fuel (BioCNG and BioLNG)

Biomethane used as vehicle fuel must meet automotive-grade gas specifications. Because biomethane is indistinguishable from natural gas and has an LHV around 36 MJ/m3, it is fully compatible with natural gas vehicles, but only when the biogas to biomethane process yields a clean, consistent product. Requirements are particularly tight for BioLNG, where cryogenic conditions magnify any residual impurities.

• High methane content and stable energy quality: Consistent Wobbe/methane number for engine calibration.

• Very low sulphur (H2S/total): Protects engines, catalysts and lubricants.

• Dry gas: Low water dew point; for BioLNG, ultra‑dry to avoid freezing/ice formation.

• Low CO2 and inerts: Deep CO2 removal for BioLNG to prevent CO2 solids.

• Siloxanes/VOCs essentially removed: Prevents hard deposits and knock.

• Oxygen tightly controlled: Suppliers commonly target ppm‑level O2 at the dispenser.

• Cleanliness/odorisation: Filtration to remove particulates; LNG is typically unodorised, CNG follows local rules.

Safety, compliance and monitoring

Safety is engineered into the biogas to biomethane process from first principles: pressure parts and piping to recognised codes (API/ASME), electrical and installation to CSA, and emissions control aligned with EPA‑style requirements. Equally, compliance depends on proving gas quality continuously. That means precise oxygen control during desulphurisation and polishing, verified odorisation where required, and calibrated metering at the grid or fuel interface. Modern plants add automated trips and remote monitoring so operators can maintain integrity and uptime without being on site.

• Compliance envelope: Environmental permits, grid code conformance, and documented odorisation/CV adjustment before export.

• Continuous quality monitoring: Online CH4, CO2, H2S, O2 and moisture at the injection point and on any vent/flare to manage methane slip.

• Protection and control: Pressure and temperature interlocks, automated shutdown sequences, and permitted flare for safe disposal of residual off‑gas.

• Measurement integrity: Calibrated meters and analysers with audit trails; scheduled verification to keep certificates current.

Methane recovery, methane slip and energy use

Two numbers define upgrader performance: Recovery = CH4_out / CH4_in and Slip = CH4_vented / CH4_in. In the biogas to biomethane process you want near‑total recovery and near‑zero slip, because methane is a potent greenhouse gas and any loss hurts both revenue and CO2e performance. Best‑in‑class integrated systems now guarantee 99.5% biomethane recovery alongside a 99.5% CO2e reduction, with continuous monitoring to prove it. Energy use is dominated by compression, pumping and any heat duty (e.g., solvent regeneration or cryogenics), so technology choice and configuration have a big impact.

• Maximise recovery: Multi‑stage membranes/PSA with recycle, tight seals, and leak‑free piping.

• Minimise slip: Continuous CH4 analysers on vents, recycle off‑gas, and only flare residues.

• Optimise energy: Right‑size compression, recover heat where available, keep gas dry and clean upstream, and match the upgrader (membrane/scrubber/amine/cryogenic) to your feed and off‑gas strategy.

• Prove performance: Online CH4, CO2, H2S, O2 and moisture at export plus audited metering—central to any credible biogas to biomethane process.

Sizing, scalability and economics

Start by matching the upgrader to the raw‑gas reality: average/peak flow, composition, hours, and the grid or fuel spec you must meet. Modular, containerised skids let you right‑size day one and add trains later; practical ranges run from compact 30 Nm3/h units to multi‑train systems above 1,300 Nm3/h. In a rigorous biogas to biomethane process, high turndown, quick installation and standardised interfaces keep CAPEX and downtime down.

Project economics hinge on where and how you sell methane, incentives, carbon credits, and the energy you spend compressing and cleaning the gas. The biggest value levers are methane recovery/slip, power intensity, and CO2 handling (utilisation or liquefaction), plus automation that cuts O&M. Guaranteed high recovery and low slip translate directly into higher revenue and deeper CO2e reductions.

What to look for in an integrated system

If you want fewer surprises and faster payback, choose an end‑to‑end, modular package that treats the biogas to biomethane process as one controlled system, not a string of vendors. Focus on assured performance, low OPEX, compliance by design, and options to monetise the CO2 stream.

• True end‑to‑end integration: From digester outlet to grid/dispenser, single PLC/SCADA with remote monitoring.

• Robust cleaning/polishing: Desulphurisation, VOC/siloxane control, medium‑pressure drying, and ppm‑level O2 removal.

• Upgrading performance: Multi‑stage separation with recycle, high CH4 recovery, low slip, continuous analysers.

• Compliance built‑in: API/ASME pressure parts, CSA electrical, EPA‑style emissions, odorisation and CV trim at interconnect.

• CO2 optionality: Recycle/utilise or capture and liquefy CO2 (≈12–66 bar, >99 mol%).

• Scalable, efficient hardware: Containerised trains (~30 to >1,300 Nm3/h), quiet efficient compressors, firm delivery and quantified guarantees.

Project planning checklist

Good projects start with a tight checklist that turns risk into certainty. Use the biogas to biomethane process as your backbone: prove the feed, select the right upgrader, design for compliance, and lock in revenue. Work through these items before you commit capital.

• Feedstock and gas profile: Volume, variability, uptime, impurities.

• Composition baseline: Campaign sampling (CH4 45–75%), H2S, VOCs, moisture.

• Spec and offtake: Grid code/Wobbe, BioCNG/BioLNG, odorisation, CV trim.

• Permits and approvals: Environmental, interconnect, flare/oxidiser.

• Technology selection: Membranes, scrubbing, PSA, amine or cryogenic—fit spec/OPEX.

• CO2/off‑gas strategy: Recycle, utilisation/liquefaction, emissions limits.

• Site layout and tie‑ins: Knock‑out, compression, utilities, hazardous zoning.

• Power and utilities: Electrical load, cooling, instrument air, drains.

• Instrumentation and QA: Online CH4/CO2/H2S/O2/H2O; calibrated metering.

• Safety and HAZOP: Relief, trips, ignition control, emergency venting.

• Performance guarantees: Methane recovery, slip, availability, energy intensity.

• Contracts and incentives: Tariffs, credits, M&V, settlement terms.

• O&M and spares: Service plan, adsorbents/media, compressor care.

• Schedule and logistics: Delivery, cranage, commissioning, operator training.

Key takeaways

Upgrading biogas to biomethane is a disciplined sequence: condition, clean, compress, separate CO2, polish, and prove quality. Winning projects align technology with the feed, meet grid or vehicle specs first time, and control CO2 and methane slip with integrated monitoring and safety.

• Start with composition: it dictates design, OPEX and risk.

• Protect the upgrader: remove H2S, VOCs and moisture early.

• Choose upgrading tech for recovery, OPEX and off‑gas strategy.

• Prove export quality: CH4/CO2/H2S/O2/H2O, CV/Wobbe, odorisation.

• Monetise CO2 and recycle off‑gas to minimise slip.

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