Biogas Upgrading Technologies: How Biogas Is Upgraded to Biomethane

Biogas upgrading technologies remove carbon dioxide and unwanted trace components from raw biogas so that the methane-rich product can be used as biomethane. Depending on the final specification, upgraded gas can be injected into a gas network, compressed for vehicle fuel, liquefied as bio-LNG or used as a renewable substitute for fossil natural gas.

The main commercial biogas upgrading technologies include membrane separation, water scrubbing, pressure swing adsorption (PSA), chemical absorption and physical solvent systems. Cryogenic and biological upgrading methods are also developing for particular applications. There is no single technology that is best for every project.

The appropriate system depends on factors such as raw biogas composition, plant size, methane recovery, pressure, electricity and heat availability, methane slip, water use, operator skills, maintenance support and the quality specification required for the final biomethane.

This guide compares the principal technologies used for upgrading biogas to biomethane, explains how methane is separated from carbon dioxide and discusses pretreatment, methane losses, costs, grid injection and technology selection.

Key Takeaways

• Biogas upgrading is different from basic biogas cleaning. Cleaning removes contaminants such as hydrogen sulphide, water and siloxanes; upgrading principally raises methane concentration by removing carbon dioxide and, where required, other unwanted gases.
• The main commercial biogas upgrading technologies are membranes, water scrubbing, PSA and solvent absorption. Each has different energy, maintenance, water, heat and methane-recovery characteristics.
• Membrane separation has become particularly important in new biomethane installations. IEA Bioenergy reports that membranes are now among the most commonly selected technologies for new plants in Europe and North America.
• High methane recovery matters economically and environmentally. Methane lost in reject gas or process water reduces product yield and increases greenhouse-gas emissions.
• Pretreatment is essential. Hydrogen sulphide, moisture, particulates, siloxanes and other contaminants may need to be removed before the main CO₂-separation stage.
• Biomethane grid injection involves more than the upgrader. Gas quality monitoring, compression, metering, network-entry requirements and compliance with the relevant gas specification are also required.
• Technology selection is site-specific. The cheapest capital option is not automatically the lowest-cost or lowest-emission solution over the life of the plant.

What Is Biogas Upgrading?

Biogas upgrading is the process of increasing the methane concentration of raw biogas by removing carbon dioxide and other unwanted components.

Raw biogas produced by anaerobic digestion normally contains methane and carbon dioxide as its two principal constituents, together with smaller concentrations of hydrogen sulphide, water vapour, nitrogen, oxygen, ammonia, siloxanes and other trace compounds depending on the feedstock.

Raw gas may be suitable for some boilers and CHP engines after appropriate cleaning, but it does not normally meet the specification required for natural-gas networks or high-quality vehicle fuel.

Upgrading converts this raw gas into biomethane by increasing its methane concentration and reducing unwanted gases to acceptable levels.

Watch our video which explains the best/ most used available upgrading technologies. Please return after viewing the video, SCROLL DOWN, and read the full article below:

Biogas Cleaning vs Biogas Upgrading

The terms are sometimes used interchangeably, but there is a useful engineering distinction.

Biogas cleaning generally means removing contaminants that may damage equipment, create safety problems or prevent downstream treatment.

This can include:

• hydrogen sulphide removal;
• water removal and drying;
• particulate filtration;
• siloxane removal;
• ammonia removal; and
• removal of volatile organic or halogenated compounds where present.

Biogas upgrading goes further by removing a substantial proportion of the carbon dioxide and other inert gases so that methane becomes the dominant component of the product gas.

In England, Environment Agency guidance specifically distinguishes treatment requirements according to final gas use and identifies carbon-dioxide removal as a requirement to consider when upgrading biogas to biomethane.

Why Upgrade Biogas to Biomethane?

Upgrading greatly expands the potential uses of biogas.

Biomethane can potentially be used for:

• gas-grid injection;
• industrial boilers and burners;
• commercial heating;
• compressed biomethane vehicle fuel;
• liquefied biomethane or bio-LNG;
• high-temperature industrial processes;
• combined heat and power where gas quality requirements justify upgrading; and
• replacement of fossil natural gas in compatible applications.

This ability to use existing gas infrastructure is one of the major reasons biomethane production has become increasingly important.

How Is Methane Separated from Biogas?

A common search question is “how do you separate methane from biogas?”

In practice, most commercial systems do not simply extract individual methane molecules from a mixed gas stream. Instead, they exploit differences in the physical or chemical behaviour of methane and carbon dioxide.

Depending on the technology, the system may:

• allow CO₂ to pass preferentially through a membrane;
• dissolve CO₂ more readily than methane in water;
• chemically bind CO₂ in an amine solution;
• adsorb CO₂ onto a solid under pressure; or
• separate gas components by cooling and phase change.

The methane-rich fraction is retained as product biomethane while the carbon-dioxide-rich fraction becomes an off-gas or potential feedstock for further CO₂ recovery.

Main Biogas Upgrading Technologies

The commercial market is dominated by a relatively small group of proven technologies.

1. Membrane Biogas Upgrading

Membrane separation uses differences in the permeation rates of gases through selective membrane materials.

Most commercial systems compress pretreated biogas and pass it across one or more membrane stages. Carbon dioxide permeates through the membrane more readily than methane in the commonly used systems, leaving a methane-enriched product stream.

Multi-stage designs are often used to improve both methane purity and methane recovery.

Advantages can include:

• compact equipment;
• modular construction;
• no liquid solvent inventory;
• relatively simple operation;
• good suitability for packaged systems; and
• ease of capacity expansion by adding modules.

Potential disadvantages include:

• compression energy demand;
• sensitivity to contaminants;
• need for effective pretreatment;
• membrane replacement over time; and
• the need to manage methane in permeate or reject streams.

Recent reviews continue to identify membrane separation as one of the major commercial upgrading technologies, and a 2026 review notes its increasing importance in modern biomethane systems.

How Does a Biogas Membrane System Work?

A typical biogas membrane installation may include the following stages:

1. Raw biogas pretreatment to remove hydrogen sulphide, water, particulates and other contaminants.
2. Compression to provide the pressure difference needed for membrane separation.
3. First membrane stage where carbon dioxide preferentially permeates through the membrane.
4. Additional membrane stages to increase methane recovery and product purity.
5. Recycle or treatment of intermediate streams where worthwhile.
6. Product-gas quality monitoring before biomethane leaves the upgrading unit.

Membrane performance is therefore not determined solely by the membrane material. Pretreatment, pressure, staging, recycle configuration and reject-gas management all affect the final result.

2. Water Scrubbing

Water scrubbing exploits the fact that carbon dioxide is much more soluble in water than methane.

Compressed biogas is contacted with water in an absorption column. Carbon dioxide dissolves preferentially into the water while methane passes through as the methane-rich product gas.

The water can then be regenerated by reducing pressure or using stripping air and recirculated through the process.

Advantages include:

• mature technology;
• relatively simple process chemistry;
• no specialist chemical solvent;
• simultaneous removal of some hydrogen sulphide; and
• good methane recovery when properly designed.

Disadvantages can include:

• water requirement;
• pumping and compression energy;
• need to manage dissolved gases;
• possible cooling requirements; and
• methane losses through process water or off-gas if poorly controlled.

Water scrubbing is a mature commercial method, and published reviews continue to regard it as a well-established biogas upgrading technology.

3. Pressure Swing Adsorption (PSA)

Pressure swing adsorption uses solid adsorbents that retain carbon dioxide and certain other gases more strongly than methane.

Raw gas is compressed and passed through adsorption vessels. Carbon dioxide, water and other selected components are adsorbed while methane passes through as product gas.

When an adsorption bed becomes loaded, pressure is reduced and the adsorbed gases are released. Several vessels normally operate in sequence so that gas production can continue while individual beds regenerate.

Advantages can include:

• dry separation process;
• no liquid solvent;
• high product methane concentration;
• potential removal of nitrogen and other contaminants depending on design; and
• commercial maturity.

Potential disadvantages include:

• compression demand;
• adsorbent replacement;
• complex valve sequencing;
• sensitivity to some contaminants; and
• methane in tail gas if recovery is not optimised.

PSA remains one of the major proven technologies for biomethane production.

4. Chemical Absorption – Amine Scrubbing

Amine scrubbing removes carbon dioxide through reversible chemical reaction with an amine solution.

Biogas passes through an absorber where the solvent captures CO₂. The CO₂-rich solvent is then heated in a regeneration stage, releasing the carbon dioxide so that the amine can be reused.

Advantages can include:

• very high methane purity;
• high methane recovery;
• low methane concentration in the CO₂ off-gas when well operated; and
• good suitability where heat is available for solvent regeneration.

Disadvantages can include:

• thermal energy requirement;
• chemical management;
• solvent degradation;
• corrosion considerations; and
• greater process complexity than some dry systems.

Recent reviews continue to identify chemical absorption as a major established upgrading technology.

5. Physical Solvent Scrubbing

Physical solvents also absorb carbon dioxide preferentially, but without the same chemical reaction used in amine systems.

Performance generally improves at higher pressures because gas solubility increases.

These processes may remove several contaminants simultaneously and can be appropriate for some larger gas streams, although solvent circulation and regeneration still require energy.

6. Cryogenic Biogas Upgrading

Cryogenic upgrading separates gas components by cooling them to very low temperatures.

Carbon dioxide and methane have different condensation and freezing behaviour, allowing separation under controlled pressure and temperature conditions.

Cryogenic processes can offer:

• high biomethane purity;
• potential integration with bio-LNG production;
• high methane recovery; and
• potential recovery of relatively pure CO₂.

However, the equipment is more complex and capital-intensive and is generally more relevant to larger or specialist projects. Reviews continue to regard cryogenic separation as an emerging or more specialised option rather than the default technology for typical upgrading plants.

7. Biological Methanation

Biological upgrading takes a different approach.

Instead of physically separating all of the carbon dioxide, hydrogen can be supplied to methanogenic microorganisms that convert CO₂ and H₂ into additional methane.

The overall reaction is:

CO₂ + 4H₂ → CH₄ + 2H₂O

This can potentially increase methane yield while providing a route for renewable hydrogen utilisation.

Biological methanation remains less widely deployed than membrane, PSA, water or amine systems, but it is an important developing technology.

Comparison of the Main Biogas Upgrading Technologies

Membrane Upgrading vs Water Scrubbing

Because both technologies are widely used, membrane upgrading and water scrubbing are often compared directly.

Membranes are typically attractive where:

• compact footprint is important;
• modular expansion is desirable;
• water use should be minimised;
• operators prefer a dry separation system; and
• electric power for compression is readily available.

Water scrubbing may be attractive where:

• a mature, well-understood process is preferred;
• water is readily available;
• operators are comfortable with absorption-column equipment;
• combined CO₂/H₂S removal is advantageous; and
• process water can be effectively regenerated and recirculated.

Neither technology is universally superior. Site-specific energy costs, methane recovery, maintenance, water availability and final gas specification should drive the decision.

Membrane Upgrading vs PSA

Membranes and PSA are both dry upgrading technologies but work very differently.

Membrane systems depend on selective gas permeation through a membrane material, while PSA depends on selective adsorption onto a solid material.

Both generally require gas compression and effective pretreatment.

The choice may depend upon:

• gas flow;
• raw gas composition;
• desired methane recovery;
• nitrogen concentration;
• required product purity;
• operator preference;
• maintenance support; and
• expected lifetime cost.

Pretreatment Before Biogas Upgrading

A biomethane upgrader should not normally be expected to accept untreated raw biogas directly from the digester.

Depending on the feedstock, upstream treatment may be required for:

• hydrogen sulphide;
• water vapour;
• particulates;
• siloxanes;
• ammonia;
• oil aerosols;
• volatile organic compounds; and
• halogenated compounds.

This is particularly important for membrane and adsorption systems because contaminants can damage membranes or adsorbents and reduce performance.

Environment Agency guidance for permitted biological waste-treatment plants specifically requires operators to consider dewatering and removal of hydrogen sulphide, oxygen, nitrogen, ammonia, siloxanes, particulates and CO₂ according to the intended end use of the gas.

Why Methane Slip Matters

Methane slip is methane that is lost from the upgrading process instead of becoming product biomethane.

It can occur in:

• membrane permeate;
• PSA tail gas;
• water-scrubber regeneration gas;
• solvent systems; or
• other reject streams.

Methane slip matters for two reasons.

First, it is lost product. Every cubic metre of methane emitted from the plant is methane that cannot be sold or used.

Second, methane is a potent greenhouse gas, so uncontrolled emissions can materially weaken the climate benefit of biomethane production.

Modern upgrading plants therefore aim for high methane recovery and appropriate treatment of methane-containing off-gases. IEA Bioenergy reports that methane losses have fallen as upgrading technologies have matured, although the typical values still vary between technology types and individual installations.

What Happens to the CO2 Removed from Biogas?

Traditionally, the carbon dioxide separated from biogas was commonly released after methane recovery.

Increasingly, operators are investigating biogenic CO₂ recovery.

Potential uses include:

• food and beverage applications where purity requirements can be met;
• greenhouse enrichment;
• industrial uses;
• mineralisation;
• synthetic-fuel production; and
• carbon capture and storage where technically and economically feasible.

CO₂ recovery can improve project economics in suitable locations, but purification, liquefaction, transport and market availability all need to be considered.

For a more detailed discussion of CO₂ separation methods, see our specialist article on how to remove CO₂ from biogas.

Biogas Upgrading Cost

There is no useful single answer to the question “how much does biogas upgrading cost?”

Capital and operating costs vary significantly according to:

• raw biogas flow rate;
• methane concentration;
• H₂S concentration;
• siloxanes and other contaminants;
• required biomethane specification;
• methane recovery target;
• plant pressure;
• electricity price;
• heat availability;
• water cost and availability;
• redundancy requirements;
• CO₂ recovery;
• grid connection pressure;
• maintenance contract;
• equipment lifetime; and
• plant utilisation factor.

Smaller installations often suffer from higher unit costs because compressors, analysers, controls and safety systems do not scale down in direct proportion to gas throughput.

Technology selection should therefore be based on whole-life cost per unit of saleable biomethane rather than simply the purchase price of the upgrader.

Biogas Upgrading and Biomethane Grid Injection

Upgrading is only one part of a gas-to-grid project.

Once biomethane has been produced, the installation may also require:

• final drying;
• continuous gas-quality analysis;
• compression to network pressure;
• fiscal metering;
• odourisation where required;
• calorific-value adjustment where required;
• flow control;
• network-entry equipment; and
• shutdown and off-specification gas handling.

In England, biomethane intended for injection into the gas grid must be of a quality acceptable to the network, meet the relevant Gas Safety (Management) requirements and be supplied under the necessary network arrangements.

The Green Gas Support Scheme also supports eligible biomethane injected into the gas grid, subject to scheme eligibility and sustainability requirements.

Biomethane Quality Is More Than Methane Percentage

A common mistake is to assume that an upgrader has succeeded simply because the methane concentration is high.

Grid-quality biomethane may also need limits on:

• hydrogen sulphide;
• total sulphur;
• oxygen;
• water;
• ammonia;
• halogenated compounds;
• siloxanes;
• calorific value; and
• other trace constituents.

Current Environment Agency biomethane guidance specifies monitoring requirements and limits for a range of contaminants, not methane concentration alone.

Biomethane for Transport: Bio-CNG and Bio-LNG

Not all upgraded biogas needs to enter the gas grid.

Biomethane can also be compressed to produce bio-CNG or liquefied to produce bio-LNG.

These routes may be attractive for:

• heavy goods vehicles;
• bus fleets;
• refuse collection vehicles;
• off-grid industrial users; and
• locations where a gas-grid connection is unavailable or uneconomic.

Vehicle-fuel projects require their own gas quality, compression or liquefaction equipment, storage and dispensing systems.

Can Biogas CO2 Be Converted into More Methane?

Yes, at least in principle and increasingly in practice.

If renewable hydrogen is available, the carbon dioxide fraction can be converted into additional methane through methanation.

This can be done biologically using methanogenic microorganisms or chemically using suitable catalysts.

Potential benefits include:

• higher methane output from the original biogas stream;
• use of renewable hydrogen;
• reduction in CO₂ reject gas; and
• integration between renewable electricity and renewable gas systems.

However, economics depend heavily on hydrogen cost, conversion efficiency and the value of the additional methane.

How to Choose a Biogas Upgrading Technology

Technology selection should begin with a clear process specification rather than a preferred supplier.

Important questions include:

• How much raw biogas will be produced?
• What is the minimum and maximum flow?
• What is the methane concentration?
• How much CO₂ is present?
• What are the H₂S levels?
• Are siloxanes present?
• Is nitrogen or oxygen significant?
• What final gas specification is required?
• What methane recovery is guaranteed?
• What methane slip occurs at normal and turndown operation?
• What electricity demand is guaranteed?
• Is process heat available?
• Is water readily available?
• What pretreatment is included?
• What happens to reject gas?
• Can the CO₂ be recovered?
• What is the minimum stable operating flow?
• What redundancy is included?
• How quickly can specialist maintenance support attend?
• What are membrane, solvent or adsorbent replacement costs?
• What availability is guaranteed?

A good biogas upgrading procurement exercise compares guaranteed whole-system performance rather than headline methane purity alone.

Biogas Upgrading Technologies Are Still Evolving

Biogas upgrading is now a mature commercial industry, but technology continues to develop.

Areas of ongoing improvement include:

• lower-energy compression;
• improved membrane selectivity;
• lower methane slip;
• better heat integration;
• hybrid membrane/PSA systems;
• biological methanation;
• CO₂ recovery;
• smaller modular systems; and
• better monitoring of fugitive methane emissions.

IEA Bioenergy data indicates that membrane separation has become particularly prominent among newer upgrading installations in Europe and North America, while water scrubbing, chemical scrubbing and PSA remain important mature technologies.

Biogas Upgrading Technologies: Frequently Asked Questions

What is biogas upgrading?

Biogas upgrading is the process of removing carbon dioxide and other unwanted components from raw biogas so that the methane concentration rises sufficiently to produce biomethane.

What are the main biogas upgrading technologies?

The main commercial technologies are membrane separation, water scrubbing, pressure swing adsorption (PSA), chemical absorption such as amine scrubbing and physical solvent scrubbing. Cryogenic and biological systems are also used or being developed for particular applications.

What is the difference between biogas cleaning and biogas upgrading?

Biogas cleaning primarily removes contaminants such as H₂S, water, particulates and siloxanes. Upgrading additionally removes a substantial proportion of CO₂ and other inert gases to produce methane-rich biomethane.

How does a biogas membrane work?

A membrane system compresses pretreated biogas and passes it across a selective membrane. Carbon dioxide generally permeates through the membrane faster than methane, producing a methane-rich stream. Several stages may be used to improve methane recovery and purity.

What is water scrubbing in biogas upgrading?

Water scrubbing uses the greater solubility of carbon dioxide in water compared with methane. Pressurised biogas contacts water in an absorber, CO₂ dissolves preferentially and methane exits as the upgraded gas.

What is PSA biogas upgrading?

Pressure swing adsorption uses solid adsorbents that preferentially retain CO₂ and certain contaminants at pressure. The methane-rich gas passes through, while the adsorbent is regenerated by reducing pressure.

Which biogas upgrading technology is best?

There is no universal best technology. Selection depends on gas flow, composition, methane recovery, product specification, electricity and heat costs, water availability, maintenance capability, plant scale and required flexibility.

How much does biogas upgrading cost?

Cost varies widely with plant size, raw-gas quality, technology, required gas specification, methane recovery, pressure, electricity demand, pretreatment and redundancy. Whole-life cost per unit of saleable biomethane is more meaningful than equipment purchase price alone.

What is methane slip?

Methane slip is methane lost from an upgrading plant in permeate, tail gas, process water or other reject streams. It reduces product yield and can weaken the greenhouse-gas benefit of biomethane production.

Can upgraded biogas be injected into the natural gas grid?

Yes, provided it meets the relevant gas-quality, safety, metering, network-entry and regulatory requirements. Grid injection normally requires additional equipment beyond the upgrader itself.

What happens to the CO2 removed from biogas?

It may be discharged as biogenic CO₂, treated to reduce residual methane, recovered for industrial use or further purified and liquefied where a suitable market exists.

Can biomethane be used as vehicle fuel?

Yes. Upgraded biogas can be compressed as bio-CNG or liquefied as bio-LNG for suitable vehicles and transport applications.

Further Reading

• How to Eliminate CO₂ from Biogas – Scrubbing Explained – detailed coverage of CO₂ removal methods.
• Anaerobic Digestion Gas to Grid – a practical gas-to-grid example.
• 10 Uses of Biogas – where upgraded and raw biogas can be used.
• What Is Biogas? – the basics of raw biogas composition and production.

Conclusion

Biogas upgrading technologies turn a relatively low-calorific-value raw gas into a high-value renewable gas that can replace fossil natural gas in many applications.

Membrane separation, water scrubbing, PSA and chemical absorption are all proven commercial technologies, while cryogenic and biological systems are expanding the available options.

The best choice depends on more than methane purity. Methane recovery, energy demand, methane slip, pretreatment, maintenance, pressure, plant scale, operator capability and final gas specification all matter.

For project developers, the correct question is therefore not simply:

“Which biogas upgrading technology produces the highest methane percentage?”

It is:

“Which upgrading system will deliver the required biomethane specification reliably, with the lowest acceptable whole-life cost, methane loss and operating risk for this particular plant?”

[Published November 2014. Rewritten September 2026.]