How to Eliminate CO2 from Biogas? “Scrubbing” Explained

Here we explain how to Eliminate CO₂ from Biogas, (or CO₂ Scrubbing). Biogas can be upgraded to pipeline natural gas quality (biomethane) for use as a renewable natural gas, but as part of the upgrading process, it will be necessary to remove the carbon dioxide (CO₂) from the biogas. This upgraded gas may also be used for cooking, residential heating and as vehicle fuel. So there are many good reasons for removing the CO₂. 

Article Summary: How to Remove CO2 from Biogas

• Raw biogas is composed of 25–45% CO2, which must be eliminated before it can be utilized as pipeline-quality biomethane or renewable natural gas.
• Scrubbing is the general term for the CO2 removal process — and there are several methods, each appropriate for different scales and budgets.
• Water scrubbing is the most commonly used method, capable of increasing methane content from approximately 58% all the way up to 82% in a single pass.
• A surprisingly simple option using iron wool and PVC pipe can remove CO2 at a small-scale level — and it actually works.
• Selecting the incorrect scrubbing method for your plant size can cost you significantly in efficiency and operating expenses — continue reading to discover which method is suitable for your setup.

Raw biogas is beneficial, but if left untreated it loses a lot of energy value — and CO2 is the main culprit.

When organic matter decomposes in an anaerobic digester, it produces a gas mixture known as biogas. The valuable component of this mixture is methane. However, CO2 is also present, which reduces the energy content and makes the gas unsuitable for use in natural gas pipelines and most high-efficiency applications. The process of removing this CO2 is known as scrubbing. This is what turns raw biogas into biomethane, a truly competitive renewable fuel. For those interested in learning more about the equipment and systems used in this process, BiogasPurifier.com offers detailed technical information on carbon dioxide scrubbers and upgrading systems.

The Problem with CO2 in Biogas and Why It Matters

The problem with CO2 in biogas isn't that it's harmful — it's that it's worthless, and it decreases the energy output of your biogas. CO2 doesn't burn. It doesn't produce heat. It simply occupies space in the gas mixture, lowering the calorific value and making it more difficult to use the gas efficiently on a large scale.

• CO2 lowers the calorific value (energy content) of the gas
• It makes biogas incompatible with natural gas grid injection
• It reduces the efficiency of gas engines and turbines running on biogas
• Combined with moisture, it can form carbonic acid, which corrodes pipelines and equipment
• It limits the commercial value of the gas as a fuel product

The CO2 present in biogas must be eliminated — not just reduced — for the gas to reach its full potential as a renewable energy source. That's the whole point of the upgrading process.

The Composition of Biogas

Raw biogas produced by an anaerobic digester typically consists of approximately 50–75% methane (CH4) and 25–45% carbon dioxide (CO2), along with minor amounts of water vapour (H2O), hydrogen sulphide (H2S), nitrogen (N2), and trace oxygen (O2). The exact composition can vary based on the feedstock — for example, food waste digesters usually generate more methane than agricultural waste systems — but in all cases, CO2 is the primary contaminant that must be removed.

2022 Update: Think Laterally and Consider Hydrogenation

Why is it Necessary to remove CO2 for Pipeline-Quality Gas?

There are strict quality standards that natural gas grids must adhere to. In most countries, the gas that is injected must contain at least 95–98% methane by volume. Raw biogas, which at best contains 50–75% methane, does not meet this standard without being upgraded. Even off-grid applications such as vehicle fuel (biomethane as compressed natural gas) or industrial heat need a much cleaner gas than what is produced directly from a digester.

Getting rid of CO2 also has a lot to do with the lifespan of your equipment. When CO2 and water vapour — which is almost always found in raw biogas — mix, they create carbonic acid. This acid can eat away at metal pipelines, compressors, and gas engines over time, causing them to have a shorter lifespan and significantly increasing the cost of maintenance.

“CO₂ Removal & Biogas Separation …” from www.mtrinc.com and used with no modifications.

What Makes Biomethane Different from Unprocessed Biogas?

Biomethane is nothing more than biogas that has undergone an upgrade. This upgrade purifies the gas until it is chemically identical to natural gas derived from fossil fuels, but it is made entirely from organic waste. The upgrade process eliminates CO2, H2S, water vapor, and other trace contaminants, leaving behind a high-purity methane stream that can be used in any application that requires natural gas.

• Untreated Biogas: 50–75% CH4, 25–45% CO2, trace H2S and H2O
• Refined Biomethane: 95–99% CH4, <3% CO2, almost no H2S

The increase in methane concentration is what makes the refinement process — and specifically CO2 scrubbing — so financially beneficial for biogas plant operators.

Unpacking the Term “Scrubbing”

When we talk about scrubbing in relation to biogas, we're referring to any process that selectively removes unwanted gases — mainly CO2 and H2S — from the biogas stream, while leaving the methane untouched. The term has its roots in industrial gas processing, where to “wash” or “scrub” a gas is to pass it through a medium that absorbs or filters out certain components. Depending on the method used, this medium could be water, a chemical solvent, a solid adsorbent material, or a semi-permeable membrane. For those interested in the broader benefits of biogas technology, you can explore more about biogas plant benefits.

All scrubbing techniques work in the same way: they use the fact that CO2 behaves differently from methane under different physical or chemical conditions. CO2 is more soluble in water than methane. It adsorbs more readily onto certain materials under pressure. It passes through certain membranes faster. Each scrubbing technology uses a different method to take advantage of these differences and extract the CO2 from the gas stream.

Water Scrubbing: The Prevalent Method of Removing CO2

Water scrubbing is the most commonly used method of upgrading biogas across the globe, and for good reason — water is inexpensive, non-toxic, and incredibly efficient at absorbing CO2 and H2S when the conditions are right. The process is entirely physical, which means that no chemical reactions occur, keeping the operating costs relatively low and making the system easy to maintain.

The basic idea is straightforward: CO2 and H2S dissolve in water much more readily than methane does. When biogas under pressure is exposed to water, the CO2 and H2S are absorbed into the water, while the methane is largely unscathed. The water is then regenerated — either released or stripped of the gases it has absorbed and reused — and the upgraded gas, which is rich in methane, leaves the system.

“CO2 Removal from Biogas by Water …” from www.sciencedirect.com and used with no modifications.

Step-by-Step Process of Water Scrubbing

First, the biogas is pressurised and then sent to the bottom of a packed absorption column. Water is introduced from the top and flows downwards through the column, counter-current to the rising gas. The two streams meet in the packed bed media, where CO2 and H2S are transferred from the gas phase into the water. The methane-rich gas exits from the top of the column, and the water, now loaded with CO2, exits from the bottom. In closed-loop systems, this water is sent to a desorption column where the pressure is reduced, and the absorbed gases are released. This process allows the water to be reused.

Why Methane Doesn't Dissolve in Water While CO2 and H2S Do

The difference in how these gases interact with water comes down to their molecular structures and solubility. CO2 has a strong chemical affinity for water because it reacts with it to form carbonic acid (H2CO3), even at the physical absorption level. H2S also dissolves easily in water because it is a polar molecule. On the other hand, methane is a nonpolar molecule and has a very low solubility in water, meaning it doesn't mix with water the way CO2 does. This difference in behaviour is exactly why water is such an effective and selective scrubbing medium for upgrading biogas.

Simple Iron Wool Water Scrubbing System for Small-Scale Plants

For small-scale or farm-level biogas systems, a remarkably effective CO2 and H2S scrubber can be constructed using basic materials. The typical setup involves a section of 4-inch PVC pipe (approximately one foot long) filled with steel wool — the same type used for pot scrubbing — inserted into the gas line. This is connected to a water scrubber column and a 500-litre water tank, with two storage tubes used to store pre-scrubbed (raw) biogas and post-scrubbed (purified) biogas, respectively. Results from systems like this have shown methane content increasing from 58% to 82% after scrubbing, with noticeable reductions in both CO2 and H2S.

“iron wool packed bed …” from www.researchgate.net and used with no modifications.

Pressure Swing Adsorption (PSA): CO2 Removal at an Industrial Level

Pressure Swing Adsorption is a leading technology for biogas upgrading on a large scale, especially when a steady, high-purity biomethane output is necessary. Unlike water scrubbing, which depends on liquid absorption, PSA operates by pushing pressurized biogas through vessels filled with solid adsorbent materials. These materials are usually activated carbon, zeolite molecular sieves, or carbon molecular sieves. They have a strong attraction for CO2, water vapor, nitrogen, and oxygen, but not for methane.

A typical PSA system uses four vessels in a row, each filled with adsorbent media. As biogas flows through under pressure, CO2 and other impurities bind to the adsorbent surface while methane passes through. When the adsorbent becomes saturated, the pressure is rapidly reduced (the “swing”), causing the adsorbed gases to release and regenerating the vessel for the next cycle. The four-vessel configuration allows continuous operation by cycling each vessel through adsorption, depressurisation, regeneration, and re-pressurisation phases in sequence, ensuring uninterrupted methane output.

How PSA Works to Separate CO2 from Methane

PSA systems separate gases at the molecular level. They use carbon molecular sieves and zeolites, which have pore structures that are just the right size to trap CO2 molecules. At the same time, they let the smaller, less reactive methane molecules pass through without any trouble. When the pressure is increased — usually to somewhere between 4 and 10 bar — CO2 attaches to the surface of the media at a much higher rate than methane. This effectively removes it from the gas stream each time the gas goes through the vessel.

The high purity of biomethane that a well-designed PSA system can deliver is what makes it a particularly effective method. Biomethane can be produced with methane concentrations above 97%, which meets the most stringent pipeline injection standards. The CO2, nitrogen, and oxygen that are captured during the adsorption phase are vented or recovered during the pressure-swing regeneration cycle. This process keeps the adsorbent material active without needing chemical regenerants or large volumes of water.

Why Large Biogas Operations Prefer PSA

PSA systems are designed for large-scale operations. They manage high gas flow rates efficiently, and because the system is fully automated, cycling through its four-vessel adsorption sequence without the need for manual intervention, it is perfect for continuous industrial operations where downtime can be expensive. Biogas plants that process hundreds or thousands of cubic meters of gas per hour are ideally suited to PSA upgrading systems.

Running a PSA system is expensive due to the energy needed to compress the biogas, which is necessary for the adsorption process to work. On the other hand, you don't need to handle any chemical consumables, treat any wastewater streams, and the adsorbent media lasts a long time before it needs to be replaced. If your plant is big enough, it might be more cost-effective to use PSA instead of water scrubbing once you're dealing with a certain amount of gas.

PSA doesn't just get rid of CO2. It also captures water vapour, nitrogen, and oxygen from the biogas stream, which means you get a cleaner final product without having to treat each contaminant separately. This ability to remove multiple contaminants at once is one of the main reasons why big biogas operators prefer PSA when they're upgrading to grid-injection quality biomethane.

“Biogas Scrubbing , Compression …” from www.semanticscholar.org and used with no modifications.

Membrane Separation: Filtering CO2 on a Molecular Scale

Membrane separation is one of the more sophisticated methods used in the upgrading of biogas. This technique involves passing biogas under pressure through a semi-permeable membrane. This membrane is usually made from hollow-fibre polymeric materials and allows CO2 and other small molecules to pass through while keeping methane on the high-pressure side. There is no need for water, chemicals, or moving parts in the separation stage itself.

The main factor that makes membrane separation work is the difference in pressure on either side of the membrane surface. CO2 can pass through most polymeric membrane materials much more easily than methane can. So, when biogas is pressurised and comes into contact with the membrane, the CO2 rushes through to the side with lower pressure, while the methane builds up on the side with higher pressure. This results in a concentrated, purified stream of methane that is ready for use or to be injected into the grid.

Understanding Membrane Systems

Membrane upgrading units work by first compressing and drying raw biogas. This process removes moisture that could potentially harm the membrane material. Once the gas is dried and pressurised, it is sent into a module that contains thousands of hollow fibre membranes bundled together. As the gas flows through or around these fibres, CO2, H2S, water vapour, and oxygen are able to permeate through the walls of the membranes and are collected as a low-pressure waste stream. The methane-enriched gas that remains on the retentate side is then exited as upgraded biomethane. Many commercial systems use two or three membrane stages in series to achieve higher methane recovery rates and minimise methane slip, which is when valuable methane is inadvertently lost in the permeate stream.

The amount of methane that can be recovered greatly depends on the design of the system and the number of membrane stages. Single-stage systems can recover about 85–92% of methane, while multi-stage configurations can recover over 99% of methane, making them competitive with PSA and amine scrubbing for high-value uses such as vehicle fuel or grid injection.

Benefits Over Other Scrubbing Techniques

Membrane systems are compact and have fewer moving parts, which means they require less maintenance and can be installed in places where space is limited. They are also modular — to increase capacity, you simply add more membrane modules instead of having to redesign the entire system.

They can be started and stopped almost instantly, unlike chemical scrubbing systems, which makes them ideal for plants that produce gas at varying rates. The main downside is that the materials used in membranes can be damaged by H2S or siloxanes, so raw biogas usually needs to be pre-treated before it can be processed by the membrane. For more insights on the advantages of biogas systems, explore the benefits of biogas plants.

“Integrated Energy Industries Pte Ltd …” from www.integratedenergyindustries.com and used with no modifications.

Gas Treatment Techniques Using Chemicals and Amines

Chemical absorption techniques are fundamentally different from physical scrubbing in terms of CO2 removal. Instead of using differences in solubility or molecular size, chemical absorption uses a reactive solvent, most commonly an amine-based solution. This solution chemically bonds with CO2 molecules as soon as they come into contact, thereby removing them from the gas stream with high selectivity and efficiency. For more information on the benefits of biogas, you can explore this detailed guide on biogas plant benefits.

The most commonly used chemical solvents for improving biogas are monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). These amine compounds interact with CO2 in a reversible way, creating stable compounds at absorption temperatures and then releasing the CO2 again when the solvent is heated during the regeneration process. This ability to reverse the process is what makes amine scrubbing economically feasible — the solvent can be recycled over and over again through absorption and regeneration cycles, instead of being used up in each cycle.

Amine scrubbing is famous for providing some of the purest biomethane — often surpassing 99% methane content — and also accomplishing very low CO2 slip in the product gas. This level of selectivity and purity makes it appealing for applications where gas quality requirements are strict, such as direct grid injection in markets with tight regulatory specifications.

Chemical Scrubbing Explained

Usual solvents: MEA, DEA, MDEA
Achievable methane purity: >99%
CO2 selectivity: Very high
H2S removal: Yes (at the same time)
Solvent regeneration: Necessary (thermal, ~120–150°C)
Best for: Large-scale, high-purity biomethane production
Main disadvantage: High energy requirement for solvent regeneration

How CO2 is Chemically Bound by Amine Scrubbing

When biogas comes into contact with the amine solution in the absorption column, the CO2 reacts with the amine molecules to create carbamates and bicarbonates — stable compounds that keep the CO2 in the liquid phase. The CO2-loaded solvent then moves to a regeneration column (also known as a stripper), where it is heated to between 120–150°C. At this temperature, the chemical bond between the amine and CO2 is broken, releasing the CO2 as a concentrated gas stream and returning the amine solution to its active state for recirculation back to the absorber.

Why Use Chemical Absorption Instead of Physical Methods?

When you need the cleanest possible product and the biogas feed has a low H2S content, amine scrubbing is the best method to use. The amine solution reacts strongly and selectively with CO2, making it a better choice than water scrubbing and PSA when you need to keep methane losses as close to zero as possible.

One of the main drawbacks of chemical scrubbing is its energy usage. To regenerate the amine solvent, a lot of thermal energy is needed, usually in the form of steam. This increases operational costs and the carbon footprint unless there's waste heat from a combined heat and power (CHP) unit available on-site. For biogas plants that already have a CHP system running, the waste heat can be used for the amine regeneration process, significantly improving the overall energy efficiency of the upgrading system.

For operations of a medium size, which fall between small farm systems and full-scale industrial plants, MDEA-based scrubbing often provides the right balance between purity and operating cost — particularly when the plant already has heat recovery infrastructure in place.

CO2 Removal by Cooling: How to Extract Dry Ice from Biogas

The basic principle of cryogenic CO2 separation is simple: CO2 turns into a liquid or a solid at much higher temperatures than methane. If you cool a pressurised stream of biogas to extremely low temperatures — as low as −78°C — the CO2 will condense out of the gas and can be captured as liquid CO2 or dry ice (solid CO2), while the methane stays in the gas phase. This process can produce a stream of biomethane that is more than 99% pure, and the captured CO2 can be sold as a product — liquid CO2 for industrial use, food-grade CO2, or dry ice — turning a waste stream into a source of additional revenue. The downside is that the refrigeration systems needed to reach and maintain these low temperatures use a lot of electricity, so this method is usually used only in large-scale operations where it is economically beneficial to recover CO2.

How to Choose the Right CO2 Scrubbing Method for Your Biogas Plant

There isn't a one-size-fits-all solution. The scrubbing technology that will be best for your biogas plant depends on several factors. These include the volume of gas you produce, the intended final use of the biomethane, your existing infrastructure, and the balance between your available upfront capital and the ongoing operating costs you can manage. It's crucial to make the right choice. If you select an oversized industrial system for a small farm digester, or a basic water scrubber for a grid-injection operation requiring high-purity, you'll end up with poor economics and operational difficulties.

Small to medium-scale operations — such as farm digesters, community biogas plants, or pilot systems — often start with water scrubbing. The iron wool packed-bed system is a good option because it doesn’t require a lot of money to start and can be built with basic materials. Even a simple PVC and steel wool scrubber connected to a 500-litre water tank can increase methane content from 58% to 82%. This isn’t pipeline quality, but it’s a big improvement for off-grid energy use.

If you're running a large biogas operation and your goal is to inject the gas into the grid or use it as vehicle fuel, then PSA and membrane systems are your best bet. They offer the efficiency, automation, and purity you need to meet commercial and regulatory standards. If your plant has access to waste heat, you should also consider amine scrubbing. The thermal energy needed to regenerate the solvent can be offset by your existing CHP infrastructure.

Cryogenic separation is a unique method. It's ideal for large plants where the CO2 has a commercial value. This could be for food-grade CO2 production or industrial gas supply. This turns the upgrading process into a dual-income operation instead of just a cost center.

Small to Medium Scale: Start With Water or Iron Wool Scrubbing

If you're running a farm-level digester or a small community biogas system, a water scrubber — particularly one using a packed iron wool bed — is where to start. The capital cost is minimal, the materials are widely available, and the performance gain is real. Raising methane content from 58% to 82% won't get you to pipeline quality, but it will meaningfully improve combustion performance, reduce corrosion risk in your gas lines, and increase the practical energy value of every cubic meter of gas your system produces.

“Biogas scrubber – Blonergy Biogas” from blonergy.com.ng and used with no modifications.

On a Larger Scale: PSA and Membrane Systems for Better Efficiency

When your biogas plant is producing gas at a level that requires industrial upgrading infrastructure, PSA and membrane systems are the technologies to seriously consider. Both can consistently produce biomethane with over 97% methane purity, with fully automated operation and little manual intervention.

PSA systems are especially good for plants with a constant, high-volume gas output, where the four-vessel adsorption cycle can run continuously without interruption. Membrane systems offer a more modular path – you can scale capacity by adding membrane modules rather than redesigning the core system, which gives operators more flexibility as production volumes grow over time.

Both methods' energy costs are primarily driven by compression. Before entering either a PSA vessel or a membrane module, the biogas must be pressurized, and this compression load is your main operating cost. When considering the total cost of ownership, the energy cost of compression should be calculated against your local electricity tariff and compared to the revenue value of the upgraded biomethane you will produce.

What You Should Consider Before Choosing a Method

Before you settle on a CO2 scrubbing technique, you should think about these essential factors:

• Gas volume: How many cubic meters per hour does your digester produce? Small volumes favor water scrubbing; large volumes favour PSA or membranes.
• Target purity: Off-grid energy use can tolerate 80–85% methane. Grid injection requires 95–99%.
• H2S concentration: High H2S levels in raw biogas may require pre-treatment regardless of which CO2 removal method you choose.
• Available utilities: Amine scrubbing requires thermal energy. Do you have waste heat from a CHP unit that can offset that cost?
• CO2 end use: If there's a commercial market for CO2 near your plant, cryogenic separation turns a cost centre into a revenue opportunity.
• Capital vs. operating cost balance: Water scrubbing has low upfront cost but higher water handling requirements. PSA has a higher capital cost but lower consumable expenses over time.

Upgraded Biogas Opens the Door to Bigger Opportunities

Eliminating CO2 from biogas isn't just a technical checkbox — it's the step that transforms a useful but limited fuel into a fully competitive renewable energy product. Biomethane can be injected directly into the natural gas grid, used as compressed renewable natural gas (CNG) for vehicle fleets, sold as a certified green gas commodity, or used in high-efficiency industrial processes that raw biogas simply cannot power.

The scrubbing step is where biogas graduates from a local energy solution to a scalable, tradeable renewable fuel that can compete directly with fossil natural gas — on energy content, on reliability, and increasingly on economics as carbon pricing and renewable fuel incentives continue to strengthen globally.

Commonly Asked Questions

How much CO2 does raw biogas usually contain?

Depending on the feedstock and digester conditions, raw biogas usually contains about 25% to 45% carbon dioxide by volume. The rest is mainly methane (50–75%), with minor amounts of hydrogen sulphide, water vapor, nitrogen, and trace oxygen.

Biogas produced from food waste digesters usually contains a higher percentage of methane, while that produced from agricultural residue and manure-based digesters often contains less. However, regardless of the source, CO2 is the main impurity that must be removed before the gas can be used in high-efficiency or grid-connected applications.

Can water scrubbing eliminate both H2S and CO2?

Indeed, water scrubbing can get rid of both CO2 and hydrogen sulphide (H2S) at the same time. These two gases are much more soluble in water compared to methane, so they mix with the scrubbing water as it moves in the opposite direction to the pressurized biogas flow. This ability to remove two gases at once is one of the reasons why water scrubbing is a practical method for biogas upgrading.

With smaller iron wool systems, the steel wool has a secondary function beyond simply providing physical packing. It also reacts chemically with H2S to create iron sulphide compounds, which offers another level of H2S removal in addition to the water absorption effect. This means that iron wool scrubbers are especially good at reducing both target contaminants in one affordable unit.

What level of methane purity is needed for biomethane that is of pipeline quality?

The standards for pipeline injection can change depending on the country and the operator of the grid, but the usual standard for biomethane that is of pipeline quality is a methane content of 95–98% by volume. Typically, the CO2 needs to be below 2–3% and H2S needs to be below 5 mg/m³. There are some grids that have more strict specifications depending on where the injection point is specifically and what the applications downstream are.

When it comes to vehicle fuel applications (such as biomethane as CNG or LNG), they often require similar purity levels. However, industrial heat applications can tolerate slightly lower methane concentrations. If you're aiming for grid injection or vehicle fuel as your end use, you can rely on PSA, multi-stage membrane systems, or amine scrubbing to consistently deliver the required purity levels.

Is it possible to capture and reuse CO2 removed from biogas?

Definitely — and in cryogenic separation systems, CO2 recovery is the primary objective. The CO2 that is liquefied or solidified during cryogenic upgrading can be sold as industrial-grade liquid CO2, food-grade CO2 for the beverage industry, or dry ice. In amine scrubbing systems, the concentrated CO2 that is released during solvent regeneration can also be captured and compressed for commercial use.

Even in water scrubbing systems, the CO2-rich off-gas from the desorption column can theoretically be captured, although this is less common at a small scale. Turning the CO2 stream into a marketable product is one of the most attractive economic reasons for investing in more advanced upgrading technologies.

Can I get rid of CO2 from biogas without breaking the bank?

Absolutely — and the iron wool water scrubber is the perfect example. You can put together a simple CO2 scrubbing system using materials that are easy to find and won’t cost you an arm and a leg. This makes it a great option for small-scale and DIY biogas projects.

Here is a list of the main elements you will need to construct a basic biogas scrubber using iron wool:

Main Components of a Basic Iron Wool Biogas Scrubber

• 4″ diameter PVC pipe section, approximately 1 foot (30 cm) long
• Steel wool (pot-scrubbing grade) to pack the PVC column
• 500-litre water tank connected to the scrubber column
• Two storage tubes: one for raw (pre-scrubbed) biogas, one for purified biogas
• Basic fittings to connect the column in-line with the biogas pipe

Expected result: Methane content raised from ~58% to ~82%; measurable reduction in both CO2 and H2S.

While a DIY system does have a limitation in terms of the purity of methane it can achieve, it still significantly improves the quality of your biogas. However, it won’t get you to 95%+ methane on its own. For personal use, off-grid cooking, or local power generation, that’s often sufficient — and the cost-to-benefit ratio is hard to beat at that scale.

Should your endgame be grid injection, vehicle fuel, or certified biomethane sales, a more advanced upgrading system will be required. However, it is perfectly reasonable to start with a basic water scrubber when your operation is still small. It enhances gas quality, shields your equipment from H2S corrosion, and provides you with practical experience with the scrubbing process before making a commitment to industrial-scale infrastructure.

What's important to remember is that you don't have to go all in when it comes to removing CO2 from biogas. You can start small and gradually increase your efforts as your production volume and commercial goals grow. The key is to actively work on reducing the CO2 content in your biogas instead of letting potential efficiency and energy go to waste.

Whether you're filling a PVC column with steel wool on a farm in rural India or setting up a 1,000 Nm³/h PSA upgrading system at an industrial anaerobic digestion facility, the goal is the same: remove the CO2, increase the methane, and get the most out of the renewable gas your digester is already producing.

For full technical specifications on carbon dioxide scrubbers and biogas upgrading systems suitable for any scale, check out BiogasPurifier.com. It's a useful resource for operators at all levels of the industry. Additionally, for those interested in the broader benefits of biogas technology, consider exploring the benefits of a biogas plant, but consider Biomethanisation by Hydrogenation

Instead of removing CO₂, as the sale of the CO₂ may be of limited value. Why not convert it to additional methane?

The sale of CO₂ from raw biogas can be difficult. This occurs due to concerns about its use as a waste-based product, with the potential for the presence of impurities, which make it unpalatable for use in food production.

Converting the carbon dioxide within a digester into methane by injecting hydrogen was a new idea at the 2022 Biogas Expo, and the word is that it is being done successfully in trials at several digester locations in the UK.

A paper published in June 2022 on the “Potential for Biomethanisation of CO2 from Anaerobic Digestion of Organic Wastes in the United Kingdom [Ref: 1], concludes as follows:

“Based on the available UK data, … significant increases in biomethane productivity could potentially be achieved, ranging from 38–68% for different feedstock types and equivalent to an overall uplift in the contribution of AD to UK bioenergy from 15 to 22%.

Again, there are many issues to consider: the current survey only looked at data on the highest level, and for realistic assessments of the potential scale and impact of technology application, it will be necessary to take into account both the end-uses of biomethane and techno-economic viability on individual sites. The potential contribution from CO₂ biomethanisation of organic wastes is large enough, however, to warrant consideration in both short and long-term planning.”

The following flow chart shows the hydrogen injection concept:

It appears that equipment, such as the GasMix Digester Tank Mixer systems supplied by Landia which normally re-inject biogas to aid mixing, is being modified to inject pure hydrogen generated on-site from solar cells.

Rumour has it that a remarkably higher biomethane output can be achieved, possibly as high as quoted in the above paper, “ranging from 38–68%”!

At the same time, the CO₂ concentration is drastically reduced, and the resulting quality of the biogas is rumoured to be close to gas grid injection quality.

Reference:

1. Bywater, A.; Heaven, S.; Zhang, Y.; Banks, C.J. Potential for Biomethanisation of CO₂ from Anaerobic Digestion of Organic Wastes in the United Kingdom. Processes 2022, 10, 1202. https://doi.org/10.3390/pr10061202

[Originally published: September 20018. Article Updated: July 2022. FAQs Added August 2023. Rewritten March 2026.]