Activated carbon for biogas purification removes selected contaminants that can damage engines, interfere with upgrading equipment or prevent gas from meeting its intended specification. Common applications include hydrogen sulphide removal and the adsorption of siloxanes and volatile organic compounds.
However, an ordinary activated carbon filter does not, by itself, turn raw biogas into biomethane. Removing trace contaminants and separating the bulk carbon dioxide are different treatment duties.
This guide explains where activated carbon fits into a biogas treatment system, how to select appropriate media and how operators establish when replacement is needed.
Originally published on 1 February 2026. Updated on 20 October 2026, incorporating revised material from our earlier main-site article published on 25 October 2019.
What Does Activated Carbon Remove from Biogas?
Activated carbon is a porous adsorbent. Molecules attach to its internal surfaces, while some specially treated grades also support chemical reactions that capture particular contaminants.
The appropriate carbon depends on the substance being removed and the conditions inside the filter. “Activated carbon” describes a family of materials, not one interchangeable product.
| Treatment duty | Why it matters | Main qualification |
|---|---|---|
| Hydrogen sulphide removal | Controls a toxic, corrosive contaminant and protects downstream equipment. | Requires media selected for the gas composition and operating conditions. |
| Siloxane removal | Reduces compounds that can form damaging deposits during combustion. | Performance depends on siloxane species, moisture and competing contaminants. |
| Volatile organic compound removal | Protects equipment and helps achieve the required gas quality. | Different compounds have different adsorption behaviour. |
| Bulk carbon dioxide separation | Raises methane concentration during biomethane upgrading. | Requires a dedicated separation process; an ordinary contaminant-removal bed is not equivalent. |
Calgon Carbon’s biogas application guidance describes several distinct carbon treatment duties. Product selection must follow the actual duty rather than a general claim that a carbon “purifies biogas”.
Activated Carbon Filters in a Biogas Plant
Gas passes through a bed of suitable carbon inside a purpose-designed vessel. The bed gradually accumulates contaminants and eventually needs replacement or an approved regeneration route.
Its position in the treatment system depends on the application. Carbon may provide final polishing after another hydrogen sulphide removal stage, or protect sensitive equipment before further gas processing.
The treatment train should follow the requirements of the intended use of the biogas. Engine fuel, boiler fuel and gas entering an upgrading plant do not necessarily need identical treatment.
Hydrogen Sulphide Removal
Hydrogen sulphide, usually written as H2S, is an important contaminant to control. Carbon grades used for this duty may be impregnated with reactive substances or have catalytic properties.
The capture mechanism and reaction products depend on the selected medium. It is misleading to describe every carbon as converting hydrogen sulphide through the same reaction.
For example, the manufacturer’s SULFUSORB 10 data sheet describes a copper-oxide-impregnated carbon. Its properties should not be assumed to apply to unrelated products.
Carbon treatment can be useful for polishing gas to a low outlet concentration. Where incoming H2S loading is substantial, comparing a bulk-removal stage followed by carbon polishing may help avoid excessive media consumption.
Ask suppliers to assess the contaminant mass arriving per hour, not just the gas flow. Two plants with the same gas flow can require very different carbon replacement schedules.
Siloxane and VOC Removal
Volatile siloxanes can occur in sewage-derived biogas and landfill gas. During combustion they can form silica-containing deposits that affect engines and other equipment.
Suitable activated carbon can adsorb these compounds. Volatile organic compounds, or VOCs, may also require removal, including substances that compete with siloxanes for adsorption capacity.
This means a carbon selected for one contaminant may not provide the required service life when exposed to the complete gas mixture. Gas analysis should identify relevant contaminants rather than assume every feedstock produces the same gas.
Follow the equipment supplier’s limits and sampling requirements. There is no universal siloxane concentration that guarantees suitability for every engine or application.
Our guide to biogas engines and generators explains why fuel quality affects reliability and maintenance.
Granular, Pelletised, Impregnated and Catalytic Carbon
These descriptions refer to different aspects of a product:
- Granular carbon: describes its physical form.
- Pelletised carbon: describes shaped particles, commonly cylindrical.
- Impregnated carbon: contains added substances intended to improve a particular treatment duty.
- Catalytic carbon: has properties that promote specified reactions.
A pelletised product can also be impregnated. Physical shape alone does not tell you which contaminants it removes.
Selection should consider gas composition, pressure, temperature, humidity, flow, target outlet quality, bed dimensions and acceptable pressure drop. Supplier capacity figures are meaningful only alongside their stated test conditions.
Humidity, Condensation and Oxygen
Moisture can influence carbon performance in different ways. Some H2S-removal mechanisms benefit from specified humidity, while liquid condensation within the bed can cause operating problems.
DESOTEC’s hydrogen sulphide removal guidance discusses the relationship between humidity, oxygen and breakthrough for particular carbon grades. Those conditions should not be generalised to every medium or treatment duty.
Use the supplier’s operating envelope. Any oxygen addition must be part of an engineered process with appropriate controls, rather than an operator adjustment made simply to improve adsorption.
How Do You Know When the Carbon Needs Changing?
Measure treatment performance. Carbon can lose useful removal capacity while gas still flows through the vessel normally.
Breakthrough occurs when the target contaminant begins passing through the bed at an unacceptable concentration. It is different from physical blockage.
A monitoring plan should address:
- Inlet and outlet contaminant concentrations.
- Gas flow and changes in loading.
- Pressure drop across the bed.
- Temperature and moisture conditions where relevant.
- Sampling frequency, alarm limits and replacement criteria.
Pressure drop helps identify flow restrictions, but does not prove that adsorption capacity remains. Smell is not a safe or reliable way to judge hydrogen sulphide breakthrough.
Do not adopt a universal monthly change interval or a fixed number of cubic metres per kilogram of carbon. Actual service life depends on the complete operating conditions and the required outlet limit.
Lead–Lag Filters and Media Replacement
Some installations use two vessels in series. The lead vessel performs the main treatment, while the lag vessel provides further protection.
Sampling between the vessels can help identify breakthrough from the first bed before the final outlet exceeds its limit. Changeover arrangements must be designed to maintain the required protection.
This differs from keeping a separate standby vessel ready for use. The appropriate configuration depends on treatment reliability, maintenance arrangements and the consequences of off-specification gas.
Spent carbon needs a planned handling route. Depending on its composition and captured contaminants, specialist reactivation, regeneration or disposal may be appropriate. Regeneration is not available for every medium or a suitable improvised on-site procedure.
Carbon handling also requires appropriate precautions. Manufacturer guidance warns that wet activated carbon can deplete oxygen in enclosed spaces. Isolation, gas freeing, temperature control and vessel access should follow the equipment and media suppliers’ procedures.
Does Activated Carbon Produce Biomethane?
An ordinary carbon filter removing H2S, siloxanes or VOCs generally leaves most of the bulk carbon dioxide in the gas.
Biomethane production normally requires a dedicated upgrading process, such as membrane separation, water scrubbing, amine absorption or pressure swing adsorption. Some specialised adsorption systems use carbon-based materials, but their engineered separation cycles are different from a simple contaminant-removal filter.
Likewise, an ordinary carbon bed should not be assumed to remove nitrogen to the required specification. Nitrogen separation is a distinct process duty.
Our guides to upgrading biogas to biomethane and biogas upgrading technologies explain the wider treatment choices.
Frequently Asked Questions
Can any activated carbon clean biogas?
No. The grade must suit the contaminants, gas conditions and target outlet quality. Carbon sold for another application should not be assumed suitable.
Is activated carbon filtration the same as adsorption?
The equipment is commonly called a filter, but contaminant capture mainly involves adsorption and, for some media, chemical reactions. It is not simply mechanical particle filtration.
Does carbon cleaning increase methane production?
A downstream gas-cleaning bed treats gas already produced. It does not directly increase biological methane production inside the digester.
Can one carbon bed remove H2S and siloxanes?
Some systems address multiple contaminants, but media compatibility, competing adsorption and outlet requirements must be assessed. Separate treatment stages may be preferable.
What determines the cost?
Consider the complete cost of compliant gas treatment: vessels, media consumption, monitoring, pressure losses, maintenance, changeouts and spent-carbon handling. Purchase price per kilogram alone is an incomplete comparison.
Does removing H2S make biogas safe to breathe?
No. Treated biogas remains a combustible gas mixture and can create an oxygen-deficient atmosphere. Gas cleaning does not make it breathable.
Conclusion
Purifying biogas using activated carbon filtration techniques with replenishment of spent carbon media using off-site regeneration of the carbon media is a popular method of biomethane production in the anaerobic digestion industry.
Further sources of information on siloxane removal from biogas (landfill gas) are the specialist landfill gas engine and turbine equipment manufacturers.
Within this market, the primary criterion for a biogas cleaning technology is efficacy. For instance the ability to remove siloxanes to a level where the biogas is no longer a danger to use in delicate motors. Ideally, this would be below the 100 parts-per-billion range.
Other desired characteristics include ease-of-use (the ability for a technology to be dropped into an existing biogas production process). This being without extensive engineering, with ease-of-handing, and cost-effectiveness. via landfill-gas.com
Further reading: Activated Carbon For Biogas Purification – Techniques: A One Page Guide
[Published on 1 February 2026. Updated on 20 October 2026.]
Greetings! I’ve been following your blog for some time now and finally got the courage to go ahead and give you a shout out. Just wanted to say keep up the good work publicising the possibilities of the biogas process. We are all going through a big change in attitude caused by the coronavirus and recognise that we need to get back to basics and helping nature. Well done!
How can we tell if the carbon filter is full? I’m not sure when to change the carbon media. Please express your thoughts.