METHO-FILTER is an innovative biogas filtration medium designed as an alternative to traditional activated carbon filters for removing hydrogen sulphide and other impurities from biogas. It consists of specially formulated iron hydroxide pellets (Fe(OH)₃) that physically and chemically scrub H₂S out of the gas stream. These pellets are used to fill a filter vessel through which raw biogas passes before reaching your engine or upgrading equipment.
The key advantage of METHO-FILTER over regular activated carbon is its higher H₂S capacity and the fact that spent pellets can be reused within the biogas plant (for example, added into the digester), eliminating costly disposal of used media.
By using METHO-FILTER, biogas plant operators can extend the life of their CHP engines, reduce oil change frequency, and cut down on the recurring expense of purchasing and disposing of activated carbon.
High H₂S Removal Capacity: METHO-FILTER has a greater hydrogen sulphide filtering capacity than standard activated carbon filters. This means it can treat more biogas (or higher H₂S concentrations) before it becomes saturated, resulting in longer intervals between media changes.
No Disposal Costs: Unlike spent activated carbon (which often must be treated as special waste), spent METHO-FILTER pellets can be utilised in the biogas plant itself. For instance, once the pellets are spent, you can add them into the digester; the iron sulphide within them can break down and integrate into the digestate. This eliminates disposal costs and adds value back to the system.
Protects Engines and Equipment: By effectively removing H₂S and possibly other contaminants, METHO-FILTER prevents damage to CHP engines, generators, and boilers. This protection can result in significantly longer service life for engine components and exhaust systems, and it can extend the oil change intervals because the oil is not getting contaminated by sulphur acids.
Cost-Effective Operation: Although the initial media might be an investment, the extended life and reuse aspects make METHO-FILTER very cost-effective. You’ll spend less frequently on replacements and avoid fees for hazardous waste removal. Over time, this can be cheaper than constantly replacing activated carbon, particularly for plants with high H₂S levels.
Operational Flexibility: METHO-FILTER pellets come in different sizes (small and large) to be layered for optimal filtration. This gives flexibility in filter design and can minimise pressure drop while maximising contact with the gas. They can be used in existing carbon vessels (with some modifications) or new filter units designed for pellet media.
METHO-FILTER works through a combination of adsorption and chemical reaction. The filter is filled with iron hydroxide pellets, which have a high surface area and are chemically reactive with hydrogen sulphide:
As biogas flows through the bed of pellets, H₂S in the gas is adsorbed onto the pellet surfaces.
The iron hydroxide in the pellets reacts with H₂S to form iron sulphides (similar to how iron oxide/hydroxide powders react in a digester) – effectively binding the sulphur onto the pellet in solid form.
The result is that H₂S is removed from the gas, and the gas exiting the filter has a much lower H₂S concentration, making it safe for engines or gas upgrading.
Because these pellets can hold a lot of sulphur, their lifespan in operation is longer. When they do eventually become saturated with sulphur (i.e., mostly converted to iron sulphide), the media is considered “spent.”
However, instead of having to throw it away, those iron sulphide pellets can be added back into your anaerobic digester. Inside the digester, two things can happen:
(1) The iron sulphide remains as part of the digestate (essentially adding micronutrients like iron back to the system),
or (2) some sulphide might be released and immediately consumed by the ongoing digestion chemistry (which likely has fresh iron to capture it). In any case, it closes the loop for sulphur management and reduces waste.
Additionally, by removing H₂S more effectively, METHO-FILTER ensures that corrosive hydrogen sulphide doesn’t make it to the engine. This is why engines see less corrosion and oils don’t acidify as quickly – the filter is stopping those harmful compounds upstream. A secondary effect is that because you can layer large and small pellets (large ones at the base for support and flow distribution, small ones on top for fine filtration), the pressure drop across the filter can be kept moderate while still achieving high filtration efficiency. The large pellets (5–25 mm) create channels and prevent clogging, while the smaller pellets (2–8 mm) provide a dense bed for thorough H₂S capture.
Application: METHO-FILTER is used in a gas filtration vessel – typically a vertical or horizontal tank through which biogas is flowed (after it leaves the digester and before it reaches the engine or gas upgrader). To implement METHO-FILTER:
Fill the vessel: Pour in a layer of large pellets (5–25 mm) to form the base (about 20–30% of the vessel volume). These larger pellets ensure good gas distribution and support.
Top up with small pellets (2–8 mm) to fill the remaining ~70–80% of the vessel. These smaller pellets have higher surface area for H₂S capture.
Make sure the vessel is properly sealed and the gas flow is set to pass uniformly through the pellet bed. It may be useful to have flow distributors or screens to keep pellets in place.
Commissioning: Slowly introduce biogas flow and monitor the outlet H₂S. Initially, the filter will remove a large fraction of H₂S. If the outlet is near zero H₂S, you may increase flow or wait until some saturation occurs.
There isn’t a “dosage” per se like liquid additives – rather, you size the filter and amount of media based on your gas production and H₂S content. For example, if you produce 500 m³/hour of biogas with 2000 ppm H₂S, you’ll need enough pellet volume to handle that load for a given time. Realistic Agri or Methodo will provide guidance on how many kg of pellets per m³ of gas or per ppm of H₂S.
Usage & Maintenance: Check the H₂S levels after the filter regularly. When you notice H₂S slip (i.e., the H₂S level after the filter begins to rise indicating media saturation), it’s time to replace or regenerate media:
Replace/Recycle: Take the spent pellets out. They can be shovelled or vacuumed out of the vessel. Then refill the vessel with fresh pellets in the same layering as before. The spent ones can be carefully added into the digester (perhaps gradually over several days to avoid overwhelming the system with sulphide).
Interval: The interval between media changes could be several months to over a year, depending on the H₂S load and filter size. This is much longer than many activated carbon change intervals.
Safety note: Always depressurise and ventilate the filter vessel before opening it to remove pellets. The spent pellets might have absorbed not just suphur but also moisture and possibly CO₂; handle them with gloves (iron sulphide can generate a bit of odour or even slight heat if exposed to air, though typically it's safe). When adding to the digester, do so during feeding times to mix them in.
Compatibility: METHO-FILTER pellets can often be used in the same canisters that held activated carbon, with minimal modification (maybe adding a screen if pellet size is smaller than the carbon granules to prevent carry-over).
METHO-FILTER pellets are shipped in bulk containers:
Small pellets (2–8 mm size) are usually in big bags (~550 kg) or drums, since you often need a larger volume.
Large pellets (5–25 mm size) are often in 25 kg bags, which are easier to handle when layering the bottom of the vessel.
Upon receiving them, store the pellet bags in a dry area. The pellets can absorb moisture from the air (since iron hydroxide is somewhat hydrophilic), and you don’t want them to react or clump before use. Keep them in their original packaging until you’re ready to fill the filter.
When handling the pellets:
Personal Protective Equipment: Wear gloves (to avoid any possible irritation or just dirt on hands) and a dust mask. While pellets produce far less dust than powder, some fine particles may be present in the bags, especially with the small pellet size.
Pouring/Loading: The big bags might require a forklift or hoist to position over the vessel and a chute to pour. The 25 kg bags can be manually lifted and dumped. Take care to pour slowly to avoid dust clouds. If possible, avoid windy days or do it indoors.
Spent Media Handling: When removing spent pellets, again wear appropriate PPE. The pellets might smell of sulphur. They are not hazardous waste, but standard precautions for handling used filter media apply (use tools to avoid direct contact, ventilate area).
Disposal/Recycle: If you choose not to put spent media into the digester, it can typically be disposed of as solid waste or potentially used as a soil amendment if regulations allow (it’s basically iron with sulfur). But the beauty of METHO-FILTER is you don’t have to pay for special disposal, as you can recycle it into the AD system.
METHO-FILTER can significantly improve the economics of gas cleaning:
Lower Media Costs Over Time: While high-quality activated carbon is expensive and must be replaced frequently, METHO-FILTER’s longer life and reusability mean you buy media less often and essentially get more H₂S removal per pound of media purchased. Over a year, many plants find the cost of using METHO-FILTER is lower than the cost of the multiple carbon refills they would have needed.
Elimination of Disposal Fees: Spent carbon often requires special handling and disposal (sometimes even classified as hazardous if sulphur content is high). These fees add up. With METHO-FILTER, disposal costs drop to near zero because the media is not wasted – it’s fed to the digester as an iron source. This not only saves money but also aligns with sustainability (waste-to-value principle).
Engine Maintenance Savings: By providing extremely clean gas to your engines, you save on maintenance. Oil changes can be extended (some operators see significantly less frequent oil acidification), and engine overhauls can be postponed because components wear out slower. These maintenance savings can be quite large, improving the ROI of the system. One noted benefit is that METHO-FILTER can extend the oil change interval of the co-generator, which directly reduces oil and labour costs.
Avoided Downtime: Media changes for carbon can be a messy, time-consuming job often requiring contractors. If METHO-FILTER allows longer intervals and quicker change-outs, you have less downtime or derating of your plant. Every hour your engine runs at full power instead of being down for maintenance is income earned rather than lost.
Improved Biogas Yield (Indirect): When you recycle the spent media into the digester, the sulphur captured eventually ends up in the digestate rather than vented or combusted. In some cases, this can slightly improve the overall sulphur balance of your process (for instance, you might be able to tolerate a bit more protein in feedstock because you have a strong sulphur removal mechanism). More importantly, the iron added back could help with nutrient balance. These subtle process improvements might increase biogas yield or stability, which again contributes positively to your bottom line.
In conclusion, METHO-FILTER provides a smart economic advantage by turning a typically consumptive process (gas scrubbing with one-time-use media) into a more circular, cost-saving system. The investment in the filter media and possibly a dedicated vessel is paid back through ongoing savings in media replacement, disposal, and engine longevity – crucial factors for any biogas plant’s profitability.