IRON OXIDE is a ferric oxide-based additive (Fe₂O₃) used for daily hydrogen sulphide (H₂S) control in biogas plants. Hydrogen sulphide is a common biogas contaminant that can corrode equipment and reduce the quality of the biogas; IRON OXIDE helps tackle this problem directly inside the digester. This fine powder additive is introduced regularly to the fermenter, where it reacts with dissolved sulphides and H₂S, thus lowering the H₂S content in the biogas. By doing so, it protects the downstream equipment (like gas engines or scrubbers) and helps maintain a healthy microbial environment (excess H₂S can inhibit certain microbes). IRON OXIDE is especially recommended for installations that consistently need to reduce biogas H₂S levels and require additional iron to stabilise their biological process.
Reduces H₂S in Biogas: IRON OXIDE directly lowers the hydrogen sulphide concentration in the biogas, resulting in cleaner gas that often requires less scrubbing or cleaning downstream. This helps meet H₂S emission limits and protects engines from corrosive gas.
Prevents Biological Inhibition: By releasing iron into the fermenter, it prevents H₂S-related inhibition of the digestion process. Hydrogen sulphide in solution can be toxic to microbes; binding it with iron forms insoluble iron sulphide, reducing toxicity and odour.
Enhances Process Stability: Iron is an essential micronutrient for certain anaerobic bacteria. IRON OXIDE provides a source of iron that can help stabilise the biological process in the digester, especially if the feedstock is low in trace nutrients.
Operational Cost Savings: With less H₂S in the biogas, you’ll experience lower maintenance costs – engine oil lasts longer, gas filters and scrubbers have a lighter load, and you avoid corrosion damage. It can reduce the frequency of activated carbon replacements or chemical scrubbing, saving money.
Simple Daily Use: The product is applied as part of the daily routine, making it a straightforward solution to implement. It can be added along with feedstock, requiring minimal extra labour or changes to your process.
IRON OXIDE’s mode of action relies on the chemical reaction between iron oxide and hydrogen sulphide. When the fine powder is added to the digester, it disperses in the slurry. The ferric oxide (Fe₂O₃) reacts with dissolved sulfide ions (S⁻²) and H₂S gas present in the digestate, resulting in the formation of iron sulfides (such as FeS or Fe₂S₃). This reaction effectively locks up the sulphur in a solid form that remains in the digestate instead of releasing as H₂S gas. As a result, the biogas that bubbles out of the digester has a lower concentration of H₂S.
Additionally, the iron from IRON OXIDE serves a dual purpose: once it reacts, the iron is still in the system (as iron sulphide or other forms) and can be utilised by microorganisms or help precipitate other impurities (like phosphate). The continuous supply of iron can improve the nutritive balance of the digester if iron was a limiting element. Microbially, certain anaerobes that process sulphur compounds (like sulphate-reducing bacteria) will produce H₂S as a byproduct; having readily available iron means that H₂S is immediately captured, thereby reducing its inhibitory effect on methanogens. In summary, IRON OXIDE works by chemically scavenging hydrogen sulphide and fortifying the digester with iron, leading to cleaner biogas and a more stable environment for methane-producing microbes.
IRON OXIDE is intended for daily use. It is typically added into the digester feed system or mixing tank so that it disperses well:
Solid Feeding System: If your plant has a solid feeder (like a conveyor or hopper for substrates), you can sprinkle or dose the daily amount of IRON OXIDE powder onto the feedstock each day.
Premix/Slurry Tank: If there’s a premix tank, add the powder to this tank. It can be added directly or mixed with some process water first to help distribution.
Direct to Digester: In some cases, operators may blow or flush the powder directly into the fermenter.
The recommended dosage is to include IRON OXIDE in every daily feed cycle at a rate consistent with your H₂S levels. A general guidance from Realistic Agri is to dose each day via the solid loading system or premix tank. The exact amount will depend on the size of the plant and the H₂S challenge:
Smaller plants (e.g., farm-scale 100 kW systems) might start with a few hundred grams per day.
Larger plants (e.g., 1 MW) might dose multiple kilograms per day.
The dose can be adjusted based on biogas H₂S measurements – the goal is to find the amount that keeps H₂S consistently low without over-supplying iron.
It’s often beneficial to consult with a Realistic Agri representative to determine the starting dose. They might perform an analysis or use prior experience with similar feedstocks to recommend a quantity (for instance, “X kg per 100 m³ of digester volume per day”). It’s also important to distribute the dose well (don’t clump it in one spot) for effective H₂S capture..
IRON OXIDE is provided as a very fine powder (to maximise its surface area and reactivity). It typically comes in 25 kg biodegradable paper bags, arranged on 1100 kg pallets for bulk delivery. The biodegradable bags mean you can potentially add them whole if they are designed to dissolve, but often with fine powders, you might open the bag and scoop/apply as needed.
Storage: Keep the bags in a dry location to prevent clumping or premature reaction (the powder can absorb moisture from air). The powder is stable under normal conditions, but storing it off the ground and covered will maintain its quality. Avoid areas with extreme humidity or where the bags could tear.
Handling: As a fine powder, IRON OXIDE can be dusty. It’s advisable to wear a dust mask or respirator, gloves, and goggles when handling it to avoid inhalation or eye contact. The powder is not toxic, but inhaling any fine particulate isn’t healthy. Use dedicated scoops or feeders to handle the product. If it comes in soluble bags, handling is simpler – just move the bags and drop them in as needed (gloves are still good to have, as the bags can have powder residue). Be aware that iron oxide powder is a rusty brown color; it can stain skin or clothing and make a mess if spilled, so handle it carefully. Any spills should be swept up and can be added to the digester or disposed of as benign waste (since it’s essentially an iron compound found in nature).
Controlling H₂S with IRON OXIDE can yield substantial cost savings and protect your revenue streams:
Engine and Equipment Protection: Lower H₂S means less corrosion in gensets, gas boilers, and piping. This prolongs the life of engines and reduces the frequency of oil changes and overhauls. A well-protected CHP engine can save tens of thousands in maintenance over its lifetime. Those savings contribute directly to ROI by avoiding downtime and replacement costs.
Reduced Gas Cleaning: In instances where activated carbon or chemical scrubbers are used for H₂S removal, adding IRON OXIDE in the digester can lighten the load on those systems. Carbon filters will last longer before saturation, and chemical usage (like ferrous chloriaustic for scrubbers) can be reduced. Lower consumable usage translates to monthly operational cost savings.
Compliance and Biogas Utilisation: High H₂S can sometimes force flaring of biogas or reduced generator output to stay within emission limits. Using IRON OXIDE helps you fully utilise your biogas for energy without curtailment, maximising your income from FITs or RHI (incentives). Compliance fines or environmental fees are also mitigated.
Process Yield: While the primary role is H₂S scrubbing, you may also benefit from slightly enhanced biomethanation if iron was a limiting nutrient. More stable digestion (with no sulphide toxicity) can increase methane yield a bit, which adds to revenue.
Minimal Investment & Easy Implementation: The cost of IRON OXIDE additive is relatively low compared to major equipment. Its implementation is simple (no new machinery needed), so the payback is often immediate as soon as it starts reducing other expenses. When you consider the value of protecting a multimillion-pound biogas plant and ensuring continuous power generation, the peace of mind gains alone can justify the investment.
In essence, IRON OXIDE helps to safeguard your biogas plant’s performance and assets, which is a smart investment for any operator aiming for long-term profitable operation.