IRON HYDROXIDE is a ferric hydroxide-based additive (FeO(OH)) formulated to combat hydrogen sulphide in biogas, with a focus on fast-acting H₂S control. It can be used in daily H₂S management, similar to iron oxide, but is particularly effective when you need to quickly address spikes of H₂S in the biogas. When your digester experiences sudden surges in H₂S levels – perhaps due to a transient feedstock issue or a disturbance – IRON HYDROXIDE reacts swiftly to sequester the sulphur. This helps maintain safe H₂S concentrations and prevents those spikes from causing harm to the biogas utilisation equipment or the microbial process. Additionally, like other iron additives, it contributes iron to the digester, aiding in overall biological stability. IRON HYDROXIDE is recommended for AD installations that periodically face high H₂S challenges and require a robust solution to keep levels in check.
Fast Reaction to H₂S Spikes: IRON HYDROXIDE has a high reactivity, allowing it to quickly capture sudden increases in hydrogen sulphde. This makes it ideal as a “shock treatment” when H₂S levels threaten to rise beyond normal.
Continuous Sulphur Control: Beyond just emergencies, it serves as a reliable daily H₂S control additive. Regular use lowers overall H₂S content in biogas, reducing the need for extensive gas scrubbing downstream.
Prevents Process Inhibition: By binding H₂S, the additive prevents the inhibitory effects of sulphide on your digester’s microbes. A well-buffered sulphide level means methanogens and other bacteria can operate without sulphide toxicity, keeping methane production robust.
Augments Iron Levels: IRON HYDROXIDE adds bioavailable iron into the fermenter, which can help stabilise the digestion process if your feedstock is low in iron. Iron is important for enzyme systems and can enhance breakdown of certain compounds.
Equipment Protection: With effective sulphur removal at the source, your CHP engines, boilers, and gas pipelines see less corrosion and wear, prolonging their life and reducing maintenance costs (similar benefit as iron oxide, just often even more needed when spikes occur).
Iron hydroxide operates on a similar principle to iron oxide – by chemically reacting with hydrogen sulphide. The active substance, ferric hydroxide [FeO(OH)], when introduced into the anaerobic digester, will encounter sulfide (S²⁻) and hydrogen sulfide (H₂S) present in the slurry. In effect, IRON HYDROXIDE converts H₂S gas into solid iron sulphide precipitate. This precipitate stays mixed with the digestate and eventually exits with it, thus removing H₂S from the biogas phase.
Ferric hydroxide is often considered slightly more reactive or faster-acting in wet conditions compared to ferric oxide, due to its hydroxide form which can be more readily soluble. This means IRON HYDROXIDE can begin scavenging sulphides very quickly after dosing, which is why it’s favored for spike control. The presence of iron hydroxide can also co-precipitate other contaminants and provide trace iron to microbes. The net effect is a rapid drop in H₂S gas levels after application, and maintenance of those low levels with continuous use.
From a biological standpoint, by removing H₂S, IRON HYDROXIDE alleviates stress on methane-forming microbes that can occur if H₂S accumulates. This ensures the fermentation process continues smoothly even during what would have been a “sour” event. In summary, the mode of action is chemical neutralisation of sulphide, working swiftly to guard both the process and the equipment from sulphur’s harmful effects.
IRON HYDROXIDE can be used in two modes:
Preventative Daily Dosing: Similar to iron oxide, you might add IRON HYDROXIDE every day as part of your routine to keep baseline H₂S levels low.
Curative Spike Dosing: Kept on hand to add quickly when you detect a rising H₂S trend (for instance, if a monitoring sensor shows an upward spike or if high-sulphur feedstock was added).
In practice, many operators will incorporate a small daily dose and have the flexibility to increase the dose if needed. The product is a powder that can be added via:
Solid feed hopper: Mix the iron hydroxide powder with your substrates or drop the soluble bag in.
Liquid recirculation line: Sometimes, powders can be mixed with a bit of water and added through a recirculation pump or injector to spread it quickly.
Top feeding port: Dumping the powder directly into the top of the digester (if accessible) for rapid distribution.
Dosage guidelines: IRON HYDROXIDE is typically added in quantities similar to iron oxide. It can be added daily into the solid loading system or premix tank, with or without water-soluble packaging. Specific amounts will depend on your H₂S levels:
For ongoing use, an approximate starting point might be on the order of 0.5–1 kg per 100 m³ of digester volume per day (this is a rough estimate; for a 1,000 m³ digester that might be 5–10 kg/day).
To combat a spike, you might temporarily double or triple the daily dose until H₂S is under control.
Always consult the product guidance or a Realistic Agri specialist to tailor the dose. They may recommend doing a sulphide test on your digestate to know how much free sulphide is present and dose accordingly. Since IRON HYDROXIDE comes in 20 kg bags on 1000 kg pallets, you might measure out a portion of a bag each day. If using water-soluble bags, each bag could be sized for a certain daily dose (e.g., a 500 g or 1 kg soluble packet per feeding for smaller plants).
When handling dosing, try to distribute the powder or packets across the feeding period (if you feed multiple times a day, split the dose accordingly) so that the iron is always present to catch H₂S as it’s produced.
IRON HYDROXIDE is provided as a powder, typically packaged in 20 kg biodegradable paper bags, with large orders delivered as 1000 kg (1 tonne) pallets of those bags. The bags are water-soluble, which allows adding the whole bag without opening it.
Storage: Keep the bags palletised in a dry storage area. The material should not get wet before use, as moisture will cause it to clump or react prematurely. It’s best stored similarly to iron oxide – off the ground, covered, and away from direct moisture.
Handling: Wear appropriate PPE such as dust mask, gloves, and eye protection when handling the powder. Ferric hydroxide can be a yellow-brown color and is fine like talcum; it will create dust if not handled gently. If using water-soluble bags, the handling is easier – just avoid puncturing the bags. During application, ensure any mixing equipment (if used to pre-mix with water) is corrosion-resistant (plastic or stainless) since iron compounds can be a bit abrasive. Clean any equipment or surfaces that come into contact with the powder to avoid staining or lingering dust.
Because IRON HYDROXIDE may be used sporadically for spikes, make sure partially used bags are sealed tightly to avoid absorbing moisture from the air. The product is stable, so leftover material from a spike event can be stored for future use as long as it’s kept dry.
IRON HYDROXIDE can be viewed as both an insurance policy and a performance enhancer for your biogas plant:
Damage Prevention (Insurance): By suppressing H₂S spikes, it prevents sudden damage or shutdowns. A single H₂S surge that goes unchecked could cause a costly failure (for instance, damaging an engine’s exhaust system or causing a sulphuric acid corrosion issue). Using IRON HYDROXIDE avoids these catastrophic costs, which by itself may pay for the product many times over.
Maintaining Power Output: H₂S spikes can force operators to temporarily throttle down CHP engines or flare gas to avoid damage. With effective control, you keep generating power at full capacity, securing your revenue. In this way, IRON HYDROXIDE indirectly secures your income stream by ensuring gas quality remains within usable range.
Reduced Consumable Costs: Facilities often treat biogas H₂S either in-situ or ex-situ. If you rely on external gas scrubbing (like iron sponge, carbon, or liquid scrubbers), using IRON HYDROXIDE in-situ can reduce the frequency of media change-outs or chemical use. This saves on purchasing those consumables and the labour to maintain them.
Microbial Health = Efficiency: By keeping the microbial inhibitors at bay, your digester can run at optimum health, meaning more biogas per feedstock input. Over time, that higher efficiency (even if a few percent) accumulates into more kWh produced. Essentially, you’re ensuring that a potential efficiency loss due to sulphide stress is averted – a subtle but important ROI factor.
Versatility and Longevity: Unused IRON HYDROXIDE doesn’t go bad quickly – if your plant’s H₂S is under control, the product can sit until needed. This means your investment is not wasted; you have a tool ready for when a problem arises. Think of it as having a fire extinguisher in the control room: inexpensive relative to the asset it protects, and invaluable when needed.
In financial terms, the cost of daily iron hydroxide dosing is typically minor compared to the gains of prolonged engine life, consistent output, and fewer operational hiccups.