Biogas is a renewable energy source with great potential. However, it contains hydrogen sulphide (H₂S), a toxic and corrosive gas that limits its use. Iron hydroxides are the safest and most effective solution for its removal. At Nalon Minerals, we offer N-Bio, a medium designed to maximise process efficiency and simplify operations in biogas plants.
How do iron hydroxides act in biogas
Iron hydroxides react directly with H₂S. They transform it into iron sulphide (FeS), a solid compound that separates from the gas. This chemical reaction is simple, does not require the addition of oxygen, and works under normal operating conditions.
In specialised products, such as formulations designed for the biogas sector, the medium can be partially regenerated by means of controlled aeration. This extends its useful life and optimises costs.
Advantages of iron hydroxides over other methods
1. High efficiency under different conditions
They remove H₂S stably even with varying concentrations. This flexibility makes them ideal for plants with fluctuating loads.
2. Guaranteed operational safety
No oxygen is introduced into the gas line, reducing ATEX risks and preventing explosive scenarios.
3. Easy integration into existing facilities
They can be dosed in situ in the digester or applied in external beds. They do not require complex modifications or additional equipment involving significant investment.
4. Simple and predictable maintenance
Monitoring is limited to checking H₂S output and media pressure drop. This allows replacement to be planned in advance.
5. Added value in digestate
The iron and sulphur present in the by-products are incorporated into the digestate. This can increase its agronomic value as a fertiliser.
Limitations and how to manage them
Although iron hydroxides are effective, they also present challenges. The medium becomes saturated over time, so it is necessary to monitor the quality of the biogas and plan for replacement. Partial regeneration is feasible in some products, although it depends on the H₂S load. The iron sulphide generated must be managed in accordance with local regulations.
Comparison with other H₂S collectors
| Method | Advantages | Inconvenients | Suitability |
| Injection of oxygen / air | – Reactive inexpensive and available. – Initial implementation is simple. – Reduces H₂S through oxidation. | – ATEX risk due to O₂–CH₄ mixture. – Requires sensors and continuous monitoring. – May affect methanogenesis in the digester. – Generates sulphur deposits. | Plants with very stable flows and a high technical level. |
| Activated carbon | – High adsorption capacity under optimal conditions. – Well-known and widely used technology. | – High cost due to frequent replacement. – Waste treated as hazardous. – Lower efficiency with flow variations or H₂S. – Sensitive to humidity and temperature. | Facilities with low-medium loads and high OPEX budget. |
| Iron hydroxides (N-Bio) | – Consistent efficiency even with fluctuations. – No oxygen in gas → maximum safety. – Predictable and competitive OPEX. – Easy integration (on-site dosing or external beds). – By-products enrich the digestate. | – Medium becomes saturated over time. – Requires replacement or partial regeneration planning. – FeS management in accordance with regulations. | Small, medium and large plants seeking security, simplicity and sustainability. |
Conclusion: an effective and safe solution
Desulphurisation with iron hydroxides is a solid alternative to other H₂S scrubbers. It offers high efficiency, operational safety and low maintenance. It also provides additional benefits such as digestate recovery. It is therefore establishing itself as the preferred option for biogas plants seeking profitability and sustainability.
Frequently asked questions about iron hydroxides
Is it safe to use iron hydroxide in biogas?
Yes. Iron hydroxides remove H₂S without introducing oxygen into the gas line, avoiding ATEX risks and simplifying plant operation.
Can iron hydroxide media be regenerated?
In certain formulations, such as N-Bio, the medium can be partially regenerated with controlled aeration. Viability depends on the H₂S load and operating conditions.
What is the cost of iron hydroxide compared to oxygen injection?
CAPEX for iron hydroxides is usually lower and OPEX more stable (planned replacement). Oxygen injection requires less expenditure on reagents, but involves high costs for sensors, monitoring and safety.
