Biogas Desulphurisation: removal of hydrogen sulphide (H₂S)
With our biogas desulphurisation solutions, we remove hydrogen sulphide (H₂S) at source to produce clean biogas, protect equipment, reduce costs and maximise energy efficiency, ensuring safe, cost-effective and environmentally friendly processes.
What is Biogas Desulphurisation?
Biogas desulphurisation is the process of removing hydrogen sulphide (H₂S, also called sulfhydric acid) from raw (untreated) biogas.
This step is key to optimising biogas quality, as H₂S is a corrosive and toxic gas that must be removed before biogas can be used as an energy source. In the current transition to renewable energy, achieving clean biogas through biogas desulphurisation has become essential to harness this resource efficiently and safely.
Why is biogas desulphurisation necessary?
Desulphurisation of biogas is essential for several reasons:
Natural formation of H₂S
In anaerobic digestion, sulphur compounds in organic matter (e. g. sulphates and amino acids) are biologically converted into hydrogen sulphide (H₂S). In other words, H₂S occurs naturally in raw biogas as a result of the microbiological process that generates methane, so all raw biogas contains a certain proportion of this pollutant gas.
Harmful effects of H₂S
H₂S is highly toxic and corrosive. In high concentrations it can seriously damage human health and generate odours even at low levels. In addition, it causes accelerated corrosion of engines, piping and cogeneration equipment by combining with moisture to form hydrogen sulphide. In short, without removing H₂S, biogas would be hazardous to equipment, people and the environment.
Regulations and quality standards
For reasons of operational safety and environmental regulation, it is mandatory or highly recommended to remove almost all H₂S from biogas prior to energy utilisation. Complying with these standards not only avoids penalties and corrosion, but also ensures a methane gas with high calorific value and commercial value.
Our solution for biogas desulphurisation
Our product N-Bio has been specifically developed to capture H₂S in a simple and economical way. N-Bio is an iron-based compound (functional oxides and hydroxides) that is added directly to the fermentation reactor.
The technical benefits of N-Bio are remarkable: by removing H₂S at source, it improves reactor productivity and final biogas quality, and acts as a process stabiliser ( buffer effect). It also brings advantages in terms of operation and maintenance: by not requiring external equipment and expensive consumables, operating costs are reduced.
Advantages of the use of iron hydroxides in biogas desulphurisation
The use of an iron hydroxide compound stands out for several technical and operational advantages in H₂S removal. Our N-Bio range is proof of this, offering an effective and sustainable solution for biogas desulphurisation.
More efficient biogas desulphurisation process
Desulphurisation of biogas with our compound allows an earlier uptake of H₂S.
Improved productivity in the reactor
More biogas with higher percentage of methane. Lower CAPEX and OPEX.
Buffer effect
The kinetics of the N-Bio reaction gives it a buffering effect that prevents rapid rises in H₂S levels.
Corrosion risk minimised
The cost of equipment maintenance is reduced.
Deodorisation
Efficiently prevents the spread of unpleasant odours in and around the biogas plant.
Physical hazards and toxicity are avoided
It is not harmful to people, equipment or the environment.
Compost with higher added value
The use of N-Bio produces iron sulphide and pure sulphur, both of which improve the properties of the fertiliser.
No explosive mixtures, no risk
With N-Bio, biogas desulphurisation does not require oxygen injection. This eliminates risks associated with explosive mixtures and improves the safety of the operation.
On-site biogas desulphurisation methods
In-situ technology aims to remove or neutralise H₂S before it leaves the digester by acting directly within the digestion process. The most widespread strategy is the dosing of iron compounds into the anaerobic digester.
However, not all iron compounds act in the same way, and it is key to differentiate between ferric salts and iron hydroxides, as their behaviour, efficiency and technical requirements are different.
Iron hydroxides (as N-Bio)
Compared to ferric salts, iron hydroxides such as those used in the N-Bio range present a safe, efficient and easy to handle alternative for in-situ biogasdesulphurisation. They are applied in solid form ( powder or pellet) directly to the digester or feed system, reacting progressively with the H₂S.
Advantages:
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They are non-corrosive and non-toxic, which simplifies storage and handling.
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They generate a buffering effect that stabilises H₂S levels for longer, even if dosing is momentarily interrupted.
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They do not adversely affect the pH of the digester.
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They can improve the fertiliser value of digestate by incorporating iron and sulphur in assimilable forms.
Limitations:
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The reaction is more gradual compared to FeCl₃, so the decrease in H₂S is not immediate when first administered.
Ferric salts (such as ferric chloride - FeCl₃)
One of the most commonly used products is ferric chloride (FeCl₃). Its application is based on its high solubility and immediate reactivity with H₂S, which enables fast and effective biogas desulphurisation from the very beginning.
Advantages:
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Immediate reduction of dissolved H₂S in the digester.
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Competitively priced compared to other alternatives.
Limitations:
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It is a highly corrosive compound that acidifies the medium, which can affect the balance of the digester and the health of the active biomass.
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It requires the installation of a specific liquid dosing system, due to its toxicity, with corrosion resistant materials (pumps, pipes, containers…).
- Its liquid format complicates safe handling and storage.
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Does not provide a buffer effect: if dosing is stopped, H₂S levels may rise rapidly.
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It poses a high risk if not handled correctly, both to personnel and equipment.
Oxygen injection
Another in-situ technique that some plants employ for biogas desulphurisation is controlled oxygen injection or microaeration within the digester. This strategy consists of introducing a very small amount of oxygen (usually in the form of air) into the anaerobic environment, with the aim of oxidising H₂S to elemental sulphur through the action of oxidising bacteria.
Advantages:
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Can partially reduce the concentration of H₂S without the need for chemical additives.
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It does not require the addition of external compounds to the digester, which facilitates its implementation in some installations.
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In certain cases, it can generate usable elemental sulphur.
Disadvantages:
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High risk of overdosing: if too much oxygen is introduced, the anaerobic balance of the digester may be disturbed, negatively affecting methane production.
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Potential risk of formation of explosive mixtures if the amount of added oxygen is not strictly controlled.
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It does not always keep H₂S levels within the desired limits, especially at high sulphur loads.
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It requires a very precise injection system and often constant monitoring to avoid dangerous deviations.
Frequently asked questions
Do you need technical advice on the process? Our team is at your disposal to recommend the right solution for you. Please do not hesitate to contact us with any questions you may have.
What is biogas desulphurisation?
Biogas desulphurisation is the process of removing hydrogen sulphide (H₂S) from biogas produced in anaerobic digesters or landfills. In other words, it consists of scrubbing the biogas to remove this sulphur-rich pollutant gas. This results in a much cleaner and safer biogas, suitable for use as an energy source without causing corrosion or toxic emissions. There are different methods to achieve this H₂S removal but they all share the goal of minimising the hydrogen sulphide content in the biogas.
Why is it important to eliminate H₂S?
Removing H₂S from biogas is important for technical, economic and environmental reasons. On the technical side, H₂S is corrosive: if not removed, it will attack metal parts, causing breakdowns and high maintenance costs. . From a health and safety point of view, H₂S is a toxic gas – breathing biogas with high concentrations of H₂S can be very dangerous for operators. And environmentally, burning biogas with H₂S produces sulphur gases (SO₂) that cause pollution (acid rain). Therefore, by eliminating H₂S we protect the installation’s equipment, ensure the health of the personnel and avoid polluting the environment.
What solutions are available for desulfurization?
There are several biogas desulphurisation technologies, and they are often combined to achieve maximum efficiency. In general terms, the solutions can be grouped into:
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Dry physico-chemical methods: Such as adsorption on solids. Here the biogas is passed through materials that capture H₂S, e.g. iron oxide filters, impregnated activated carbon beds or zinc oxide cartridges. These are simple systems: the H₂S reacts chemically on the surface of the solid and the biogas comes out clean. .
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Biological methods: These use microorganisms in biofilters or trickling filters(biotrickling reactors). Bacteria convert H₂S into elemental sulphur or sulphate, achieving very effective removal with low operating costs. A small amount of air is required to give the bacteria oxygen, keeping the process under control.
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Absorptionmethods (scrubbers): These involve washing the biogas with a liquid. This can be a physicalwash with high pressure water, where the H₂S is dissolved in the water; or a chemicalwash with special solutions (e .g. caustic soda, amines, chelated iron solutions ) that react with the H₂S and remove it from the gas. These systems can remove H₂S at very low levels, although they involve handling the liquid afterwards (regeneration or disposal).
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In-situ technology: This consists of preventing H₂S from being generated as a gas. It is achieved by dosing certain compounds into the digester; the most common is to add iron salts to the substrate, which precipitate the sulphide in solid form and prevent H₂S from reaching the biogas. Another variant is to inject traces of oxygen (microaeration) into the digester to oxidise the H₂S there. These in-situ techniques are often complementary to the previous ones, reducing the H₂S load that the other solutions have to treat.
In practice, the choice of solution depends on plant size, H₂S concentration, purity requirements and economic considerations. For example, small agricultural plants sometimes only dose iron, while a large biomethanisation plant may combine biofilter + activated carbon as final polishing. In any case, there are many solutions, and specialised companies (such as ours) can help to determine the most suitable one for each project.
What are the advantages of iron hydroxides in biogas desulphurisation?
Iron hydroxides are a highly efficient and safe solution for biogas desulphurisation. Their application allows hydrogen sulphide (H₂S) to be removed early in the anaerobic digestion process, improving the quality of the biogas at source. Unlike other compounds, iron hydroxides do not generate explosive mixtures and do not require oxygen injection, which significantly reduces operational risks.
Among its main advantages are the following:
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Higher H₂S capture performance, resulting in cleaner biogas with higher methane content.
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Reduction of corrosion in motors and equipment by removing H₂S before it comes into contact with the system.
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Improved digester productivity, thanks to its buffer effect that stabilises sulphide levels and avoids inhibitions in the process.
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Simplicity of application, with dosing systems that are easy to install and maintain.
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Safety and sustainability, as they are non-toxic to personnel and the environment, and provide a digestate with higher added value as a fertiliser.
In summary, iron hydroxides represent a reliable and sustainable alternative for plants looking for efficient and technically uncomplicated biogas desulphurisation.
How does N-Bio work?
N-Bio is our specialised solution for desulphurising biogas directly in the digester. It is a product formulated with iron compounds (oxides and hydroxides) that is dosed into the feed stream or into the anaerobic digester. Once inside, N-Bio reacts chemically with the H₂S generated by the bacteria, transforming it into solid compounds: mainly iron sulphide (FeS) and elemental sulphur. These compounds are trapped in the digestate sludge and no longer pass into the biogas, thus achieving in-situ desulphurisation. This process occurs continuously as the digester produces biogas – the product acts as a “chemical sponge” capturing H₂S as it is formed.
Thanks to this mechanism, N-Bio eliminates the need to install external filters or add subsequent cleaning stages. Its operation is very simple and safe: it does not require the addition of air (avoiding risks), it does not generate foam or negatively impact the microorganisms in the digester. On the contrary, by lowering the concentration of dissolved H₂S, it contributes to a friendlier environment for methanogenic bacteria. In operational terms, using N-Bio is as easy as using any nutrient or liquid additive: you set the optimum dosage according to the sulphur concentration you want to remove and the biogas flow rate, and the dosing system takes care of the rest. In short, N-Bio works by trapping the sulphur from the biogas inside the digester, ensuring that the outgoing gas is virtually H₂S-free, all with simple implementation and a positive impact on overall plant performance.