Removing hydrogen sulphide from biogas is a technical necessity. But as more plants move towards biomethane production, the bigger question is changing: how much should H2S removal continue to cost once the plant is running?
Hydrogen sulphide is one of the most problematic contaminants in raw biogas.
It is corrosive and must normally be reduced before biogas can be used in CHP engines or upgraded to biomethane. But for operators looking at how to remove H2S from biogas, removal efficiency is only part of the decision. Chemical consumption, variable sulphur loads and downstream protection also affect long-term plant economics.
This is where the difference between biological desulphurisation and chemical H2S removal becomes important.
Chemical H2S removal comes with recurring inputs
Several established technologies can remove hydrogen sulphide from biogas.
An iron sponge uses iron oxide to react with H2S. Activated carbon adsorbs H2S and is often used where low residual concentrations are required. Chemical scrubbers, including caustic scrubbers, remove H2S through reactions with chemical reagents.
These technologies can be effective, but they depend on consumables.
Reactive media eventually becomes exhausted, chemicals must be replenished, and spent materials handled or disposed of. As gas volume or sulphur concentration increases, consumption typically increases with it.
The issue is therefore not whether chemical systems can remove H2S. They can. The more relevant question is what the plant manager must continuously buying and replacing throughout its operating life.
What’s the difference between biological desulphurisation and chemical desulphurisation?
Biological systems take a fundamentally different approach.
Instead of relying primarily on consumable chemical media, biological desulphurisation uses specialised microorganisms to convert hydrogen sulphide into elemental sulphur or sulphate.
In a biological trickling filter reactor, microorganisms convert H2S under controlled conditions. The process still requires air, water and nutrients, but avoids continuous replacement of large quantities of reactive media or chemicals.
For plants with continuous gas production and significant H2S loads, that can create a more stable operating-cost structure.
Biogasclean uses this principle in its DS-BTR and DS-MBR systems, which are designed to handle variable gas volumes and H2S concentrations with limited operator intervention.
The H2S load does not stay constant
That ability to respond to changing conditions matters because biogas production is rarely static.
Changes in feedstock can alter both gas production and sulphur concentration. With consumable technologies, higher H2S loads can mean faster media saturation or greater chemical consumption.
Biological systems can adapt to changing sulphur loads within their designed operating range, helping to stabilise operating costs and reduce the need for manual operator attention.
How can I reduce OPEX in a biogas plant?
H2S treatment is only one part of a biogas plant’s operating expenditure, but its cost impact extends beyond the desulphurisation system. Direct costs include media, chemicals, transport, replacement and disposal, while unreliable H2S removal can create additional downstream costs.
In the presence of moisture, H2S contributes to highly corrosive conditions. That can affect blowers, heat exchangers, engines and other downstream equipment. In biomethane plants, effective pretreatment also protects the equipment used later in the upgrading process.
This makes H2S removal part of a larger asset-protection strategy.
A low-cost treatment step is not necessarily inexpensive if unstable performance increases maintenance requirements or threatens more valuable downstream equipment.
For that reason, the economics should be evaluated across the gas train rather than at the H2S removal vessel alone.
Activated carbon and chemical treatment still have a role
The comparison is not an absolute biological-versus-chemical choice. Activated carbon, for example, can be useful for polishing when very low H2S concentrations are required, while chemical treatment may suit specific gas volumes, contaminant loads or operating conditions.
The distinction is often between bulk removal and final polishing.
Using consumable media for the complete H2S load can create significant ongoing consumption. Using biological desulphurisation for bulk removal and reserving polishing technologies for the final gas specification can reduce that exposure.
The more useful question is therefore not which single technology is best.
It is where each technology should be used in the gas-treatment process.
H2S removal becomes more important when producing biomethane
This becomes particularly relevant when the goal is grid-quality biomethane.
Raw biogas contains methane and carbon dioxide together with water and contaminants. Before upgrading, H2S must be reduced to protect downstream equipment and support reliable gas treatment.
Depending on feedstock and final gas requirements, additional treatment such as siloxane removal or VOC removal may also be necessary.
Biogasclean’s approach places biological desulphurisation at the front of the gas-treatment process, with further upgrading and polishing technologies applied according to the required gas quality.
That puts the H2S system in a different context.
Its job is not simply to produce a good outlet measurement. It is to create stable conditions for everything that follows.
The comparison changes over the lifetime of the plant
This is where biological desulphurisation can outperform chemical H2S removal.
Not because chemical technologies are unable to remove hydrogen sulphide, but because the long-term operating model is different.
At low sulphur loads or where final polishing is required, a consumable treatment technology may be entirely appropriate.
But as gas volumes, H2S loads and operating hours increase, the economics increasingly depend on what the plant must continue purchasing and replacing.
For long-life biogas and biomethane facilities, the most important H2S figure may therefore not be the outlet concentration.
It may be the cost of keeping it there.
