Biogas plants – how do they work and where to use them?

What is a biogas plant? What is biogas?

A biogas plant is a technological installation in which the process of anaerobic fermentation (i.e., decomposition of organic matter without access to oxygen) of biomass takes place. Biomass is, for example, agricultural waste, food production waste, slurry and manure, or municipal bio-waste. As a result of fermentation, biogas is produced, which is a mixture of mainly methane (CH₄) and carbon dioxide (CO₂). The methane content in biogas is usually 50–70%, which makes it a valuable fuel.

Biogas can be used for:

• electricity production,
• heat production,
• powering cogeneration engines (in so-called biogas cogeneration),
• purification and injection into the gas network (in the form of biomethane).

What does a biogas plant consist of?

A typical industrial or agricultural biogas plant consists of several main elements:

• a raw material (substrate) storage facility – e.g., silos, tanks, silage halls, slurry, organic waste,
• a substrate supply system – devices (conveyors, pumps, dispensers) ensuring even feeding of the fermenter,
• a fermenter – the “heart” of the biogas plant. It is a tight, heated tank in which anaerobic fermentation takes place,
• a digestate tank – a place where fermented biomass (digestate) goes, often used as fertilizer,
• a biogas tank – a flexible dome or separate tank storing the produced biogas,
• a biogas purification system – removes hydrogen sulphide, water, and other contaminants, preparing the biogas for combustion,
• a cogeneration unit (CHP) – a device that converts biogas into electricity and heat,
• systems control and monitoring – they enable automation and control of the fermentation process.

What can be processed in a biogas plant?

In a biogas plant, fermentation leads to the decomposition of raw materials and gas production. However, what goes into the fermenter is crucial for the efficiency and quality of biogas. Biogas plants can use, among others:

• slurry and manure,
• silage (e.g., from corn, grass),
• waste from the food industry (whey, fats, slaughterhouse waste),
• plant waste from agricultural production,
• sewage sludge,
• municipal bio-waste.

It is important that the raw materials are properly prepared and mixed – this affects the efficiency of fermentation and the amount of biogas produced.

Does a biogas plant stink?

Odour is one of the most common concerns related to biogas plants, but modern installations are designed to minimise the emission of unpleasant odours. The tightness of the system is of the greatest importance – from storage and transport of raw materials, through fermentation, to storage of the digestate. Proper management of substrates (e.g., quick covering of silage, closed feeding systems) and regular cleaning and ventilation of technical facilities allow for significant reduction of unpleasant odours. In practice, a well-designed and properly operated biogas plant should not cause bothersome odours in the environment, even if it processes organic waste. Especially since each emission of odour is potentially associated with the loss of valuable gas.

Is biogas zero-emission?

Biogas is not completely zero-emission, but it is significantly less emission-prone than traditional fossil fuel-based energy sources. The combustion of biogas also produces CO₂, but this is carbon dioxide of biological origin, i.e., previously absorbed from the atmosphere by plants. Therefore, the emission balance is largely climate-neutral.

Biogas with a negative emission coefficient is also gaining increasing importance on the market. It is produced by fermentation of substrates that, in the event of uncontrolled natural decomposition (e.g., slurry, bio-waste), would emit significantly larger amounts of methane and carbon dioxide into the atmosphere than during controlled combustion of biogas. As a result, the emission balance for such a fuel is not only neutral but even negative. Biogas with a negative carbon footprint opens up new opportunities for the industry in the context of achieving climate goals.

"Biogas plants reduce methane emissions from uncontrolled decomposition of organic waste (e.g., slurry), which in natural conditions would be released into the atmosphere in a much more harmful form. For this reason, biogas plants are considered to support a low-emission economy, although they are not fully 'zero-emission' like photovoltaic installations." says Piotr Danielski PhD, President of the Management Board of DB Energy.

Advantages and disadvantages of biogas plants

Advantages of biogas plants:

• renewable energy source – biogas is produced from organic waste, which is constantly available and considered renewable,
• local energy production – reduction of transmission losses and independence from external energy suppliers,
• reduction of methane and CO₂ emissions – this means less burden on the environment,
• management of organic waste – especially in the agri-food industry,
• production of fertilizer – fermentate can replace artificial fertilizers,
• possibility of working in cogeneration – increased energy efficiency.

Disadvantages of biogas plants:

• high investment costs – especially in large industrial installations,
• complex technological process – requires knowledge, experience, and constant supervision,
• dependence on substrate suppliers – if the fermented waste does not come from own production,
• cost of disposal of fermentate – in cases where there is no possibility of using waste after fermentation from biogas plants, it should be disposed of,
• potential odour nuisance – with improper waste management.

Where are biogas plants best used?

Industrial biogas plants work best in places where significant amounts of organic waste are generated and there is a constant demand for energy and heat (in order to be able to effectively use, for example, cogeneration). The most typical industries include:

• food and agri-food industry – e.g., dairies, vegetable and fruit processing plants, meat plants,
• agricultural industry and large-scale farms – with access to slurry and silage,
• plants processing sewage sludge – e.g., sewage treatment plants,
• municipal and waste management plants – processing urban bio-waste.

Biogas cogeneration – a combination of electricity and heat production

Biogas cogeneration is a technology in which biogas is burned in a cogeneration unit to simultaneously produce electricity and heat. This achieves high energy efficiency, often exceeding 80%.

In practice, this means that:

• electricity powers the plant's installations or is sold to the grid,
• heat is used locally – e.g., for heating buildings, technological processes, or maintaining the fermentation temperature.

Biogas cogeneration is perfect for industrial plants that have a constant demand for energy and heat – it allows for a significant increase in the efficiency of biogas use and a shorter payback period.

Biomethane plant and biogas plant – what's the difference?

Biomethane plants are a modern development of traditional biogas plants, offering more advanced and efficient use of biomass. Unlike classic biogas production facilities, biomethane plants purify it into biomethane, which has parameters similar to natural gas and can be injected directly into the gas network. This process not only increases the energy value of the fuel produced but also enables its storage and transport over longer distances. Biomethane plants are also a real alternative to biogas plants if there is no heat recipient in the area, using gas combustion only to maintain the fermentation process and directing the entire surplus to the gas network. Importantly, biomethane can be used both in the energy sector and in transport, being an alternative to LPG or CNG.

To sum up, biogas plants and biomethane plants are a real alternative to traditional energy sources, especially in industry. They allow not only for the management of problematic organic waste but also for independence from external energy suppliers and reduction of its costs. Thanks to biogas cogeneration, it is possible to fully use the fuel produced, which makes this technology particularly attractive in the context of energy and economic efficiency.

Investing in a biogas plant can also be part of a broader ESG strategy and a response to EU environmental regulations. By producing energy from local, renewable raw materials, industrial plants not only reduce their carbon footprint but also strengthen the positive image of the brand as a responsible and innovative company. Combined with other energy efficiency solutions, a biogas plant can be an important step towards circular and sustainable production.