13 Août 2026

Anaerobic Digester Tanks: Which Storage Solution for Biogas Production?

1,781

Anaerobic digestion plants were operating in France as of January 2025, with approximately 70% located on agricultural farms.

Source: Observ'ER / ADEME, Anaerobic Digestion Market Overview, 2025.

15.5 TWh per Year

Biomethane injection capacity reached 15.5 TWh per year by the end of 2025, representing an 8% increase compared with the previous year.

Source: SDES, Biomethane Market Dashboard, Q4 2025.

1,678

Biomethane production sites were operating across Europe in June 2025, compared to 483 in 2018 — a 3.5-fold increase in just seven years.

Source: European Biogas Association (EBA), European Biomethane Map, 2025.

Anaerobic digestion has become a key pillar of the global energy transition. By converting organic waste into renewable energy and valuable by-products, biogas plants contribute to both decarbonization and circular economy objectives. However, achieving optimal performance depends heavily on selecting the right digester and storage infrastructure. The choice of tank directly influences plant efficiency, reliability, maintenance requirements, and long-term profitability.

Key Takeaways

Anaerobic digestion converts organic materials into renewable energy and nutrient-rich digestate.
Storage tanks must withstand corrosive effluents and anaerobic operating conditions.
Proper sizing depends on feedstock volumes, retention time, and expected gas production.
APRO Industrie tanks are factory-coated (glass-fused-to-steel, stainless steel, or Duplex systems); capacities of up to 1,500 m³ can be delivered using a standard truck, and tanks can be dismantled, relocated, or expanded as projects evolve.

How an Anaerobic Digestion Plant Works?

Before selecting a storage solution, it is useful to understand the biological process behind biogas production.

Anaerobic digestion is a biological process in which microorganisms break down organic matter in the absence of oxygen. The process generates methane-rich biogas and produces digestate, a nutrient-rich residue that can be used as an agricultural fertilizer.

The Anaerobic Digestion Process

Anaerobic digestion occurs through four successive biological stages: hydrolysis, acidogenesis, acetogenesis, methanogenesis. During these stages, bacteria convert agricultural residues, organic waste, manure, and industrial by-products into methane within a sealed and temperature-controlled tank. Feedstocks may originate from agriculture, food and beverage industries, municipal organic waste streams and wastewater treatment facilities

The process also generates renewable heat and produces digestate that can be reused as a valuable soil amendment.

Contribution to Renewable Energy Production

Biogas can be upgraded into biomethane and injected into natural gas networks, or it can be converted into electricity and heat through combined heat and power (CHP) systems. By transforming waste into energy, anaerobic digestion helps reduce greenhouse gas emissions, decrease dependence on fossil fuels, and support local energy production.

Storage Challenges in Biogas Plants

Biogas facilities handle large volumes of liquids throughout the process. Incoming substrates, digesting slurry, and outgoing digestate all require dedicated storage infrastructure designed to withstand demanding operating conditions.

Reliable containment is essential to ensure environmental protection, process stability, and regulatory compliance.

Technical Requirements for Digester Tanks

Storage tanks used in anaerobic digestion plants must meet several critical requirements:

Chemical resistance to aggressive agricultural and industrial effluents.
Compatibility between internal coatings and feedstock characteristics (pH, sulfur content, and organic acidity).
Complete gas-tightness to prevent biogas leakage.
Resistance to anaerobic environments and temperature fluctuations.
Easy access for inspection and maintenance.
Compatibility with biogas upgrading and gas treatment systems.

One of the main challenges comes from hydrogen sulfide (H₂S), a highly corrosive gas naturally generated during digestion and particularly aggressive toward steel structures and equipment.

Safety and Regulatory Compliance

Anaerobic digestion (methanization) plants are classified under the ICPE regime (Installations Classified for Environmental Protection), primarily under category 2781 for the digestion of non-hazardous waste. Depending on the plant's treatment capacity, the facility may require either a simple declaration or an administrative authorization issued by the prefecture. The latter requires an environmental impact assessment and a public consultation process.

Tanks are directly subject to these obligations:

Certified tank tightness/leak-proofing.
Biogas leak detection systems.
Overpressure safety devices.
Management of runoff water in contact with digestate.

Digestate storage tanks are also subject to the nitrates action program when the facility is located in a vulnerable zone.

From a technical standpoint, most digesters in France operate using the CSTR process (Continuous Stirred Tank Reactor): a cylindrical tank heated to between 35 and 42 °C for mesophilic digestion, with continuous agitation. This mode of operation imposes specific requirements in terms of tightness, thermal insulation, and wall resistance to the pressure variations associated with biogas production.

Available Tank Technologies

Two major technologies currently dominate the sector: industrial concrete tanks and steel tanks. Both solutions offer very different characteristics, and each plant requires a solution tailored to its specific needs and constraints.

Concrete vs. Bolted Steel Tanks

Criteria	Concrete Tank	Bolted Steel Tank
Installation Time	Several months	Several weeks
Modularity	Limited	High
Chemical Resistance	Good depending on coating	Excellent
Maintenance	Complex	Individual components replaceable
Gas Tightness	Variable	Excellent
Coating Application	Applied on site	Factory-applied
Transportation	Built in place	Up to 1,500 m³ delivered by standard truck
Site Footprint	Large	Compact
Relocatable	No	Yes

Advantages of Bolted Steel Tanks

Bolted steel tanks offer several decisive advantages for anaerobic digestion plants. Unlike concrete, whose lining is applied on-site, APRO panels arrive ready for assembly: glass-fused for general chemical resistance, and in stainless steel or Duplex for the more exposed courses. This eliminates the risk of application errors under real field conditions and significantly shortens construction time.

Transport is also optimized: up to 1,500 m³ of capacity can be shipped on a standard truck, reducing the project's carbon footprint.

The land footprint is limited, making this solution competitive even on urban or peri-urban sites with space constraints.

Finally, the structure is fully demountable and relocatable, allowing the facility to be expanded or moved as the project evolves.

APRO Equipment for a Complete Anaerobic Digestion Plant

An anaerobic digestion facility isn't limited to a single digester. Each stage of the process requires specific equipment, sized and lined according to the demands of the stream being treated.

Anaerobic digesters: The heart of the facility. The digestion tank receives the substrates and ensures anaerobic fermentation under controlled temperature, tightness, and pressure conditions.

Hydrolysis tanks: Positioned upstream of the main digester, they carry out the first stage of breaking down solid matter before it enters the digestion process.

Post-digesters: Extend digestion beyond the main tank to maximize biogas production and reduce residual organic matter content in the digestate.

Digestate storage tanks: At the end of the process, digestate must be stored before land application. These tanks are particularly exposed to residual sulfur compounds and require suitable linings.

Sludge silos: Designed for storing sludge from agro-industrial or municipal processes, complementing facilities with high solid-matter output.

Hygienization tanks: Mandatory for certain substrate categories (domestic organic waste, fats, etc.), these raise material temperature to 70 °C for at least one hour before entry into the digester, in compliance with sanitary regulations.

Degassing towers: Remove dissolved gases from the digestate, particularly H₂S (hydrogen sulfide), before storage or land application. They contribute to both facility safety and the quality of the recovered digestate.

Criteria for Selecting a Tank

Tank selection depends mainly on the substrates treated, the volumes to be stored, and expected performance.

Substrate Compatibility

Chemical compatibility of the interior lining is a top priority. Anaerobic digestion effluents—such as slurry, digestate, and acidic substrates—generate H₂S, a particularly corrosive compound. APRO tanks meet this requirement with a glass-fused lining on the main wall, a stainless steel or aluminum roof, and the top two courses built in stainless steel for the most exposed areas.

Capacity and Sizing

Storage capacity depends on inlet volumes and hydraulic retention time (between 20 and 40 days). Sizing must also account for seasonal variations in activity. For example, for a livestock operation processing 10,000 m³ of slurry per year with a 30-day retention time, the required tank volume falls between 800 and 1,000 m³ — a standard capacity within the APRO range.

APRO Industrie Expertise

Since 1987, APRO Industrie has specialized in the design, manufacture, and installation of bolted steel tanks for industrial liquid storage. Our solutions support biogas projects ranging from small agricultural digesters to large-scale industrial biomethane facilities.

We adapt every solution according to:

Feedstock characteristics.
Site constraints.
Environmental conditions.
Operational requirements.

DISCOVER APRO DIGESTERS

Our tanks are available in capacities ranging from 4 m³ to 10,000 m³ and can be customized to meet project-specific requirements.

Comprehensive Project Support

From feasibility studies through commissioning, APRO Industrie provides complete project support.

Our teams assist clients with:

Engineering and sizing.
Tank selection.
Installation supervision.
Commissioning.
Preventive maintenance.

Whether for individual farm digesters, agricultural cooperatives, or large industrial biogas facilities, every solution is engineered to meet the site's technical requirements.

FAQ about Anaerobic Digester Tanks

What is the purpose of an anaerobic digester tank?

An anaerobic digester tank converts organic waste into biogas through anaerobic biological processes. The resulting biogas is used to produce renewable energy, while digestate can be used as fertilizer.

Which type of tank is best for a biogas plant?

Bolted steel tanks are often preferred due to their modular design, rapid installation, corrosion resistance, and ease of maintenance. Concrete tanks may be suitable for certain very large-scale projects with longer construction schedules.

What are the main challenges in anaerobic digestion facilities?

The primary challenges include:

Chemical resistance to organic effluents.
Complete liquid and gas tightness.
Regulatory compliance.
Accessibility for maintenance and inspection.

Why choose a steel tank for anaerobic digestion?

Factory-applied coatings ensure consistent quality and eliminate the need for on-site coating or lining work. Bolted steel tanks are easy to transport, install, expand, relocate, and maintain throughout their service life.

How is a digester tank sized?

Sizing depends on feedstock volume, hydraulic retention time, gas production objectives, and operational constraints. APRO Industrie provides customized engineering support to optimize tank dimensions.