Biogas Storage Tanks: Types, Selection, and Process Fit

'Biogas tank' is shorthand for several different vessels, and mixing them up is the fastest way to mis-specify a project. Some tanks digest the feed; others only store the gas; some are buried in a process train while others stand alone on a farm. This overview separates the types, the materials and the process numbers that actually drive selection.

A biogas tank is usually one of three roles: the digester (where anaerobic digestion happens, sized to 20-40 day retention at 35-38C mesophilic and 55-65% methane), the gas holder (storing biogas at 5-30 mbar, often a double membrane), and buffer/mixing tanks around them. Material choice follows the stream - GFS for the corrosive digester, stainless for aggressive streams, membrane for the gas. Select by role and chemistry, not by a single 'biogas tank' label.

The Three Roles

The digester is the reactor where microbes convert feed to biogas; its volume follows feedstock and hydraulic retention time. The gas holder stores the produced methane, typically at low pressure in a dual-membrane holder. Buffer, equalization and mixing tanks sit around the digester to steady the feed. Each is specified differently.

• Digester: reaction vessel, sized to retention.
• Gas holder: 5-30 mbar biogas storage.
• Buffer/mix tanks: steady the feed.

Material by Environment

The digester is the harshest zone - acidic liquor and an H2S-rich gas space - so GFS (inert glass face) is the common choice, with stainless (304/316L) for aggressive or high-chloride streams. The gas holder is usually a flexible membrane. Welded or bolted steel serves buffers depending on coating and budget.

• GFS: corrosive digester, inert face.
• Stainless 304/316L: aggressive streams.
• Membrane: flexible gas holder.

The Numbers That Size It

Digester sizing hinges on hydraulic retention time (commonly 20-40 days), mesophilic temperature (35-38C) and the resulting methane content (55-65%). These set both the digester volume and the gas-holder capacity. Getting the retention right matters more than the tank shape.

Project Reference

Biogas tanks in service span the family: the South Africa biogas reactor (2017, 2 x 32.87 m digesters), the France biogas plant (2020, SS304 bolted roof digester), and the Turkey biogas plant (2020, 2 x 3,727 m3 digesters with SS316 roofs). The Sweden biogas project (2024) used multiple GFS digesters with membrane roofs.

• South Africa 2017: 2 x 32.87 m GFS digesters.
• France 2020: SS304 bolted-roof digester.
• Turkey 2020: 2 x 3,727 m3, SS316 roofs.

Company Expertise

Center Enamel supplies the full anaerobic-tank family - GFS digesters, stainless digesters and membrane gas holders - with ISO 28765 design and process know-how across agricultural, municipal and industrial biogas.

Frequently Asked Questions

What is the difference between a digester and a biogas tank?

The digester is the reactor where digestion occurs; other 'biogas tanks' may only store the gas or buffer the feed. They are specified differently.

What material is best for a digester?

GFS for the corrosive, H2S-rich digester; stainless (304/316L) for aggressive or chloride-heavy streams.

How long is the retention time?

Typically 20-40 days at 35-38C mesophilic; retention sets the digester volume.

How is the biogas stored?

Usually in a double-membrane gas holder at 5-30 mbar, or as fixed-roof headspace pressure.

What methane yield should I expect?

Biogas from anaerobic digestion is commonly 55-65% methane; the exact figure depends on feedstock.

Can one tank do both digest and store gas?

Often the digester holds some headspace pressure, but dedicated membrane holders are used when gas storage is large.

'Biogas tank' hides three roles - digest, hold gas, buffer - and the right material follows the chemistry of each. Size the digester from retention and temperature, store the gas at low pressure, and choose GFS or stainless by the stream, and the system fits the process instead of fighting it.

Tell us your feedstock and gas strategy and we will lay out the digester, holder and buffer tanks your biogas plant actually needs.