Anaerobic Digestion Tank: What It Is And What It Contains

An anaerobic digestion tank is the sealed, temperature-controlled vessel in which anaerobic microbes break down organic matter and release biogas, and understanding it means understanding its parts: a coated shell, a gas-tight roof rated for 5-30 mbar, process nozzles, and an internal environment split into a liquid zone and a gas zone with different chemistry. It is not merely a storage tank; it is a reactor, and the coating must follow the zone. Center Enamel builds anaerobic digestion tanks as GFS, FBE, stainless-steel and carbon-steel bolted vessels.

At its core the tank is a reactor, not a container. Inside, microbes convert organic feedstock - manure, food waste, sewage sludge, agricultural residue - into biogas over a retention time of 20-40 days at mesophilic 35-38 C. The tank holds a saturated slurry, keeps it warm, keeps it mixed, and keeps the biogas in. That combination of seal, temperature and coating is what separates a digestion tank from a simple water tank.

• A reactor, not just a container.
• Feed: manure, food waste, sludge, residues.
• 20-40 day retention at 35-38 C mesophilic.
• Seal, temperature, mixing and coating combined.

The shell carries the slurry and is coated for the liquid zone. The roof carries the gas and is rated for 5-30 mbar, often a flexible membrane. The nozzles handle feed in, digestate out, biogas out and mixer access. The weak point is the boundary where coating, gasket and metal meet at a process zone change, which is why the coating is specified per zone rather than across the whole tank.

• Shell: coated for the liquid organic-acid zone.
• Roof: 5-30 mbar membrane, gas-tight.
• Nozzles: feed, digestate, biogas, mixer.
• Weak point: coating boundary at zone change.

These product numbers define an anaerobic digestion tank and its specification: retention of 20-40 days at 35-38 C, feed total solids of 8-12%, gas pressure of 5-30 mbar on the roof, methane content of 55-65%, and per-zone coating - GFS 2C2F at 0.25-0.45 mm or FBE - confirmed by a 1,500 V holiday-spark test and a shell calculation to AWWA D103-19 and ISO 28765. They separate a true reactor from a simple storage tank.

A 2021 biogas engineering project in France used a single Glass-Fused-to-Steel bolted digestion tank of 2,215 m3. As a delivered digestion tank it demonstrates the product - a coated, gas-tight, temperature-rated vessel - built for European biogas duty. Diameter and height are not recorded in the verified project data and are reported Not Provided.

A digestion tank does not operate alone; the ancillary equipment defines the system. The mixer delivers the W/m3 power density and is specified with the tank, not bolted on later. The heating circuit holds 35-38 C and is routed through nozzles the tank already provides. The biogas train - flame arrester, relief, water seal, detection - connects at the roof. Digestate and feed pumps complete the loop. Specifying the tank with its ancillaries in one package is what keeps the gas-zone boundary intact and commissioning short.

• Mixer specified at W/m3 with the tank.
• Heating circuit routed through tank nozzles.
• Biogas train connects at the roof interface.
• Feed and digestate pumps complete the loop.
• Tank plus ancillaries in one scope.

Center Enamel builds digestion tanks as GFS, FBE, stainless-steel and carbon-steel bolted vessels, specifying the coating per zone and the roof for the operating gas pressure. The company has produced GFS tanks since 2008, holds ISO 9001, ISO 45001, NSF/ANSI 61, EN 1090 (CE), ISO 28765 and WRAS approvals, and has delivered more than 30,000 storage projects across 100+ countries, with a standard ex-works lead time of about 30 days for 1,000 to 10,000 m3 tanks.

• GFS fired at 820-930 C; 1,500 V tested.
• Shell to AWWA D103-19 and ISO 28765.
• Per-zone coating, documented per bid.
• 8.8-grade bolts; 30-50 year design life.

It is the sealed, temperature-controlled vessel in which anaerobic microbes break down organic matter and release biogas. Unlike a simple storage tank, it is a reactor that must hold a warm, mixed, gas-tight slurry for 20-40 days at 35-38 C.

A saturated organic slurry at 8-12% total solids, kept at 35-38 C and mixed, with biogas collecting above. The liquid zone meets organic acid; the gas zone meets H2S and condensation; the roof holds the gas at 5-30 mbar.

Because it must seal biogas, hold temperature, mix the slurry and resist acid and H2S at the coating boundary - functions a water tank never faces. The coating follows the process zone, not a single uniform spec.

GFS 2C2F (pH 2-10) or FBE for the aggressive side, specified per zone because the liquid acid and the gas-phase H2S differ. A 1,500 V holiday-spark test on every panel confirms gas tightness.

A flexible-membrane roof typically operates at 5-30 mbar, with flame arrester, relief and hazardous-area detection. That pressure class, not a water-tank roof, defines the digestion tank roof.

Yes. Center Enamel builds GFS, FBE, stainless-steel and carbon-steel bolted anaerobic digestion tanks, specifying the coating per zone and the roof for the operating gas pressure, with certificates to AWWA D103-19 and ISO 28765.

Biogas is typically 55-65% methane, with the balance mostly CO2 and trace H2S, produced at about 0.25-0.35 m3 per kg of COD removed at mesophilic temperature.

A 2021 France biogas engineering project used a single GFS bolted digestion tank of 2,215 m3 - a coated, gas-tight, temperature-rated vessel for European duty.

Usable gas volume is only what sits above the low-pressure setpoint, not the full geometric tank volume, so any attached or separate holder must be sized to recoverable volume.

An anaerobic digestion tank is a sealed, temperature-controlled reactor, not a storage tank - it holds a warm, mixed, gas-tight organic slurry for 20-40 days at 35-38 C and releases biogas of 55-65% methane. Its coating follows the zone because the liquid acid and the gas-phase H2S differ, and the roof is rated for 5-30 mbar. Center Enamel builds these as GFS, FBE, stainless-steel and carbon-steel bolted vessels, demonstrated by a 2021 France digestion tank of 2,215 m3.