10 Questions you ask most about anaerobic digesters

Commentary - February 2022

10 Questions you ask most about anaerobic digesters


Q1. What materials are biogas tanks made from?

Anaerobic digesters can be manufactured from glass-coated steel, epoxy-coated steel or stainless steel (AISI 316 or 304) – or a combination of these materials.

There is a misconception that epoxy-coated anaerobic digesters are not as good as glass and stainless steel tanks. They are if you specify the new advanced epoxy fusion-bonded biogas tanks now available.

Q2. How much do anaerobic digesters cost?

This depends on the size of the tank. There is no hard and fast rule per cubic metre because each biogas plant is unique.

It is important to consider the lifetime cost of the tank – and how the low maintenance benefits of bolted steel digesters can far outperform similar welded and concrete tanks that need more frequent maintenance.

Email us to discuss the cost of anaerobic digestion tanks.

Q3. How corrosion resistant are biogas tanks?

Up to 5,000ppm H₂SO₄ sulphides and pH 2-11 depending on the temperature and concentration of the effluent. They operate up to 60 degrees C (140 degrees F).

Q4. What is the tanks’ wind loading? What is their snow loading?

Tanks in biogas plants can be designed for:

  • cyclonic wind – more than 155mph/hour (249km/hour)
  • heavy snow loads – over 4.0kN/m2
  • up to seismic zone IV (severe intensity zone).

Q5. How long does it take to construct an anaerobic digestion tank?

It depends on the size of the tank. Typically, a 3,000m3 tank will take around 30 days to construct.

Q6. How much manpower is needed to build the tanks?

A biogas plant construction crew is three to five people – depending on the tank size and the job location.

Q7. What foundations are needed – How are the tanks sealed to the floor?

Anaerobic digesters always have concrete foundations. We can seal using a flat-to-base system for smaller tanks, a rebate-style system or an embedded starter ring system.

Q8. How much insulation do biogas tanks need?

This depends on where the anaerobic digestion tanks are sited. In hot countries, some operators specify insulated tanks – but some don’t.

The thickness of insulation for each tank is determined by the:

  • hydraulic retention time (HRT) – the time when productivity could start to decline (while the organic fermentable substrate remains in the digester)
  • type of process – thermophilic or mesophilic.

Specifying the thickness of the insulation is the responsibility of the biogas plant designer.

We have supplied tanks with insulation as thin as 50 mm and as thick as 150 mm. Thicker insulation is available but we have rarely been asked to supply this.

Q9. How soon after ordering can the tanks be delivered? How long before they can become operational?

Typical delivery time (ex-works) is eight to 10 weeks from drawing approval. The time from build to operation is the responsibility of the main contractor tasked to complete the construction of the biogas plant.

Q10. How long are the warranties for biogas tanks?

Warranties for AD tanks are typically one to two years but we can offer extended warranties depending on the biomass being digested and the requirements of the project.

Further reading

Supplying the US agriculture sector with advanced anaerobic digestion solutions
Where are America's anaerobic digestion plants?

Why Balmoral Tanks?

Balmoral Tanks is a global leader in the manufacture of anaerobic digestion tanks. Projects include some of the world’s largest digesters for multi-tank biogas plants.

Balmoral has decades of experience and, since 2018, the company has invested more than $27 million in its 150,000sq ft state-of-the-art design and manufacturing facilities. They represent the most technically advanced production facilities in the industry – supported by unrivalled levels of expertise and service.

For this reason, many biogas project co-ordinators, investors, designers and EPC contractors choose to specify Balmoral-built tanks for their AD plants.

Contact us now for expert technical advice on anaerobic digester tanks
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