Concrete vs. steel vs. prefab tanks for biogas, digestate and water treatment
Content
Short answer: In-situ (cast-in-place) reinforced concrete tanks are usually the best choice when you need a durable, gas-tight, low-maintenance tank for a biogas digester, digestate storage or industrial water treatment. Steel and prefabricated tanks can be quicker to erect or lighter, but they trade off lifespan, gas-tightness and size flexibility. This guide compares the three options and explains the key terms.
Comparison: in-situ concrete vs. prefab concrete vs. steel
| Criterion | In-situ concrete | Prefab concrete | Steel |
|---|---|---|---|
| Lifespan | Decades (monolithic, seamless) | Long, but panel joints are wear points | Shorter; depends on coating and corrosion |
| Gas-tightness | Excellent – seamless cast structure | Good, depends on joint sealing | Good when new; relies on coatings and welds |
| Maintenance | Low | Low to medium (joints) | Medium to high (corrosion protection) |
| Size flexibility | Very high – engineered on-site, Ø 4.5–50 m, up to 25 m high | Limited to panel modules | High, but large diameters need stiffening |
| Build time on site | Longer (cast and cure) | Faster assembly | Fast assembly |
| Resistance to aggressive media | High | High | Needs protective lining |
| Best suited for | Biogas digesters, digestate, long-term storage, water treatment | Standard storage where modular sizes fit | Temporary, relocatable or lightweight needs |
When to choose which
- Choose in-situ concrete for biogas digesters, digestate storage and water-treatment tanks that must stay gas- and watertight for decades with minimal maintenance, and for non-standard sizes.
- Choose prefab concrete when a standard modular size fits and on-site build time must be shorter.
- Choose steel when weight, speed of erection or future relocation outweigh long-term durability.
Key terms explained
Digestate
Digestate is the nutrient-rich material that remains after anaerobic digestion in a biogas plant. It can be stored, further processed, or applied on agricultural land as fertiliser. Storage tanks for digestate must resist an aggressive, often corrosive medium.
Anaerobic digestion
Anaerobic digestion is the biological breakdown of organic material by micro-organisms without oxygen, producing biogas (mainly methane) and digestate. It takes place in a sealed, gas-tight digester tank.
In-situ (cast-in-place) tank
An in-situ tank is poured on the construction site as one continuous, monolithic structure rather than assembled from prefabricated panels. The result is a seamless, gas- and watertight tank with a long service life.
Post-sedimentation, buffer and aeration tanks
These are core tanks in an industrial water-treatment line: post-sedimentation tanks separate solids after treatment, buffer tanks balance flow, and aeration tanks add oxygen to support biological treatment.
Frequently asked questions
Is concrete or steel better for a biogas digester?
Concrete generally wins on lifespan, gas-tightness, fire safety and low maintenance, and it withstands the aggressive environment inside a digester. Steel can be faster and lighter. The right choice depends on capacity, subsoil and budget.
What sizes of concrete tank are possible?
In-situ concrete tanks range from 4.5 m to 50 m in diameter and up to 25 m in height, with or without roof, above or below ground – each engineered to the project.
Can a concrete tank store digestate?
Yes. Reinforced concrete is well suited to digestate storage and can be built open or covered. A cover limits emissions and odour.
How long does an in-situ concrete tank last?
A correctly engineered in-situ concrete tank lasts for decades with minimal maintenance, thanks to its seamless monolithic construction.
Talk to Bio-Dynamics
Bio-Dynamics builds in-situ reinforced concrete tanks for biogas, storage and water treatment – with 30+ years’ experience and 5,000+ tanks built. Contact our team for advice on the right tank for your project.