Fixed Dome vs Floating Drum Biogas Digester: Difference and Comparison

Key Takeaways

1. A fixed dome biogas digester is a low-cost underground structure made of bricks, concrete or locally available materials.
2. The floating drum biogas digester, also known as a floating drum plant, is an alternative design to the fixed dome system.
3. Fixed dome digesters have higher efficiency in biogas production while floating drum digesters have slightly lower efficiency due to potential gas losses.

What is a Fixed Dome?

The fixed dome biogas digester is one of the oldest and most widely used designs for small to medium-scale biogas production. It consists of a cylindrical underground chamber made of brick, concrete, or reinforced fibreglass with a dome-shaped gas holder.

Some of the advantages of using this include- a simple and robust design which is easy to construct and maintain. It can also handle a wide range of organic materials and is suitable for rural areas with limited resources. It is a cost-effective application for small to medium-scale industries.

The fixed dome biogas digester is a time-tested and reliable technology widely adopted worldwide, particularly in rural and agricultural communities. It offers a sustainable solution for addressing two critical challenges: managing organic waste and generating renewable energy in the form of biogas. One of the unique features of the fixed dome biogas digester is the storage of biogas under pressure within the dome. 

What is a Floating Drum?

The floating drum biogas digester consists of a cylindrical underground digester chamber and a movable gas holder or drums floating on the top of the slurry. The digested slurry is removed from the digester through the outlet. 

Some of the advantages of it include- more efficient gas storage compared to fixed dome biogas digesters, higher gas pressure for improved distribution to end-use appliances and suitability for varying quantities of organic waste. They have a distinct advantage in gas storage. The gas holder rises and falls based on the gas production and consumption, allowing for better control and storage of biogas,

Floating drum biogas digesters contribute significantly to a greener and more sustainable future by promoting sustainable waste management and reliance on fossil fuels. It is a promising asset in the pursuit of a greener future.

Difference Between Fixed Dome and Floating Drum

1. A fixed dome biogas digester has a compact and immovable design. In contrast, a floating drum biogas digester consists of two main components- a digester tank and a gas holder.
2. In fixed dome digesters, the gas produced during the anaerobic digestion process is stored within the dome itself, preventing gas from escaping, while in the floating drum, the gas holder rises and falls, allowing for better control and storage of the biogas,
3. Constructing a fixed dome biogas digester requires skilled labour, as it requires building a gas-tight dome structure, whereas creating a floating drum biogas digester is relatively simpler.
4. Fixed dome digesters have limited flexibility in handling varying feedstock quantities while floating drum digesters offer more flexibility in gas production and provide a buffer for varying feedstock quantities,
5. Fixed dome digesters have higher efficiency in biogas production due to their well-sealed design, resulting in minimal gas leakage, while floating drum digesters have slightly lower efficiency due to potential gas losses.

Comparison Between Fixed Dome and Floating Drum

Parameter of Comparison	Fixed Dome	Floating Drum
Structure	Compact and immovable design	It contains two main components: a digester tank and a gas holder
Gas storage	Within the dome itself	The gas holder rises and falls for better storage of the biogas
Construction	Requires skilled labour	Relatively simpler
Flexibility	Limited	More flexibility
Efficiency	Higher	Slightly lower

References

1. https://www.tandfonline.com/doi/abs/10.1080/01425919108941455
2. https://onlinelibrary.wiley.com/doi/abs/10.1002/er.4440120411