2.3.2 Floating Dome Digester

The floating dome plant is commonly referred to as the Indian floating-drum plant and is the most popular type of biogas plant in India. It consists of two main elements: the usually underground-constructed digester with an open top and the above-ground gasholder (a drum inserted into the digester). The produced biogas is collected in the gasholder that goes up or down depending on how much gas is inside, whereas the drum level shows how much gas is available. The gas is released at a steady pressure determined by the weight of the drum. If more pressure is needed, extra weights can be added to the top of the drum. Agitators can be installed inside the drum to break up the scum layer.

The digester is made of bricks, concrete, and quarry-stone masonry or is prefabricated with high/low-density polyethene. The digester size typically varies from 1 to 50 m³. Conversely, the gasholder is usually made of steel and coated with paint to prevent corrosion. In regions characterised by elevated humidity levels, a well-maintained metal gasholder can be expected to endure approximately 3 – 5 years, whereas, in arid areas, it extends to 8 – 12 years. Alternatively, deploying fibreglass-reinforced plastic or galvanised sheet metal is a viable substitute for traditional steel.

Listed below are the pros and cons of using floating dome digesters, as illustrated in the table.

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