Parts of Biogas Plants
• Influent collecting tank
• Inlet and outlet
• Digester
• Gasholders
• Gas pipe, valves and accessories
• Stirring facilities
• Heating systems
• Pumps
• Weak Ring
Influent collecting tank
Size and homogenization
Fresh substrate is usually gathered in an influent
collecting tank prior to being fed into the digester.
Depending on the type of system, the tank should hold
one to two days’ substrate. An influent collecting tank can
also be used to homogenize the various substrates and to
set up the required consistency, e.g. by adding water to
dilute the mixture of vegetable solids (straw, grass, etc.),
or by adding more solids in order to increase the bio-
mass. The fibrous material is raked off the surface, if
necessary, and any stones or sand settling at the bottom
are cleaned out after the slurry is admitted to the digester.
The desired degree of homogenization and solids content
can be achieved with the aid of an agitator, pump or
chopper. A rock or wooden plug can be used to close off
the inlet pipe during the mixing process.
Location
A sunny location can help to warm the contents before
they are fed into the digester in order to avoid thermal
shock due to the cold mixing water. In the case of a
biogas plant that is directly connected to the stable, it is
advisable to install the mixing pit deep enough to allow
installation of a floating gutter leading directly into the pit.
Care must also be taken to ensure that the low position of
the mixing pit does not result in premature digestion. For
reasons of hygiene, toilets should have a direct
connection to the inlet pipe.
Inlet and outlet
Figure 15: Installation of a fixed-
dome plant in Thailand: The
influent collecting tank is in front
of the photo, the digester and the
outlet are located behind it.
Photo: Kossmann (gtz/GATE
Size and material
The inlet (feed) and outlet (discharge) pipes lead straight into the digester at a steep angle.
For liquid substrate, the pipe diameter should be 10-15 cm, while fibrous substrate requires a
diameter of 20-30 cm. The inlet and the outlet pipe mostly consist of plastic or concrete.
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