Fixed-dome plants are only recommended in cases where experienced biogas technicians are
available for building them, and when the user is amply familiar with how the plant operates.
Fixed-dome plant with central entry hatch (cf. fig. 5.10)
The digester has the form of a hemispherical dome which is easy to build. Floating scum can be
removed from the full digester through the central entry hatch.
Fixed-dome plant with suspended dome (cf. fig. 5.11)
Providing a separate foundation for the gas dome yields a statically advantageous, material-saving
configuration that is very well suited for fixed-dome plants of ample size. The dome's foundation
helps prevent cracking due to tensile stress, and the digesting space is made less expensive, since
it can be built of thinner masonry, ferrocement rendering or - in the case of impervious soil - even
left unlined.
Fig. 5.10: Fixed-dome plant
with central entry hatch. 1
Mixing pit, 11 Fill pipe, 2
Digester, 3 Gas holder, 31
Entry hatch, 32 Gas cover, 33
Seal coating, 34 Rated break
ring, 4 Displacement pit, 41
Outlet pipe, 42 Overflow, 43
Cover, 5 Gas pipe, 51 Water
trap, 52 Cover (Source: Sasse
1984 / BEP Tanzania 1987 /
OEKOTOP)
Fig. 5.11: Fixed-dome plant
with suspended dome. 1
Mixing pit, 11 Fill pipe, 2
Digester, 21 Digester
rendering, 3 Gas holder, 31
Entry hatch, 32 Cas cover, 33
Seal coating, 34 Dome
foundation, 35 Dome masonry,
4 Displacement pit, 41 Outlet
pipe, 42 Overflow, 43 Cover, 5
Gas pipe (Source: BEP
Tanzania 1987/ OEKOTOP)
5.3.3 Other types of construction
In addition to the two most familiar types of biogas plant, as described above, a selection of special-
purpose and otherwise promising designs are briefly presented below.
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