4.4. Fixed Dome Digester
The Fixed dome digester consists of a dome shaped digester with a fixed immovable
gas storage area at the top of the digester. The system is a closed unit constructed of
masonry. It is lined with paraffin or bitumen to make it airtight for the gas storage.
The digester is buried underneath ground and is suitable for colder climate.
The slurry is added to the inlet (1) where it feeds into the main digester (2). The gas
is produced and stored at the top of the unit (3). A gas feed line is connected to top of
the digester (5) to supply the desired plant. The pressure created by the production
of biogas pushes the processed slurry out of the overflow (4).
Figure 4: Fixed Dome Digester
(Image source - Humanity Development Library 2.0
http://www.greenstone.org/greenstone3/nzdl;jsessionid=CCAD051FBDE15DA095307FB3A8E93C25?a=d&c=hdl&d=
HASH01a3f321d0f133a6e59c9949.6.4.pp&sib=1&p.s=ClassifierBrowse&p.sa=&p.a=b)
Advantages
• Ground level loading
• The digester has improved temperature stability because it is buried beneath
the ground
• Continuous batch flow and displacement well for effluent
• Airtight seal
• Gas pressure increases with production and pushes effluent into
displacement well
• Low initial cost
• Long life system
Disadvantages
• Fixed unit and must be constructed where it is to be used
• Closed system difficult to maintain when necessary
• Difficult construction method
• Requires the use of a sealant.
• Cracking often causes irreparable leaks.
• Unreliable gas pressure