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Biogas for households
Mariska Ronteltap, PhD
Lecturer Sanitary Engineering and Resource Oriented Sanitation
Department of Urban Water Supply and Sanitation, UNESCO-IHE
Biogas systems
• Not so suitable for sole households without
animals
• Very suitable for block of households / in
combination with other wastes
• Relatively cheap; requires experience but no
high tech skills / equipment
Size of the system
• The size of the plant depends on the substrate
available
• Volume chosen for number of cattle/ pigs
• Larger plants = longer HRT = more gas
• But: amount of daily fed substrate more
important for gas production than digester
volume
Standard sizes
• In some countries where biogas systems are important,
standard sizes are chosen
• This simplifies construction, operation and maintenance;
makes material cheaper
Example:
• 16 m³ for gas for cooking and lighting for a normal family
• 12 m³-plant for places of little gas demand
• 30 and 50 m³-plants: fuel for big institutional kitchens
and special appliances (refrigerators, power engines)
Construction
The plant consists of
• non-load bearing bottom (A),
• lower slurry-tight digester (B),
• the upper gas-tight gas storage
part (C),
• neck (D) and gas-tight lid (E).
• Gas storage part and digester
are separated by the weak ring
(10) in order to allow free
reaction of the strong-ring (3)
and to prevent cracks which
have developed in the lower
part of the digester to "grow"
into the gas storage space.
Construction
• Plant rests on foundation ring (1),
bearing mainly the vertical loads of'
the construction and the soil cover
(7).
• The surrounding soil supports the
construction to resist gas pressure
(5) and slurry pressure (6).
• Concrete at the outside of the
lower layer of bricks (2) helps to
reduce tangential forces at the foot
point (9).
• The ring forces of the upper part
are absorbed by the strong-ring
(3).
Inlet and outlet
• Inlet and outlet pipe must be
placed in connection with bricklaying (Breaking holes spoils the
whole structure)
• The pipe rests below on a brick
projecting 2 cm to the inside.
• Above, it is kept in position at the
rim of the excavation.
• Inlet: 10 cm diameter; in line with
top of weak ring
• Outlet: 15 cm; starts at 4th brick
layer