Biogas use in Reconstruction
Practical Action
Products of Biogas Plants
Biogas: The digestion of organic matter in the biogas plant forms methane commonly referred to
as biogas. This is a combustible gas that bums with a hot blue flame. Biogas is neither
poisonous nor as flammable as other gases used for cooking or lighting. In some countries
such as Kenya, biogas is mainly used for cooking and lighting. It is also used, to a limited
extent in community systems, to run refrigerators, and diesel and petrol engines.
Sludge: The residue or sludge from the fermentation process in the biogas digester is the main
product of the plant. It is a fertiliser of better quality than undigested waste because the
nitrogen previously unavailable to crops is transformed into water-soluble ammonia which
is readily taken up by plants.
Experiments have proved that sludge is a better fertiliser than commercial, inorganic fertiliser. It
improves crop yields when and if properly used, and farmers can save considerable amounts of
money that would otherwise be spent on purchasing commercial fertilisers.
Selection Criteria for Biogas Plant in a PCR Context
When building a biogas digester, certain criteria must be met if it is to be successful, and the
ones below apply specifically in a post-disaster context:
Technical:
The temperature has to be high enough to cause the digestion process to work.
For fixed-dome type digesters, the quality of the building materials must be high as the
biogas is held under pressure within the dome.
Skills and know-how are needed both to build and to maintain biogas plants; this must be
transmitted to the local population in-line with a PCR context.
Social:
Providing operators with a financial stake in the system they are using could encourage
greater responsibility for operation and maintenance, being directly linked to earnings and
investments.
Handling animal and human wastes is a sensitive cultural issue and even the use of the
gas may be unacceptable in some societies, although this is only very occasionally.
Promotion and dissemination of the benefits of biogas will be needed if it is to be
accepted by communities not used to the concept.
The use of human waste appears to be more successful when it is associated with an
institution such as a hospital or a communal facility such as a refugee camp, rather than
an individual home, as the amounts of waste available tend to be much higher.
Financial / political:
Government promotion and involvement can assist in dissemination. This can be a win-
win solution as it provides clean energy and reduces problems associated with waste;
significant government investment early on in reconstruction may reduce /prevent
problems from occurring later on.
Private sector investment will support long-term sustainability, but is more suited to
individual family units.
Set-up costs are relatively high but in some cases a special budget and aid located for
post-disaster reconstruction can be used to introduce biogas, which can continue to
provide clean fuel during and after reconstruction.
6