Feasibility Study for a National Domestic Biogas Programme in - SNV

Feasibility Study for a National Domestic Biogas Programme Burkina Faso
which means that the demand for cooking energy could be completely
covered. 96
• Toilet effluent
A septic tank is beyond the means of the average rural household due to the
high cost and the unavailability of the mechanical devices for periodic
cleaning. Openly disposed human wastes are hazardous to public health and
the environment; recycling of human excreta for biogas generation is
therefore an important option in order to avoid these health hazards.
Calculation based on the common diet in Burkina Faso results in 0.2 - 0.3 m³
of biogas/person which add to the daily gas production.
3.1.3 Technical description of appropriate biogas plant
A biogas digester is a physical structure, commonly known as a biogas plant. As
various chemical and microbiological reactions take place in the digester, it is also
known as bio-reactor, biogas generator or anaerobic reactor. The main function of
this structure is to provide anaerobic conditions within it. As a chamber, it should
therefore be air and water tight. It can be made of various construction materials and
in different shape and size. Building this structure forms a major part of the
investment cost. Since 1962, when the Khadi and Village Industries Commission
(KVIC) of India approved Mr. Patel’s simple floating drum design, it became popular
in India and the developing world. In this design, the digester chamber is made of
brick masonry in cement mortar. A steel drum is placed on top of the digester to
collect the biogas produced from the digester. Thus, there are two separate
structures for gas production and collection.
Floating drum design elements were basically used to develop the Burkina Faso
batch design. As this design has proven too expensive and too demanding in
operation and maintenance, a plant like this is obviously not appropriate to the
country’s conditions.
With the world wide introduction of the improved fixed dome Chinese model at the
end of the ‘80’s, the floating drum plants became obsolete because of comparatively
high investment and maintenance costs along with other design weaknesses. Fixed
dome Chinese model biogas plants were built in China as early as 1936 and in the
currently known round shape since the 1970’s. It consists of an underground brick
masonry compartment (fermentation chamber) with a brick dome, concrete or
prefabricated plastic dome on the top for gas storage. In this design, the fermentation
chamber and gas holder are combined as one unit. This design eliminates the use of
expensive steel gas holder which is susceptible to corrosion and depends on metal
workshop and transport facilities. Under Burkina Faso’s arid climate conditions
lifetime of a fixed dome type plant is estimated to range from 20 to 50 years,
compared to floating drum plants lifetime of an estimated maximum of 20 years.
Based on the principles of the fixed dome model from China, GTZ/GATE and
BORDA developed the first standardized design and demonstrated this in Burkina
Faso in 1982/83. This system worked for about 12 years in a secondary school in
Pabré near Ouagadougou and has been abandoned only for institutional
management reasons. Particular elements of this design that do not conform to other
fixed dome plants disseminated in Asia (China, Nepal, and India) are:
• Site planning started from the fertilizer point of demand (convenience of
fertilizer utilization);
• Planning and installation with the use of a reference line;
96 Biogas Community Plants Manual – Borda - GTZ 1985
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