Biogas
Practical Action
Technical issues
There are several technologies for obtaining biogas:
• The most common is the fermentation of human and/or animal waste, diluted to slurry, in
specially designed digesters.
• Where water is scarce, an adapted technology uses a drier mix with high yields and more
manageable residues
• A recent approach using starches from waste foods and grain in much smaller quantities
has created a small-scale technology appropriate for both urban and rural communities
• Where there are no cattle, new technologies show that fuel crops can yield biogas
• Larger-scale, more recently developed technologies capture methane from municipal
waste landfill sites.
When building a biogas digester, certain criteria must be met if it is to be successful.
Technical
• Sufficient raw feedstuffs must be available on a long-term basis and over the whole year,
or supplies will be inconsistent and people will lose confidence in the technology
• The temperature has to be high enough to cause the digestion process to work or
additional building work to create a warm environment may make it prohibitively
expensive
• 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. Many units
built in the past have been abandoned for lack of servicing skills
Social
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It is more likely to succeed if there is a market for the fertilizer end product. This supply
chain should be part of the planning stage of biogas introduction
Even if the set-up costs are subsidised, those who will use the gas should have some
financial stake in the construction or they may not have a sufficient sense of ownership
to maintain the plant
Handling animal and human wastes is a sensitive cultural issue and even the use of the
gas may be unacceptable in some societies
Collection of dung may be problematic if the livestock is not held in a fixed place but is
allowed to wander freely
Promotion and dissemination of the benefits of biogas will be needed if it is to be
accepted in the rural areas where feedstock is available
The use of human waste appears to be more successful when it is associated with an
institution such as a school or a hospital, rather than an individual home
NGO involvement can ensure that technologies are appropriate and acceptable to the
target community
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.
• Private sector investment will support long-term sustainability
• Set-up costs are relatively high so may only be affordable to those on higher incomes
Micro-credit can be used to reduce this problem. Credit schemes, or well-targeted
subsidies, will enable a larger number of people to access biogas technologies and thus
stimulate the market. For example, USAID’s Nepal Biogas Microfinance Capacity
Building Program has established appropriate financial institutions to help continue and
sustain the development of the biogas sector in Nepal.
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