Cooking with Biogas

Introduction

Biogas is a mixture of mainly methane and carbon dioxide produced during the digestion of organic matter, such as animal and kitchen waste as well as crop residues, in the absence of oxygen. Anaerobic bacteria ferment biodegradable matter into methane (40-70%), carbon dioxide (30-60%), hydrogen (0-1%) and hydrogen sulfide (0-3%). The ideal process temperature for the fermentation process is at about 35°C, which might require additional heat or insulation of the digester in regions with daily or seasonal temperature fluctuations.

Viability of Biogas Production

Biogas production depends on the availability of sufficient biomass feedstock, water and space for the digester. As the biogas cannot be transported over long distances, the digester has to be placed close to the home of its user, which requires sufficient space. Yet, changing from a three-stone fire to using a biogas stove requires complex changes for a rural household, as well as for the user.

In order to check the viability of biogas in a certain area some basic points might be helpful to consider:

• The complex fermentation process in the biogas plant needs a continuous supply of suitable feedstock (preferably dung or other agricultural waste). This requires an appropriate farming system: a sufficient amount of livestock must be kept confined (no free-range grazing).
• It requires a continuous supply of water all year round, which can be a limiting factor in arid areas or areas with a pronounced dry season.
• Households must be able to afford the construction of a digester with a corresponding stove. The economic viability increases if the slurry from the digester can be applied as fertilizer on fields close-by.
• There must be enough labor available for the daily feeding and maintenance of the digester.
• Biogas might not be advisable in cultures where maintenance and preventive action is not a common habit.
• The rule of thumb says that 3-4 cows are needed to make biogas production viable at household level. This may be a problem especially for poorer families.