5.5.3  Biogas latrines

In a biogas latrine or bio-latrine (Figure 5.13), the waste enters an airtight tank situated underground, and undergoes anaerobic digestion, resulting in the production of biogas and digested sludge. Biogas is a clean and convenient fuel that contains about 60% methane. Anaerobic digestion is the process whereby bacteria and other micro-organisms break down (decompose) organic material in the absence of air, yielding biogas. The digested sludge collects in a separate tank and can be used as a soil fertiliser.

Figure 5.13  Basic components of a biogas latrine.

Biogas can be used for cooking and lighting, refrigeration, engine operation and electricity generation. Animal wastes can also be added to the digester. Being a relatively expensive system, this has been applied in Ethiopia only at public latrines (Figure 5.14) and institutions such as schools, colleges, universities, hotels and prisons, where large numbers of people use the latrine.

Figure 5.14  (a) Public biogas pit latrines in Addis Ababa, constructed by the Emmanuel Development Association and financed by WaterAid. (b) Biogas is piped from the anaerobic digester to a nearby cafeteria where is it used for cooking.

5.5.2 Urine-diverting latrine

5.6 Water-flushed systems