Biogas systems take wet organic material (feedstock) into an air-tight tank, where bacteria break down the material and release biogas – a mixture of methane with some carbon dioxide. A pipe takes the biogas to the kitchen, where it is used to cook with a biogas stove or for other purposes. Most biogas plants in Nigeria and elsewhere are designed to use animal manure as their main feedstock, and are therefore only used in rural areas. Powerstove developed a compact single unit biogas plant which uses organic materials available in urban areas, such as waste flour or kitchen waste, as feedstock.
Performance
The Kitchen feedstock has a higher
energy density compared to manure, and digestion takes place much more quickly
(typically 1 to 2 days, compared with 30 to 40 days for a manure-based plant),
so a smaller quantity of decomposing material needs to be held in the plant at
any one time. One kg (dry matter) food waste feedstock produces about 0.25 kg
of methane, whereas 20 kg of cattle dung feedstock would be needed to produce
the same quantity of methane.
Environmental
benefits
Powerstove estimated that using only household food waste in
a biogas plant halves the use of LPG or kerosene for cooking, saving a typical
urban household 100 kg/year of LPG or 250 litres/year of kerosene. This is
equivalent to 300 to 600 kg/year CO2. Further reductions in fossil fuel use and
CO2 emissions arise from not having to transport LPG cylinders to be re-filled.