Biogas Digestor in rural Zimbabwe. Image credit

ZIMSEC O Level Geography Notes: Natural Resources: Energy:Small scale energy sources and plants:Biogas plant

  • To install a bio-gas plant, a pit is dug underground near to the kitchen the depth of which is determined by the size of the plant the family wants to build.
  • Then a brick and mortar chamber is built or a used oil drum is inserted into the pit.
  • At least three pipes are drilled into this underground unit.
  • One is for occasionally pouring a little water into the fermenting chamber.
  • The second one is for releasing gas into the air if it is not being drawn to the kitchen.
  • The third is to direct the gas to the kitchen where it is used.
  • A lid is placed at the top of the chamber.
  • To produce the biogas, organic matter in the form of raw cow dung or green foliage of plants and crops is placed in the chamber.
  • The lid at the top is tightly sealed.
  • A little water is poured through one of the pipes.
  • Valves for the other two pipes are closed.
  • A process called anaerobic decay takes place on the organic matter, with biogas produced as a by-product.
  • Through the safety pipe, one can smell that the gas is being produced and can now be used in the kitchen.
  • When the organic matter no longer produces large amounts of the gas.
  • The lid is opened and the organic matter is removed and replaced with fresh supplies.
  • The removed, partially decayed matter can be used safely as garden manure.
  • Tis is cheap, simple and environmentally friendly source of energy.

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