ZIMSEC O Level Combined Science Notes: Biogas as a source of energy

  • Biogas is the gas that is obtained from fermenting manure and other organic waste
  • It is a mixture of methane, carbon dioxide and hydrogen sulphide
  • Cattle manure is commonly used as a waste to feed biogas plants
  • Small plants have been built in some parts of Zimbabwe
  • Manure (from both cattle, other animals and humans) as well as organic waste is put into a sealed pit
  • Bacteria digests the manure and the gas is given off, collected and then piped to burners
  • The sludge in the pit has to be agitated by rotating the floating gasometer tank on top several times a day
  • Eventually the sludge collected has to be  removed and the process started again
  • The sludge can be used as a fertilizer for crops
  • The bacteria responsible for the fermentation of waste requires an environment lacking oxygen
  • \text{organic waste}\xrightarrow{fermentation}\text{methane + carbon dioxide}
  • Biogas is not easy to store so it is used as it is produced
Biogas plant design

Biogas plant design

Factors affecting the production of biogas

  • Several factors affect the amount of gas that is produced by a biogas plant
  • These factors include:
  • The type of waste
  • The temperature-optimum temperatures for the production of biogas are between 35°C and 55°C
  • The pH of the solution which should not be too acidic or too alkaline
  • Metals such as copper and zinc will stop the fermentation of the waste by bacteria
  • Time-the length of time that the waste is in the digestor will depend on the type of waste and factors mentioned above

Uses of biogas

  • Biogas has several uses including:
  • cooking
  • refrigeration
  • in gas lights

To access more topics go to the Combined Science Notes page.

Quick NetOne, Telecel, Africom, And Econet Airtime Recharge

If anything goes wrong, chat with us using the chat feature at the bottom right of this screen