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
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.