- A mixture of flammable gases formed by the break down of human and animal waste in anaerobic conditions.
- Up to 80% is methane, but this can vary.
- A 'cleaner' and renewable alternative to the fossil fuels.
Biogas Generator (1)
- Waste contains carbohydrates, which can be utilised as an energy source, it is put into the generator.
- Also added is bacteria, the optimum temperature for this is 30C (hence the more efficient systems being in hotter climates).
- Anaerobic respiration takes place to form products of biogas (methane) and slurry (can be used as fertiliser).
- Overall the reaction is exothermic, so the generators can be modified to insulate this heat reducing the energy required.
Floating Drum Plant
- Used mainly on small/medium farms.
- Gas is collected above the digester but released to the side.
- Advantages: Easy to construct and operate, reliable technology and steady gas pressure.
- Disadvantages: Metal gas holder can be expensive and liable to rusting.
Fixed Dome Generator
- Gas is collected and released from above digester.
- Advantages: Low initial cost and running costs (well insulated hence less energy required), long life (no metal parts).
-Disadvantages: Gas pressure likely to fluctuate and sealing of gas not secure.