Decomposition

Temperature - the lower the temperature, the slower the rate of decomposition - because decomposers will be less active

Water - the lower the volume of water, the slower the rate of decomposition - because decomposers won't be able to survive

Oxygen - the less oxygen available, the slower the rate of decomposition - becuase decomposers need oxygen to respire, grow and multiply

Large vessels in which animal waste or specially grown crops are allowed to anaerobically digest.

Uses the process of anaerobic decay (in absence of oxygen) to provide fuel.

Produces biogas (methane and carbon dioxide)

Biogas can be used for 

• Cooking
• Heating
• Lighting (from a naked flame)
• Refrigeration (after generating electricity)

Renewable energy source

Bacteria

Fungi