decomposition

• • compost is decomposed organic matter (food waste) that is used as a natural fertiliser for crops
• • microorganisms and detritus feeders cause decay
  • the rate at which they decay is affected by:
  • temperature
  • oxygen availability
  • water availability
  • number of decay organisms
• temperature:

  • warm temperatures increase the rate of decomposition
  • this is because the rate of which the enzymes work increases
  • too hot temperatures slows down or stops decomposition
  • this is because the enzymes denature
• oxygen availability:

  • organisms need oxygen to respire, to survive
  • microorganisms involved in anaerobic decay do not need oxygen
• water availability:

  • moist conditions increase the rate of decay
  • this is because microorganisms need water to carry out biological proceses like respiration
• number of decay organisms:

  • more microorganisms increases the rate of decay
• • biogas is made up of methane, which can be burned as a fuel
  • microorganisms produce biogas by decaying plant and animal waste anaerobically, and this produces methane gas
  • sludge waste from sewage works or sugar factories is used to make biogas on a large scale
• • biogas is made in a fermenter (generator)
  • biogas generators need to be kept at a constant temperature to keep the microorganisms respiring
  • biogas cannot be stored as a liquid because it needs too high of a pressure
  • so, biogas must be used straight away for heating, cooking, lighting or to power a turbine to generate electricity
• • biogas can be made in either a batch generator or a continuous generator
  • batch generators make biogas in small batches
  • they are manually loaded with waste
  • continuous generators make biogas continuously
  • waste is continuously fed in, and is produced at a steady rate
  • continuous generated are used on large scales