c10 - using resources

• what is potable water?


  water that is safe to drink
• why isn't potable water pure?

  it contains other dissolved substances
• what are the three criteria's that make water potable?

  • the levels of dissolved substances need to be low
  • must have a pH between 6.5 to 8.5
  • has no microorganisms
• ways to sterilise water to make potable water

  • bubble chlorine gas through it
  • expose it to ozone or ultraviolet light
• what are the steps of treating fresh water?

  • pass fresh water through a wire mesh. which filters out any big solids
  • pass it through a bed of sand and gravel which filters out smaller solids
  • sterilise water to kill any harmful microbes
• what is desalination?


  the extraction of potable water from sea water
• when is desalination required?

  when the supply of fresh water is limited
• what are the two methods of desalination?

  • distillation
  • processes that use a membrane (reverse osmosis)
• what is the disadvantage of desalination?

  expensive as it requires a great deal of energy
• outline the process of using membranes in desalination

  • pass the salty water through a membrane so only water molecules can pass through
  • ions and larger molecules are trapped and separated
• how does desalination using distillation work?

  • test pH of the water using a pH meter
  • test the water for sodium chloride
  • do simple distillation to collect the pure water
  • retest the water to ensure sodium chloride has been removed and the pH is neutral (pH 7)
• what are the four stages of the life cycle assessments (LCAs)?

  • gathering the raw materials
  • manufacturing and packaging
  • using the product
  • disposing of the product
• what are two disadvantages of lifecycle assessments?

  -
• what are the three main sources of waste water

  • domestic (household)
  • agricultural systems
  • industrial processes
• what two things must be removed from sewage and agricultural waste water?

  • organic matter
  • harmful microbes
• why does water from industrial processes require additional treatment?

  it could contain harmful chemicals formed during the industrial chemical reactions
• outline the steps in the treatment of sewage

  1. sewage - the sewage is passed through gratings and meshes to remove anything large
  2. sedimentation - sewage is left to sit in a settlement tank. heavier particles settle at the bottom, known as sludge. lighter particles sit at the the top as effluent.
  3. aerobic digestion - air is pumped through the effluent to supply the bacteria with oxygen
  4. anaerobic digestion - the sludge is sealed in a container to prevent the entry of air, which ensures anerobic respiration
• after sewage treatment, what can the products of the anaerobic digestion process be used for?

  • the methane can be burned as an energy source
  • the sludge can be used as a fertiliser