10.3 - Potable, purification and treatment of water

• What is potable water?

  Water that has been treated or is naturally safe for humans to drink. It is not pure, pH is between 6.5 and 8.5, no dangerous bacteria or microbes.
• Fresh water:

  1. extraction - choosing appropriate water source
  2. screening - metal grids that remove large objects
  3. settling/filtration - using settling tanks so solids sink to the bottom. Using filter beds to remove small insoluble matter
  4. sterilisation - chlorine to remove dangerous microorganisms
• Sea water:

  • Same as fresh water but desalination between setting and sterilisation
  • desalination - simple distillation; reverse osmosis
• Fill in the water purification practical:

  A) water vapour

  B) salt water

  C) pure water

  D) water vapour condenses

  
• Waste water:

  • screening - removing large materials
  • sedimentation - heavy solids sink to the bottom
  • aerobic digestion - air is pumped through water to encourage aerobic bacteria to break down any organic matter
  • anaerobic digestion - The sludge at the bottom of the settlement tank is broken down through anaerobic digestion.
• Fill in the blanks:

  A) fertiliser

  B) natural gas

  C) sedimentation