Water

• What is essential for life?

  Water
• What is water that is safe for humans to drink called?

  Potable water
• Why is potable water not considered pure water?

  It contains dissolved impurities
• What must potable water have to be safe for consumption?

  Low levels of dissolved salts and microbes
• Why can dissolved salts be harmful to humans?

  They can sometimes be harmful
• What can microbes in water cause?

  Illnesses
• What influences the methods used to make water potable?

  Where you live
• Why is starting with fresh water easier than sea water for making it potable?

  Fresh water requires less energy to process
• What provides enough fresh water in the UK?

  Rain
• What happens to water reserves in the UK during summer months?

  They can run low
• What are people encouraged to do when water reserves run low in the UK?

  Conserve tap water
• Where does rainwater collect in the UK?

  Rivers, lakes, and underground rocks
• What does rainwater contain in terms of dissolved substances?

  Low levels of dissolved substances
• How is most potable water in the UK produced?

  From naturally occurring fresh water
• What are the two main processes used to produce potable water in the UK?

  Filtering and sterilising
• What is used to remove insoluble particles from water?

  Filter beds
• What is the purpose of sterilising water?

  To kill microbes
• What methods are used for sterilisation of water?

  Chlorine, ozone, and ultraviolet light
• What is the process of making potable water from sea water called?

  Desalination
• Why is it preferable to make potable water from fresh water reserves?

  It requires less energy than desalination
• How much sodium chloride is in every kilogram of sea water?

  35 grams
• What are the two main methods of desalination?

  Distillation and reverse osmosis
• What is the process of distillation in desalination?

  • Sea water is heated until it boils
  • Salt remains in the liquid
  • Steam produced is pure water
  • Steam is cooled and condensed to make potable water
• What are the energy requirements of distillation?

  It requires a lot of energy to boil and cool
• What is a significant environmental concern regarding waste water from distillation?

  It is very salty and harms marine ecosystems
• How does reverse osmosis work in desalination?

  • Water is put under high pressure
  • Passed through a membrane with tiny pores
  • Pores allow water molecules through
  • Prevent most ions and molecules from passing
• What is a consequence of reverse osmosis in terms of waste?

  It produces a large volume of waste water
• What is a drawback of reverse osmosis regarding its materials?

  It requires expensive membranes
• Why is the efficiency of reverse osmosis often quite low?

  Due to the large volume of waste water produced
• What must waste water be treated before being released into?

  The environment
• Why is human waste a concern in waste water?

  It contains harmful bacteria and nitrogen compounds
• What harmful substances can industrial waste water contain?

  Toxic metal compounds
• What can agricultural waste water disrupt?

  Sensitive ecosystems
• What are the steps involved in sewage treatment?

  1. Screening and grit removal
  2. Sedimentation
  3. Anaerobic digestion of sewage sludge
  4. Aerobic treatment of effluent
• What is the purpose of screening and grit removal in sewage treatment?

  To remove large particles
• What happens during sedimentation in sewage treatment?

  Tiny particles settle out from still water
• What is produced from sedimentation in sewage treatment?

  Sewage sludge and effluent
• How is sewage sludge treated in sewage treatment?

  It is digested anaerobically by specific bacteria
• What is the role of aerobic bacteria in sewage treatment?

  To reduce the volume of solid waste in effluent
• How does anaerobic digestion differ from aerobic treatment in sewage treatment?

  Anaerobic digestion occurs without oxygen, aerobic with oxygen