Waste water treatment

• I’m what ways are large amounts of water wasted?

  Baths/showers, flushing toilets, washing clothes. A great deal is also used in agriculture
• What does this waste water contain?

  Large amounts of organic molecules e.g. urine/faeces and harmful microorganisms such as bacteria
• What‘s the process for waste water treatment? Part 1

  1. The sewage is screened by passing through mesh removing solids and grit
  2. Sewage now settles in large sedimentation tanks producing a liquid effluent and sludge
  3. The sludge is taken away and digested by anaerobic bacteria (which produce biogas which burns for electricity)
  4. The digested sludge is used as fertilisers for farming
  5. The liquid effluent contains organic molecules and harmful microorganisms which need to be reduced
  6. Air is bubbled through the liquid effluent allowing aerobic bacteria to multiply
• What is the process for waste water treatment? Part 2


  1. In the presence of oxygen, the aerobic bacteria digest the organic molecules and harmful microorganisms
  2. The liquid effluent can now be safely discharged into nearby rivers or the sea.
• What is a lot of water in industry’s used for?

  Making paper or chemicals, when this water is treated, any harmful chemicals need to be removed first, after this the water can safely enter general sewage treatment.
• How is treatment sewage used in some countries?

  Used directly to produce potable water, however, this takes many purification steps so this is only done where water is scarce
• Which is the easier way to produce potable water?

  To use ground water from aquifer, usually this is safe to drink once it has been treated with chlorine. However, aquifers can sometimes be polluted e.g. with fertilisers from farms. These aquifers need to be tested carefully.
• What has to happen to salt water to produce potable water?

  Needs to be desalinated which requires lots of energy and is expensive