Waste water treatment

• What are some uses of water besides drinking?


  Personal hygiene, flushing toilets, and washing clothes
• What does wastewater contain that makes it necessary to treat?

  Organic molecules and harmful microorganisms
• What is the first stage of wastewater treatment?

  Sewage is screened by passing through a mesh
• What happens to sewage after it is screened?


  It settles in large sedimentation tanks
• What is produced when sewage settles in sedimentation tanks?


  A liquid effluent and semi-solid sludge
• What happens to the sludge after it is produced?


  It is taken away and digested by anaerobic bacteria
• What do anaerobic bacteria produce from the sludge?


  Biogas
• How can biogas be used?


  It can be burned for electricity
• What needs to be done to the liquid effluent before it is discharged?


  Reduce organic molecules and harmful microorganisms
• How are aerobic bacteria involved in wastewater treatment?


  They digest organic molecules and harmful microorganisms in the presence of oxygen
• Where can liquid effluent be safely discharged after treatment?


  Into nearby rivers or the sea
• What is a common use of water in industry?


  Making paper and chemicals
• What must be removed from industrial wastewater before treatment?

  Harmful chemicals
• What is a method of producing potable water from treated sewage?


  Directly using treated sewage
• Why is groundwater from aquifers often used for potable water?


  It is usually safe to drink once treated
• What can pollute aquifers?


  Fertilizers from farms
• What is required to produce potable water from salt water?

  Desalination
• What is a drawback of desalination?


  It requires a lot of energy and is expensive
• What are the steps involved in wastewater treatment?

  1. Screening of sewage through a mesh
  2. Settling in sedimentation tanks
  3. Digestion of sludge by anaerobic bacteria
  4. Aeration to promote aerobic bacteria
  5. Discharge of treated liquid effluent into rivers or the sea
• Compare the sources of potable water: groundwater, salt water, and wastewater.


  • Groundwater: Usually safe after chlorine treatment, but can be polluted.
  • Salt water: Requires desalination, which is energy-intensive and costly.
  • Wastewater: Can be treated to produce potable water, but involves many purification steps.