waste water treatment

• waste water comes from many different sources

  • toilets
  • baths
  • washing up
• agricultural systems- produce much water waste including nutrient run off from fields and slurry from animal farms
• the amount of fresh water available on earth has not changed but the demand for it has increased due to population growth and industrialisation
• sewage from domestic or agricultural sources has to be treated to remove any organic matter and harmful microbes before butting back into fresh water sources otherwise would create polluted rivers and health risks
• industrial processes such as the haber process also produce much waste water that has to be collected and treated
• industrial waste may contain harmful chemicals so there is extra stages to remove it
• What is the first step in sewage treatment?

  Sewage is screened to remove large molecules.
• What is the purpose of screening sewage?

  To remove large molecules such as twigs and leaves.
• What happens to sewage after it is screened?

  It stands in a settlement flask and undergoes sedimentation.
• What occurs during sedimentation in sewage treatment?

  Heavier solids sink to the bottom, leaving sludge.
• What is done with the effluent from the sedimentation tank?

  It is removed and treated with biological aerobic digestion.
• How is biological aerobic digestion facilitated in sewage treatment?

  Air is pumped through water to encourage aerobic bacteria to break down organic matter.
• What is the fate of the sludge collected from the bottom of the tank?

  It is removed and transferred into large tanks for anaerobic digestion.
• What is the process of anaerobic digestion in sewage treatment?

  It breaks down organic matter in sludge, releasing methane gas.
• What is methane gas used for after anaerobic digestion?

  It is used as an energy source.
• What is done with the remaining waste after methane is extracted?

  It is used as fertilizer.
• What additional stage may be involved if waste contains toxic substances?

  Chemicals, UV radiation, or membranes may be added.
• What are the main steps in sewage treatment?

  1. Screening to remove large molecules
  2. Sedimentation to separate solids and sludge
  3. Biological aerobic digestion of effluent
  4. Anaerobic digestion of sludge
  5. Use of methane gas as energy
  6. Additional treatment for toxic substances
• recycling means reusing something instead of throwing it away
• sewage treatment requires more processes however requires less energy than destination of salt water