Waste Water Treatment

• Sources that produce large amounts of waste water

  • Urban Lifestyles / Domestic waste e.g bathwater
  • Agricultural systems
  • Industrial processes
• What does sewage and agricultural waste require?

  Removal of organic matter and harmful microbes.
• What does industrial waste water require the removal of?

  • Organic matter and harmful chemicals
• Sewage treatment includes :

  1. Screening and grit removal
  2. Sedimentation to produce sewage sludge and effluent
  3. Anaerobic digestion of sewage sludge
  4. Aerobic biological treatment of effluent
• If waste water was not treated what would happen?

  • Fresh water sources like rivers and lakes would be polluted
  • This poses health risks and harmful to human health
• 1. Screening

  • Involves removing any large bits of material ( twigs or plastic bags), as well as removal of grit
• 2. Sedimentation

  1. Screened waste stands in a settlement tank and undergoes sedimentation.
  2. Heavier suspended solids sinks to the bottom to produce sludge while the less dense effluent floats to the top.
• 3. Aerobic digestion

  • Effluent in the settlement tank is removed and treated by biological aerobic digestion.
  • Air is pumped through the water to encourage aerobic bacteria to break down any organic matter
  • Including other microbes in the water
• 4. Anaerobic digestion

  1. Denser sludge at the bottom of the settlement tank is transferred to large tanks.
  2. Anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas in the process
• Uses of methane gas

  • Energy resource
• Uses of remaining digested waste

  • Fertilisers
• Products of anaerobic digestion

  • Fertiliser
  • Natural gas (methane)
• Products of aerobic digestion

  • Fertilisers
• Potable water from waste water treatment

  • Can be retrieved from wastewater
  • Where there isn't as much freshwater
• Sewage Treatment in comparison to desalination

  • Requires more processes
  • Uses less energy than desalination