waste water

• large amounts of waste water are produced by urban lifestyles and industrial processes

  these require treatment before being released in the environment as they contain a large amount of organic molecules (urine and faeces) and harmful micro-organisms (bacteria)
• Sewage and agricultural waste water require removal of organic matter and harmful microbes.

  Industrial waste water may require removal of organic matter and harmful chemical
• sewage treatment:

  • screening and grit removal
  • sedimentation to produce sewage sludge and effluent
  • anaerobic digestion of sewage sludge
  • aerobic biological treatment of effluent
• step 1: screening and grit removal

  by passing through a mesh

  this removes solids and pieces of grit
• step 2: sedimentation

  prices a liquid effluent and a semi-solid sewage sludge

  which sinks
• step 3: anaerobic digestion

  of the sewage sludge,

  the bacteria produce biogas in the absence of oxygen, which can be burned for electricity
• step 4: aerobic biological treatment of effluent

  air is bubbled through the liquid effluent which allows aerobic bacteria to multiply which digest the organic molecules and harmful micro-organisms

  so the sludge can be used was fertilisers for farming
• what needs to be reduced before the water is returned to the environment?

  • organic molecules
  • harmful micro-organisms
• water that is used by industry

  need to remove harmful chemicals first , then the general sewage treatment
• "Students should be able to comment on the relative ease of obtaining potable water from waste, ground and salt water."

  • the easiest way to produce potable water is to use ground water from aquifers
  • this is usually safe to drink once it has been treated with chlorine
  • however, aquifers can sometimes be polluted e.g. with fertilisers
  • potable water can be made from waste water, but this requires many purification steps
  • salt water must be desalinised which is expensive