Water Purification and Sanitisation

Describe and assess the effectiveness of methods used to purify and sanitise mass water supplies



  • The steps involved in the purification and sanitising of water supplies are:
    • Screening: The removal of large debris.
    • Aeration: The increasing of dissolved oxygen by spraying, which causes iron salts to be oxidised to insoluble oxides.
    • Flocculation: The coagulation of colloidal and particulate matter to form flocs.
    • Sedimentation: The settling of flocs to form a sludge.
    • Filtration: Formation of clear water by removal of substances that cause turbidity and colouration, using beds of sand and gravel as well as charcoal filters.
    • Chlorination: The disinfecting of water using chlorine gas and various hypochlorites, which kill microorganisms.
    • pH Adjustment: The adjustment of pH to between 7 and 8.5 using buffering chemicals.
    • Fluoridation: Adding of fluoride compounds to help prevent tooth decay (resulting in a fluoride concentration of about 1 ppm).
  • The treatment of mass water supplies requires a balance between cost, speed and the quality of the finished product.
  • Current methods are not perfect at removing disease-causing agents, as shown through events such as the Giardia and Cryptosporidium incident in Sydney in 1998.
  • Further techniques could be introduced, such as the use of membrane filters and ozone sterilisation, although this would be much more costly.
  • Instead, water is monitored daily at treatment plants.

Easychem - Water Purification and Sanitisation


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