VPE 511: Environment and Environmental Hygiene (2+1)

CHEMICAL STERILISATION

• Its aim is to destruction of all non sporulating pathogenic organisms, particularly those of intestinal origin, which may be present in it.
• Sterilization of water, whether on a large or small scale by the use of chemicals should always be preceded by some form of filtration so as to remove the grosser particles of organic matter.
• The chemical substance used for sterilization must not impart a disagreeable taste to the water nor make it harmful to animals or people, while at the same time it must possess sufficient germicidal power to effect its purpose.
• The sterilizing agent most frequently used for the treatment of potable waters are chlorine and ozone. Chorination is more generally applicable and is cheaper than ozonisation, although the latter process possesses certain advantage over the former.
• In both processes the essential feature is the introduction into the water of the sterilizing agent in such concentration as to leave a small residuum of free agent after a contact time between agent and water of sufficient duration to ensure destruction of pathogenic bacteria.
• Efficient sterilization can only be carried out in water free from suspended organic matter, since bacteria embedded in particles of organic material may not be reached by the sterilizing agent .
• Also organic matter reduces the efficiency of most chemical sterilizing or disinfecting agents, the concentration of sterilizing agent available for the destruction of bacteria being reduced rapidly to negligible proportions.