DISINFECTION OR STERILIZATION Disinfection means killing pathogenic bacteria whereas sterilization means killing pathogenic and nonpathogenic bacteria both.

Methods of Disinfection

Minor Methods

a) Boiling- It is the best method that removes 100% bacteria and another microorganism. Since the method is costly hence not suitable for mass public supply.

b) Treatment with lime- Lime increases the pH and when pH >11 then removes approx. 100% bacteria. Generally used for boiler feed after as it also removes hardness. Excess lime can be removed by carbonation of the water.

c) Treatment with silver ions- Also called electro citation process. Metallic silver ions have strong killing action.

d) Treatment with Iodine and Bromine – It may be used for army troops and by private plants

e) Treatment with UV light- Efficient method for sterilization. Rays are generated using a Mercury vapor lamp. The method is costly and often adopted for treating surgical water, swimming pool water.

f) Treatment with KMnO4- This Pink in color commonly used for the open wells in rural areas. It can kill bacteria and can oxidize bad taste producing organic matter. If the pink color disappears quickly then it indicates oxidation and the presence of organic matter. Dose- 1-2 ppm

g) Ozone- Reaction is as follows

The powerful oxidizing agent, it can be produced in a high voltage electrical field. Ozonised water is tasty and no residue is left and no color is produced. The method is very costly.



Chlorine in its various forms is almost used for disinfecting public water supply. This method is very cheap, easy to handle and having residual disinfecting effects for long period.
Forms of Chlorine – In the form of Liquid chlorine, Chloramine, Chlorine dioxide, hypochlorite, or bleaching powder.
ii) Disinfecting Action of chlorine When chlorine is added to water, it forms Hypchlorous acid or hypochlorite ions.

  • NH3+HOCL is called combined chlorine
  • HOCL is a most destructive form for this reason pH value of water is kept between5-7
  • NCL3 has no disinfecting property


(i) Plain chlorination- No other treatment is given to water except chlorination. Dose 0.5mg/l. Removes bacteria, organic matter, and colour.

(ii) Pre-chlorination- Apply Chlorination before filtration. Normal dose 5-10mg/l

(iii) Post-chlorination- Apply Chlorine at the end. The dose should be such that around 0.1 to 0.2 mg/lit is left after contact of 20 min.

(iv) Double chlorination- Pre and Post Chlorination applied

(iv) Breakpoint chlorination- It gives an idea about the extent of the chlorine added to water. Beyond the breakpoint free residual appears. The difference between applied chlorine and residual chlorine is called chlorine demand of water.

(v) Super chlorination – When excess chlorine is added say 5-15mg/l. Generally used in some special cases ex. Epidemic

(vi) Dechlorination- Required when super chlorination is done ( Generally to remove excess chlorine) Agents used are SO2 gas, activated carbon, Sodium Bisulphite(NaHSO3), Sodium Thiosulphate (Na2S2O3)


Disinfection and sterilization are both decontamination processes. While disinfection is the procedure of putting off or lowering dangerous microorganisms from inanimate gadgets and surfaces, sterilization is the procedure of killing all microorganisms. Sterilization additionally destroys the spores of diverse organisms gift on surfaces, in liquids, in medication, or in compounds that include an organic way of life media. Such “extreme” styles of decontamination are wanted at some point of vital instances like surgery, or in environments like industrial, laboratory, or hospital. It is greater sensitivity to apply disinfection in regular life.

Disinfection has typically achieved the use of chemical substances, frequently solutions, however additionally vapors and gases. When chemical substances are used to smash all styles of microbiologic life, they may be known as chemical sterilants. These equal germicides used for shorter publicity durations additionally may be a part of the disinfection procedure (i.e. high-stage disinfection).


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