Q. Define : Disinfection, Sterilization
Disinfection is a process of killing all pathogens.
Sterilisation is a process in which the total and complete destruction of all types of bacteria
takes place.
Safe water means
(a) water free from bacteria
(b) water aesthetically acceptable
(c) water free from excessive minerals and poisonous matter
Thus, the process of killing pathogenic bacteria from water and make it safe for use is called
disinfection. The chemicals or substances used for disinfection is called disinfectant.
10.2 DISINFECTING AGENTS
Q. What are the different disinfecting agents? Explain.
Physical Agents
Chemical Agents
Potassium permanganate (used in hospitals)
Ozone, $\mathrm{O}_{3} \stackrel{\text { heat }}{\longrightarrow} \mathrm{O}_{2}+\mathrm{O}$ Nascent oxygen
Chlorine and its compounds
Bromine (used in swimming pools)
lodine (used in tablet form)
Phenol and phenolic compounds
Acids and alkalies
Heavy metals and related compounds
Dyes
Soaps and synthetic detergents
Hydrogen peroxide
Quaternary ammonium compounds.
Historically, the disinfectant widely used is chlorine. Chlorine may be applied as a gas $\left(\mathrm{Cl}_{2}\right)$ or
as the salts of hypochlorite $\left[\mathrm{Ca}(\mathrm{OCl})_{2}, \mathrm{NaOCl}\right]$ .
Bromine and Iodine are occasionally used for swimming pool water.
Ozone is produced on site by passing pure oxygen, or dry, clean air in a high strength
electric field. Ozone is highly effective disinfectant. Its use now-a-days is increasing.
Highly acidic and alkaline water can also be used to kill pathogenic bacteria.
Irradiation with ultraviolet light (UV) has also been used for disinfection. Although it
provides no residual disinfectant, UV is effective in inactivating bacteria and viruses.
The use of electron beam as a method of disinfection is now under active research in the
United States. Gamma-ray irradiation is used in Germany and along with the electron beam,
is in active research in Japan.
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