Disinfection

Disinfection

Destruction or inactivation of harmful microorganisms or substances present in water.

The chemical added to kill harmful substances is known as a Disinfectant.

Good Quality of Disinfectant:

  • Kills existing bacteria (present contamination)
  • Takes care of future contamination (should have residual capacity)

Factors Affecting Disinfection:

  • Nature and concentration of microorganisms
  • Nature of water to be disinfected (interfering substances like NH3, ions, organic matter)
  • Temperature of the water and % contact time

Requirement of Ideal Disinfection:

  • Able to destroy all harmful pathogenic organisms in water
  • Should act rapidly
  • Should not change or substitute the quality of water
  • Should be economical and easily available
  • Should not make water poisonous
  • Safe to handle
  • Method of application should be simple
  • Should not require high skill and costly equipment
  • Should be capable of dissolving in water
  • Should be effective over normal range of pH and temperature
  • Must be able to leave some residual concentration after disinfection is over

Mechanism of Disinfection

  • Damage cell wall of microorganisms
  • Alter cell permeability
  • Change the colloidal nature of cell protoplasm
  • Inactivate critical enzyme systems responsible for metabolic activity

Method of Disinfection

  • Physical method (boiling)
  • Chemical method (oxidizing chemicals like chlorine, bromine, and iodine)
  • Metal ions (silver and copper)
  • Acid and alkalis (pH < 3 and pH > 11) (caustic lime)
  • Surface active chemicals (cationic detergents)