Removing living organisms from water (disinfection):

After going through various stages of purification, water must be disinfected to the required extent, depending on what it is used for. For example, after purification and removal of suspended and soluble substances in drinking water, it must be cleaned of any microbial contamination so that it does not pose any health risks to the consumer.

Disinfecting water is known as destroying or inactivating living organisms and pathogenic microorganisms.

The following methods are used for disinfection:

a) Using chemicals, including adding chlorine and its compounds, bromine, iodine and ozone.

b) Using physical factors that include heat, ultraviolet rays and gamma rays.

Disinfectants have been described through four mechanisms, which include:

a) Cell wall destruction

b) Change in cell permeability

c) Change in the colloidal nature of protoplasm

d) Enzyme activity disruption

Rupture and destruction of the cell wall leads to cell death, which causes the destruction of microorganisms. The selective penetration of the cell cytoplasm membrane is changed by some disinfectant compounds and causes substances such as nitrogen and phosphorus, which are vital nutrients for the cell, enter it instead of leaving the membrane

Radiation, acidic and alkaline agents are another group of antiseptic agents that change the colloidal nature of radio plasm. For example, they cause cell protein to clot and as a result prepare the conditions for cell death. Also, disinfectants such as chlorine and ozone disrupt the chemical structure of enzymes by oxidation and slow down or destroy their activity.

Factors affecting the effectiveness of disinfectants:

Several conditions and factors affect the performance of disinfectants. These factors include the type of microorganisms, temperature, contact time, concentration and type of disinfectant.

Contact time: For a certain concentration of disinfectant, usually, as the contact time of disinfectants increases, the percentage of bacteria death increases as well.

Temperature: increasing in temperature makes the death of microorganisms faster.

The concentration and type of disinfectant: Disinfectant efficacy in a certain range is affected by its concentration, which this effect is shown in the following empirical relationship:

Cn.tp = constant

C = concentration

n = constant

tp = time required to achieve a constant percentage of microorganism’s death