How is chlorine used in water treatment?

Chlorine is used in water treatment as a disinfectant to kill harmful bacteria and other microorganisms.

Chlorine is a powerful oxidising agent and when it is added to water, it reacts with organic matter to form compounds known as disinfection by-products. The most common method of chlorination is the use of chlorine gas, which is highly effective in killing bacteria, viruses, and other microorganisms that can cause diseases. This process is known as primary disinfection.

The chlorine gas is injected into the water under controlled conditions. It reacts with the water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). The hypochlorous acid is the active disinfectant that kills the microorganisms. It does this by penetrating the cell walls of the microorganisms and disrupting their metabolic processes, effectively killing them.

In addition to primary disinfection, chlorine is also used for secondary disinfection. This is where a small amount of chlorine is left in the water after it leaves the treatment plant to ensure that the water remains safe to drink as it travels through the distribution system to consumers' taps. This residual chlorine continues to kill any microorganisms that might enter the water after it leaves the treatment plant.

However, the use of chlorine in water treatment is not without its challenges. The disinfection by-products formed when chlorine reacts with organic matter can be harmful if consumed in large quantities over a long period of time. Therefore, water treatment plants must carefully control the amount of chlorine used to ensure that it is effective in killing microorganisms, but does not produce harmful levels of disinfection by-products.

In summary, chlorine plays a crucial role in water treatment by acting as a disinfectant to kill harmful microorganisms, ensuring the water is safe to drink.