Chlorination

Chlorination is the process of introducing chlorine or chlorine-containing compounds into a material. It is widely used for disinfection, decontamination, and chemical modification, and can refer to simple chlorine gas application or the use of hypochlorite solutions in water and other systems.

In drinking water and wastewater treatment, chlorination aims to inactivate disease-causing organisms and provide residual disinfection as water moves through a distribution system. The active disinfectant is hypochlorous acid (HOCl) and the hypochlorite ion (OCl−). HOCl is more effective, especially at lower pH.

Dosing and performance depend on water quality, temperature, contact time, and pH. Chlorine can be applied as chlorine gas, sodium hypochlorite, or calcium hypochlorite, with choices influenced by safety, cost, and infrastructure.

Disinfection by-products can form when chlorine reacts with natural organic matter or bromide, producing compounds such as trihalomethanes and haloacetic acids. Regulatory guidelines limit these by-products while maintaining adequate microbial control.

Chlorination is also used in swimming pools, food processing, pulp and paper, and other industrial contexts to sterilize equipment and control microbial growth, or to introduce reactive chlorine for chemical modification.

Safety and environmental considerations include the toxic and corrosive nature of chlorine gas, potential formation of chloramines if ammonia is present, and the need to safely handle, store, and neutralize residual chlorine in effluents.

Historically, chlorination became a standard method for public water disinfection in the early 20th century and is still widely used today, often in combination with other disinfectants to balance microbial control and by-product risks.