Chlorine is widely used for which process in water treatment?

• A. Disinfection
• B. Coagulation
• C. Sedimentation
• D. Filtration

Answer: (A)

Disinfection is the step focused on destroying or inactivating harmful microorganisms to make water safe to drink. Chlorine is widely used for this purpose because it effectively kills bacteria, viruses, and many protozoa, and it provides a residual disinfectant in the distribution system to keep water safe as it travels to users. In water, chlorine forms hypochlorous acid, which penetrates cell walls and disrupts essential cellular processes, quickly reducing microbial viability. It can be applied in liquid or gaseous form, is relatively inexpensive, and has a long history of successful use in public water supplies. That residual disinfection helps prevent regrowth and contamination after treatment, which is why chlorine is favored over other methods for simply removing pathogens. Coagulation, sedimentation, and filtration are primarily aimed at removing particulates and turbidity, not maintaining a chemical disinfection level, so chlorine’s main role is disinfecting water rather than physical removal.