Previous Year Question

Water Disinfection is the process of destroying or inactivating Pathogenic Microorganisms present in water, including Bacteria, Viruses, and certain Protozoa. Ozone (O₃), Chlorine Dioxide (ClO₂), and Chloramine are all used for water disinfection. These are Chemical Disinfectants, but they differ in their mechanisms of action, effectiveness, and ability to remain active in water.

Ozone (O₃) is a powerful Oxidizing Agent that inactivates microorganisms by damaging their cell membranes, proteins, and other essential biological structures. It is used for Primary Disinfection in Water Treatment Plants. Ozone is effective against many bacteria, viruses, and certain protozoa. However, it does not remain active in water for long periods. Therefore, another Residual Disinfectant is required to prevent recontamination within distribution pipelines.

Chlorine Dioxide (ClO₂) is also an effective oxidizing agent used to inactivate bacteria, viruses, and certain protozoa in drinking water. It disrupts microbial functions by oxidizing proteins and other cellular components. One advantage over conventional chlorine is its lower tendency to form Trihalomethanes (THMs). However, its use can produce by-products such as Chlorite and Chlorate, whose concentrations must be carefully controlled.

Chloramines are a group of compounds formed through reactions between chlorine and ammonia. Monochloramine (NH₂Cl) is the principal form used in drinking-water treatment. Its disinfecting action is slower than that of Free Chlorine, but it remains active in water for a longer period. Consequently, it is primarily used for Secondary Disinfection to control microbial growth while treated water travels from treatment plants to consumers. Disinfection effectiveness depends on chemical concentration, contact time, pH, and water quality.