1. Dissolution: Chlorine tablets are made primarily of sodium dichloroisocyanurate (NaDCC), which is a solid compound. When the tablet comes in contact with water, it starts to dissolve and release the sodium dichloroisocyanurate into the surrounding water.
2. Hydrolysis: The sodium dichloroisocyanurate undergoes a chemical reaction with the water molecules through a process called hydrolysis. During hydrolysis, the chlorine atoms in the compound react with the hydrogen and oxygen atoms in water, releasing hypochlorous acid (HOCl) and cyanuric acid (C3H3N3O3).
a) Formation of Hypochlorous acid: HOCl is a powerful oxidizing agent that exhibits strong disinfection and sanitizing properties. This is the active chlorine compound that is primarily responsible for the effectiveness of chlorine tablets in water disinfection.
b) Formation of Cyanuric acid: Cyanuric acid acts as a stabilizer for the chlorine in the water. It protects the HOCl from reacting with sunlight and ultraviolet radiation, preventing the rapid breakdown and loss of available chlorine.
3. Chlorination: The hypochlorous acid released during hydrolysis is free to react with organic matter, microorganisms, and other impurities in the water. Chlorine kills bacteria, viruses, algae, and many other microorganisms by damaging their cell walls, proteins, and genetic material.
4. Residual Chlorine: After the initial disinfection process, some HOCl remains in the water as a residual disinfectant. This residual chlorine continues to provide protection against recontamination by killing or inhibiting the growth of microorganisms in the water over time.
5. By-products: Over time, chlorine can also react with other substances in water to form by-products, some of which may pose health risks. The most notable by-product of chlorine disinfection is trihalomethanes (THMs), which are regulated due to their potential carcinogenicity.
6. Evaporation and pH changes: As the water is treated with chlorine tablets, some hypochlorous acid and chlorine gas may evaporate into the atmosphere. Additionally, the addition of chlorine can affect the pH balance of the water.
