What is meant by free chlorine and combined chlorine in water treatment?

Free chlorine refers to the chlorine that is present in water in its molecular form, which is available to react with contaminants. This form includes hypochlorous acid and hypochlorite ion, both of which actively disinfect and kill pathogens in the water. When chlorine is added to water during the treatment process, it acts as a powerful sanitizer, targeting harmful microorganisms.

Combined chlorine, on the other hand, refers to chlorine that has already reacted with ammonia and organic nitrogen compounds in the water, forming chloramines. These chloramines do provide some level of disinfection but are generally less effective than free chlorine at killing pathogens. Their presence can also contribute to unpleasant odors and tastes in the water, which is why monitoring the balance between free and combined chlorine is essential for effective water treatment.

When discussing chlorine residual in water treatment, it is crucial to understand that it encompasses both free and combined chlorine. However, the specific question focuses on the significance of free versus combined chlorine in the treatment process and highlights the importance of maintaining appropriate chlorine residual levels to ensure water safety and quality for consumption.