What is the main factor affecting the rate of reaction for chlorine disinfection?

The pH level of the water is indeed a central factor influencing the rate of reaction for chlorine disinfection. Chlorine exists in different forms depending on the pH of the water, primarily as hypochlorous acid (HOCl) and hypochlorite ion (OCl-). Hypochlorous acid is a much more effective disinfectant than hypochlorite ion.

At lower pH levels (generally below 7.5), the concentration of hypochlorous acid increases, thereby enhancing the disinfection capability of chlorine. Conversely, as the pH rises above this level, the proportion of hypochlorite ion increases, which is less effective for killing pathogens. Therefore, maintaining an optimal pH range is crucial for maximizing the efficacy of chlorine as a disinfectant in water treatment processes.

While temperature, presence of organic matter, and age of chlorine may also play roles in the disinfection process, they are secondary factors compared to the influence of pH on the chemical form and reactivity of chlorine.