What factor affects the disinfecting ability of chlorine the most?

The disinfecting ability of chlorine is significantly influenced by hydrogen ion concentration, which essentially reflects the pH level of the water. Chlorine exists in different forms depending on the pH of the solution. At lower pH levels (more acidic conditions), chlorine exists in its more effective form—hypochlorous acid (HOCl)—which is a powerful disinfectant. As the pH rises (more alkaline conditions), the effectiveness of chlorine decreases because it converts to hypochlorite ion (OCl-), which is less effective at inactivating pathogens.

Since microbial inactivation is heavily reliant on the form of chlorine present, maintaining an appropriate pH level ensures optimal chlorine disinfection. Therefore, controlling hydrogen ion concentration is crucial for maximizing the efficiency of chlorine as a disinfectant in water treatment processes.