Disinfection with chlorine is most effective at which pH level?

The effectiveness of chlorine as a disinfectant is significantly influenced by the pH level of the water being treated. Chlorine exists in two primary forms in water: hypochlorous acid (HClO) and hypochlorite ion (ClO-). Hypochlorous acid is the more effective form for disinfection.

At a pH around 6.0, the concentration of hypochlorous acid is at its highest, which enhances the disinfection capabilities of chlorine. This is due to the fact that as the pH increases, less of the chlorine remains in the form of hypochlorous acid and more converts to the hypochlorite ion. Therefore, while pH levels can be acceptable in a broader range for some disinfection processes, a pH around 6.0 represents a balanced point where optimal disinfection occurs, maximizing the proportion of the more effective hypochlorous acid.

In practical applications, disinfection efficiency can decline as the pH rises beyond this level, which is why maintaining an appropriate pH level, ideally around 6.0, is crucial for effective chlorine disinfection in wastewater treatment processes.