What is the relationship between pH and the formation of disinfection byproducts?

The correct understanding of the relationship between pH and the formation of disinfection byproducts, specifically trihalomethanes (TTHMs), is that higher pH levels often lead to higher concentrations of TTHMs. This occurs because the chlorination process, which is commonly used for water disinfection, produces TTHMs as a byproduct when chlorine reacts with organic matter present in the water. When the pH is elevated, the equilibrium of the chlorinated species shifts in a way that promotes the formation of these disinfection byproducts.

Higher pH levels generally result in a more favorable environment for the reaction between chlorine and bromide (when present in the source water), leading to an increase in the production of TTHMs. In contrast, lower pH levels may favor the stability of chlorine but also reduce the overall reactions that form TTHMs.

Understanding this relationship is critical for water treatment operators to control the quality of drinking water effectively and to minimize the health risks associated with the consumption of disinfection byproducts.