What is the role of ammonia in a system using free chlorine?

The role of ammonia in a system using free chlorine is closely associated with disinfection processes. When ammonia is introduced to water containing free chlorine, it reacts to form chloramines, which include compounds such as monochloramine, dichloramine, and trichloramine. This reaction effectively alters the disinfection process.

While free chlorine is highly effective as a disinfectant, the formation of chloramines can provide a longer-lasting residual disinfectant in the water supply. This is particularly beneficial in systems where longer-term disinfection is required, as chloramines are more stable and less volatile than free chlorine. Furthermore, they can inhibit the regrowth of bacteria and other microorganisms in the distribution system.

In contrast, the other options do not accurately capture the mechanism of ammonia's role in water treatment. Enhancing the taste of water or stabilizing chlorine levels is not directly tied to ammonia's primary function. Similarly, although ammonia can affect the system's pH, it is not its main purpose in relation to disinfection. Therefore, the correct answer aligns with the established role of ammonia in water treatment systems using free chlorine, emphasizing its function in forming chloramines for improved disinfection efficacy.