Which disinfectant is less effective than free chlorine residuals but lasts longer in the distribution system?

Chloramine is a compound formed when ammonia is added to chlorine, and it serves as a secondary disinfectant in water distribution systems. One of its key characteristics is that it provides a more stable and longer-lasting residual compared to free chlorine. This stability is valuable for maintaining disinfection throughout the water distribution system, especially in preventing microbial regrowth.

While chloramine is generally less effective than free chlorine when it comes to rapid disinfection of pathogens, particularly at low concentrations, its longevity makes it beneficial for continuous protection against contaminants as water travels through the system to consumers.

In contrast, other disinfectants like ozone and chlorine dioxide are highly effective for disinfection but do not provide long-lasting residuals in the distribution system, often breaking down quickly. Hydrogen peroxide also acts as a strong oxidant but is typically not used for maintaining a disinfectant residual in distribution systems. Thus, chloramine’s unique combination of being less effective in immediate pathogen kill rates while providing prolonged disinfection residual makes it the correct choice.