Which disinfection method is described as chemical-free but provides no residual disinfection in drinking water treatment?

• A. UV disinfection
• B. Chlorination
• C. Chloramination
• D. Boiling

Answer: (A)

Disinfection methods differ in whether they add chemicals and whether they leave a residual disinfectant in the water. Ultraviolet (UV) disinfection uses UV-C light to inactivate microorganisms without introducing any chemical sanitizer into the water, so there is no residual disinfectant left after the water leaves the UV reactor. This makes it truly chemical-free, but its protection ends once the water has passed the UV exposure and it can be compromised by high turbidity or post-treatment contamination, since nothing chemical is providing ongoing disinfection in the distribution system.

Chlorination and chloramination both add chemical disinfectants that persist as residuals in the water supply, offering ongoing protection in the distribution system but with potential disinfection-by-product formation and taste/odor considerations. Boiling is not a standard plant-scale disinfection method for drinking water; while it is chemical-free, it isn’t used in a distribution system to provide residual disinfection.

So the method described as chemical-free and providing no residual disinfection is UV disinfection.