Which disinfection method produces the fewest regulated disinfection byproducts (DBPs)?

Ultraviolet (UV) disinfection produces the fewest regulated disinfection byproducts (DBPs). Disinfection is the process of killing or inactivating harmful microorganisms, like bacteria and viruses, in water to make it safe for consumption or other uses. Disinfection byproducts (DBPs) are chemical compounds that can form when disinfectants react with naturally occurring organic matter (NOM) present in water. Regulated DBPs are those specifically monitored and controlled by environmental agencies, such as the U.S. Environmental Protection Agency (EPA), due to potential health concerns. Common regulated DBPs include trihalomethanes (THMs) and haloacetic acids (HAAs).

Chlorine, chloramine, and ozone are widely used disinfectants, but they all react with NOM to form regulated DBPs. Chlorine, the most common disinfectant, reacts with organic matter to produce THMs and HAAs. Chloramines, a weaker disinfectant than chlorine, also form DBPs, though generally in lower concentrations. Ozone, a powerful oxidant, generates a different set of DBPs, including bromate, which is also regulated. The amount of DBPs formed depends on factors like the concentration of NOM, the disinfectant dose, pH, and water temperature.

UV disinfection, however, uses ultraviolet light to damage the DNA of microorganisms, preventing them from reproducing. This process does not involve chemical reactions with NOM; therefore, it does not produce regulated DBPs. UV light simply inactivates the microorganisms without adding any chemicals to the water. While UV disinfection doesn't create regulated DBPs, it's important to note that it doesn't provide a residual disinfectant effect. This means that the water is only disinfected while it's passing through the UV reactor, and microorganisms can regrow downstream if the water isn't protected. Therefore, UV disinfection is often used in conjunction with a residual disinfectant like chlorine or chloramine to provide both DBP reduction and ongoing protection.