UV disinfection implementation status in US water treatment plants

The implementation of ultraviolet light (UV) disinfection in drinking water applications in the United States has gained momentum in recent years. An online survey and field sampling of full-scale drinking water treatment plants (WTPs) were performed with a focus on evaluation of sequenced disinfection (UV and chlorine/chloramines). Twenty-seven WTPs responded to the survey. Nearly all of these WTPs were treating an impaired water source (subject to upstream agricultural or wastewater discharges) and using UV with a design dose of 40 mJ/cm2installed as part of a plant retrofit. The majority ( n = 16) of the disinfection systems used polychromatic mediumpressure UV. Twelve WTPs applied all or part of their secondary disinfectant (free chlorine or chloramines) upstream of the UV reactor. The majority of the WTPs reported no effect on chlorine residual or formation of disinfection by-products. Full-scale sampling indicated minimal (±3 μg/L) change in trihalomethane formation resulting from UV disinfection during multiple sampling events.