A 2007 expansion of the Town of Ayer (Massachusetts) Wastewater Treatment Plant included UV disinfection to replace gaseous chlorine, eliminating safety concerns and significantly reducing chemical and operation and maintenance costs.
Soon afterward, plant personnel observed that the UV units were not robust enough to meet the NPDES permit limits for coliform. To avoid permit violations, the plant had to supplement the UV process with the addition of chemicals.
Rather than continue under that scenario, the plant team investigated alternative UV disinfection systems, and in 2014 it installed a noncontact UV system in which water flows through transparent tubes and UV
