Application of Ultraviolet Light for Inactivation of Adenovirus

In the United States, the Safe Drinking Water Act requires that surface waters and ground waters under the direct influence of surface water (GUDI waters) be treated to achieve a minimum 4-log reduction of viruses. Upcoming U.S. Environmental Protection Agency (EPA) guidelines for the application of ultraviolet light (UV) are expected to set the dose requirement for 4-log inactivation of viruses based on the most resistant waterborne virus known: adenovirus (US EPA, 2003). This will mean that utilities planning to use UV alone, without additional physical or chemical treatment, would have to install systems capable of applying a dose in excess of 200 mJ/cm2, compared to a more traditional dose of 40 mJ/cm2. One practical solution would be to apply another disinfectant in concert with UV, to which adenovirus is more susceptible.Previous studies have shown that adenovirus, although extremely resistant to inactivation by UV light, is quite susceptible to chlorination (Shin et al., 2002 and Thurston-Enriquez et al., 2003). Therefore, a drinking water utility wishing to install UV for primary disinfection could subsequently apply chlorine to easily achieve the required 4-log reduction of adenovirus. However, this strategy may not be practical for a GUDI source water where physical space constraints may prevent the installation of a tank for chlorine contact time. for example, a common scenario could be a GUDI well located in an urban area. As the time between disinfectant application and the first consumer may be mere seconds, it is important to determine if this would be sufficient to control adenovirus.This paper outlines the results of a study conducted to determine if UV, applied in concert with chlorine or monochloramine at a very low CT (product of disinfectant concentration and contact time), can provide the required 4-log inactivation of adenovirus in a GUDI water. Experiments were conducted in triplicate to determine the inactivation kinetics of adenovirus types 5 and 41 in the presence of UV, chlorine, and monochloramine. In order to simulate “worst case” conditions under which the chemical disinfectants are least effective, the experiments were conducted at 5°C and pH 8.5.Confirming earlier work by other researchers (Gerba et al., 2002; Jacangelo et al., 2002; Meng and Gerba, 1996), it was found that a traditional UV dose of 40 mJ/cm2 will provide only 1-log inactivation of both types of adenovirus. However, even at low temperature and high pH, chlorine was found to be very effective against both adenovirus type 5 and 41, with a CT of 0.22 mg·min/L sufficient to achieve 4-log inactivation. Monochloramine was, not unexpectedly, much less effective, with a CT of 350 mg·min/L providing at most 2.5-log inactivation of both types of adenovirus.Further experiments were also conducted using adenovirus type 2 to determine if UV and monochloramine behave synergistically when applied sequentially, as reported by Ballester et al. (2004). Samples of the virus suspended in water buffered at pH 7 were exposed to UV light, followed by application of monochloramine at doses of 2.1-2.4 mg/L. Parallel virus suspensions were disinfected using monochloramine and UV individually. No evidence of synergy was observed between the UV and monochloramine under the conditions tested.The results of this study provide confirmation that 4-log inactivation of adenovirus may be achieved with a conventional UV dose of 40 mJ/cm2, followed by the application of a low chlorine residual for a short contact (CT of about 0.15 mg·min/L). Therefore, UV in combination with a low dose of chlorine is a feasible treatment option for a GUDI water with minimal chlorine contact time available, even under low temperature and high pH conditions.