Inactivation of Microbial Contaminants in the USEPA's Drinking Water Contaminant Candidate List (CCL) by Various Disinfectants

The Environmental Protection Agency (EPA) is required under the Safe Drinking Water Act (amended in 1996) to publish a list of unregulated contaminants that are known or expected to occur in public water systems that may pose a risk in drinking water. The first of these lists published in 1998 is referred to as the Drinking Water Contaminant Candidate List (CCL). The CCL includes 50 chemical and 10 microbiological contaminants. Research is needed on the occurrence of these microorganisms in water and their resistance to disinfection in order for the EPA to decide which microbiological contaminants may require possible regulatory action.A study was conducted to evaluate the inactivation of various CCL microorganisms by various disinfectants, including ultraviolet (UV) irradiation and ozone. The CCL viruses evaluated by UV included Adenovirus 2, Coxsackie B5, Coxsackie B3, Echovirus 1 and Echovirus 11. The CCL bacteria evaluated by the same method included Mycobacterium fortuitum, Mycobacterium intracellulare and Aeromonas hydrophila. The viruses evaluated by ozone included Adenovirus 2, Coxsackie B5, and Poliovirus 1. Microsporidia (Encephalitozoon intestinalis), an emerging protozoa, was also evaluated by ozone to determine its inactivation by this alternative disinfectant.A collimated beam apparatus which housed a low-pressure mercury lamp was used to conduct the UV irradiation experiments. Ozone was generated by a corona discharge and the ozone residual was measured by Standard Method 4500 B Indigo Colorimetric Method.The results show that Microsporidia may be the most resistant microorganism to ozone and UV irradiation. Adenovirus 2 was significantly more resistant to UV irradiation than other entericviruses but less resistant than Microsporidia. It was also found to be slightly more resistant to ozone than other enteric viruses. All the viruses evaluated were very sensitive to inactivation by ozone. The bacteria tested were less resistant to UV irradiation than the viruses and protozoa.Data for the ozone experiments will be compiled to fit into models to generate C*t values for 2 or 3 log10 inactivation of the microorganism tested. This data will also be presented.