UV Experience For Inactivating Cryptosporidium In Surface Water PlantsSource: Calgon Carbon Corporation
The disinfection of pathogenic microbes in drinking water has been successful over the last century largely due to the use of chlorination. However, research conducted in the 1970’s revealed that by-products formed during the chlorination process are potentially carcinogenic and that there is a direct correlation between the concentration of chlorination by-products and the probability of certain cancers and other health problems. Following these discoveries, drinking water regulators have struggled within the confines of technological and economic limitations to find a balance between the benefits of chlorination and its harmful side effects.
In the U.S.A., the Surface Water Treatment Rule (SWTR) of 1989 mandates inactivation levels for Giardia cysts and enteric viruses, and also sets treatment standards for Trihalomethanes (THM’s, a common disinfection by-product). The SWTR provides guidance to drinking water facilities through “CT” tables that prescribe the inactivation efficacy of various processes under varying water quality conditions. By following this guidance, most water treatment plants were able to provide an adequate degree of disinfection while not compromising their Disinfection By-Product (DBP) limits and without requiring major changes to their plants. However, continuing DBP health effect research indicated that even the DBP standards required in the SWTR of 1989 produced an unacceptable level of risk and the SWTR was amended in 1996 to lower the level of DBP’s.
The new DBP standards have caused many plants to fall out of compliance, requiring either extensive plant modifications or new disinfection strategies. In addition, a major outbreak of cryptosporidiosis in Milwaukee in 1993, and other minor cryptosporidiosis and giardiasis outbreaks caused regulators to create a removal requirement for Cryptosporidium oocysts in the 1998 Interim Enhanced Surface Water Treatment Rule (IESWTR) and a further treatment requirement in the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) which was promulgated in December 2005. The LT2ESWTR includes a treatment requirement for Cryptosporidium and many surface water plants will fall out of compliance due to the very poor ability of chlorination to inactivate Cryptosporidium. A void was created for water treatment technologies that will inactivate protozoa and viruses, not create DBPs, and are economically feasible. One technology that meets all three criteria is ultraviolet (UV) disinfection.