Controlling Giardia spp. and Cryptosporidium spp. in drinking water by microbial reduction processes

Abstract

Drinking water microbial reduction has evolved from simple, effective chlorination to control waterborne diseases such as cholera and typhoid fever to advanced systems using ozone, chlorine dioxide, ultraviolet radiation, and combinations of disinfectants to control waterborne diseases such as poliomyelitis, hepatitis, giardiasis, and cryptosporidiosis. Giardia spp. and Cryptosporidium spp. have posed a major challenge to the water industry from a variety of perspectives. They occur in low concentrations in source waters, their infective doses in humans are low when compared with typical waterborne viruses and bacteria, they are difficult to inactivate with chlorine compounds, and they are difficult to determine if they are dead when detected in the environment or after microbial reduction in water treatment. However, Giardia spp. and Cryptosporidium spp. are readily controlled by ozone or ultraviolet radiation over a wide range of water-quality conditions. Chlorine dioxide provides a simple alternative to chlorine in some circumstances. Using modern microbial reduction process design techniques such as the integrated disinfection design framework (IDDF) ensures the provision of drinking water with a low risk of transmitting human pathogens to the consumer. Key words: ozone, chlorine dioxide, chlorine, ultraviolet, disinfection, microbial reduction, drinking water, Giardia, Cryptosporidium, parasite.