Development ofGiardia C · tvalues for the surface water treatment rule

Abstract

As a consequence of the 1986 Amendments to the Safe Drinking Water Act (SDWA) the U.S. EPA has issued a Surface Water Treatment Rule (SWTR) for systems using surface and ground waters under the direct influence of surface water. In the Guidance Manual to the SWTR, the EPA recommends C·t values (product of disinfection concentration in milligrams per liter and disinfectant contact time in minutes) for different disinfectants to achieve required levels of inactivation for Giardia lamblia. This paper describes the procedure by which C·t values were calculated for Giardia lamblia by chlorine disinfection in the SWTR. A model has been developed which can be used to approximate the C't values that are embodied in the SWTR. It was found that C·t values increased due to higher pH, the level of inactivation required, and chlorine concentration, and were inversely related to temperature.

Assessment of the risk of infection by Cryptosporidium and Giardia in non-potable reclaimed water

“…The disinfection process at four utilities (CA1, CA2, CA3 and TX1) included only chlorination and, at sites TX2, NV and AZ, chlorination was supplemented with ultraviolet (UV) irradiation (Ryu, 2003). Since both oocysts and cysts are very resistant to chlorination, no inactivation of oocysts and 0.5 log-units reduction of cysts at traditional chlorination conditions used in water plants were considered (USEPA, 1989;Clark and Regli, 1993;Finch et al, 1997). It is well known that UV irradiation is much more effective at killing oocysts and cysts than chlorination (Clancy et al, 2000;Morita et al, 2002;Zimmer et al, 2003).…”

Drinking water from forests and grasslands: a synthesis of the scientific literature

“…As little as one cyst may be able to cause infection (Medema and others 1995, Rose and Gerba 1991, Rose and others 1991. What is more, these organisms are resistant to disinfection (Campbell and others 1982, Clark and Regli 1993, Craun 1981, Haas and Heller 1990, Hoff and Rubin 1987, Jarroll and others 1981, Kong and others 1988, Quinn and Betts 1993, Rice 1981, Rubin and others 1989. Although there are medications that are effective in treating giardiasis, currently there are no drugs available to treat infections caused by Cryptosporidium.…”

Estimation of Giardia Ct Values at High pH for the Surface Water Treatment Rule

“…Clark et al [3] treated log inactivation as a fixed random variable and exposure time as a random variable in developing a model for predicting Ct values. In the current paper it was felt that it was more appropriate to consider the exposure time t, concentration of chlorine C, pH, and temperature T as fixed independent variables and log inactivation as a random dependent variable.…”

“…These studies are included in developing the proposed general model for Ct values. Clark et al [3] described the procedure by which Ct values were calculated in the Guidance Manual for the SWTR, based on earlier work [4] utilizing the Chick-Watson theory, in which the survival rate of microorganisms is linked to a first order chemical reaction…”