(19e) Analytical Determination of the Baffle Factor for Disinfection Contact Systems Based on Hydraulic Analysis, Disinfection Kinetics and Ct Tables

The Surface Water Treatment Rule specifies the "Ct'' calculation as the means by which both disinfection efficacy and compliance is determined. The baffle factor used to obtain the amount of times used for the calculation has been a topic of discussion. In this work, an extended baffle factor formulation is developed using disinfection contact system performance equations that reflect the requirements imposed by the Surface Water Treatment Rule. The performance equations are based on chemical reactor models that have been utilized and validated extensively in the literature. A comparison is made between the extended baffle factor formulation and those methods that use hydraulic considerations alone. The comparison shows that failing to account for the entire residence time distribution and disinfection kinetics can lead to significant errors in the value of the computed Ct. The result of this work is an extended baffle factor that is used in a similar way as are existing formulations, is compliant with the Federal rules and is useful for troubleshooting those utilities that are experiencing either disinfection inadequacy or high levels of disinfection byproducts.