Modeling the inactivation of particle-associated coliform bacteria

An equation was derived for describing the measured inactivation of particl e-associated coliform bacteria in wastewater secondary effluent exposed to UV light disinfection. Parameters of importance are the inactivation rate c oefficient and the total number of particles that contain coliform bacteria . Prediction of coliform bacteria dose-response is possible to within the e rror associated with the multiple-tube fermentation test. The theoretically derived modeling equation can be used with other design approaches that ha ve specific strengths (e.g., incorporation of regulatory permit limitations or hydraulic characteristics). A minimum particle size seems to govern the ability of a particle to shield coliform bacteria from UV light. Particles smaller than that size do not contain regions shielded from UV light. At s izes greater than the critical particle size, size is not significant in de termining shielding of coliform bacteria. Coliform bacteria are not typical ly located in the most shielded regions within particles, and therefore the inactivation of coliform bacteria within a particle does not indicate the application of UV light throughout that particle.