Modeling the Inactivation of Particle‐Associated Coliform Bacteria

Abstract

An equation was derived for describing the measured inactivation of particle-associated coliform bacteria in wastewater secondary effluent exposed to UV light disinfection. Parameters of importance are the inactivation rate coefficient and the total number of particles that contain coliform bacteria. Prediction of coliform bacteria dose-response is possible to within the error associated with the multiple-tube fermentation test. The theoretically derived modeling equation can be used with other design approaches that have 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 sizes greater than the critical particle size, size is not significant in determining shielding of coliform bacteria. Coliform bacteria are not typically 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. Water Environ. Res., 72, 432 (2000).

UV treatment efficiency for E. coli in storm water containing different size fractions of suspended solids

“…Two models were used to describe bacterial survival, (1) a common biphasic firstorder decay model [20] and (2) a modified version of the model proposed by Emerick et al [16] for which TSS is used to predict the particle number.…”

“…The deactivation of bacteria, particularly the tailing observed, in a batch system can be predicted using a model that accounts for the particle-associated bacteria (PAB) formulated by Emerick et al [16]. Similar to the biphasic first-order decay model, the initial rate of bacterial decay must be known, or fitted to observed data, to predict survival.…”

“…The model proposed by Emerick et al [16] is described by the following equation: (5) where N(t) is the total number of measured coliform bacteria at time t, N D (0) is the total number of dispersed coliform bacteria at D = 0, D is the dose (mW sec cm -2 ); k is the rate constant for disinfection of dispersed bacteria, and N P (0) is the total number of particles containing at least one coliform bacteria at D = 0.…”

“…To address the tailing observed Emerick et al [16] is one of many that has developed a model to describe the increase in bacterial survival observed during tailing that is assumed to be from particle-associated coliform bacteria. When models such as the one proposed by Emerick et al [16] are combined with existing knowledge regarding suspended solids in stormwater, it may be possible to describe the observed tailing as a function of TSS, providing for a quick and effective means of evaluating UV treatment efficiency of CSO water.…”

“…Two models, a modified version of the model proposed by Emerick et al [16] and a biphasic model, were evaluated to determine their ability to describe the tailing effect observed during UV treatment. Three types of CSO samples were tested: (1) unfiltered, (2) <20µm fraction and (3) <5µm fraction.…”