This paper presents a mathematical model for estimating the UV dose distribution delivered by continuous-flow UV disinfection processes. The model adopts fractal concepts and a stochastic method to simulate microorganism (particle) trajectories through the irradiation zone of an open-channel UV system. The irregularity of particle trajectories attributable to random movements was characterized by fractal dimension. In turn, trajectory-specific doses were calculated by integrating UV intensity over travel time. Results of these simulations indicated that radiation intensities along the trajectories could be highly variable. Therefore, microorganisms are expected to receive a broad range of radiation doses as a result of variations in radiation intensity along their trajectories and spatial heterogeneity in the radiation intensity field. This supports previous assertions that the conventional averaged-dose approach will result in substantial deviations between predicted and actual system performance. Implications of the results in terms of treatment efficiency and system design are discussed. The presented approach is found to be useful as a tool for rapid estimation of the dose distribution delivered by UV processes.

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