The Eulerian and particle tracking approaches, two commonly utilized numerical methods, were evaluated for modelling drinking water ozone disinfection systems. The Eulerian approach predicts disinfection performance by solving an advection-diffusion equation. Alternatively, the particle tracking (Lagrangian) approach calculates disinfection efficiency by numerically introducing particles into the flow and predicting their trajectories through a spatially varying field of ozone residuals. The two approaches were used for modelling two hypothetical ozone reactors and a full-scale operating ozone contactor. For ozone reactors with plug flow characteristics, the two approaches match well in evaluating disinfection efficiency (represented by the CT value). For reactors with non-ideal hydraulic performance, the particle tracking model predicted slightly lower CT values than did the Eulerian approach. This may be due to the trapping of particles in the dead zones of non-ideal reactors, and the limitation on the particle numbers that could be used for data processing. The results of a full-scale contactor study further confirmed these observations. The study also found that the effect of particle size (1–100 μm) used in this study on the particle tracking method was negligible. The Schmidt number has minor impacts on the Eulerian approach modelling results.

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