Academic journal article Journal of Environmental Engineering and Science

Computational Fluid Dynamics for Predicting Performance of Ultraviolet Disinfection-Sensitivity to Particle Tracking Inputs (1)

Academic journal article Journal of Environmental Engineering and Science

Computational Fluid Dynamics for Predicting Performance of Ultraviolet Disinfection-Sensitivity to Particle Tracking Inputs (1)

Article excerpt

Abstract: A three-dimensional (3-D) computational fluid dynamic model that predicts the performance of a full-scale medium-pressure lamp ultraviolet (UV) reactor for disinfection of drinking water is described. The model integrates velocity field, fluence rate distribution, and particle trajectory calculations with a microorganism inactivation kinetic model to arrive at predictions of reduction equivalent dose and microorganism inactivation for MS2 coliphage. A rational approach to determining an appropriate number of fluid particles that would generate the required computational precision is presented. Predictions of inactivation and equivalent dose were found to be sensitive to computational mesh geometry (hexahedral versus tetrahedral) but were less sensitive to the value of the Lagrangian empirical constant used in the random walk model and to choice of turbulence model ([kappa] - [epsilon] versus Reynolds stress). Non-steady-state (dynamic) simulations produced results that were similar to those of steady-state simulations. Utility of the model for evaluating different lamp operating modes and alternative physical arrangements of the baffles and lamps was demonstrated.

Key words: ultraviolet, UV reactor, disinfection, water, computational fluid dynamics, modeling.

Resume: Cet article decrit un modele tridimensionnel de dynamique des fluides numerique qui predit le rendement d'un reacteur UV, pleine echelle, a lampe a moyenne pression pour desinfecter l'eau potable. Le modele integre le champ de vitesse, la distribution du taux de fluence et les calculs de la trajectoire des particules dans un modele de cinetique d'inactivation des microorganismes pour arriver a predire la dose equivalente de reduction et d'inactivation des microorganismes par rapport au coliphage MS2. Une approche rationnelle pour determiner le nombre approprie de particules de fluide qui genereraient la precision computationnelle requise est presentee. Les previsions d'inactivation et de la dose equivalente se sont averees sensibles a la geometrie computationnelle (hexaedre p/r tetraedre) mais elles etaient moins sensibles a la valeur de la constante empirique Lagrangienne utilisee dans le modele de parcours aleatoire et au choix du modele de turbulence ([kappa] et [epsilon] p/r a la tension de Reynolds). Les simulations en regime non permanent (dynamique) ont produit des resultats similaires a ceux des simulations en regime permanent. L'utilite du modele pour l'evaluation des differents modes de fonctionnement des lampes et des autres dispositions physiques des deflecteurs et des lampes a ete demontree.

Mots-cles: ultraviolet, reacteur UV, desinfection, eau, dynamique des fluides numerique, modelisation.

[Traduit par la Redaction]


Interest in application of ultraviolet (UV) light technology for primary disinfection of potable water in large drinking water treatment plants has increased significantly in recent years. This has been due in part to the recent discovery that UV is effective against waterborne pathogens of regulatory interest, particularly Cryptosporidium parvum (Clancy et al. 1998; Craik et al. 2001) and Giardia lamblia (Campbell and Wallis 2002; Linden et al. 2002). The United States Environmental Protection Agency (US EPA)'s Long Term 2 Enhanced Surface Water Treatment Rule has identified UV as an acceptable technology for providing protection against these parasites in filtered surface water (US Environmental Protection Agency 2003b). One of the engineering challenges in design and operation of full-scale (UV) reactor systems is that it is difficult to predict and monitor the UV dose delivered to microorganisms and the level of protection provided. The concentrations of pathogens in drinking water under normal circumstances are usually well below the level that would permit a direct measurement of the level of inactivation. In addition, the dose received by microorganisms that pass through a UV reactor system is determined by the spatial fluence rate distribution within the reactor and the hydrodynamic flow pattern. …

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