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This work presents the development of a novel methodology for the simulation of photochemical processes for water disinfection using computational fluid dynamics (CFD). A new approach was implemented to calculate and visualise the disinfection performance as the microorganisms move along the photoreactor. Hydrodynamics and microorganism's statistical trajectories were computed using the discrete phase model, which also provides the distribution of microbial residence times. The distribution of radiation in the reactor was calculated using the discrete ordinate method. The local values of incident radiation were integrated over each statistical trajectory path to get the accumulated dose received for each microbial particle. The coupling in situ of the cumulative radiation dose with the inactivation kinetics allows monitoring of the disinfection process concurrently with the particle tracking. This methodology introduces significant advantages over the traditional estimation of the microorganism inactivation sequentially after calculating the dose histograms estimated from the statistical trajectories. The developed tool enables evaluating the photoreactor efficiency in each reactor position, a useful capability for optimising and scaling up complex geometries. It also allows the easy, intuitive visualisation of microbial inactivation trajectories, improving the understanding of the influence of the reactor features on the disinfection process. Application of this computational approach to two different photoreactor geometries using a virus as a representative target microbe is presented. [Display omitted] • Multiphysics CFD simulation of microbial inactivation in photochemical reactors. • Residence time distribution calculated with the discrete phase model. • Cumulative radiation dose computed along the microbial trajectory. • In situ coupling of radiation calculation with the inactivation kinetics. • Application to virus inactivation in two different photoreactors. [ABSTRACT FROM AUTHOR]

• Enhanced radiation transport model validated in commonly used photoreactors. • Isotropic, parallel and cone-shaped emission tested, representing common UV sources. • Increase of precision reached for sun direct light simulations. • Great improvement in LEDs simulations, from finer cone radiation and power cosine. This work presents the enhanced numerical simulation of the radiation transport in three different types of photocatalytic reactor using a novel Discrete Ordinate Method model recently developed for the open-source Computational Fluid Dynamics (CFD) platform OpenFOAM. The photoreactors represent commonly used geometries and illumination sources in the field of heterogeneous photocatalysis: an annular reactor illuminated by a mercury fluorescent lamp, a tubular reactor coupled to a compound parabolic collector illuminated by sunlight, and a tubular reactor illuminated by LEDs. Simulations were carried out for different photocatalyst concentrations, considering absorption and anisotropic scattering, showing differences smaller than 2.4% with respect to the results obtained by commercial CFD software for systems with isotropic emission, such as fluorescent lamps. Moreover, the model was able to improve the simulation of solar reactors and dramatically outperformed the simulation of LED sources, due to the combined effect of quadrature rotation and cone-limit fitting for cone-shaped sources, as well as a LED-specific power-cosine light distribution. The developed model has been thoroughly validated and is now available to the open-source CFD community. It allows a comprehensive numerical simulation of radiation transport using any type of light source, with applications in numerous engineering fields where optical phenomena affect the performance of the process. [ABSTRACT FROM AUTHOR]

• Development of a numerical simulation model for SODIS processes in flow reactors. • Coupling of solar vector calculation with radiation field resolution. • Application of mechanistic kinetic model with explicit radiation absorption effect. • Validation of the model in a tubular photoreactor coupled with a CPC reflector. • Good prediction of experimental data under both simulated and natural sunlight. A novel procedure for the simulation of solar water disinfection (SODIS) processes in flow reactors is presented. The modeling approach includes the rigorous description of hydrodynamics, radiation transfer, mass transport and bacterial inactivation phenomena within the reactor by means of a computational fluid dynamics (CFD) software. The methodology has been evaluated in a tubular reactor coupled with a compound parabolic collector (CPC). Velocity profiles have been validated versus theoretical fully developed flow, and radiation fields versus both ray tracing and experimental actinometrical measurements. Incorporation of the solar vector calculation significantly improves the model capabilities for prediction of the potential performance of the SODIS process at different geographical coordinates and operation time. A mechanistic kinetic model was used for the description of the bacterial inactivation rate with explicit radiation absorption effects, coupling the radiation field with the mass balances of viable bacterial species. Model predictions successfully reproduce the experimental data of E. coli inactivation under different irradiances of both simulated and natural solar light with a normalized root mean squared logarithmic error (NRMSLE) of 6.65% and 9.72%, respectively. Therefore, this novel methodology is confirmed as a useful tool for the scaling-up of the SODIS process to large volume systems to be installed in remote communities where safe drinking water is not available. [ABSTRACT FROM AUTHOR]