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• Mechanistic modelling of E. coli inactivation by photo-Fenton at circumneutral pH. • Radiation transport considering optical properties of iron hydroxide precipitates. • Reversible serial n-event kinetic model successfully describes solar inactivation. • Photo-Fenton cycle mediated by precipitated iron reproduces photosaturation effect. • Multiple target – multiple hit model reproduces synergy of photons and radicals. This work focuses, for the first time, on the mechanistic modelling of wastewater disinfection by the solar photo-Fenton process using controlled solar simulated radiation. At circumneutral pH, iron precipitates forming hydroxides and significantly affecting the optical properties of the water. In this regard, radiation transfer in the reactor has been taken into account. The proposed model considers that the solar inactivation of bacteria follows a serial n-event mechanism with n reversible steps of photonic attacks leading to the bacterial inactivation. Dark Fenton cyclic process of hydroxyl radical formation from hydrogen peroxide is considered to be mediated mainly by precipitated iron species, prevailing at circumneutral pH. Finally, the photo-Fenton process was modelled using a multiple target – multiple hit mechanistic approach that accounts for the synergistic effect between the photonic and the hydroxyl radical attacks to the bacteria. Model predictions successfully reproduce experimental data of solar disinfection, hydrogen peroxide consumption, and photo-Fenton disinfection at circumneutral pH. [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]