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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]