Mechanistic modelling of solar disinfection (SODIS) kinetics of Escherichia coli, enhanced with H2O2 – Part 2: Shine on you, crazy peroxide

In this second part of the development of a mechanistic kinetic model of the solar inactivation of E. coli enhanced
with hydrogen peroxide, we evaluate the mechanisms based on photonic inactivation and integrate them into the
kinetic model of the dark process developed in Part 1. The direct photonic inactivation was modelled using a
series-event model based on the accumulation of damage by photons and it was coupled with the model used in
Part 1 for modelling the damage caused by radicals using a multiple target – multiple hit model, including recovery
constant to define the ability of cells to face the specific photonic damage. Catalase and superoxide dismutase
inactivation, the intracellular photo-Fenton reaction, and the overproduction of O2•- in the NADH/NAD+ cycle
under solar light were included in the model. Finally, the synergistic effect of the photonic damage with thermal
inactivation was included in the kinetic constant of the series-event expression in terms of an Arrhenius equation.
The kinetic parameters were obtained by model regression using experimental data at different temperatures,
solar radiation, as well as initial cellular and H2O2 concentrations. Our model predictions can accurately describe
the experimental data of the SODIS process enhanced with H2O2, thus being very useful to estimate disinfection
profiles and inactivation routes at different irradiance conditions, water temperature and H2O2 concentration.
Finally, an integrated mechanism of E. coli inactivation under the SODIS/H2O2 process is provided.