Mechanistic modelling of solar disinfection (SODIS) kinetics of Escherichia coli, enhanced with H2O2 – part 1: The dark side of peroxide

The present bi-partite work describes the development and validation of a mechanistic kinetic model of SODIS
E. coli inactivation, enhanced with H2O2. In this first part, the mechanism of the baseline dark phenomena is
modelled. A mechanistic model involving E. coli cellular respiration, inactivation due to HO⋅ and O2⋅- radicals,
and bacterial thermal inactivation, was developed using a series-event model based on the accumulation of
damage and cell recovery corrected with the Arrhenius equation for inclusion of the thermal events. The
contribution of external H2O2 was included in the internal H2O2 balance, while the balance of extracellular H2O2
considered the consumption caused by its self-decomposition, interactions with cells’ membrane, and organic
matter from dead cells. Specifically, the kinetic parameters of the external H2O2 sinks, the oxidation reaction of
intracellular Fenton, and bacterial thermal inactivation were independently estimated by model regression from
experimental data of E. coli inactivation and H2O2 consumption at different controlled conditions of temperature
and initial H2O2 concentration. We complemented the values of the kinetic constants available in the literature
with the unknown kinetic parameters estimated from experimental and literature data. The missing kinetic
parameters were successfully validated (bacteria error = 4.5%, H2O2 error = 12.9%). This kinetic model helps to
understand the intracellular mechanisms and the contributions of each source of inactivation, with the role of
radicals’ damage being most important at temperatures below 40 ◦C, and the thermal inactivation for temperatures
above this value.