Lack of Influence of Extracellular Polymeric Substances (EPS) Level on Hydroxyl Radical Mediated Disinfection of <i>Escherichia coli</i>

Photolysis of nitrate, a prevalent constituent in agriculturally impacted waters, may influence pathogen attenuation in such systems through production of hydroxyl radical (^•OH). This study focuses on the efficacy of ^•OH generated during nitrate photolysis in promoting <i>E. coli</i> die-off as a function of extracellular polymeric substances (EPS) coverage. EPS levels of four <i>E. coli</i> isolates were systematically altered through a sonication extraction method and photochemical batch experiments with a solar simulator examined isolate viability loss as a function of time in nitrate solutions. <i>E. coli</i> viability loss over time exhibited two regimes: an initial induction time, <i>t</i>_s, with little decay was followed by rapid exponential decay characterized by a first-order disinfection rate constant, <i>k</i>. Increasing steady-state ^•OH concentrations enhanced <i>E. coli</i> viability loss, increasing values of <i>k</i> and decreasing <i>t</i>_s values, both of which were quantified with a multitarget bacterial disinfection model. Notably, at a given steady-state ^•OH concentration, values of <i>t</i>_s and <i>k</i> were independent of EPS levels, nor did they vary among the different <i>E. coli</i> strains considered. Results herein show that while ^•OH generated via nitrate photolysis enhances rates of disinfection in surface water, the mechanism by which ^•OH kills <i>E. coli</i> is relatively insensitive to common bacterial variables