Photocatalytic activation of sulfite using Fe(II) and Fe(III) for Enterococcus sp. Inactivation in urban wastewater

Abstract

The application of sulfite in advanced oxidation-reduction processes has shown good results in the degradation of organic pollutant, but very few researches have addressed its application for wastewater disinfection. In this study, the efficacy of a sulfite system activated by different iron species and/or UV-A radiation in the inactivation of Enterococcus sp. was studied for the first time, achieving complete disinfection (>5-log) after 90 min. Different sulfite (0.1–10 mM), Fe(II) and Fe(III)-cit (0.1–2 mM) concentrations, were assessed in simulated and real wastewater matrices and experiments with radical scavengers were carried out to identify the main radical species involved in the disinfection. In addition, the influence of the nature of the aqueous matrix and the presence of other bacteria species as E.coli was assessed. Fe(III)-cit was the best sulfite activator, reaching complete bacteria inactivation (>5-log), while a maximum disinfection rate of 2.3-log units was achieved when using Fe(II). The performance of the treatment was greatly affected by the composition of the matrix, as the use of real wastewater resulted in a decrease in the disinfection rate to 0.5 and 1.4-log when using Fe(II) and Fe(III)-cit, respectively. The presence of Escherichia coli also proved to negatively influence the Enterococcus inactivation result, leading to a inactivation of 2.1-log in the sulfite/Fe(III)-cit system, opening the door to new studies to find out the selectivity of the radicals towards the different microorganisms in the matrix. Even though deeper studies are needed for a better understanding of the reaction mechanisms, this work opens the door to the use of sulfite-based processes applied to the disinfection of wastewater, proposing an alternative to the use of traditional oxidants.