A systematic investigation on the bactericidal transient species generated by photo-sensitization of natural organic matter (NOM) during solar and photo-Fenton disinfection of surface waters

Abstract

In this work, the role of dissolved oxygen in the solar and the photo-Fenton-mediated E. coli inactivation process was put under scrutiny. The effect of transient species that were produced in the presence of various natural organic matter isolates (NOM), namely Suwannee River (SR) NOM, Nordic Reservoir (NR) NOM, SR Humic acid (SRHA), and SR Fulvic acid (SRFA) was studied in detail. The role of 1O2 in this reaction was systematically evaluated by modifying the O2 concentration (N2/O2 purging) and the matrix composition (10, 50, and 100% deuterium oxide (D2O) v/v). In the presence of NOM, 1O2 was generated and the enhancement of E. coli inactivation rate due to charge transfer from triplet state to molecular oxygen. The comparison between SR and NR NOM showed that for these compounds, triplet state of NOM (3NOM*), and 1O2 were the more favorable active species in E. coli inactivation, respectively. Also, the second order rate constants (kE. coli2nd) of E. coli with 3NOM*, and 1O2 were calculated by using the steady state approximation. The obtained results showed that the rate values of 1O2 related to NR NOM was ∼ 5.6 times higher than SR NOM, while the rate values of 3NOM* for SR NOM was ∼ 8.7 times higher than NR NOM. We also determined the effect of these organic matter isolates in the photo-Fenton process and its constituents (solar/Fe2+, solar/H2O2, and solar/Fe2+/H2O2). In presence of NOM, the photo-Fenton process inactivation rates increased which confirmed that the combined processes has additional pathways generated with disinfecting effect during solar exposure of bacteria.