Elucidation of in-situ produced organic matrix effect on the solar photo/photocatalytic inactivation of E. coli

Abstract Solar photoinactivation and photocatalytic inactivation of E. coli in aqueous solution was investigated in various matrix conditions in the presence/absence of humic acid as representative of natural organic matter and inorganic components focusing on the spectroscopic evaluation of in-situ produced organic matrix. Characterization of organic matter with respect to E. coli inactivation under various experimental conditions was followed by the elucidation of specified UV–vis and fluorescence parameters as well as dissolved organic carbon content. Solar light initiated destruction of bacterial cells via lysis were visualized by the occurrence of protein-like fluorophores and fluorophores of microbial by-products as presented in excitation emission matrix fluorescence contour plots indicating a variety of changes in their shape and intensity with respect to increasing irradiation periods. Moreover, under similar experimental conditions, in the presence of humic matter these fluorophores were mainly quenched by humic-like fluorophores. E. coli inactivation kinetics obeyed first order kinetic model for both solar photoinactivation and photocatalytic inactivation conditions. Rate constants for photoinactivation of E.coli ranged from 0.184 to 0.0920 min−1, whereas photocatalytic inactivation rate constants varied from 0.248 to 0.0488 min−1. Both humic acid and water matrix components had inhibitory effects on inactivation efficiency which could be attributed to competitive reactions occurring between humic matter, bacterial cells, and bacteria derived organic material. Further evaluation of bacteria inactivation was followed by detection of organic (protein and carbohydrate) and inorganic (K+ leakage) constituents under specified conditions in correlation to the spectroscopic parameters.