(56e) A Model for the Photocatalytic Oxidation of Cell Membranes During Water Disinfection

The lipid peroxidation of membrane fatty acids of bacteria is gaining acceptance as the main mechanism by which photocatalysis inactivates water pathogens such as Escherichia coli (E. coli). These cell membrane fatty acids (particularly unsaturated fatty acids) are among the most oxygen sensitive molecules in nature, and are easily oxidized when exposed to hydroxyl radicals produced during the illumination of TiO2. However, most of the models applied to photocatalytic disinfection are empirical and rooted in traditional chemical disinfection principles, which are often not appropriate for heterogeneous processes like photocatalysis.

In this study, a robust mechanistic model for the photocatalytic disinfection of bacteria in drinking water is developed. The model includes the interaction between bacteria and TiO2 particles and the subsequent process of lipid peroxidation. First, lipid peroxidation was confirmed by measuring the increase of malondialdehyde (MDA) in a series of photocatalytic disinfection experiments by using the familiar TBARS assay. MDA is a common biomarker for lipid peroxidation. Second, liposomes were used as model cell membranes prepared from the natural predominant phospholipids of E. coli, that is, phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). The oxidation of these liposomes was studied by measuring oxygen uptake during photocatalysis with a Stratkelvin O2 monitoring system and MDA production. Finally, using the results of these experiments existing data was reevaluated and, present and past findings substantiated in relation to the new model.