Inactivation of E. coli using a novel TiO2 nanotube electrode
The performance of electrochemical processes highly depends on the properties of electrodes and development of cost-effective anode materials plays an important role in supporting future adoption of electrochemical technologies for environmental applications. In this study, novel TiO2 nanotube anodes were fabricated via a simple electrochemical method and tested for inactivation of a model microbial contaminant E. coli, using a filter-press type cell with stainless steel as the cathodes. Effects of current density applied (0.66–2.63 mA cm−2), electrolyte concentration (0.3–3 mM NaCl), and different electrolytes (NaCl, Na2SO4, Na2HPO4, NaNO3, and NaHCO3) on E. coli inactivation were investigated. Electrochemically generated oxidizing species were measured as free chlorine and production of reactive oxygen species (ROS) were examined using probe compounds. Reactive chlorine species were formed mainly via a ˙OH-mediated pathway and found to be the dominant species responsible for E. coli inactivation in the presence of Cl−. Higher E. coli reduction efficiency was obtained in inert electrolytes using TiO2 nanotube anodes compared with other electrodes reported in the literature, which can be ascribed to the formation of ROS such as ˙OH and H2O2 and possibly electrolyte-specific oxidants such as sulfate and phosphate radicals. Furthermore, it has been demonstrated that the novel TiO2 nanotube anode can effectively achieve 5–7.5log reduction of E. coli with low byproduct formation (e.g. ClO3−, THMs) and energy consumption (0.1–0.19 kW h m−3 for 4log reduction) in real water matrices.