Inactivation behavior and intracellular changes in Escherichia coli during electro-oxidation process using Ti/Sb–SnO2/PbO2 anode: Elucidation of the disinfection mechanism

Abstract

This study investigates the behavior and intracellular changes in Escherichia coli (model organism) during electro-oxidation with Ti/Sb–SnO2/PbO2 anode in a chlorine free electrochemical system. Preliminary studies were conducted to understand the effect of initial E. coli concentration and applied current density on disinfection. At an applied current density 30 mA cm−2, 7 log reduction of E. coli was achieved in 75 min. The role of reactive oxygen species’ (ROS) in E.coli disinfection was evaluated, which confirmed hydroxyl (•OH) radical as the predominant ROS in electro-oxidation. Observations were carried out at cell and molecular level to understand E.coli inactivation mechanism. Scanning electron microscopy images confirmed oxidative damage of the cell wall and irreversible cell death. Intracellular and extracellular protein quantification and genetic material release further confirmed cell component leakage due to cell wall rupture and degradation due to •OH radical interaction. Change in cell membrane potential suggests the colloidal nature of E. coli cells under applied current density. Plasmid deoxyribonucleic acid degradation study confirmed fragmentation and degradation of released genetic material. Overall, effective disinfection could be achieved by electro-oxidation, which ensures effective inactivation and prevents regrowth of E. coli. Disinfection of real wastewater was achieved in 12 min at an applied current density 30 mA cm−2. Real wastewater study further confirmed that effective disinfection is possible with a low cost electrode material such as Ti/Sb–SnO2/PbO2. Energy consumed during disinfection was determined to be 4.978 kWh m−3 for real wastewater disinfection at applied current density 30 mA cm−2. Cost of operation was estimated and stability of the electrode was studied to evaluate the feasibility of large scale operation. Relatively low energy and less disinfection time makes this technology suitable for field scale applications.