Comprehensive study on the role of reactive oxygen species and active chlorine species on the inactivation and subcellular damage of E.coli in electrochemical disinfection

Abstract

Comprehensive study on the roles of reactive oxygen species (ROS) and active chlorine species (ACS) on the failure of bacteria cell were crucial for the development of electrochemical oxidation disinfection. Pure Na2SO4 and chloride-containing solution were used to generate ROS and ACS, separately. When 14.4 mA/cm2 current density was applied, 5 logs reduction of E.coli was achieved with 60 min treatment in pure Na2SO4 solution, while in the chloride-containing solution, E.coli was completely inactivated in 15 min as the initial concentration was about 7.5 logs. Cell membrane damage is a crucial step in electrochemical oxidation disinfection process. With 3.6 mA/cm2, there were ∼ 1.1 logs cells injured and it was about 37 times to that of inactivated cells with 5 min treatment in pure Na2SO4 solution. Hydroxyl radical and superoxide radical were confirmed responsible for the inactivation of E.coli in pure Na2SO4 electrolyte, while hypochlorite was dominated in chloride-containing solution. Noticeable shrinkages, wrinkles, and indentations were observed on the cell surfaces after treatment without any differences for ROS and ACS. However, total protein would be the attacking point for ROS rather than ACS. The changes of Optical density, total organic carbon, and potassium ions leakage presented slight differences. Nucleic acid matters may be destroyed in the electrochemical disinfection process, while the damage on nucleic acid fragment need more research to reveal.