Residual effects and energy cost of gliding arc discharge treatment on the inactivation of Escherichia coli in water

The present study investigated the residual effect of gliding arc discharge (GAD) treatment on the inactivation of bacteria in a large volume of water (i.e., 20 L). Pure water and air were introduced to GAD separately, and then both the gas and water treated by plasma were sent to bacteria-containing water. Water contaminated by Escherichia coli (E. coli) was first treated by GAD for 10, 13 and 16, and 25 min and then stored for the next 4 h, during which time the E. coli concentration and pH were measured. In general, GAD produced the strong anti-microbial properties, a phenomenon which increased with plasma treatment time. More specifically, E. coli was partially inactivated (i.e., approximately 2.7-log reduction) with 16-min plasma treatment. However, E. coli was almost completely inactivated (over 99.9% with 5-log reduction) during the subsequent 4-h storage period, a phenomenon that was attributed to the residual effect of the plasma treatment. The optimum plasma energy cost of the GAD treatment to inactivate E. coli in 20-L water in the present study was found to be approximately 0.57 kJ/L per 1-log reduction.