Experimental Study On The Inactivation Effect Of E. Coli By Atmospheric Pressure Plasma Jet

With the rapid development of global industrialization, the water pollution of china’s water resources has recently become even more serious, and then the drinking water shortage and hygiene problems will directly affect human survival and development. Drinking water and environmental hygeine has become a global environmental problem, especially E. coli bacteria contamination.This paper mainly discussed the atmospheric pressure plasma jet（Atmospheric Pressure Plasma Jet, APPJ） inactvated the E. coli bacteria of the surface and the aqueous environment, studied the discharge characteristics of APPJ, and examined the effects of E. coli bacteria inactvation by experimental parameters, such as, gas flow rate, discharge voltage, gas source component and so on. At the same time, this paper discussed the E. coli bacteria inactvation mechanism of APPJ by analyzing the optical emission spectroscopy（OES）, the change of aqueous chemical oxidative substances, and the change of cell structure of E. coli bacteria after APPJ treatment. The main research results are as follows:（1） APPJ length was related with the experimental parameters, such as discharge voltage, gas flow rate and gas supply. APPJ length became longer with the discharge vol tage increased, APPJ length became longer and then shorter with the increase the gas flow rate, N₂/O₂ hybrid gas source APPJ length became longer with oxygen content increased.（2） APPJ discharge generated the plume, high frequency pulse peak was found in voltage curve, the frequency of peak pulse increased with the discharge voltage increased, the peak pulse value increased as the discharge voltage became larger. In the OES of APPJ, NO_-γ, N₂⁺, OI, ·OH and other active substances were observed.（3） The inactvation of E. coli bacteria on agar surface was experimentally investigated. Under the number of bacteria, gas flow rate, discharge voltage and treat distances and N₂/O₂ ratio were 9.6（±0.3）×102, 4.0 L/min, 6.8 k V and 20 mm, treat 3 min, 1:4, respectively, the inactvation rate reached 98.4%, and its inactvation effect was close to the inactvation of oxygen source APPJ. The inactvation rate of E. coli bacteria on agar surface increased with the increase of gas flow rate and the discharge voltage. When the gas flow rate and the discharge voltage were over 4.0 L/min and 6.8 k V, respectively, the inactvation effect was stabilized and no longer obvious.（4） This paper investigated the inactvation of E. coli bacteria in aqueous environment by experimental study. Experimental study found that under the bacterial concentration, gas flow rate and discharge voltage were 3.5×106（±0.3） CFU/mL, 4.0 L/min and 6.8 kV, respectively, when gas source component was N₂/O₂ ratio at 1:4, the E. coli bacteria inactvation effect was closed to oxygen source APPJ after 40 min treatment. The inactvation of E. coli bacteria was related with bacterial concentration, discharge time, the gas source component, discharge voltage and gas flow rates. Under the same experimental conditions, the lower bacterial concentration, the better E. coli bacteria inactvation. With the changes of the discharge time, gas flow rate and discharge voltage, the E. coli bacteria inactvation also changed with a positive correlation. Gas source component as the oxygen content increased, the E. coli bacteria inactvation was better, N₂/O₂ ratio at 1:4 APPJ and O₂ APPJ were closed.（5） Through the analysis of optical emission spectroscopy under different experimental conditions, it was found that the E. coli bacteria inactvation were largely affected by the intensity of activity particles(NO_-γ, ·OH, OI). The aqueous chemical oxidative substances changed after APPJ treatment, charged particles（NO₂^-, NO₃^-） made the solution pH decrease, and the conductivity increase; when the experimental conditions changed the concentration of O₃ and H2O₂ in solution also changed. Under discharge voltage, gas flow rate and N₂/O₂ ratio were at 6.8 k V, 4.0 L/min and 1:4, respectively, O₃ and H₂O₂ concentration reached 1.4 mg/L and 15.4 mg/L after APPJ 60 min treatment. These charged particles and active substances played a pivotal role on the inactivation of E. coli bacteria.