Investigation of inactivation process for microorganism collected in an electrostatic precipitator

This study is aimed at investigating an inactivation process of microorganisms collected by a two-stage type electrostatic precipitator (ESP). The experimental system consisted of a discharging section and an electrostatic section. A bacterial culture of Staphylococcus aureus, as a model of airborne microorganisms, was put on the surface of grounded plate electrodes in these sections. Negative DC high voltages were applied to these sections. The gas flow velocity in the experimental system was 0.5 m/s. The survival ratio was calculated by the colony counting method, and the amount of 250-nm-absorbing substance, such as protein and minerals, was measured using a spectrophotometer. Living and dead microorganisms were distinguished using a fluorescence microscope, and their forms were observed using a scanning electron microscope (SEM). Reactive oxygen species (ROS) distribution on the surface of the grounded plate electrode was observed using a gel reagent. The collection efficiencies and the ozone concentrations were also measured in a single-stage ESP and the two-stage type ESP. As a result, ROS concentration was the greatest under the wire electrode. The result of the colony count showed that microorganisms were inactivated by the corona discharge. The observation using the fluorescence microscope showed that the amount of dead microorganisms was greater than that of the living microorganisms after the inactivating treatment. The SEM observation revealed that the cell walls were destroyed, and the result obtained with the spectrophotometer showed an increase in the amount of 250-nm-absorbing substance. These results indicated ROS destroys cell walls and causes cell content to flow out, whereby microorganisms collected in an ESP are inactivated. It was also revealed that the collection efficiency can be improved without increasing ozone concentration and energy consumption in the two-stage type ESP.