Investigation of inactivation process for microorganism collected in an electrostatic precipitator

Abstract This study is aimed at investigating an inactivation process of microorganismscollected by a two-stage type electrostatic precipitator(ESP). The experimental systemconsisted 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 electrodesin these sections. Negative DC high voltages were applied to these sections. The gas flow velocity in the experimental systemwas 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 microorganismswere 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 electrodewas 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 microorganismswere inactivated by the corona discharge. The observation using the fluorescence microscopeshowed that the amount of dead microorganismswas greater than that of the living microorganismsafter 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 microorganismscollected 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.