Basic Study of Sterilization at Low Discharge Voltage by Using Microplasma

Sterilization of micro-organism, such as Escherichia coli, is experimentally investigated by using microplasma. Microplasma is suitable for practical application of sterilization, since its discharge voltage is low and its apparatus could be small and inexpensive. In this study, Gram-negative Escherichia coli HB101 and Gram-positive Bacillus subtilis JCB 20036 are used as the target to be sterilized. From the series of experiments, decrease in the amount of germs is effectively obtained after microplasma treatment. The effect of sterilization increases as the discharge voltage increases. When air is used as carrier gas, sterilization rate is 100% at the discharge voltage of 1.05 kV and when nitrogen is the carrier gas, sterilization rate is 77% at the maximum discharge voltage of 1.15 kV for the Escherichia coli. These results could be the combined actions of active radical species such as ozone, UV radiation and, high electrical fields of microplasma. Bacillus subtilis was sterilized with a rate of 97% at a discharge voltage of 1.07 kV in the case of air carrier gas and in the case of gas carrier nitrogen with a rate of 70% at a discharge voltage of 1 kV.