Fundamental characteristic of reduction of energy consumption in water sterilization using nonthermal plasma

In recent years, plasma sterilization technologies have been studied and developed remarkably. Ozone (O
₃
) is effective and its application is extended to water purification. In general, O
₃
is generated with nonthermal plasma (NTP) from oxygen (O
₂
). In this process, an extra O
₂
gas cylinder or an O
₂
supplying device is needed. It takes running and energy costs. As an alternative method, air is used as a source gas. However, nitrogen oxide (NO
_x
) is also generated in the process of plasma discharge. Because NO
_x
is one of air pollutants, this method is not desirable. A method with low-energy cost and no emission of air pollutant is required. In view of this background, an energy-saving type of NTP sterilization system is proposed. The system utilizes electrolysis of water to produce oxygen and hydrogen. The oxygen is a source of ozone for sterilization, and the hydrogen is used for electric power generation in fuel cells. Fundamental understanding of ozone production is obtained, regarding energy-saving. On basis of the fundamental understanding, the NTP sterilization system is achieved. As a result, energy consumption in ozone production is reduced with a power recovery rate more than 10% and high efficient water sterilization is achieved.