Environmental improvement of hydroponics solution using discharge plasma under water

We developed a system using a discharge plasma under water for inactivating bacteria in hydroponics system, and carried out a pilot test of the developed discharge plasma system in a greenhouse for the period of 5 months using tomato plants in hydroponics system. The plasma reactor consisted of a wire electrode which was placed in an insulating circular cylinder, and a grounded electrode on cylinder outside. The reactor was sunk under the hydroponics solution and atmospheric air was injected into the cylinder using a gas pump. Repetitive nanosecond high-voltage pulses were applied to the wire electrode, using a magnetic pulse compression (MPC) pulsed power generator. Concentration of dissolved ozone into 100 L solution was approximately 0.3 ppm in the early 30 minutes. The developed system worked for 5 months in stable. The all plant bodies healthily grew and produced fruit bodies normally without infection of bacteria. This result suggested that the plants had no damage by the oxidative stress. The performance of the developed system was also evaluated using hydroponics solution contaminated with Ralstonia solanacearum, a plant pathogenic bacterium. The number of colony forming unit (CFU) of R. solanacearum in the solution was decreased from 10⁷ to 10² CFU/mL by operating the discharge plasma system for 100 minutes. The bacterial wilt disease was significantly suppressed by the discharge plasma, in contrast, all seedlings in a positive control wilted and died by infection of R. solanacearum. (author)