Development and pilot test of sterilization system using discharge reactor for hydroponics solution

A system using a discharge reactor under water for sterilizing plant pathogenic bacteria in hydroponics solution was developed and evaluated in terms of a sterilization rate through a pilot test. In the reactor part, a wire electrode was placed in an insulating cylinder, and a grounded plate electrode was placed outside of the cylinder. The reactor was sunk under the solution. Air was injected into the cylinder with 7.5 L/min in flow rate. 10 kV of nanosecond pulse was applied to the wire electrode with a pulse repetition rate of 2,000 pulse per second, using a magnetic pulse compression. The amount of dissolved ozone was estimated with decolorization efficiency of indigocarmine solution. As the result, the amount of dissolved ozone into 4 L solution in the system for a minute was obtained as approximately 0.5 mg. The sterilization property was evaluated with a number of colony-forming unit (CFU) of Ralstonia solanacearum, plant pathogenic bacterium, in hydroponics using tomato seedlings. The hydroponics solution was contaminated with R. solanacearum, operating the system for 100 minutes. As the result, the number of CFU of R. solanacearum in the solution was decreased from 107 to 102 CFU/mL. After that, bacterial wilt disease was significantly suppressed, in contrast, all seedlings in a positive control wilted and died. A pilot test of the system was carried out in a greenhouse for around 3 months using tomato plants in hydroponics without the intentional contamination with bacteria. All plant bodies healthily grew and bore fruits, and onset of bacterial wilt disease was not observed, suggesting no damage by the oxidative stress.