Takamasa Sakai

Development of agricultural soil sterilization using ozone generated by high frequency dielectric barrier discharge

Abstract We have developed the ozone generation system suitable for soil sterilization and ozone supplying system into the soil. The coaxial dielectric barrier discharge produced the ozone with high concentration at high efficiency. Injection of the on- site generated ozone gas into the soil resulted in decreasing soil pathogen and changing chemical properties of the soil. We studied ozone sterilization of agricultural soil when it was treated by varying ozone dosages and process duration. The temporal and spatial properties of the soil were monitored using the pH and electrical conductivity. The bacteria populations, pathogen and soil-borne fungi were measured after various ozone treatment procedures. 100g/m3 of ozone was injected into the soil at a flow rate of 2 liter/min during 60 min. The pH shows drastic change in 40 min that will be one of indexes indicating the sterilization level. In this treatment 100% of the bacteria in the agricultural soil was killed.

Properties of soil treated with ozone generated by surface discharge

Chemical contamination in plants, soil, and ground water has become serious by overuse of pesticides and nitrogen fertilizers in agriculture. We propose the use of ozone generated by atmospheric pressure plasma for soil disinfection as one of the plasma applications into agriculture. Because ozone has strong oxidation potential to decompose organic substances in soil, it is considered to be one of the candidates as potential alternative to both pesticide and nitrogen fertilizer. In this paper, fundamental studies on changes in acidity and amounts of nitrogen nutrients, bacteria, mold, and soil DNA remained in soil after ozone treatment were carried out with a system using a quartz chamber. Surface barrier discharge that operates in atmospheric oxygen was used in the system as the ozone generator. In addition, growth of radishes that seeded on soils in pots that were treated by ozone diffusion method was also evaluated.

Fundamental Study on Ozone Treatment of Soil for Agricultural Application

In this study, influence of ozone treatment on physical properties of soil was investigated. We used a quartz container for ozone treatment of soil. The amount of soil used for ozone treatment was 300 g. Treating time was 30 min. Flow rate of ozone gas was 1.5 L/min. We measured characteristics of soil such as pH(H2O) and inorganic nutrient content (NO3-N, NO2-N and NH4-N) before and after ozone treatment. Exhaust ozone concentration from the quartz container was monitored with an ozone monitor. The temperature of soil was measured with a thermo-couple during treatment. Ozone amount reacted with soil was about 0.99 g when soil was stirred. Ozone amount was about 0.82 g when soil was not stirred. Contents of NO3-N and NH4-N increased by one order after treatment and subsequently kept a constant quantity. The pH(H2O) decreased drastically to strong acidic region (pH(H2O)=5.0) just after ozone treatment, which is too acidic for growth of crops. However, the pH(H2O) value recovered gradually with time.

Influence of Ozone Treatment on Soil Nutrient and Acidity with Low Ozone Dose Rate

In this study, the influence of ozone treatment on physical properties of soil with low ozone dose rate was investigated. Ozone was generated by oxygen plasma using a dielectric surface barrier discharge and injected into soil in a quartz container which is rotated by a motor. The amount of soil used for the treatment was 100 g. Treating time was 1 min. The ozone dose rate, which is defined as ozone dose weight per unit weight of soil, was 0.1 %. Flow rate of ozone gas was 1.5 L/min. We measured the characteristics of soil such as inorganic nutrient contents (NO3-N, NO2-N, and NH4-N), pH(H2O), amount of fungi (nitrite and nitrate bacteria), amount of DNA of soil, and amount of exchangeable base (Ca, K, Fe, and Al) with low ozone dose. We measured physical properties of soil among three samples for confirmation of measurement reproducibility. Content of NO3-N and NH4-N increased slightly by ozone treatment for 1 min., and subsequently maintained at a constant value with time. The pH(H2O) decreased just after ozone treatment. However, the pH(H2O) value recovered gradually with time by the buffering function.