Naoya Satta

Factors affecting interaction of radioiodide and iodate species with soil

Abstract The uptake of radioiodide and iodate species by soil dried at 100 °C (particle size of less than 0.25 mm) was studied in laboratory batch experiments for three major groups of variables: (i) experimental conditions (ambient temperature, liquid-to-solid ratio and contact time), (ii) solid phase conditions (grain size and washing treatment), and (iii) liquid phase conditions (pH, and concentrations of electrolytes and carrier). Effects of the presence of soluble and insoluble organic matter were also investigated in relation to radioiodine uptake by the soil. Plural uptake mechanisms were considered for iodide species, while a simple anion exchange process for iodate.

Purification of High-Conductivity Water Using Gas–Liquid Phase Discharge Reactor

Water purification by streamer discharge using pulsed-power generator under a high-conductivity water containing pollutants has been investigated. A gas-liquid separated reactor was developed to treat highly conductive solution. A wire electrode was placed in the gas phase and a plane electrode was immersed in the water. A pulsed high voltage generated by six stacked Blumlein lines was applied to the wire electrode to generate streamer discharge in the gas phase, which propagated into the air bubble injected into the water. Indigo carmine solution was employed as a specimen. Natrium chloride was used to adjust the solution conductivity in the range from 10 to 30 000 S/cm. A solution with 30 000- S/cm conductivity was successfully decolorized with energy efficiency of 75 mg/Wh. Some species of gas such as air, oxygen, nitrogen, and argon were injected to clarify dominant reactions of the decolorization. The result showed that the ozone produced by gas-phase discharges mainly contributed to the decolorization of the solution. The decolorization rate depended on the chloride ion supplied from the natrium chloride by scavenging of hydroxyl radical and on the copper ion eluted from the plane electrode by redox reactions such as Fenton reactions.

Improvements in plant growth rate using underwater discharge

The drainage water from plant pots was irradiated by plasma and then recycled to irrigate plants for improving the growth rate by supplying nutrients to plants and inactivating the bacteria in the bed-soil. Brassica rapa var. perviridis (Chinese cabbage; Brassica campestris) plants were cultivated in pots filled with artificial soil, which included the use of chicken droppings as a fertiliser. The water was recycled once per day from a drainage water pool and added to the bed-soil in the pots. A magnetic compression type pulsed power generator was used to produce underwater discharge with repetition rate of 250 pps. The plasma irradiation times were set as 10 and 20 minutes per day over 28 days of cultivation. The experimental results showed that the growth rate increased significantly with plasma irradiation into the drainage water. The growth rate increased with the plasma irradiation time. The nitrogen concentration of the leaves increased as a result of plasma irradiation based on chlorophyll content analysis. The bacteria in the drainage water were inactivated by the plasma irradiation.

Improvement of growth rate of plants by bubble discharge in water

The effect of bubble discharge in water on the growth rate of plants was investigated experimentally for application to plant cultivation systems. Spinach (Spinacia oleracea), radish (Raphanus sativus var. sativus), and strawberry (Fragaria × ananassa) were used as specimens to clarify the effect of the discharge treatment on edible parts of the plants. The specimens were cultivated in pots filled with artificial soil, which included chicken manure charcoal. Distilled water was sprayed on the artificial soil and drained through a hole in the pots to a water storage tank. The water was circulated from the water storage tank to the cultivation pots after 15 or 30 min discharge treatment on alternate days. A magnetic compression-type pulsed power generator was used to produce the bubble discharge with a repetition rate of 250 pps. The plant height in the growth phase and the dry weight of the harvested plants were improved markedly by the discharge treatment in water. The soil and plant analyzer development (SPAD) value of the plants also improved in the growth phase of the plants. The concentration of nitrate nitrogen, which mainly contributed to the improvement of the growth rate, in the water increased with the discharge treatment. The Brix value of edible parts of Fragaria × ananassa increased with the discharge treatment. The inactivation of bacteria in the water was also confirmed with the discharge treatment.

Influence of pulse width on decolorization efficiency of organic dye by discharge inside bubble in water

Decolorization of an organic dye by discharge in high conductive water using a pulsed power generator and a discharge reactor was investigated. The discharge reactor consisted of a glass tube and a tungsten wire inserted into the glass tube, which was immersed in the water. Room air was injected into the glass tube to generate bubbles in the water. High voltage pulses were generated by an inductive-energy storage system using semiconductor opening switch (SOS) and by a magnetic pulse compression circuit. Fast recovery diodes were used as SOS diode in the inductive-energy storage system. The pulse width was changed in range from 10 to 1200 ns. The high voltage was applied to the tungsten wire. Indigo carmine was employed as a specimen to evaluate decolorization efficiency. Potassium nitrate was used to adjust the solution conductivity. The dye solution was successfully decolorized at 7 mS/cm conductivity. Energy efficiency for decolorization increased from 0.680 to 55.6 mg/Wh with decreasing the pulse width from 1200 to 10 ns owing to the reduction of ohmic loss.

Water Remediation Using Pulsed Power Discharge under Water with an Advanced Oxidation Process

Abstract In the present study, the degradation of organic contaminants by streamer discharge using a pulsed power generator under water is investigated. The experiments are conducted based on the decolorization of two dyes, Acid Red 1 and Acid Blue 74, and the decomposition of 1,4-dioxane. A gas-liquid separated reactor is developed and employed to achieve degradation with high energy efficiency. A tungsten wire electrode is placed in the gas phase, and a grounded 316 stainless steel wire is immersed in the water. The pulsed high voltage is generated by a magnetic pulse compression circuit and is applied to the wire electrode to generate streamer discharges in the gas region, which propagate into the bubble injected into the water. Oxygen and argon gases are injected to identify the dominant reactions of the degradation of organic contaminants. Acid Red 1 and Acid Blue 74 solutions are successfully decolorized by the discharges. The ozone produced by discharges in the gas region primarily decolorizes the dye solutions. The total organic carbon (TOC) of the 1,4-dioxane solution decreases due to discharge when argon is injected. The decrement rate of TOC does not increase through gaseous ozone injection or by discharges in the case of oxygen injection. These results show that the chemical species produced by discharges and by chemical reactions in the solution, such as hydroxyl and hydroperoxyl radicals, primarily decompose 1,4-dioxane. Iron ions dissolved by electrolysis enhanced the TOC decrement rate according to the Fenton reaction in acidic conditions.

Development of Pulsed Discharge Inside Bubble in Water

The development of pulsed discharges inside a stationary air bubble in water was observed using an intensified charge-coupled device camera with high-speed gate. The discharges were ignited from a tungsten wire inserted into a glass tube, which was immersed in the purified water. The pulsed high voltage was applied to the wire by an inductive energy storage system pulsed-power generator. The streamer discharge was propagated into the bubble from the wire tip with a propagation velocity of 0.5 mm/ns. A back discharge was observed due to a charge accumulation on the water surface and the glass tube.

Influence of sodium carbonate on decomposition of formic acid by pulsed discharge plasma inside bubble in water

The influence of sodium carbonate on the decomposition of formic acid by discharge inside bubbles in water was investigated experimentally. Oxygen or argon gases were injected into the water through a vertically positioned glass tube, in which the high-voltage wire electrode was placed to generate plasmas at low applied voltage. The concentration of formic acid was determined by ion chromatography. In the case of sodium carbonate additive, the pH increased owing to the decomposition of the formic acid. In the case of oxygen injection, the percentage of conversion of formic acid increased with increasing pH because the reaction rate of ozone with formic acid increased with increasing pH. In the case of argon injection, the percentage of conversion was not affected by the pH owing to the high rate loss of hydroxyl radicals.

Determination of Iodide, Iodate and Total Iodine in Natural Water Samples by HPLC with Amperometric and Spectrophotometric Detection, and Off-line UV Irradiation

We developed a rapid, simple method for the iodine speciation analysis of water and applied it to natural water samples. Simultaneous determinations of I(-) and IO3(-) were achieved with an HPLC system with amperometric detection for I(-) and spectrophotometric detection after a postcolumn reaction for IO3(-). We determined the I(-) and IO3(-) concentrations in 20-μL water samples within 10 min. Total I concentrations in water samples were determined after the decomposition of organics by off-line UV irradiation for 30 min, followed by reduction to I(-). The analytical conditions were optimized by using test solutions rich in organic matter extracted from soils. We tested the new method with samples of groundwater, spring water, precipitation, soil percolate, stream water, and seawater as well as solutions extracted from soil. The method worked well, although the concentrations of some I species were below detection. This method is suitable for routine speciation analysis, which is important for studies of I behavior in the environment.

Soil Solution Ni Concentrations over which Kd is Constant in Japanese Agricultural Soils

The soil-soil solution distribution coefficient (K d) is one of the most important parameters required by the models used for radioactive waste disposal environmental impact assessment. The models are generally based on the assumption that K d is independent of the element concentration in soil solution. However, at high soil solution concentrations, this assumption is not valid. Since the sorption of most radionuclides in soil is influenced by their stable isotope concentrations, it is necessary to consider if the range in the naturally occurring stable isotope concentrations in the soil solution is within the range over which K d is valid. The objective of this study was to determine if the K d for nickel (Ni) can be assumed to be constant over the ranges of stable Ni concentration in five main Japanese agricultural soil types. To obtain Ni sorption isotherms for five Japanese soils, two types of batch sorption tests were carried out using radioactive 63Ni as a tracer. The concentration at which the relationship between soil and soil solution concentration became nonlinear was determined using the two types of sorption isotherms: the Langmuir and Henry isotherms. The result showed that the Ni concentration in the soil solution at which the assumption of a constant K d becomes valid is at least ten times higher than the natural Ni concentrations in solutions of Japanese agricultural soils. This value is sufficient to treat K d for Ni as constant for environmental impact assessment models for the disposal of radioactive waste.