A Novel Wastewater Treatment Method Using Electrical Pulsed Discharge Plasma over a Water Surface

Electrical pulsed discharge plasma produces various powerful oxidizing agents, such as hydroxyl radicals and ozone, which have high oxidation potential. These species play an important role in the decomposition of persistent organic compounds in wastewater. Because highly concentrated oxidants are directly produced inside the plasma, plasma realizes high-speed wastewater treatment without pretreatment of samples, such as pH adjustment. The pulsed discharge plasma generated over the water surface and inside bubbles is highlighted as a highly efficient method for plasma generation and radical supply into wastewater. In this paper, the physical and chemical properties of the discharge plasma generated over a water surface are described. The decomposition of persistent organic compounds dissolved in wastewater, such as 1,4-dioxane, formic acid, and dichloromethane, by plasma discharge is demonstrated, and their mechanisms are discussed. These persistent compounds, which have strong toxicity and stability, can be efficiently decomposed and removed quickly from solutions by plasma treatment. Furthermore, the treatment of nutrient solutions used in hydroponic systems for plant cultivation is also introduced as a novel application of plasma, and the effects of bacterial inactivation, decomposition of allelochemicals, and improvement in plant growth by plasma are demonstrated

Soil solution Ni concentrations over which Kd is constant in Japanese agricultural soils

The soil-soil solution distribution coefficient (Kd) 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 Kd 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 Kd is valid. The objective of this study was to determine if the Kd 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

Determination of Chemical Form of Antimony in Contaminated Soil around a Smelter Using X-ray Absorption Fine Structure

Only limited information is available about the behavior of antimony (Sb) in contaminated soils. However, understanding the behavior of Sb in contaminated soils is important, because the toxicity or solubility of this element depends on its chemical state. In this study, we investigated the levels of Sb and the chemical forms of Sb in the soil around a smelter using X-ray absorption fine structure (XAFS) spectra. The highest Sb concentration in the contaminated soil was 2900 mg/kg dry soil. According to Sb-K edge X-ray absorption near edge (XANE) spectra, the Sb in the soil was in the form of Sb(V) compounds. The similarity of extended XAFS (EXAFS) spectra suggests that Sb speciation was independent of the sampling site, which indicates that Sb or Sb2O3 emitted from the smelter was converted into Sb(V) compounds in the soil