Methane hydrate (MH) in Nankai-trough is expected as a Japanese domestic future energy resource of natural gases. It is mainly condensed in the pores of unconsolidated oceanic sedimentary layers. CO₂ hydrate that formed from CO₂ and water shows functions of exothermic heat and phase equilibrium in the same environment under the sea bottom. The functions of CO₂ hydrate could be used for enhanced recovery of methane hydrate. We had shown experimental validations that warming ability of the layer sediments by using exothermic heat of CO₂ hydrate and CO₂ injection method using the phase equilibrium of CO₂ hydrate. In this paper, we show experimental validation about the phenomena about the exothermic heat of CO₂ hydrate formation and CO₂ permeation when CO₂ is injected into super cooling layer sediments, which temperature is lower than phase equilibrium temperature by few degrees Celsius. We think that this validation made higher adaptability of CO₂ for enhanced recovery of methane hydrate.

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 In this study, leaching behaviors of heavy metals from the tsunami sediments by the Great East Japan Earthquake and their risks to human were evaluated. There were any samples in excess of Japanese criteria for the leaching values of arsenic and lead. The heavy metals content in the tsunami sediments were lower than Japanese criteria, which geometric means were calculated to be 1.1 mg/kg for arsenic, 6.7 mg/kg for lead, 0.064 mg/kg for cadmium and1.7 mg/kg for chromium. The risk levels of heavy metals in tsunami sediment to human health were not so much high, because the exposure rates, which were estimated to be 1.4×10^-2 μg/kg/d for arsenic, 8.1×10^-3 μg/kg/d for lead, 4.6×10^-3 μg/kg/d for cadmium and 8.9×10^-3 μg/kg/d for chromium, were much lower than their acceptable intakes.

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 It seems important to examine heavy metal concentration in playgrounds, to evaluate potential risk for heavy metal ingestion by children. In this study, heavy metal concentrations of soil samples in 40 playgrounds in K-city were investigated by the voltammetric method. To visualize heavy metal concentration distribution in playgrounds, free GIS software MANDARA was used. According to the comparison between the 1 N HCl dissolved concentration and the PTWI (Provisional Tolerable Weekly Intake), playgrounds in K-city may not have intake risk of lead. Even if the possibility of the risk was very low, there are differences of the intensities. As for the specific playground where concentration is high, investigating continuously may be desirable hereafter.

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 Charcoal produced from excess sludge appeared to be useful for removing SMP (soluble microbial products) in MBR (membrane bioreactors) and therefore for reducing membrane fouling. Batch experiments and long-term MBR experiments were performed by using charcoal made of actual excess sludge. In the batch experiments, SMP was removed effectively through charcoal addition. This approach proved especially effective for the removal of carbohydrate. Charcoal would serve as an absorbent and coagulant in SMP removal. High BOD (biochemical oxygen demand) removal efficiencies produced no negative effects on biological activity in the reactors during the long-term MBR experiments involving charcoal addition. The decrease of humic substances and COD (chemical oxygen demand) through charcoal addition suggested that this approach effectively enhanced the performance of activated sludge treatment. A charcoal addition of more than 0.1% in long-term MBR experiments effectively decreased the membrane fouling frequency. The use of charcoal therefore served to mitigate membrane fouling. A decrease in carbohydrate, corresponding to the increase in the mean fouling period, suggested that a charcoal addition of more than 0.1% effectively removed SMP, especially carbohydrate. A charcoal cyclic reuse system is also proposed. This system would involve charcoal production and charcoal addition to MBR.

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