Journal of Environmental Conservation Engineering

There is an urgent need for use of treated water in conservation efforts in terms of biodiversity and the efficient use of water resources. This study investigated the effect on, and use of, treated water for a compensatory mitigation project on the endangered species, Mortonagrion hirosei. This project was undertaken in 2006, and has used treated water since 2007. The changes in population size and habitat were studied and little change was noticed between 2006 and 2007. Therefore, it is conceivable that the use of treated water for conservation caused few problems for the compensatory mitigation of M. hirosei. On the other hand, it is possible that the effects on habitat appear only after a few years, because rhizomes such as Phragmites australis absorb nutrients in the treated water. Thus, sustainable conservation success requires long term continuous monitoring.

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　The removal of high-concentration nitrogen using subcritical hydrothermal reactions of equivalent mixtures of NO₂^－ converted from the original NH₄^＋ and NH₄^＋ without a catalyst was studied. This reaction was carried out in a pressure bottle shaken for 1h with three kinds of initial substrate concentrations: 1,500, 3,000, and 5,000 ㎎/L of either NH₄-N or NO₂-N while setting the temperature at 140, 160, 180, or 200℃.
In the cases where the reaction temperatures were 180 and 200℃, over 90％ of the total nitrogen successfully decomposed at the initial concentrations in the artificial water. Even if the reaction temperature was lowered to 140℃, over 90％ was removed when the concentration of NH₄-N and NO₂-N were over 5,000 ㎎/L.
On the other hand, it was necessary to achieve above a 90％ total nitrogen decomposition value when the initial concentration of NO₂-N was 1.6 to 2.2 times higher than that of NH₄-N when biologically treated water were used.
The combined treatment of a subcritical hydrothermal reaction followed by a biological nitrite reaction, can effectively remove high concentrations of nitrogen in industrial wastewater.

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