固体硫黄を用いた独立栄養脱窒(SLAD)法の問題点を改善した新しい脱窒資材である硫黄-石灰石粉混合造粒物(SC11)について脱窒温度特性の測定と畑地暗渠排水における現地脱窒実験を行い,次の結果を得た。1)SC11を用いた脱窒反応の温度特性では,15℃以上で脱窒が確認された。しかし20℃以下での脱窒能力の低下は著しく,実用には20℃以上が望ましい。2)SC11(2～50mm)を用いた暗渠排水脱窒実験では,硝酸性窒素の平均濃度75mg/lに対し,1日資材重量当たり2倍量(v/w)以下の流速,または1日資材1kg量当たり160mg以下の硝酸性窒素負荷量では99%以上の除去率が得られ,処理水中に亜硝酸性窒素は認められなかった。3)1日資材重量当たり2倍量以上の流速では,不完全な脱窒により処理水中に亜硝酸性窒素が残存した。このときの脱窒速度は,流速にかかわらずほぼ一定の値を示し,生成する硫酸の総量も一定であった。したがって流速を増すほど除去率は低下した。このことから硫黄を用いた脱窒処理は最適な流速の制御が重要であることが示された。4)処理水のpHはほぼ7.0±0.5の範囲に保たれ,生成する硫酸濃度に関係なく優れた中和応答を持続した。

To improve the problem of the sulfur-limestone autotrophic denitrification (SLAD) process for treatment of nitrate-nitrogen contaminated water, novel material for denitrification bed was developed such as granulated sulfur-limestone mixture (SC11) which was made from sulfur and limestone of equal quantity in weight. The feasibility of the denitrification treatment by SC11 for underdrainage was studied. In batch experiments, the influence of temperature over the capacity of denitrification was examined with feed solution, SC11 and seed sediment. That capacity increased with the temperature in a range from 15℃ to 30℃. The decline of the denitrification ability was serious at lower temperatures. Therefore, the desirable temperature condition for SLAD process was higher than 20℃. In field experiment, nearly 100% of removal efficiency of NOx (NO_3^-+NO_2^-) was observed in the flow rate of twice as large as amount of SC11 (v/w) per day, on the effluent of the tile drain system, which contained approximately 75mg/l of NO_3^--N in average concentration. In this case, the maximum denitrification rate was 207mg of N per kilogram of SC11 per day. When the flow rate exceeded the level above, NO_2^- of the intermediate product was accumulated in the treated water, so that the removal efficiency of NOx decreased. Although the flow rate fluctuated, the pH level of the treated water was approximately neutral throughout the experiment period. The neutralization capacity of SC11 performed high responsibility independent of the concentration of SO_4^<2-> which was produced in the process.

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