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A swim-bed attached-growth bioreactor (BF reactor) using a novel acryl-fiber biomass carrier (Biofringe: BF) for treating Hanoi groundwater, which is polluted by high levels of ammonium, has been developed. The swim-bed technology is aerobic and combines the advantages of fix-bed attached-growth processes, which can retain high amounts of slowly growing nitrifiers, and moving-bed attached-growth processes, which avoid clogging problems. Experiments were conducted in 7.7-l reactors, using synthetic Hanoi groundwater, containing 30 mg-N/l of ammonium. Two reactors (BF1 and BF2) were used to investigate the ammonium removal capacities; BF1 was fed influent containing 5 mg/l of iron and BF2 was fed influent without iron. Maximum ammonium removal rates of 0.24 and 0.48 kg-N/㎥/d, corresponding to hydraulic retention times (HRTs) of 3 and 1.5 hours were achieved for BF1 and BF2, respectively and nitrification efficiencies are close to 98% for the both reactors. The ferrous form of iron was oxidized to the ferric form as a hydroxide (Fe(OH)3), which was mostly washed out. This resulted in a high iron removal efficiency (98%) with effluent suspended solid (3-6 mg/l) containing a low volatile suspended component (20%). Nitrification efficiency decreased sharply due to a decrease in temperature from 25 to 15°C, but efficiency quickly recovered following 1 day of operation, demonstrating that the attached-immobilized nitrifiers in BF reactor were able to adapt to the decrease in temperature. Nitrifying bacteria communities from BF reactors were investigated with rRNA-based molecular techniques, and ammonia oxidizers as Nitrosomonas were found in both reactors. Ammonia oxidizers identified as a Nitrosospira sp. were also found in BF2.高濃度のアンモニア性窒素に汚染されたハノイ市の地下水をアクリル繊維製の担体 (バイオフリンジ : BF) を活用する揺動床で硝化処理した。空気による循環曝気で運転される揺動床処理システムは、固定床と流動床の特性を併せ持っているので、汚泥閉塞のない状態で、生育速度の遅い硝化細菌をリアクタ内に安定して付着固定化することが可能である。容量7.7lの揺動床リアクタ2台を用いて、ハノイ市の地下水成分に基づき調整したアンモニア性窒素を30mg/lの濃度の合成地下水を硝化処理した。一つ目のリアクタ (BF1) には、Fe (II) を5 mg/lの濃度で含む合成地下水を、もう一つのリアクタ (BF2) はFe (II) を含まない合成地下水を供給した。BF1は水理学的滞留時間3時間、アンモニア性窒素容積負荷0.24kg-N/㎥/dで、BF2は水理学的滞留時間1.5時間、アンモニア性窒素容積負荷0.48kg-N/㎥/dで9598%の高い硝化率を達成することができた。処理水のSS濃度は36 mg/lで、しかもSS中のVSSの割合が20%と低いことから、揺動床リアクタがFe (II) の除去能力に優れていることが明らかとなった。処理水温を25℃から15℃に低下させると硝化能力は急減に低下したが、すぐに回復したことから、BFに付着固定化された硝化菌が温度の低下に対して適用性の高いことが判明した。BFに付着した硝化生物膜の細菌叢を分子生物学的な手法で解析した結果、BF1、 BF2両方のリアクタから、アンモニア酸化細菌Nitrosomonasが検出された。BF2では、アンモニア酸化細菌の1種であるNitrospira sp. が検出された

Evaluation of the Swim-Bed Attached-Growth Process for Nitrification of Hanoi Groundwater Containing High Levels of Iron