報告書番号

V04003

タイトル（和文）

排水中の窒素除去に関する研究（その９） --窒素除去バイオリアクターによるアンモニア態窒素を含む発電所実排水処理--

タイトル（英文）

Development of biological wastewater treatment system for nitrogen removal Part 9.- Practical application of a large-scale bioreactor using packed gel envelopes with ammonia-containing wastewater from thermal power plant -

概要 （図表や脚注は「報告書全文」に掲載しております）

アンモニア態窒素を含む発電所実排水を用いて、大型化したバイオリアクターの窒素除去能力を明らかにすると共に、リアクター容量あたりの窒素除去能力の向上を目指し、薄型浄化モジュールの開発に取り組んだ。浄化モジュール（厚さ12mm）を用いて実排水のバッチ処理を行った結果、窒素除去能力は実験室規模での結果と同等であり、アンモニア態窒素を含む実排水の処理が可能であることが立証された。さらに、従来型の３割程度の厚さ3.5mmの薄型浄化モジュールを新たに開発し、実排水の連続処理を行った。その結果、滞留時間24時間の条件において出口の全窒素濃度は9.0mg-N/L以下であり、また、薄型モジュールは従来型モジュールと同程度の窒素除去能力を示した。これらの結果を元に装置設計に関して概算したところ、本バイオリアクターを用いたシステムにより設備容量の削減が可能であると見込まれ、実用化の目処を得ることができた。

概要 （英文）

Eutrophication, which is caused by an excessive nitrogen inflow from domestic and industrial effluent, is a serious environmental problem in closed waters. To simplify the present systems for nitrogen removal, we have proposed and investigated a new nitrogen removal bioreactor using packed gel envelopes capable of simultaneously removing ammonia, nitrate and nitrite. We have already reported advantages of our system in a large-scale bioreactor (water volume 1.5 m3) using nitrate-containing actual wastewater from a thermal power plant. In this study, ammonia-containing actual wastewater from another power plant was treated with large-scale bioreactor (water volume 1.8 m3) using the packed gel envelopes (thickness was 12 mm). When batch treatment experiments were carried out with ten envelopes using actual wastewater that had various concentrations of ammonia, the system showed a maximum nitrogen removal rate (the transformation of NH4+ to N2) of 7.1 g-N/day per square meter of gel surface. This maximum rate was similar to that in the previous laboratory scale experiment. In addition, the actual wastewater was continuously treated with the ten envelopes at inflow rate of 0.075 m3/h (hydraulic residence time of 24 h). The system removed 62.3-80.3 % (average value was 67.2 %) of the total nitrogen in the wastewater. Furthermore, we newly developed thinner packed gel envelopes (thickness was 3.5 mm) using nonwoven made of polyethylene terephthalate so as to improve the nitrogen removal performance per capacity and simplify the manufacture process of envelopes. The actual wastewater was continuously treated with the thirty thinner envelopes at inflow rate of 0.075 m3/h or 0.45 m3/h (hydraulic retention time of 24 h or 4 h). The system removed 95.0 % of inlet total nitrogen on average and outlet total nitrogen concentration was below 9.0 mg-N/L at inflow rate of 0.075 m3/h. At inflow rate of 0.45 m3/h, the system accomplished a maximum nitrogen removal rate (the transformation of NH4+ to N2) of 6.0 g-N/day per square meter of gel surface. This maximum rate obtained with the thinner envelopes was equivalent to that obtained with former envelopes. These results show that our bioreactor using the thinner packed gel envelopes is capable of stable continuous operation removing nitrogen from actual power plant wastewater.

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