報告書番号

U02031

タイトル（和文）

排水中の窒素除去に関する研究（その８） --窒素除去バイオリアクターによる硝酸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 8.-Practical application of a large-scale bioreactor using packed gel envelopes with nitrate-containing wastewater from a 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）

硝酸態窒素を含む発電所実排水を用いて、大型化した窒素除去バイオリアクター（1.5m3容量）の窒素除去能力を検討した。浄化モジュール10枚を反応槽内に充填し、発電所実排水のバッチ処理を行った結果、浄化モジュールは表面積1m2あたり最大で6.5g-N/dayの窒素除去能力（実験室内での結果と同等）を有していた。さらに、反応槽内に浄化モジュール20枚を充填し、排水流入速度0.055m3/h（滞留時間24h）の条件で、発電所実排水の連続処理を約４ヶ月間行った。その結果、窒素除去率は40～80%の範囲であり、入口の全窒素濃度が100mg-N/L以下の際には、出口の全窒素濃度を50mg-N/L以下に抑えることが可能であり、安定して窒素含有実排水を処理することができた。以上の結果から、硝酸態窒素を含む発電所実排水の連続処理が可能であることが示され、本バイオリアクターの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 water such as lakes. To simplify the present nitrogen removal systems both operationally and physically, we have proposed and investigated a new nitrogen removal bioreactor using packed gel envelopes capable of simultaneously removing ammonia, nitrate and nitrite. Each envelope consists of two plate gels with a spacer in between. Ammonia oxidizer, Nitrosomonas europaea and denitrifier, Paracoccus denitrificans are co-immobilized in the plate gels, and ethanol, serving as an electron donor for denitrification, is injected into internal spaces of the envelopes. The immobilized N. europaea oxidizes ammonia to nitrite in the outer surface of envelopes in aerobic contact with wastewater containing ammonia, while the immobilized P. denitrificans reduces the nitrite to nitrogen gas in the inside of envelopes in anaerobic contact with the electron donor. In this way, the packed gel envelopes can remove ammonia from wastewater in a single step. We have already reported advantages of our bioreactor in laboratory scale experiments (water volume 0.35 m3) using ammonia-containing or nitrate-containing artificial wastewater. In this study, nitrate-containing actual wastewater from a thermal power plant was treated with a large-scale bioreactor (water volume 1.5 m3) using the packed gel envelopes. When batch treatment experiments were carried out with ten envelopes using actual wastewater that had various concentrations of nitrate, the bioreactor showed a maximum nitrogen removal rate (the transformation of NO3- to N2) of 6.5 g-N/day per square meter of gel surface. This rate was similar to that in the previous laboratory scale experiment. In addition, the actual wastewater was continuously treated with the twenty envelopes at inflow rate of 0.055 m3/h (residence time of 24 h) for four months. When the inlet total nitrogen concentration was less than 100 mg-N/L during the continuous treatments, the bioreactor was able to maintain the outlet total nitrogen concentration below 50 mg-N/L. The bioreactor accomplished a maximum nitrogen removal rate of 5.0 g-N/day per square meter of gel surface, and removed 40-80 % of the total nitrogen in the wastewater. These results show that our bioreactor using the packed gel envelopes is capable of stable continuous operation removing nitrogen from actual power plant wastewater.

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