報告書番号

U01015

タイトル（和文）

排水中の窒素除去に関する研究 (その7) --エネルギー源として生分解性プラスチックを用いたバイオリアクターの脱窒活性--

タイトル（英文）

Development of biological wastewater treatment system for nitrogen removal. Part 7. -Denitrification activity of bioreactor using biodegradable plastic as energy source-

概要 （図表や脚注は「報告書全文」に掲載しております）

生分解性プラスチックの一つであるポリ乳酸や乳酸-グリコール酸共重合体を脱窒反応のエネルギー源として、脱窒菌およびアンモニア酸化菌とともに固定化した膜状ゲルを作成し、その窒素除去活性を検討した。これらの膜状ゲルでは、窒素除去速度は、固定化した生分解性プラスチックによって差が生じ、生分解性プラスチックの加水分解速度に依存した速度が確認された。この膜状ゲルを用いたバイオリアクターは、窒素除去速度は低いものの、エネルギー源の新たな添加なしで、排水を連続的に処理することができ、1ヶ月以上その窒素除去活性を維持した。エネルギー源として生分解性プラスチックのような固体物質を用いるバイオリアクターでは、エネルギー源を供給するための装置が必要なく、リアクターの構造の簡素化や使い捨て化の可能性が示された。

概要 （英文）

Poly(lactic acid) and poly(lactide-co-glycolide) , which are biodegradable plastics, decomposed to monomers or oligomers of lactic acid and glycolic acid by hydrolysis. Using these monomers as a sole energy source for denitrification, activity of Paracoccus denitrificans was examined in an artificial wastewater containing nitrite under anaerobic condition. P. denitrificans could reduce nitrite in the wastewater containing lactic acid or glycolic acid. The nitrite-reduction rates of P. denitrificans using these energy sources were estimated 5.34 x 10-8 and 3.99 x 10-8 mg-N/h/cell, respectively, and were similar to that using ethanol. Poly(lactic acid) or poly(lactide-co-glycolide) was immobilized with Nitrosomonas europaea and P. denitrificans in photocrosslinkable polymer. The gels were formed into a plate. The nitrogen-removal activities of the plate gels were examined in the artificial wastewater containing nitrite or ammonia. Ammonia removal rates of these plate gels were approximately 2 g-N/d for 1 m2 of the gel surface. Their denitrification activities depended on the hydrolysis rate of the biodegradable plastics. The highest activity of the plate gels was 0.7 g-N/d/m2. The artificial wastewater containing 20 mg-N/L of ammonia was continuously treated by the bioreactor using the plate gel immobilized with poly(lactide-co-glycolide) and microorganisms. Although nitrogen-removal rate of the bioreactor was lower than that of the tube gel using ethanol solution, the rate was maintained over 1 month without additional energy source into the wastewater. The bioreactor was omitted an equipment for supplying an energy source to the plate gel. Therefore, the concept using solid like a biodegradable plastic as energy source would be effective to simplify the structure of our bioreactor.

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