報告書番号

V04027

タイトル（和文）

排水中の窒素除去に関する研究（その10） -－ポリ乳酸を用いたバイオリアクターの窒素除去活性の向上と長期安定化－-

タイトル（英文）

Development of biological wastewater treatment system for nitrogen removal part 10.- Improvement and stabilization of nitrogen-removal activity of bioreactor using poly(lactic acid) 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）

ポリ乳酸を用いたバイオリアクターの処理能力の向上と長期安定化を目的とし、電子供与体として適当なポリ乳酸の条件を検討し、バイオリアクター窒素除去速度を評価した。分子量の異なるポリ乳酸について加水分解試験を実施し、その分子量に依存した加水分解の誘導期間があること、その後は一定期間で分解することを明らかにした。また、複数のポリ乳酸を混合することで、長期間、連続的に有機物の放出が可能であることを明らかにした。これらの結果をもとにして、3種類のポリ乳酸を混合して電子供与体としたバイオリクターを作製し、アンモニアを含む模擬排水の連続処理を行った。バイオリアクターの窒素除去速度は、エタノールなどを電子供与体とした従来のものと同程度の処理能力が確認された。また、この窒素除去活性は3ヶ月以上維持されており、新たに電子供与体を追加しなくても長期間、安定的に連続処理が可能であることが示された。

概要 （英文）

Poly(lactic acid), which is a biodegradable plastic, was decomposed to monomer or oligomer of lactic acid by hydrolysis. To determine an elution profile of lactic acid from poly(lactic acid), we have investigated the hydrolysis of four poly(lactic acid)s, PLGA1000, PLA2000, PLA3000 and PLA6000, with a range of molecular weight 1000-6000 in physiological saline. PLGA1000, which was molecular weight of 1000, eluted lactic acid after the experiment start immediately and released 95% of the carbon as monomers or oligomers of lactic acid after 60 days. Other high molecular weight poly(lactic acid)s were decomposed with lag times that depended on the molecular weight. To elute constantly lactic acid over a long period, a poly(lactic acid) blended of PLGA1000, PLA3000 and PLA6000 was prepared. The blend was decomposed without lag times and could constantly eluted lactic acid more than three months. To study denitrification activity of Paracoccus denitrificans by using poly(lactic acid) as energy source, batch treatment of an artificial wastewater including nitrate was carried out with polymeric gel immobilized cells of P. denitrificans. The immobilized gel was low denitrification activity, approximately 0.2 g-N/day/m2, regardless quantity of poly(lactic acid). However, by using of poly(lactic acid) mixed with tricalcium phosphate, the activity of the immobilized gel depended on quantity of poly(lactic acid) and was improved to 1.2 g-N/day/m2. From the results mentioned above, we prepared a biodegradable plastic-plate by mixing three kinds of poly(lactic acid)s, PLGA1000, PLA3000 and PLA6000, and tricalcium phosphate as energy source for a bioreactor. The bioreactor was constructed with the biodegradable plastic-plate and the polymeric gel-plate, which was immobilized the pure-cultured cells of Nitrosomonas europaea and P. denitrificans. One surface of the gel-pate was in contact with an artificial wastewater, while the other side of it was in contact with the biodegradable plastic-plate. Batch treatment experiment with the bioreactor was continuously carried out with 500 mL of artificial wastewater containing 100 mg-N/L of ammonia. Nitrogen-removal rate and ammonia-oxidation rate of the bioreactor were approximately 3 and 6 g-N/day per square meter of gel-plate surface, respectively. These activities of the bioreactor were maintained for over 90 days. These results shown that the bioreactor using poly(lactic acid) as energy source could effectively remove nitrogen from wastewater as the bioreactor using ethanol.

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