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表題について執筆者の研究例を交え紹介した。硝酸態窒素による地下水汚染は、欧米をはじめ世界的な懸念事項となっている。汚染要因には地域差があるが、事例の多くは農業によるもので、安定同位体比の利用による窒素源の特定や脱窒反応に関する先進的研究が進んでいる。汚染対策は、飲用水確保としての浄水処理から抜本的対策である窒素負荷削減技術･施策にわたるが、抜本的解決には長期にわたる息の長い取り組みが必要である。

A fluidized bed reactor with polyvinyl alcohol (PVA) gel beads as a biomass carrier was used for the degradation of p-nitrophenol (PNP) in an artificial wastewater. PNP (200 mg·l-1) was completely degraded at a hydraulic retention time (HRT) of 6 hours in the presence of 10 mg·l-1 glucose. However, PNP degradation became unstable at 250 mg·l-1 PNP and did not recover, which suggests that the decrease in the activity of PNP-degrading bacteria is due to the presence of glucose. On the other hand, when only PNP was supplied to the reactor, PNP (360 mg·l-1) was almost completely degraded at an HRT of 6 hours, and the PNP removal rates per volume and total solids (TS) were determined as 54 mg·l-1·h-1 and 12.6 mg·g-1·h-1, respectively. From the PCR-DGGE result, two bacterial DNA sequences similar to those of Acidovorax and Arthrobacter, which are known for their PNP degrading ability, were determined in the biomass attached to the PVA gel beads; thus, we conclude that these bacteria mainly contribute to the PNP-degrading activity in the reactor.

Denitrification activity behavior and bacterial community structure in a poly-β-hydroxybutyrate (PHB) embedded soil-column reactor were investigated. The influent containing nitrate (NO3-N) was applied in a downward flow. The NO3-N concentration rapidly decreased only in the middle part of the column where PHB was embedded, which indicated that the denitrification activity in the reactor was related to PHB. Influent NO3-N was effectively removed in the reactor following 60 days of continuous operation. The total number of bacteria in the lower and middle parts of the column decreased after 30 days, and then increased again after 60 days; however, the number in the upper part continuously decreased with time. The number of PHB utilizing denitrifiers increased in both the middle and lower parts with time, contributing to denitrification activity in the reactor. From the result of PCR and denaturing gradient gel electrophoresis (PCR-DGGE), the presence of two denitrifing and a few other bacteria were determined, and which suggested of Ralstonia related species played an important role in the denitrification capability of the reactor., 生分解性プラスチックの一つであるポリヒドロキシ乳酸 (PHB) を充填した下降流式土壌カラムリアクター内での硝酸脱窒挙動と、それに関与する土壌中の細菌叢を解析した。PHBが充填されているリアクター中部では、リアクターの運転開始60日後に硝酸性窒素 (以下NO3-Nと略す) 除去率が98%以上となり、それ以降も安定した硝酸除去がみられたのに対し、電子供与体の供給が乏しい上部でのNO3-N除去率は75日経過時においても約15%にとどまった。また、リアクター中部と下部の土壌では、全菌数および脱窒菌数がともに経時的に増加した。以上の結果から本リアクターのNO3-N除去能がPHBを電子供与体や炭素源として利用する脱窒細菌によるものであることが明らかとなった。さらに、16S rDNAのPCR-DGGEによる細菌叢解析結果から、5種類以上の細菌の存在が示され、中でもNO3-N還元能を有するRalstonia pickettiiに近縁な細菌が、主に本リアクターのNO3-N脱窒能に寄与しているものと推定された。