報告書番号

V09009

タイトル（和文）

微生物変換における複合微生物系の利用（その１）-固定床式メタン発酵における発酵槽能力と微生物群集への担体の影響-

タイトル（英文）

Utilization of Microbial Community in Microbial Conversion (Part 1) Effects of Supporting Material in Methanogenic Packed-bed Reactor on the Performance and Microbial Community

概要 （図表や脚注は「報告書全文」に掲載しております）

廃棄物として稲わらを用いて固定床式メタン発酵を行い、発酵槽能力（稲わら分解とメタン生成）と微生物群集への担体の影響について検討した。担体設置の固定床式発酵槽では担体未設置の発酵槽と比べて、稲わらの残存量が68％減少し、メタン生成量が4.5倍増加した。この理由として、担体設置により、メタン発酵を阻害する酢酸の蓄積を回避できることがあげられた。2種類の発酵槽で能力が異なる理由を調べるために、微生物群集の多様性と微生物数を調べた。その結果、固定床式発酵槽では、（１）担体上において細菌群集が多様化すると共に高密度に存在することによって稲わらの分解能力が向上した、（２）メタン生成阻害の原因となる酢酸を除去する能力を持つ酢酸資化性メタン菌の割合と数が担体上で増加し、酢酸の蓄積を防ぐことが可能となったためメタン生成量が向上した、と考えられた。

概要 （英文）

Methane fermentation, which is capable of both waste treatment and methane gas recovery, is an important technique for the completion of the carbon circulation process. During methane fermentation, organic wastes are anaerobically degraded into methane and carbon dioxide gases by the microbial community. A methanogenic packed-bed reactor containing supporting material is a potential approach to stably maintain the valuable microbial community. However, the quantitative effects of the addition of supporting material on the performance of the reactor (organic waste degradation and methane gas production) and microbial community are unclear. In this study, cellulosic waste, i.e., rice straw, was directly applied to a methanogenic packed-bed reactor containing carbon fiber textiles (CFT) as supporting material in order to clarify the effect of the supporting material.
We used 2 types of methanogenic reactors (with and without CFT) for comparison. The rice straw remained in the reactor with CFT was decreased to 68% compared with that in the reactor without CFT. Further, the amount of methane gas produced in the reactor with CFT was 4.5-fold higher than that in the reactor without CFT. We believe that the increase in the performance was due to the addition of CFT into the reactor; CFT prevented the accumulation of acetic acid, which inhibits methane fermentation, in the suspended fraction of the reactor.
To determine the reason for the difference in the performance of the 2 types of reactors, microbial community diversity was analyzed with respect to bacteria and archaea by using terminal-restriction fragment length polymorphism analysis. The bacterial variety detected in the reactor with CFT was larger than that in the reactor without CFT. The dominant archaeal species were different in the 2 types of reactors, and the proportion of acetoclastic methanogens on the supporting material was high in the reactor with CFT. In addition, the microbial and methanogenic abundance was investigated using real-time quantitative polymerase chain reaction (PCR) analysis. We found higher densities of bacteria and methanogens on the supporting material in the reactor with CFT in comparison with those in the suspended fractions of the reactors with and without CFT. The amount of acetoclastic methanogen in the reactor with CFT was 12-fold higher than that in the reactor without CFT.
In summary, the supporting material in the reactor with CFT played the following roles: (1) the degradation rate of rice straw increased because of both a larger variety and a higher density of the microbial community on the supporting material, and (2) methane gas production increased because accumulation of acetic acid was prevented; this was because the amount of acetoclastic methanogen capable of degrading acetic acid increased on the supporting material.

報告者

キーワード