Microbial community dynamics during anaerobic digestion of SESC-treated woody biomass

○Ronald Navarro1, Yuichiro Otsuka1, Masaya Nakamura1, Tomoyuki Hori2, Hiroshi Habe2, Kenji Matsuo3, Kei Sasaki4, Ken Sasaki4, Kazuhide Kimbara5, Yutaka Nakashimada3, Junichi Kato3 (1Forestry and Forest Products Research Institute, 2National Institute of Advanced Industrial Science and Technology, 3Hiroshima University, 4Hiroshima Kokusai Gakuin University, 5Shizuoka University)

農芸化学会大会

名城大学

https://www.jsbba.or.jp/MeetingofJSBBA/2018/MeetingofJSBBA2018.pdf

[Objective] The methanogenic microbial community during anaerobic digestion of various pre-treated wood
biomass was investigated. As a new approach to wood pre-treatment, the simultaneous enzymatic
saccharification and comminution (SESC) process was employed.
[Methodology] Ten per cent aqueous mixture of wood powder (48 μm particle size) from various species, i.e.,
cedar, elm, oak and red pine heartwood, was subjected to beads milling in the presence of cellulase and
hemicellulase to achieve a median particle size of 1μm. For anaerobic digestion, 10 kg of the 10% wood slurry
enriched with vitamins, nitrogen, trace elements and dog food were fed daily to a continuous stirred-tank
reactor containing around 300 L of thermophilic methanogenic sludge collected from a sewage plant. Ten kg of
the sludge was also withdrawn daily to achieve a hydraulic residence time (HRT) of 30 days. The wood slurry
and sludge samples were subjected to chemical and microbial analysis using the Illumina platform, respectively.
[Results and Discussion] Wood pre-treatment achieved 60% saccharification efficiency based on the cellulose
content. During anaerobic digestion, an average yield of 240 L methane per kg wood was attained.
High-throughput Illumina sequencing of 16S rRNA genes clarified the relevant microorganism for the process.
The methanogenic microbial community was dominated by the species, such as Defluviitoga tunisiensis,
Coprothermobacter proteolyticus, Anaerobaculum hydrogeniformans and Methanothermobacter crinale. There
was a clear transition of the original microbial community from a protein- (represented by C. proteolyticus) to a
polysaccharide-hydrolysing (represented by D. tunisiensis) type. A. hydrogeniformans and M. crinale were the
major hydrogen-producing bacterium and methanogenic archaeon, respectively. The predominance of M.
crinale indicates that the anaerobic digestion is mediated via syntrophic acetate oxidation coupled with
hydrogenotrophic methanogenesis. The relative abundance of this archaea was kept below 5% during the
amendment with heartwood slurry but it dramatically increased upon the introduction of a cedar bark slurry as
substrate, reaching almost 30% of the total microbial population two weeks after its addition. During this period,
methane production remained stable. These results indicate the capability of SESC process to render
lignocellulosic polysaccharides readily available to anaerobic digestion, catalyzed by a combination of
syntrophic acetate oxidation and hydrogenotrophic methanogenesis.
This work was supported by the Fukushima prefecture project (2016-2017) entitled ‘Utilization of
woody biomass for methane fermentation.’