CeBiTec Colloquium
| date | Monday, January 11th 2010, 17 c.t. | |
| location | G2-104, CeBiTec Building | |
| speaker | Dr. Michael KlockeLeibniz-Institut für Agrartechnik Potsdam-Bornim e.V. (ATB) | |
| title | Microbial communities in biogas plants | |
| The generation of biogas from renewable substrates such as energy crops or waste from the agricultural production is of increasing importance for a sustainable and CO2-neutral energy production. The anaerobic digestion of biomass to biogas is conducted by a complex microbial community consisting of fermentative Bacteria and methanogenic Archaea. Despite the recent achievements in reactor design and operation, the microbiology of the process is still a “black box”. During recent years, at the ATB several studies were performed to explore the microbial community structure present in large scale biogas plants and laboratory scaled experimental fermenters. Therefore, a culture-independent polyphasic approach was established including (1) characterization of microbial diversity by 16S rDNA and mcrA nucleotide sequence analysis, (2) quantification of microorganisms by fluorescence in situ hybridization and microscopy, (3) monitoring of microbial community dynamics by quantitative real-time PCR and T-RFLP. The anaerobic digestion of biomass is conducted by a broad range of bacteria mainly of the classes Bacteroides and Clostridia. Also members of the classes Spirochaetes, Flavobacteria as well as ε-Proteobacteria are found. During the fermentation the bacterial community underlies large fluctuations even in comparatively short time. The impact of these dynamics on hydrolysis efficiency and, thus, on biomass conversion rates and total reactor efficiency is unclear because the vast majority of the bacterial species (>90%) involved in hydrolysis is up to now uncultivated and hence physiologically uncharacterized. Methanogenic Archaea are present in biogas reactor with much lower cell densities than fermentative bacteria. This group of microorganisms, which is crucial for the quality of the resulting biogas, comprises between one and ten percent of total procaryotic cell number. In biogas plants hydrogenotrophic methanogens are predominant. Depending on construction and status of the fermenters certain members of the orders Methanomicrobiales e.g. Methanoculleus spp. or Methanobacteriales such as Methanobacterium spp. or Methanothermobacter spp. are found. The enrichment of aceticlasic methanogens such as Methanosaeta spp. can be forced by enlargement of the surfaces within the fermenter (e.g. introduction of a solid bed fermenter) and reduction of microbial biomass losses during substrate refills (e.g. by cell retention systems). Additional factors for varying ratios between hydrogenotrophic and aceticlastic methanogens are temperature and concentration of free ammonia. However, the question, which kind of methanogenesis is preferable for an optimized methane yield, is still unsolved. | ||
| host | Dr. Andreas Schlüter |