Microbial community structure and dynamics of starch-fed and glucose-fed chemostats during two years of continuous operation

The microbial community structures of two mesophilic anaerobic chemostats, one fed with glucose, the other with starch as sole carbon sources, were studied at various dilution rates （0.05-0.25 d-1 for glucose and 0.025-0.1 d-1 for starch） during two years continuous operation. In the glucose-fed chemostat, the aceticlastic methanogen Methanosaeta spp. and hydrogenotrophic methanogen Methanoculleus spp. predominated at low dilution rates, whereas Methanosaeta spp. and the hydrogenotrophic Methanobacterium spp. predominated together when dilution rates were greater than 0.1 d 1. Bacteria affiliated with the phyla Bacteroidetes, Spiro- chaetes, and Actinobacteria predominated at dilution rates of 0.05, 0.1, and 0.15 d-l, respectively, while Firmicutes predominated at higher dilution rates （0.2 and 0.25 d-l）. In the starch-fed chemostat, the aceticlastic and hydrogeno- trophic methanogens coexisted at all dilution rates. Although bacteria belonging to only two phyla were mainly responsible for starch degradation （Spirochaetes at the dilution rate of 0.08 d-1 and Firmicutes at other dilution rates）, different bacterial genera were identified at different dilution rates. With the exception of Archaea in the glucose-fed chemostat, the band patterns revealed by denaturing gradient gel electrophoresis （DGGE） of the microbial communities in the two chemostats displayed marked changes during long-term operation at a constant dilution rate. The bacterial community changed with changes in the dilution rate, and was erratic during long- term operation in both glucose-fed and starch-fed chemo- stats.

Digestion performance and microbial community in full-scale methane fermentation of stillage from sweet potato-shochu production

Sweet potato shochu is a traditional Japanese spirit produced mainly in the South Kyushu area in Japan. The amount of stillage reaches approximately 8 x 105 tons per year. Wastewater mainly containing stillage from the production of sweet potato-shochu was treated thermophilically in a fullscale treatment plant using fixed-bed reactors （8 reactors ×283 m3）. Following the addition of Ni2＋ and Co2＋, the reactors have been stably operated for six years at a high chemical oxygen demand （COD） loading rate of 14 kg/（m3.day）. Analysis of coenzyme content and microbial communities indicated that similar microbial communities were present in the liquid phase and on the fiber carders installed in reactors. Bacteria in the phyla Firmieutes as well as Bacteroidetes were dominant bacteria, and Methanosarcina thermophila as well as Methanothermobacter crinale were dominant methanogens in the reactors. This study reveals that stillage from sweet potato-shochu production can be treated effectively in a full-scale fixed-bed reactor under thermophilic conditions with the help of Ni2~ and Co2＋. The high diversity of bacterial community and the coexistence of both aceticlastic and hydrogenotrophic methanogens contributed to the excellent fermentation performance.