Chika Tada

Effect of ammonium addition on methanogenic community in a fluidized bed anaerobic digestion.

After immobilization of anaerobes on carbon felt in a fluidized-bed anaerobic digester at an ammonium concentration of 500 mg N/l, the results of real-time PCR analysis indicated that the cell densities of the immobilized methanogens and bacteria increased compared with those of the free-living methanogens and bacteria in the original anaerobically digested sewage sludge, respectively. The results of the clone analysis of the original sludge suggested that the major methanogens were Methanosaeta sp. and the members of the order Methanomicrobiales, and that after immobilization, these were changed to Methanobacterium and Methanosarcina sp. The results of real-time PCR analysis also showed that the ratio of the Methanosaeta sp. in the methanogenic archaea decreased from 58.2% to 0.3% after the immobilization. Methane production decreased at ammonium concentrations of greater than 6000 mg N/l. The results of real-time PCR analysis indicated that the cell density of the immobilized archaea decreased at ammonium concentrations of greater than 3000 mg N/l. On the other hand, the cell density of the immobilized bacteria did not decrease at an ammonium concentration of 6000 mg N/l, but decreased at that of 9000 mg N/l. The major methanogenic clones immobilized on the carbon felt at an ammonium concentration of 3000 or 6000 mg N/l were Methanobacterium sp. The present results indicated that methanogens were relatively more sensitive to ammonium than bacteria.

Illumination enhances methane production from thermophilic anaerobic digestion

Incandescent lamp illumination enhanced methane production from a thermophilic anaerobic digestion reactor (55°C) supplied with glucose. After 10 days of operation, the volume of methane produced from light reactors was approximately 2.5 times higher than that from dark reactors. A comparison of the carbon balance between light and dark conditions showed that methane produced from hydrogen and carbon dioxide in the light reactors was higher than that from the dark reactors. When hydrogen or acetate was fed into the reactors, methane production with added hydrogen was faster and higher under light conditions than under dark conditions. The use of blue light-emitting diodes also enhanced methane production over that under dark conditions. The 16S rRNA gene copy numbers for Methanothermobacter spp. in the light reactor and in the dark reactor were at the same level. The copy number for Methanosarcina spp. in the light reactors was approximately double than that in the dark reactors. These results suggest that blue light enhances the methanogenic activity of hydrogenotrophic methanogens.

Photoenhancement of biogas production from thermophilic anaerobic digestion

After 46 d of anaerobic digestion at 55 degrees C, the volume of methane produced from an illuminated reactor was 2.2 times as high as that from a dark reactor. Light at a wavelength of 390-540 nm enhanced the methane production.