Changes in bacterial community during fermentative hydrogen and acid production from organic waste by thermophilic anaerobic microflora.

Aims:  Changes in fermentation pattern during the treatment of organic wastes containing solid materials by thermophilic anaerobic microflora were investigated with respect to product formation and bacterial community structure during hydrogen production. Methods and Results:  Anaerobic microflora enriched from sludge compost was cultivated using artificial garbage slurry in a continuous flow-stirred tank reactor. Product formation varied depending on pH and hydraulic retention time (HRT) applied. Community analysis by terminal restriction fragment length polymorphism and clone library analysis of polymerase chain reaction-amplified bacterial 16S rDNA indicated that difference in the fermentative product distribution could be caused by different populations of micro-organisms in the microflora. Conclusion:  Hydrogen fermentation with acetate/butyrate formation was optimized at <1·0 d HRT at pH 5·0 and 6·0. Thermoanaerobacterium thermosaccharolyticum was the dominant hydrogen-producing micro-organism. Conversely, unidentified organisms became dominant after 4·0 d HRT at pH 7·0 and 8·0, where relatively high-solubilization efficiency of solid materials was observed with no production of hydrogen. Significance and Impact of the Study:  This is the first report describing product formation in the fermentation of solid organic wastes by a mixed population of micro-organisms. Various fermentation patterns including hydrogen fermentation were characterized and evaluated from engineering and microbial aspects.