[Forming processes of micro-ecology in anaerobic sludge granulation]

By use of the fluorescence in situ hybridization (FISH) and the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) methods, the diversity and similarity of microbial community during anaerobic sludge granulation were studied. The relative abundance and their succession of H2-producing acetogens (HPA), homoacetoges (HOMA) and methanogens were monitored. And the whole forming processes of micro-ecology were investigated correspondingly. The results showed that for an anaerobic reactor during normal startup, only through 33-days continuous operation, the healthy microecology of granular sludge could be formed, which is much less than the growth period of granular sludge ( > 180 d) and the time for achieving good COD removal (about 50 d). During the granulation processes of anaerobic sludge, the Shannon-Wiener diversity index of the microbial community increased firstly to 3.11 and then decreased to 2.88, and their similarity increased from 44% to 86% continuously. It is through these three stages, namely the adaptive stage, the growth stage and the stabilization stage in turn, the stable microecology could be formed gradually. In the initial granulation stage, the methanogens had a higher growth speed, resulting in methanogens, HPA and HOMA studied being produced in a ratio of approximately 42: 2: 1, respectively. However, with the healthy mocroecology been formed gradually, the ratio of methanogens to HPA and HOMA decreased to 2.8: 2.4: 1.0 finally.