[Acidification and its effect on the population distributions of microorganisms in an anaerobic baffled reactor]

The changes of pH, COD, volatile fatty acids (VFA) and microbial morphology of the acidification process in an anaerobic baffled reactor (ABR) were investigated. And the population succession process of the anaerobic microorganisms was quantitatively analyzed by using the Fluorescent In situ hybridization technology (FISH). The results show that the ABR reactor is acidified gradually from the front to the back. After the reactor is entirely acidified, the COD removal efficiency is only 30.9%, and the pH values are lowered by 1.0-2.2, while the VFA in effluent increases by 5.1 times. Additionally, the microbial morphology is significantly affected by the acidification process, in which not only the bacteria are deformed or died, but also the internal and external mass transfer of granular sludge becomes difficult. The quantitative analyses with FISH shows that in the acidification process the Archaea growth is inhibited but the Eubacteria growth is promoted, thus resulting in the sharp decrease of the three crucial microorganisms of the anaerobic digestion. The abundance of the butyrate-oxidizing acetogenic bacteria Syntrophomonas spp. reduces by 30.9%, the propionate-oxidizing acetogenic bacteria Syntrophobacter wolinii reduces by 85.5%, the homoacetogenic bacteria Acetobacterium species E. limosum reduces by 60.0%, and methanomicrobium Methanomicrobiales reduces by 54.3%. All these result in the upsetting of the mass transfer balances of different anaerobic microorganism populations.