Eisuke TAMURA
Analysis of Microbial consortia during environmental change in the thermophilic UASB reactor
Takashi YAMAGUCHI
Since thermophilic UASB reactor is vulnerable to environmental variations, it has been widely reported that the treatment process could be easily deteriorated by the accumulation of propionic acid. However, the process of both deterioration and recovery derived from the accumulation has not yet been satisfactorily studied in details.
To achieve the aim of elucidating the deterioration process, thermophilic UASB reactor has been conducted to study the performance before and after shock loadings in terms of effluent and biogas analysis. The analysis of the results indicates at 10 times of shock loading, even VFA accumulated but if pH was maintained at the regular level, the treatment process can be restored immediately. On the other hand, when pH dropped below an appropriate level, if shock loading period continues longer, the recovery rate will also be relatively extended. For example, it would take 17 days of recovery due to 3 days of shock loading. The experiment demonstrated that the VFA accumulation was not the direct cause of the process deterioration but indirectly decreasing in pH level could severely damage the microorganisms more in numbers.
However, damage of microorganisms by low pH exposure was not elucidated. To achieve the aim of elucidating it, thermophilic UASB has been conducted to study the transition of microbial consortia by sequence-specific cleavage method during low pH exposure. The analysis of the results indicates at low pH exposure , propionate-oxidizing bacteria was damaged. In brief, as for the propionic acid accumulation in thermophilic UASB, it was suggested that there were propionate-oxidizing bacteria for receiving deadly damage among microbial consortia by indirectly decreasing pH level by the organic acid accumulation. In addition, the specific growth rate that I calculated from methane production rate during recovery phase was at the same level as it of the previous announcement propionate-oxidizing bacteria. Therefore, the propionate-oxidizing bacteria become extinct by low pH exposure, but it is thought that a long term is needed to recover to a steady state because surviving microorganisms proliferate with consumption of substrate.
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