초록
<P>Process monitoring of anaerobic digestion is typically based on operational parameters, such as pH and volatile fatty acid concentration, that are lagging on actual microbial community performance. In this study, <SUP>13</SUP>C isotope fractionation in CH<SUB>4</SUB> and CO<SUB>2</SUB> in the biogas was used to monitor process stability of anaerobic digestion in response to salt stress. A gradual and pulsed increase in salt concentration resulted in a decrease in methane production. No clear shift in δ<SUP>13</SUP>CH<SUB>4</SUB> was observed in response to the gradual increase in salt concentration, and δ<SUP>13</SUP>CO<SUB>2</SUB> of the biogas showed only a clear shift after process failure, compared with the control. In contrast, both δ<SUP>13</SUP>CH<SUB>4</SUB> and δ<SUP>13</SUP>CO<SUB>2</SUB> in the biogas changed in response to the pulsed increase in salt concentration. This change preceded the decrease in methane production. A significantly different bacterial and archaeal community profile was observed between the DNA and RNA level, which was also reflected in a different relation with the δ<SUP>13</SUP>CH<SUB>4</SUB> and δ<SUP>13</SUP>CO<SUB>2</SUB> values. This shows that isotope fractionation in the biogas can predict process stability in anaerobic digestion, as it directly reflects shifts in the total and active microbial community, yet, due to its temporal character, further validation is needed.</P><BR>[FIG OMISSION]</BR>