Isotope Fractionation in Biogas Allows Direct Microbial Community Stability Monitoring in Anaerobic Digestion

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, 13C isotope fractionation in CH4 and
CO2 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 δ13CH4 was observed
in response to the gradual increase in salt concentration, and δ13CO2 of the biogas showed only a clear shift after
process failure, compared with the control. In contrast, both δ13CH4 and δ13CO2 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 δ13CH4 and δ13CO2 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.