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Performance Comparison of Anaerobic Digesters using Next Generation DNA Sequencing

Anaerobic digesters are employed in wastewater, landfill and livestock operations worldwide to create renewable energy. Improving biogas production in a one-million gallon reactor by 5-10% can offset up to $200,000 annually in power costs when used for onsite power (Ling, A. 2020).

This study used 60 samples from 21 digesters representing a variety of industries, feedstocks, reactor design, and operational conditions. Microbial community data and digester operation and outcome data were used to understand the relationships between operation, community members, and outcomes.

Each digester and site studies had specific digester microbiomes that were more similar to each other than to other digesters. This suggests that microbial community results are site-specific. The community composition associated with optimum results will vary between sites. Despite this limitation, some general community trends were observed across the samples studied, and these may be used to make general conclusions about digester operation and community structure. Briefly,

  • Higher relative abundances of total archaea, pseudomonads, and commomonads correlated to higher percent CH4 in produced gas
  • Thermophilic conditions and blanket-type reactors correlated to higher archaea relative abundances and higher percent CH4 in produced gas
  • COD removal correlated directly to CH4 production
  • Higher VFA to alkalinity ratios and lower pH in the ranges observed (pH 6.7 to 7.8 and VFA : alkalinity 0.04-0.24) correlated to higher archaea relative abundances
  • Digesters treating municipal wastes harbored more diverse and even communities than digesters treating only industrial wastes, possibly due to the regular addition of waste activated sludge.

Based on these results, several key microbial indicators were identified for use in tracking changes in a digester microbiome:

    • Community diversity (number of microbe types)
    • Community evenness (how evenly microbe types are distributed)
    • Total relative abundance of:
      • Total methanogens (total archaea)
      • Key methanogen groups: Methanobacterium spp., Methanosaeta spp., Methanothermobacter spp.