Response of Exogenous and Indigenous Microorganisms in Alleviating Acetate–Ammonium Coinhibition during Thermophilic Anaerobic Digestion

Bioaugmentation can alleviate the inhibition of acids and ammonia by introducing functional strains in anaerobic digesters, but there is an urgent need to develop functional strains that can be effective under thermophilic anaerobic digesters. The present study constructed a bioaugmentation consortium with four functional strains, namely, Coprothermobacter, Thermacetogenium, Methanothermobacter, and Methanosarcina, to strengthen the synergistic function of syntrophic acetate oxidation and methanogenesis for inhibited thermophilic anaerobic digesters. The result shows that the bioaugmentation with cells constituting only 1.11% (on the basis of VS to VS) of the inoculum led to methane production increasing by 702% at the coinhibition of 3 g/L acetate and 7 g NH₄⁺-N/L, and by 49.5% at the coinhibition of 12 g/L acetate and 4 g NH₄⁺-N/L. Highly tolerant Coprothermobacter contributed to this microbiological domino effect by collaborating with exogenous hydrogenotrophic Methanothermobacter and priming the indigenous syntrophic acetate-oxidizing Syntrophaceticus and hydrogenotrophic Methanoculleus. This bioaugmentation enhanced hydrogenotrophic methanogenesis, evidenced by carbon isotopic signals and an upregulation of the relating genes. Up-regulated genes relating to ion transport and catalyzing energy conversion suggested that this bioaugmentation was favorable to maintain normal cellular osmolality and meet energy demand under inhibited conditions.