Bioaugmentation with marine sediment-derived microbial consortia in mesophilic anaerobic digestion for enhancing methane production under ammonium or salinity stress.

Ammonium (NH4+) and salinity (NaCl) inhibit CH4 production in anaerobic digestion. However, whether bioaugmentation using marine sediment-derived microbial consortia can relieve the inhibitory effects of NH4+ and NaCl stresses on CH4 production remains unclear. Thus, this study evaluated the effectiveness of bioaugmentation using marine sediment-derived microbial consortia in alleviating the inhibition of CH4 production under NH4+ or NaCl stress and elucidated the underlying mechanisms. Batch anaerobic digestion experiments under 5 gNH4-N/L or 30 g/L NaCl were performed with or without augmentation using two marine sediment-derived microbial consortia pre-acclimated to high NH4+ and NaCl. Compared with non-bioaugmentation, bioaugmentation reinforced CH4 production. Network analysis revealed the joint effects of microbial connections by Methanoculleus, which promoted the efficient consumption of propionate accumulated under NH4+ and NaCl stresses. In conclusion, bioaugmentation with pre-acclimated marine sediment-derived microbial consortia can mitigate the inhibition under NH4+ or NaCl stress and enhance CH4 production in anaerobic digestion.

Identification of key steps and associated microbial populations for efficient anaerobic digestion under high ammonium or salinity conditions.

Ammonium (NH4+) and salinity are major inhibitors of CH4 production in anaerobic digestion. This study evaluated their inhibitory effects on CH4 production and explored the key populations for efficient CH4 production under high NH4+ and NaCl concentrations to understand their inhibition mechanisms. Comparative batch experiments for mesophilic anaerobic digestion were conducted using three seeding sludges under different concentrations of NH4+ (1-5 gNH4-N/L) and NaCl (10-30 g/L). Although all sludges tolerated 3 gNH4-N/L and 10 g/L NaCl, NH4+ or NaCl concentrations higher than these substantially reduced CH4 production, depending on the seeding sludge, primarily by impairing the initial hydrolysis and methanogenesis steps. In addition, propionate was found to be a deterministic factor affecting CH4 production. Based on microbial community analysis, Candidatus Brevefilum was identified as a potential syntrophic propionate-oxidizing bacterium that facilitates the mitigation of propionate accumulation, allowing the maintenance of unaffected CH4 production under high inhibitory conditions.