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

Abstract

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.