Two microbial consortia obtained through purposive acclimatization as biological additives to relieve ammonia inhibition in anaerobic digestion.

Ammonia inhibition is a challenging issue in the anaerobic digestion (AD) of nitrogen-rich substrates and hinders the energy recovery from organic wastes. Bioaugmentation is promising strategy to stabilize AD systems with high ammonia concentration. The composition of microbial consortia often determines their effectiveness in bioaugmentation. Up to now, the effect of various microbial consortia as biological additives on the AD systems is not fully understood. In this study, two microbial consortia (syntrophic microbial consortium, MC, and hydrogenotrophic methanogen consortium, SS) were obtained through two domestication methods, and were applied in a nitrogen-rich AD system. The results showed that the MC and SS treatments could restore AD performance within 21 days and 83 days, respectively. The recovery of digestion performance depended on the methanogenic archaea Methanospirillum, Methanothermobacter, and Methanoculleus in the early and later stages. Analysis of the C isotope indicated that both MC and SS enhanced the hydrogenotrophic pathway. The KEGG analysis showed that the MC not only promoted the key enzyme genes in the hydrogenotrophic pathway but also had a positive effect on the related enzyme genes of propionate and butyrate degradation, which was affected by the abundant short-chain fatty acids degrading bacteria, such as Syntrophomonas, Syntrophobacter, and Tissierella in the MC. After recovery of digestion performance, there was no significant difference (p > 0.05) in methane yield between the MS and SS treatments. Therefore, the best intervention period for bioaugmentation is when the digestion performance of the AD system is unstable.