Bioaugmentation strategies based on bacterial and methanogenic cultures to relieve stress in anaerobic digestion of protein-rich substrates

Abstract

Anaerobic co-digestion of protein-rich substrates is a prominent strategy for converting valuable feedstocks into methane, but it releases ammonia, which can inhibit methanogenesis. This study developed a cutting-edge combined culturomic and metagenomic approach to investigate the microbial composition of an ammonia-tolerant biogas plant. Newly-isolated microorganisms were used for bioaugmentation of stressed batch reactors fed with casein, maize silage and their combination. A co-culture enriched with proteolytic bacteria was isolated, selected and compared with the proteolytic collection strainPseudomonas lundensisDSM6252. The co-culture andP. lundensiswere combined with the ammonia-resistant archaeonMethanoculleus bourgensisMS2 to boost process stability. A microbial population pre-adapted to casein was also tested for evaluating the digestion of protein-rich feedstock. The promising results suggest combining proteolytic bacteria andM. bourgensiscould exploit microbial co-cultures to improve anaerobic digestion stability and ensure stable productivity even under the harshest of ammonia conditions.Graphical abstractHighlights-High ammonia release from protein-rich substrates inhibits anaerobic digestion-Newly isolated bacterial strains from anaerobic digester were obtained-Proper bioaugmentation alleviates stress in casein and maize silage co-digestion-Bioaugmentation with a hydrolytic/hydrogenotrophic co-culture enhances CH4yields