Effect of bioaugmentation on psychrotrophic anaerobic digestion: Bioreactor performance, microbial community, and cellular metabolic response

Most anaerobic digestion reactors are operated under mesophilic and thermophilic conditions, requiring high levels of heat energy to maintain high temperatures. If an optimized method existed for psychrotrophic anaerobic digestion (PAD), it would have outstanding economic and environmental benefits as an alternative to mesophilic or thermophilic reactors. Therefore, this study aimed to investigate the conditions and corresponding mechanism to optimize PAD for producing high yields of methane. We found that intermittent bioaugmentation with mesophilic propionate-degrading consortia showed enhanced methane production back to uninhibited levels in a psychrotrophic anaerobic reactor under volatile fatty acid stress, with long-term effectiveness for 14 hydraulic retention times. The increase in acetoclastic methanogens (Methanothrix harundinacea and Methanosarcina fla-vescens) stimulated methanogenesis in the psychrotrophic system. Metagenomic analysis showed that bacteria carried more diverse cold-regulating gene sets and had higher DNA replication rates than methanogens, explaining the higher cold tolerance of bacterial community than that of methanogen community. By coupling reactor performance with microbial metabolic analysis, this study is the first to provide comprehensive findings that intermittent bioaugmentation with methanogenic consortia is a promising strategy to boost the PAD process.

Automated summary

Most anaerobic digestion reactors are operated under mesophilic and thermophilic conditions, but an optimized method for psychrotrophic anaerobic digestion (PAD) would have economic and environmental benefits as an alternative. This study investigated the conditions and mechanism to optimize PAD and found that intermittent bioaugmentation with mesophilic propionate-degrading consortia enhanced methane production. Metagenomic analysis revealed a higher cold tolerance of the bacterial community than methanogen community. Coupling reactor performance with microbial metabolic analysis, this study provides comprehensive findings for boosting the PAD process by intermittent bioaugmentation with methanogenic consortia.