Anaerobic digester bioaugmentation influences quasi steady state performance and microbial community

Nine anaerobic digesters, each seeded with biomass from a different source, were operated identically and their quasi steady state function was compared. Subsequently, digesters were bioaugmented with a methanogenic culture previously shown to increase specific methanogenic activity. Before bioaugmentation, different seed biomass resulted in different quasi steady state function, with digesters clustering into three groups distinguished by methane (CH₄) production. Digesters with similar functional performance contained similar archaeal communities based on clustering of Illumina sequence data of the V4V5 region of the 16S rRNA gene. High CH₄ production correlated with neutral pH and high Methanosarcina abundance, whereas low CH₄ production correlated to low pH as well as high Methanobacterium and DHVEG 6 family abundance. After bioaugmentation, CH₄ production from the high CH₄ producing digesters transiently increased by 11 ± 3% relative to non-bioaugmented controls (p < 0.05, n = 3), whereas no functional changes were observed for medium and low CH₄ producing digesters that all had pH higher than 6.7. The CH₄ production increase after bioaugmentation was correlated to increased relative abundance of Methanosaeta and Methaospirillum originating from the bioaugment culture. In conclusion, different anaerobic digester seed biomass can result in different quasi steady state CH₄ production, SCOD removal, pH and effluent VFA concentration in the timeframe studied. The bioaugmentation employed can result in a period of increased methane production. Future research should address extending the period of increased CH₄ production by employing pH and VFA control concomitant with bioaugmentation, developing improved bioaugments, or employing a membrane bioreactor to retain the bioaugment.