The fate of anaerobic syntrophy in anaerobic digestion facing propionate and acetate accumulation

How the acetate and propionate accumulation impact anaerobic syntrophy during methane formation is not well understood. To investigate such effect, continuous acetate (35 g/L), propionate (11.25 g/L) and bicarbonate (30 g/L) supplementation were used during mesophilic anaerobic digestion. The high throughput sequencing (16S rRNA and mcrA), Real-Time quantitative PCR, and stable carbon isotope fingerprinting were applied to investigate the structure and activity of microbial community members. The results demonstrated that the abundance of syntrophic acetate oxidizing bacteria exhibited a gradual decrease coupled with heavier stable carbon isotopic signature of methane (delta(CH4)-C-13) in the three reagents impacted reactors. The increased acetate and propionate concentrations exerted negative influence on biogas production but the relatively stable hydrogenotrophic methanogens together with syntrophic acetate/propionate oxidizing bacteria kept the stable methane formation facing acetate and propionate accumulation. The functional genes copy number of the hydrogenotrophic Methanocellaceae and Methanomicrobiaceae correlated significantly with delta(CH4)-C-13 (R-2 > 0.74), but only the abundance of Methanocellaceae fitted well with delta(CH4)-C-13 (p < 0.05). The delta(CH4)-C-13 signatures can predict methanogenesis, as it directly reflects the main methanogenic pathway; yet, further investigation of isotope fractionation in acetate/propionate coupled with delta(CH4)-C-13 is needed. Collectively, these results provide deep insight into anaerobic syntrophy and reveal changes of synergistic relationships, both of which may contribute to the stability of biogas reactors. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the impact of acetate and propionate accumulation on anaerobic syntrophy during methane formation. Results showed that increased acetate and propionate concentrations had a negative effect on biogas production, but stable hydrogenotrophic methanogens and syntrophic acetate/propionate oxidizing bacteria maintained stable methane formation. The study provides insights into anaerobic syntrophy and changes in synergistic relationships, contributing to the stability of biogas reactors.