Solids Retention Times Shift Methanogenic Ethanol Oxidation: Novel Insights into Metabolic Pathways, Microbial Community Dynamics, and Energy Metabolisms

Abstract

Solids retention time (SRT) is a key parameter affecting the performance of anaerobic digestion. Nevertheless, the knowledge of how SRT impacts the anaerobic ecosystem is still insufficient. In this study, the shifts in system performance, microbial population, metabolic pathway, and energy metabolism induced by different SRTs (25 and 10 days) in anaerobic reactors with ethanol as the substrate were systematically investigated. Ethanol was oxidized to acetate and propionate, and methane was generated via mixotrophic pathways at SRT of 25 days due to the enrichment of ethanol oxidizers Geobacter and Pelobacter, propionate oxidizers Smithella, and methanogens Methanothrix. However, ethanol was metabolized to only acetate by Desulfovibrio which outcompeted other ethanol oxidizers and established interspecies H 2 transfer with H 2 -utilizing methanogen Methanobacterium at a SRT of 10 days. Under short SRT conditions, acetoclastic methanogens were eliminated, resulting in the accumulation of acetate and low CH 4 yield. Additionally, the major ATPase-gene owners were shifted from bacteria (F-type ATPase) to methanogens (V/A-type ATPase) with decreasing SRT and pH, suggesting the energy-metabolism turnover of anaerobic microbes when encountering different SRTs.

Hydraulic retention time and pressure affect anaerobic digestion process treating synthetic glucose wastewater

“…The predominance of Methanobacterium was also found to be enriched in previous high-pressure studies (Lindeboom et al, 2016;Zhao et al, 2020). Previous research has also highlighted the dominance of Methanobacterium at low HRTs when using different substrates (74 % in an ethanol-fed reactor with a solid retention time of 10 d; 50-80 % in a sucrose-fed reactor with varying HRTs from 6 to 48 h) (Ta et al, 2020;Xing et al, 2021). The results of the present study identified Methanobacterium congolense as the main species of Methanobacterium, which solely utilizes H 2 and CO 2 for growth and produces CH 4 (Cuzin et al, 2001).…”

Machine Learning-Assisted Optimization of Mixed Carbon Source Compositions for High-Performance Denitrification

“…The two reactors exhibit inconsistent abundances of various acetate metabolism genes ( actP and ackA ). Given the partial overlap between the metabolic pathways of ethanol and acetate, this overlap might explain the difference in acetate metabolism gene abundances . Additionally, the acetate-feeding reactor had a higher abundance of polyhydroxyalkanoates (PHA) synthesis genes ( phaC ), suggesting that acetate-adapted denitrifier might possess enhanced PHA metabolic storage capability .…”

“…Given the partial overlap between the metabolic pathways of ethanol and acetate, this overlap might explain the difference in acetate metabolism gene abundances. 37 Additionally, the acetate-feeding reactor had a higher abundance of polyhydroxyalkanoates (PHA) synthesis genes (phaC), suggesting that acetate-adapted denitrifier might possess enhanced PHA metabolic storage capability. 38 The presence of multiple carbon sources led to an increased abundance of denitrifying microbes, potentially contributing to a significant increase in the flux of carbon to denitrification.…”