New insights into syntrophic ethanol oxidation: Effects of operational modes and solids retention times.

Anaerobic ethanol oxidation relies on syntrophic interactions among functional microorganisms to become thermodynamically feasible. Different operational modes (sequencing batch reactors, SBRs, and continuous flow reactors, CFRs) and solids retention times (SRT, 25 days and 10 days) were employed in four ethanol-fed reactors, named as SBR 25d , SBR 10d , CFR 25d , and CFR 10d , respectively. System performance, syntrophic relationships, microbial communities, and metabolic pathways were examined. During the long-term operation, 2002.7 ± 56.0 mg COD/L acetate was accumulated in CFR 10d due to the washout of acetotrophic methanogens. Microorganisms with high half-saturation constants were enriched in reactors of 25-day SRT. Moreover, ethanol oxidizing bacteria and acetotrophic methanogens with high half-saturation constants could be acclimated in SBRs. In SBRs, Syner- 01 and Methanothrix dominated, and the low SRT of 10 days increased the relative abundance of Geobacter to 38.0%. In CFRs, the low SRT of 10 days resulted in an increase of Desulfovibrio among syntrophic bacteria, and CFR 10d could be employed in enriching hydrogenotrophic methanogens like Methanobrevibacter. [Display omitted] • Ethanol oxidation remained favourable under all operational conditions. • 10-day SRT and CFRs enriched microorganisms with high half-saturation constants. • Geobacter was highly enriched in an SBR with 10-day SRT or a CFR with 25-day SRT. • CFR 10d benefited hydrogenotrophic methanogens like Methanobrevibacter. [ABSTRACT FROM AUTHOR]