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 re-actors, named as SBR25d, SBR10d, CFR25d, and CFR10d, respectively. System performance, syntrophic relation-ships, microbial communities, and metabolic pathways were examined. During the long-term operation, 2002.7 +/- 56.0 mg COD/L acetate was accumulated in CFR10d due to the washout of acetotrophic methanogens. Mi-croorganisms 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 abun-dance of Geobacter to 38.0%. In CFRs, the low SRT of 10 days resulted in an increase of Desulfovibrio among syntrophic bacteria, and CFR10d could be employed in enriching hydrogenotrophic methanogens like Methanobrevibacter.

Automated summary

This study investigated the performance, syntrophic relationships, microbial communities, and metabolic pathways of ethanol-fed reactors with different operational modes and solids retention times. The results showed that different microorganisms were enriched under different SRT conditions, and syntrophic bacteria related to methane production could be enriched under low SRT conditions.