The Establishment and Characteristics of Dominant Syntrophic Propionate Oxidation Bacteria and Sulfate-Reducing Bacteria in a Mixed Culture

The anaerobic bio-treatment of lower COD/SO₄ ^2- ratio wastewater constitutes a bottle-aqneck due to the limited carbon source. In this type of environment, interactions between acidogenic fermentation bacteria and methane-producing bacteria (MPB) are aided by syntrophic fatty acid oxidation bacteria present in the functional niche; MPB and sulfate-reducing bacteria (SRB) compete with each other due to the availability of sulfate. Therefore, introduction of syntrophic fatty acid oxidation bacteria into an SRB dominated culture can achieve maximum utilization of the substrate, weakening the competition of MPB. In this study, the mixed culture of dominant syntrophic propionate oxidation bacteria (SPOB) and SRB was established and characterized at 35°C. The dominant SPOB and SRB were enriched in a continuous flow stirred-tank reactor and in batch experiments, respectively. Subsequently, an equal proportion of the enriched sludge was mixed and incubated in conical flasks with propionate as the sole substrate. Six parallel experiments (SP1–SP6) were conducted and two of them (SP2 and SP4) were chosen. The results revealed that the sulfate removal efficiencies of SP2 and SP4 were 91.83% and 93.03%, respectively. Furthermore, the outcome of the microbial analysis showed that the dominant microbial communities included Uncultured Smithella spp., Uncultured Desulfobacteraceae bacterium and sequences related to members of the family Desulfovibrio. Excess propionate was mainly syntrophically decomposed via sulfate reduction. Findings from this study could provide valuable information for the establishment of new processes and the regulation of parameters in the treatment of lower COD/SO₄ ^2- ratio wastewater.