Improvement of organic acid production with sulfate addition during syngas fermentation using mixed cultures

Abstract

The aim of this study is to investigate the effect of sulfate on conversion of CO2 into organics using syngas fermentation with mixed culture. Fermentation tests were operated under H2 concentrations of 2.14 and 21.4 ​mmol/d, respectively, using substrates contained different initial concentrations of sulfate (i.e. 0, 2, 4, 6, 8, 10, and 12 ​mM). The addition of sulfate improved the acetate and formate production, and the enhancement was positively correlated with the sulfate concentrations from 2 to 8 ​mM. With 8 ​mM sulfate, the maximum acetate concentrations reached 75.4 ​± ​4.51 and 76.1 ​± ​7.77 ​mM under H2 concentrations of 2.14 and 21.4 ​mmol/d, respectively, which were 1.47 and 2.58 times higher than those of the treatment without sulfate. The biomass achieved with the sulfate addition was 52%–97% higher than that without sulfate. High-throughput pyrosequencing showed that with the presence of sulfate, Acetobacterium and Desulfovibrio were dominant in the microbial community with high relative abundance of 43% and 38%, respectively. This study suggested that the performance of syngas fermentation could be improved with co-metabolism between homoacetogen and sulfate-reducing bacteria.

Keywords

• Syngas fermentation
• Sulfate
• Organics production
• Homoacetogenic bacteria
• Sulfate reducing bacteria