Microbial insights of enhanced anaerobic conversion of syngas into volatile fatty acids by co-fermentation with carbohydrate-rich synthetic wastewater

Abstract

Background: The co-fermentation of syngas (mainly CO, H 2 and CO 2) and different concentrations of carbohydrate/ protein synthetic wastewater to produce volatile fatty acids (VFAs) was conducted in the present study. Results: It was found that co-fermentation of syngas with carbohydrate-rich synthetic wastewater could enhance the conversion efficiency of syngas and the most efficient conversion of syngas was obtained by co-fermentation of syngas with 5 g/L glucose, which resulted in 25% and 43% increased conversion efficiencies of CO and H 2 , compared to syngas alone. The protein-rich synthetic wastewater as co-substrate, however, had inhibition on syngas conversion due to the presence of high concentration of NH 4 +-N (> 900 mg/L) produced from protein degradation. qPCR analysis found higher concentration of acetogens, which could use CO and H 2 , was present in syngas and glucose co-fermentation system, compared to glucose solo-fermentation or syngas solo-fermentation. In addition, the known acetogen Clostridium formicoaceticum, which could utilize both carbohydrate and CO/H 2 was enriched in syngas solofermentation and syngas with glucose co-fermentation. In addition, butyrate was detected in syngas and glucose co-fermentation system, compared to glucose solo-fermentation. The detected n-butyrate could be converted from acetate and lactate/ethanol which produced from glucose in syngas and glucose co-fermentation system supported by label-free quantitative proteomic analysis. Conclusions: These results demonstrated that the co-fermentation with syngas and carbohydrate-rich wastewater could be a promising technology to increase the conversion of syngas to VFAs. In addition, the syngas and glucose co-fermentation system could change the degradation pathway of glucose in co-fermentation and produce fatty acids with longer carbon chain supported by microbial community and label-free quantitative proteomic analysis. The above results are innovative and lead to achieve effective conversion of syngas into VFAs/longer chain fatty acids, which would for sure have a great interest for the scientific and engineering community. Furthermore, the present study also used the combination of high-throughput sequencing of 16S rRNA genes, qPCR analysis and label-free

Hydrogen as a Co-electron Donor for Chain Elongation With Complex Communities

“…For instance, abundant CO 2 supply was reported to favor MCC production in mixed communities ( Roghair et al, 2018a ), but high partial pressure of H 2 makes CE by Clostridium kluyveri less favorable ( Schoberth and Gottschalk, 1969 ; Angenent et al, 2016 ). Besides, the continuous presence of H 2 in the fermenter is a main factor that shapes the community composition ( Wu et al, 2019b ; Liu C. et al, 2020 ).…”

“…Although co-feeding of conventional EDs has been an extensively adopted strategy to increase MCC yields ( Wu et al, 2019a ; Stamatopoulou et al, 2020 ), only a handful of studies tested the effect of co-feeding H 2 and CO 2 together with conventional EDs, short-chain carboxylates (SCC), and/or complex substrates. Among these studies, some evidence has been shown for a net positive effect of H 2 co-feeding ( Steinbusch et al, 2011 ; Arslan et al, 2012 ; Nzeteu et al, 2018 ; Wu et al, 2019b ; González-Tenorio et al, 2020 ; Liu C. et al, 2020 ). However, the underlying mechanisms and the involved microorganisms as well as the boundaries of such synergy remain unknown.…”

Enhanced Ethanol Production From Carbon Monoxide by Enriched Clostridium Bacteria

“…1) after 15 d ( Figure 7C ), and the butyric acid to butanol conversion efficiency reached almost 100%. Therefore, two metabolic reactions can be assumed to co-exist in the fermentation process: one being butanol production from exogenous butyric acid and CO ( Liu et al, 2020 ) and the other being acetic acid production from CO with ethanol production via the WLP ( Fernández-Naveira et al, 2017c ). Interestingly, the molar ratio of ethanol/acetic acid reached 9.86 at the end of the incubation ( Figure 7C ), which is much higher than in other commonly reported studies of ethanol production from CO ( Table 2 ).…”

Effect of Endogenous and Exogenous Butyric Acid on Butanol Production From CO by Enriched Clostridia

“…Mixed cultures have the advantage of no need of sterilization and resistance to unfavorable environmental conditions, such as their tolerance to a wide pH range for alcohol production. This enables an easier implementation at large scale compared to pure cultures ( Liu et al, 2020 ).…”