A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol

Abstract

Abstract:We have established a two-stage continuous fermentation process for production of ethanol from synthesis gas (syngas) with Clostridium ljungdahlii. The system consists of a 1-L continuously stirred tank reactor as a growth stage and a 4-L bubble column equipped with a cell recycle module as an ethanol production stage. Operating conditions in both stages were optimized for the respective purpose (growth in stage one and alcohol formation in stage two). The system was fed with an artificial syngas mixture, mimicking the composition of syngas derived from lignocellulosic biomass (60% CO, 35% H 2 , and 5% CO 2 ). Gas recycling was used to increase the contact area and retention time of gas in the liquid phase, improving mass transfer and metabolic rates. In stage two, the biocatalyst was maintained at high cell densities of up to 10 g DW/L. Ethanol was continuously produced at concentrations of up to 450 mM (2.1%) and ethanol production rates of up to 0.37 g/(L·h). Foam control was essential to maintain reactor stability. A stoichiometric evaluation of the optimized process revealed that the recovery of carbon and hydrogen from the provided carbon monoxide and hydrogen in the produced ethanol was 28% and 74%, respectively.

Trash to treasure: production of biofuels and commodity chemicals via syngas fermenting microorganisms

“…Lastly, metabolic modeling has been used to optimize media formulations, for instance, based on energy demands [82]. These models can help optimize and reduce the cost of media, which is a challenge the needs to be addressed before commercial deployment of syngas fermentation [83,84].…”

“…www.sciencedirect.com Current Opinion in Biotechnology 2014, 27: [79][80][81][82][83][84][85][86][87] converted to butyrate at the end of the fermentation, indicating the need for further genetic modifications to prevent the loss of butanol. Yet, the reversibility of this and similar alcohol forming enzymatic reactions was exploited by providing external short-chain carboxylic acids and syngas to C. ljungdahlii for the production of alcohols [58].…”

Continuous Ethanol Production from Synthesis Gas by Clostridium ragsdalei in a Trickle-Bed Reactor

“…Bioreactors such as air-lift reactors, continuous stirred tank reactors (CSTRs), trickle-bed reactors (TBRs) and hollow fiber membrane (HFM) reactors have been characterized for their capabilities for CO mass transfer into fermentation medium [12,[15][16][17][18][19]. Further, improved ethanol production over batch bottle fermentations was reported when fermentations were performed in various bioreactors that provided larger working volume, greater cell recycling, continuous addition of nutrients and syngas, and better control of operating parameters [1,16,[20][21][22][23]. For example, C. carboxidivorans produced only 0.9 g/L ethanol in batch bottles [24] compared to 1.6 g/L ethanol in bubble column [21].…”

Syngas Fermentation: A Microbial Conversion Process of Gaseous Substrates to Various Products

“…Biofilms retain cells, but long-term mass transfer and fouling may limit application. Ethanol productivity was reported to increase in a two-stage CSTR and bubble column with gas and cell recycling because more cells can be accumulated and more gas can be processed in two-stage bioreactors [103]. Chen et al [93] developed differential equations to describe syngas fermentation through a bubble column, but as yet lack appropriate data for modeling and validation.…”