Using gas mixtures of CO, CO₂ and H₂ as microbial substrates: the do's and don'ts of successful technology transfer from laboratory to production scale

Abstract

SummaryThe reduction of CO 2 emissions is a global effort which is not only supported by the society and politicians but also by the industry. Chemical producers worldwide follow the strategic goal to reduce CO 2 emissions by replacing existing fossil‐based production routes with sustainable alternatives. The smart use of CO and CO 2/H2 mixtures even allows to produce important chemical building blocks consuming the said gases as substrates in carboxydotrophic fermentations with acetogenic bacteria. However, existing industrial infrastructure and market demands impose constraints on microbes, bioprocesses and products that require careful consideration to ensure technical and economic success. The mini review provides scientific and industrial facets finally to enable the successful implementation of gas fermentation technologies in the industrial scale.

Syngas Fermentation to Alcohols: Reactor Technology and Application Perspective

“…The pilot plants of Ineos Bio and Coskata are no longer in operation, solely LanzaTech is still successful at larger scale. Takors et al name a "continuously operated bubble column/gas lift loop reactor" as reactor type for the planned industrial plant in Ghent, Belgium . A loop reactor or a bubble column with circulation of the fermentation broth is expected to be an advantageous concept for the commercial realization of syngas fermentation.…”

“…Hurst and Lewis showed that an increase in p CO from 0.35 atm to 2.0 atm increased cell mass of C. carboxidivorans by 440 %, also leading to a considerable rise in ethanol concentration [69]. In general, a mildly increased pressure appears to be reasonable in gas fermentation [8,64,70] and the increase of total pressure or the partial pressure of a gas component has been investigated in different fermentation systems [27,69,[71][72][73][74][75][76][77][78][79][80][81][82][83][84]. However, the impact of pressure increase is not fully understood and in order to avoid possible subtrate inhibition, a balance between mass transfer and substrate consumption of the bacterial cells has to be found [9].…”

“…According to Takors et al, an suitable specific energy input for a gas fermentation process is in the range of < 0.3 kW m -3 [64]. Typical P/V ratios for aerated stirred tanks are in the order of 1 kW m -3 [9], in laboratory studies, even higher values are common (e.g., Kantzow et al: 11.9 kW m -3 [47]).…”

“…Ethanol productivity up to 26.6 g L -1 d -1 after 30 days of continuous operation. [40] type for the planned industrial plant in Ghent, Belgium [64]. A loop reactor or a bubble column with circulation of the fermentation broth is expected to be an advantageous concept for the commercial realization of syngas fermentation.…”

Robust and biocompatible catalysts for efficient hydrogen-driven microbial electrosynthesis

“…Hybrid processes have been proposed that couple the electrocatalytic H 2 production in one process to microbial CO 2 reduction in a second microbial gas fermentation step for the production of chemicals [26][27][28] . However, such two-step processes entail the pumping and mixing of a low-soluble and explosive gas (H 2 ) at significant costs and safety risks 29 .…”