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Mechano-activation as a stimuli response in 4D printing offers advantages such as orthogonality to other stimuli and control over the magnitude of applied force. Herein, we demonstrate mechanically...

Microbial batch production of alcohols by fermentation of CO-rich gases with Clostridia is limited by low volumetric productivities due to the need for formation of organic acids first (acidogenic phase) followed by re-consumption of the acids to form alcohols (solventogenic phase). Continuous autotrophic production of alcohols was made possible with C. carboxidivorans by use of two continuously operated stirred-tank bioreactors in series without cell retention. The pH in the first reactor was controlled to pH 6.0 for continuous growth of the cells. Steady-state concentrations of 3.0 g L−1 acetate and 0.1 g L−1 butyrate were measured at a mean hydraulic residence time of 8.3 h. The pH in the second reactor was controlled to pH 5.0 for enhancing continuous formation of alcohols resulting in steady-state concentrations of 6.1 g L−1 ethanol, 0.7 g L−1 butanol, and 0.1 g L−1 hexanol at a mean hydraulic residence time of 12.5 h. Continuous formation of alcohols from CO was already observed in the first stirred-tank reactor parallel to the formation of acids, whereas re-consumption of acids as well as de-novo syntheses of alcohols from CO was shown in the second stirred-tank reactor. Thus, high final alcohol-to-acid ratios of 3.9 gethanol gacetate−1 and 4.4 gbutanol gbutyrate−1 were achieved in the continuous syngas-fermentation process with C. carboxidivorans.