Biohydrogen production by dark fermentation

The reactive nature of hydrogen means that, in the industrial world, dihydrogen (H ₂ ) is widely used as a reagent in many fine chemicals, petrochemical and food processing processes. In the current context of energy transition, fuel cell applications for transport are developing rapidly, making H ₂ an energy carrier of interest. The production of "green", or decarbonized, hydrogen is therefore a highly promising future field.

In the living world, hydrogen is a ubiquitous biochemical reaction intermediate, playing a major role as an electron carrier between microbial species, particularly under fermentative conditions. However, so-called "dark" fermentation, as opposed to light-dependent photo-bioprocesses, is a hydrogen-production-oriented process that has only recently appeared on the biotechnology scene. Long considered an undesirable process for degrading organic matter, generating odor nuisances and by-products of little economic interest, namely acetate and butyrate, it has recently become particularly attractive for its hydrogen production. What's more, the benefits of producing hydrogen by fermentation lie in the use of a wide range of organic substrates, whether pure or non-pure carbohydrates, organic waste or other agricultural residues. The hydrogen thus produced would be "biosourced" hydrogen (otherwise known as biohydrogen).

From an industrial standpoint, the production of "green" hydrogen by fermentation has not yet really taken off, given the still-emerging hydrogen market. The development of this type of biotechnology therefore remains at the pilot-scale stage. These H ₂ production processes also still have certain limitations when it comes to their immediate industrialization. Indeed, even if current processes present good productivities (several tens of $m_{H2}^3\text{/}{m}_{réacteur }^{\text{3}}\text{/ }jour$ , average conversion yields often remain below 2 mol _H2 .mol _{hexose_equivalent} ^–1 whereas a total conversion would allow to reach a theoretical yield of 12 mol _H2 .mol _{hexose_equivalent} ^–1 , i.e. 1.6 m ^...