6. Conclusion

It is now widely accepted that hydrogen will be a major player in the future energy economy, thanks to its ability to play a highly efficient role as an energy carrier. The success of this compound in this role also depends on the implementation of production processes using renewable substrates. This is the context in which the fermentative production of hydrogen is presented here. The main current limitations concern synthesis speeds and yields, which remain relatively low. Optimization of these processes will most probably involve valorizing carbonaceous co-products (volatile fatty acids, alcohols) and recycling the carbon dioxide produced. This approach should therefore lead to the implementation of processes involving several stages, in the manner of a biorefinery process. These stages may call on very different technologies, since they will most probably involve dark anaerobic and/or...