Chapter 5 - Thermophilic Fermentation for Enhanced Biohydrogen Production

Abstract

Moderate thermophilic fermentation appears to be superior on hydrogen production rate (98–152mmol/L/h) with satisfactory hydrogen yield of 2–2.4mol/mol C6, while extreme thermophilic fermentation has a lower hydrogen production rate (15–30mmol/L/h) with rather high hydrogen yield of 2.8–3.5mol/mol C6 when using pure sugar as substrate. Both moderate thermophilic and extreme thermophilic fermentation has similar hydrogen yield for the real-world substrate (2.4–2.8mol H2/mol C6), such as wastewater and organic wastes. Extreme thermophilic fermentation has less variety of side-products than moderate thermophilic fermentation. Significant improvement in H2 production yield could be achieved to near maximum of 4mol H2/mol C6 by in situ gas separation, microbial population optimization, and metabolic engineering in the microorganisms. Bioreactor design by integrating dark fermentation with volatile fatty acids oxidation by microbial electrolysis could have the potential to increase the hydrogen yield gone beyond the current maximum of 4mol H2/mol C6 and address technical barriers that currently limit the technoeconomic feasibility of fermentative hydrogen production.