Continuous dark-fermentative H2 production using carbon components of lignocellulose hydrolysates: Insight into the difference between mixed and single substrates

Abstract

Hydrogen produced from lignocellulosic biomass via dark fermentation is a promising alternative to fossil fuels. This study assessed fermentative H2 production from single sugars and sugar mixtures mimicking real lignocellulose hydrolysates during a continuous process. The highest hydrogen production rate (HPR) was obtained with pentose sugars, reaching 8.80 and 8.09 L/L-d for arabinose and xylose, respectively. Glucose showed the lowest HPR (6.19 L/L-d), while in the case of sugar mixtures (glucose, cellobiose, xylose, arabinose), HPR was approximately 7.3 L/L-d and was lower than expected from calculations. Thus, cofermentation reduced the H2 production potential. It was shown that pentose sugars are preferred for hydrogen production, but their utilization is limited by the presence of glucose, which is utilized preferentially in sugar mixtures. Xylose, arabinose and sugar mixtures showed similar H2 yields (approximately 0.29 mol H2/mol C), so the efficiency of substrate conversion into H2 was comparable for these substrates. The microbial community distribution showed that the Clostridium genus was dominant regardless of the substrate, with Clostridium beijerinckii and Clostridium guangxiense being the main bacterial species. Different substrates did not significantly affect the type of microorganisms present in the microbiome and changed only their relative abundance.