Hydrogen Fermentation of the Galactose-Glucose Mixture

A review on the biomass pretreatment and inhibitor removal methods as key-steps towards efficient macroalgae-based biohydrogen production

(Red, green and brown) macroalgal biomass is a propitious candidate towards covenant alternative energy resources to be converted into biofuels i.e. hydrogen. The application of macroalgae for hydrogen fermentation (promising route in advancing the biohydrogen generation process) could be accomplished by the transformation of carbohydrates, which is a topic receiving broad attention in recent years. This article overviews the variety of marine algal biomass available in the coastal system, followed by the analyses of their pretreatment methods, inhibitor formation and possible detoxification, which are key-aspects to achieve subsequent H₂ fermentation in a proper way.

Changes in performance and bacterial communities in response to various process disturbances in a high-rate biohydrogen reactor fed with galactose

High-rate biohydrogen production was achieved via hybrid immobilized cells fed with galactose in a continuous reactor system. The hybrid immobilized cells were broken down after 20 days and began to form granules by self-aggregation. The peak hydrogen production rate (HPR) and hydrogen yield (HY) of 11.8 ± 0.6 LH2/L-d and 2.1 ± 0.1 mol H2/molgalactose(added), respectively, were achieved at the hydraulic retention time (HRT) of 8h with an organic loading rate (OLR) of 45 g/L-d. This is the highest yet reported for the employment of galactose in a continuous system. Various process disturbances including shock loading, acidification, alkalization and starvation were examined through bacterial community analysis via pyrosequencing of the 16S rRNA genes. The proportion of Clostridia increased during the stable biohydrogen production periods, while that of Bacilli increased when the reactor was disturbed. However, due to the stability of the self-aggregated granules, the process performance was regained within 4-7 days.