Improvement of hydrogen fermentation of galactose by combined inoculation strategy

This study evaluated the feasibility of anaerobic hydrogen fermentation of galactose, a red algal biomass sugar, using individual and combined mixed culture inocula. Heat-treated (90°C, 30 min) samples of granular sludge (GS) and suspended digester sludge (SDS) were used as inoculum sources. The type of mixed culture inoculum played an important role in hydrogen production from galactose. Between two inocula, granular sludge showed higher hydrogen production rate (HPR) and hydrogen yield (HY) of 2.2 L H₂/L-d and 1.09 mol H₂/mol galactose_added, respectively. Combined inoculation (GS + SDS) led to an elevated HPR and HY of 3.1 L H₂/L-d and 1.28 mol H₂/mol galactose_added, respectively. Acetic and butyric acids are the major organic acids during fermentation. Quantitative polymerase chain reaction (qPCR) revealed that the mixed culture generated using the combined inoculation contained a higher cluster I Clostridium abundance than the culture produced using the single inoculum.