Hydrogenic and methanogenic fermentation of birch and conifer pulps

Conifer and birch pulp fermentation to hydrogen and methane was studied using dry and wet pulps with a compost enrichment culture at a pH range from 6 to 9. Hydrogen was produced at each pH, whilst methane was produced at all other pH values except pH 6 with dry conifer pulp and pH 9. Hydrogen and methane yields were generally higher with birch than with conifer pulp and the overall energy yields were higher with wet than dry pulp. The highest hydrogen and methane yields were 560 mL H2/g TS with wet birch pulp at pH 6 and 4800 mL CH4/g TS with wet conifer pulp at pH 7, respectively. Fermentation of dry pulps at pH 6 resulted in 160 mL H2/g TS. Hydrogenic bacteria belonging to phyla Bacteroidetes, Firmicutes and Proteobacteria were present in the cultures. Hydrogen was also produced from chemically hydrolyzed pulps. The highest hydrogen yield from dry conifer pulp hydrolysate was 63 mL H2/g TS. In summary, hydrogen and energy (calculated as H2) yields were higher with direct fermentation than from chemically hydrolyzed pulps. However, chemical hydrolysis followed by hydrogen production required less than 10 days compared to 28 days required for direct pulp fermentation to hydrogen.