High-calorific bio-hydrogen production under self-generated high-pressure condition

For the use of biologically produced H₂, removal of CO₂ is an indispensable process. Unlike conventional CO₂ removal methods, this study proposed a self-generated high-pressure dark fermentation (HPDF) process as a novel strategy for directly producing high-calorific bio-H₂. The pressure was automatically increased by self-generated gas, while the maximum pressure inside fermenter was restricted to 1, 3, 5, 7, and 10 bar in a batch operation. As the pressure increased from 1 to 10 bar, the H₂ content increased from 55% to 80%, whereas the H₂ yield decreased from 1.5 to 0.9 mol H₂/mol hexose_added. The highest H₂ content of 80% was obtained at both of 7 and 10 bars. Increased lactate production with increased abundance of lactic acid bacteria was observed at high-pressure. Despite the lower H₂ yields at high-pressure conditions, HPDF was found to be economically beneficial for obtaining high-calorific bio-H₂ owing to the low CO₂ removal cost.