High-calorific biohydrogen production under high pressure: Ca 2+addition, theoretical prediction, and continuous operation

초록

The removal of CO 2 (called "upgrading ") is essential in bio-H 2 production processes including dark fermentation (DF), which is energy -intensive and adds economic burden. Here, it was attempted to generate high calorific bioH 2 (high H 2 -content) directly from the fermenter under high pressure in the presence of Ca 2+ . High pressure was automatically generated by holding the produced gas at a certain limit. Batch test results showed that Ca 2+ addition was helpful to keep the pH by precipitating with dissolved CO 2 , resulting in the gradual increase of H 2 content to 93 % at 17.5 bar (vs. 77 % at 11.2 bar in the control). Then, the theoretical approaches, based on balance and equilibrium equations, were made to investigate the effects of Ca 2+ addition at different dosages (0 -1 g CaCl 2 /L) under different pressures during continuous operation. It was found that the H 2 content of 90 % at the permissible pressure (<= 10 bar) can be only achieved at 1 g CaCl 2 /L addition. Lastly, continuous operation of DF was conducted in an up -flow anaerobic sludge blanket reactor fed with glucose (10 g COD/L) with 1 g CaCl 2 /L addition. The H 2 content in bio-H 2 gradually increased with the pressure increase, from 49.5 % at 1 bar to 84.9 % at 9 bar. No distinct changes in morphological and physico-chemical properties were observed in the granules exposed at different pressures. Although there was a drop in H 2 production due to the increase in dissolved H 2 portion and metabolic shift at high pressure, the decrease in upgrading cost made high-pressure DF economically feasible.

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