EKC2023

High calorific biohydrogen/biogas production by operating under high pressure

Not scheduled

20m

Orion 2

Environment and Energy [EE3] Sustainable organic waste/wastewater management

Speaker

Dong-Hoon Kim (Inha University)

Description

Hydrogen (H2) and methane (CH4) are the two important energy carriers and are usually considered as the cleanest energy form, when they are coming from biomass. However, their content in the biogas is far below the standard limit (>95%), which limits their application without biogas upgrading. Autogenerative high-pressure digestion has the advantage of producing high-calorific biogas directly from the reactor. However, it has never been attempted for high-calorific bio-H2 production, and its continuous operation has rarely been discussed for CH4 upgrading. Two upflow anaerobic sludge blanket reactors (UASB) were operated simultaneously. The first UASB was operated for bio-H2 production at an OLR of 60 g COD/L/d with increasing pressure from 1 to 9 bar. At the same time, the effluent from the bio-H2 producing reactor was fed into the second UASB (for CH4 production) at an OLR of 10g COD/L/d with a pressure increase from 1 to 8 bar. As the pressure gradually increased, the bio-H2 content increased from 45% at 1 bar to 77.8% ± 0.5% at 9 bar, whereas the bio-H2 yield decreased from 1.5 to 1.2 mol/molhexose. Glucose removal was >96%, and the effluent pH was 5.10.2. High butyrate concentration in organic acid production can be considered a thermodynamically favorable reaction. In the second UASB, as the pressure increased, the CH4 content in the biogas increased gradually, reaching 96.70.8% at 8 bar (309 MJ/m3 biogas). The pH was dropped from 8.2 to 7.2 with pressure increase, but COD removal efficiency was maintained >90%. The high pressure of up to 8 bar did not adversely impact the physicochemical properties of granules. The current approach can be considered an advanced form of anaerobic digestion for high calorific biogas production. Increasing interest in utilizing the high-content bio-H2 for improving the CH4 content to 99% would influence the process for maximal benefits.

References

Om et al. (2023) Upflow anaerobic sludge blanket reactor operation under high pressure for energy-rich biogas production