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Abstract
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One of the major issues in biomethanation studies, especially a batch strategy without mixing, is gaseous substrate
mass transfer between gas and liquid phases. The strategy can be assumed as a simplified form of a
stagnant underground gas reservoir. Hydrogen gas, as the limiting substrate, plays significant role in biomethanation.
Being informed of hydrogen content diffused within the liquid phase for calculating percentage of
active volume, help researcher to make a proper decision on bioreactor design or adjusting process parameters.
For this purpose, a mass transfer modelling was developed which strengthened with a set of optimized biokinetic
parameters. Parameter optimization was accomplished with the help of a predefined optimization algorithm and
using a set of experimental data with the source of literature. Active volume calculation was successfully performed
via the verified model and response surface methodology was served for maximizing it under variety of
process conditions. It was found that the bioreactor height to width ratio significantly affected on active volume
followed by pressure and temperature. In addition, working with a bioreactor with a circle cross section, in
comparison with a square one, improved the maximum active volume up to 43% due to providing higher surface
area for mass transfer. Sensitivity analysis verified the previous findings and revealed that higher pressures and
temperatures linearly increased the active volume while increasing the bioreactor height to width ratio exponentially
decreased the response. Furthermore, a wide bioreactor have potential to promote active volume up to
72% rather than a vertical one.
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