Abstract

Gas-to-liquid mass transfer of hydrogen (H 2 ) was investigated in a gas–liquid reactor with a continuous gas phase, a batch liquid phase, and liquid mixing regimes relevant to assessing kinetics of microbial H 2 consumption. H 2 transfer was quantified in real-time with a H 2 microsensor for no mixing, moderate mixing [100 rotations per minute (rpm)], and rapid mixing (200 rpm). The experimental results were simulated by mathematical models to find best-fit values of volumetric mass transfer coefficients—k L a—for H 2 , which were 1.6/day for no mixing, 7/day for 100 rpm, and 30/day for 200 rpm. Microbiological H 2 -consumption experiments were conducted with Methanobacterium bryantii M.o.H. to assess effects of H 2 mass transfer on microbiological H 2 -threshold studies. The results illustrate that slow mixing reduced the gas-to-liquid H 2 transfer rate, which fell behind the rate of microbiological H 2 consumption in the liquid phase. As a result, the liquid-phase H 2 concentration remained much lower than the liquid-phase H 2 concentration that would be in equilibrium with the gas-phase H 2 concentration. Direct measurements of the liquid-phase H 2 concentration by an in situ probe demonstrated the problems associated with slow H 2 transfer in past H 2 threshold studies. The findings indicate that some of the previously reported H 2 -thresholds most likely were over-estimates due to slow gas-to-liquid H 2 transfer. Essential requirements to conduct microbiological H 2 threshold experiments are to have vigorous mixing, large gas-to-liquid volume, large interfacial area, and low initial biomass concentration.

Original languageEnglish (US)
JournalBiodegradation
DOIs
StatePublished - Jan 1 2019

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Keywords

  • Bioreactors
  • H -thresholds
  • Hydrogen
  • Mass transfer
  • Methanogens
  • Mixing

ASJC Scopus subject areas

  • Environmental Engineering
  • Microbiology
  • Bioengineering
  • Environmental Chemistry
  • Pollution

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