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Biohydrogen production at pH below 3.0: Is it possible?

V T Mota1, A D N Ferraz Júnior2, E Trably3

  • 1LPB, Department of Hydraulics and Sanitary Engineering, São Carlos School of Engineering, University of São Paulo (USP), Avenida João Dagnone, 1100, São Carlos, SP, 13563-120, Brazil.

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Summary

Biological hydrogen production using sucrose in acidogenic reactors achieved high yields and rates, even at a low pH of 2.7. This study demonstrates a more sustainable and feasible approach to biohydrogen production without pH control.

Keywords:
Acid-tolerant bacteriaAcidogenic reactorBiohydrogenDark fermentationHydrogenpH

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Area of Science:

  • Biotechnology
  • Renewable Energy
  • Microbiology

Background:

  • Biological hydrogen production via dark fermentation is a promising renewable energy technology.
  • Conventional methods often require strict pH control, increasing operational complexity and cost.
  • Limited understanding of microbial behavior under highly acidic conditions in continuous reactors.

Purpose of the Study:

  • To investigate biological hydrogen production from sucrose in continuous acidogenic reactors without pH control.
  • To compare the performance of different reactor configurations (fixed-bed, granular UASB, flocculent UASB).
  • To optimize conditions for stable, long-term hydrogen production at low pH.

Main Methods:

  • Operated continuous acidogenic reactors (fixed-bed, granular UASB, flocculent UASB) fed with sucrose at 30°C.
  • Varied hydraulic retention time (HRT) and organic loading rate (OLR) across experimental phases.
  • Analyzed hydrogen production rates (VHPR), hydrogen yields (HY), sucrose removal, and microbial community composition (16S rDNA sequencing).

Main Results:

  • Stable hydrogen production was achieved at an average pH of 2.8 in the first phase and 2.7 in the second.
  • The flocculent UASB reactor (UF-2) demonstrated significantly improved VHPR (175 mLH₂ L⁻¹h⁻¹) and HY (3.4 molH₂ mol⁻¹ sucrose) at a 4.6 h HRT.
  • Microbial analysis revealed dominance of Ethanoligenens and Clostridium species, suggesting their role in acid tolerance and hydrogen production.

Conclusions:

  • Continuous biological hydrogen production is feasible and efficient under highly acidic conditions (pH ~2.7) without pH control.
  • Flocculent UASB reactors are suitable for long-term, stable biohydrogen production from sucrose.
  • This approach offers a more sustainable and cost-effective pathway for biohydrogen technology.