Biohydrogen production at pH below 3.0: Is it possible?

• Published in: Water research (Oxford) Vol. 128; pp. 350 - 361
• Main Authors: Mota, V.T., Ferraz Júnior, A.D.N., Trably, E., Zaiat, M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2018; IWA Publishing/Elsevier
• Subjects: Acid-tolerant bacteria; Acidogenic reactor; Biohydrogen; Dark fermentation; Environmental Sciences; Hydrogen; Life Sciences; Acid-tolerant bacteria; pH; Acidogenic reactor; Biohydrogen; Dark fermentation; Hydrogen; dark fermentation; biohydrogen; hydrogen; acidogenic reactor; acid-tolerant bacteria
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2017.10.060

Biological hydrogen production was investigated in continuous acidogenic reactors fed with sucrose at 30 °C without pH control. In the first experimental phase, three reactors were compared: a structured fixed-bed (FB), a granular UASB (UG) and a flocculent UASB (UF-1). They were run at 3.3 h HRT and 33 gCOD L−1d−1 OLR. Hydrogen production occurred throughout the experimental period with an average effluent pH of only 2.8. The FB, UG and UF-1 reactors presented volumetric hydrogen production rates (VHPR) of 95 ± 69, 45 ± 37 and 54 ± 32 mLH2 L−1h−1, respectively; and H2 yields (HY) of 1.5 ± 0.8, 0.8 ± 0.6 and 1.2 ± 0.7 molH2 mol−1 sucroseconsumed, respectively. The UF-1 reactor showed intermediate VHPR and HY, but no declining trend, contrary to what was observed in the FB reactor. Thus, aiming at continuous and long-term H2 production, a flocculent UASB was applied in the second experimental phase. In this phase, the HRT of the acidogenic reactor, which was named UF-2, was raised to 4.6 h, resulting in an OLR of 25 gCOD L−1d−1. The VHPR and the HY increased considerably to 175 ± 44 mLH2 L−1h−1 and 3.4 ± 0.7 molH2 mol−1 sucroseconsumed, respectively. These improvements were accompanied by greater sucrose removal, higher suspended biomass concentration, less production of lactate and more of acetate, and high ethanol concentration. Contradicting the current published literature data that reports strong inhibition of H2 production by dark fermentation at pH less than 4.0, the UF-2 reactor presented stable, long-term H2 production with satisfactory yields at pH 2.7 on average. 16 S rDNA sequencing revealed that two sequences assigned as Ethanoligenens and Clostridium accounted for over 70% of the microbiota in all the reactors. The non-necessity of adding alkalizing agents and the successful H2 production under very acid conditions, demonstrated in this study, open a new field of investigation in biological hydrogen production by dark fermentation towards a more sustainable and feasible technology. [Display omitted] •Acidogenic reactors were fed with sucrose (4.7 gCOD L−1) without pH regulator.•Acetate production replaced lactate when the HRT increased from 3.3 to 4.6 h.•Continuous long-term and stable H2 production was achieved at pH always below 3.0.•H2 production of 175 mLH2 L−1h−1 and yield of 3.4 molH2 mol−1sucrose were obtained.•Bacteria affiliated with Ethanoligenens harbinense were predominant.