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 sucrose_consumed, 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 sucrose_consumed, 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.

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pH值低于3.0的生物氢生产：可能吗？

在连续的产酸反应器中，在不控制pH的情况下，在30℃下用蔗糖进料，研究了生物制氢的生物过程。在第一个实验阶段，对三个反应器进行了比较：结构化固定床（FB），颗粒状UASB（UG）和絮凝性UASB（UF-1）。它们在3.3 h HRT和33 gCOD L ^-1 d ^-1 OLR下运行。在整个实验期间都产生了氢气，平均废水pH仅为2.8。FB，UG和UF-1反应器的氢气体积产生率（VHPR）分别为95±69、45±37和54±32 mLH ₂ L ^-1 h ^-1；和H ₂产量（HY）为1.5±0.8、0.8±0.6和1.2±0.7 molH ₂ mol ^-1分别_消耗蔗糖。UF-1反应堆显示出中间的VHPR和HY，但是没有下降的趋势，这与FB反应堆中观察到的相反。因此，为了连续和长期产生H ₂，在第二个实验阶段应用了絮凝UASB。在该阶段中，产酸反应器的UF-2（称为UF-2）的HRT升高至4.6 h，导致OLR为25 gCOD L ^-1 d ^-1。VHPR和HY显着增加至175±44 mLH ₂ L ^-1 h ^-1和3.4±0.7 molH ₂ mol ^-1蔗糖_消耗， 分别。这些改进伴随着更多的蔗糖去除，更高的悬浮生物质浓度，更少的乳酸盐产生和更多的乙酸盐以及高乙醇浓度。与当前公开的文献数据相反，UF-2反应器显示了在pH小于4.0的条件下通过暗发酵对H ₂产生的强烈抑制作用，与之相比，UF-2反应器可长期稳定地产生H ₂，在pH值为2.7时的平均收率令人满意。16 S rDNA测序显示，在所有反应器中，被指定为Ethanoligenens和Clostridium的两个序列占微生物菌群的70％以上。无需添加碱化剂和成功的H ₂ 这项研究表明，在非常酸性的条件下生产氢气，为通过暗发酵生产生物制氢开辟了一个新的领域，朝着更可持续和可行的技术发展。