Syngas fermentation allows for the conversion of wastes into useful commodity chemicals. To target higher value products, the conditions can be tuned to be favourable for both acetogenic and reverse beta-oxidation pathways and produce, in one stage, butyric and caproic acid. Studies in CSTR have shown the crucial role of pH, which must be low enough to allow for ethanol generation in the acetogenic step while avoiding the inhibition of reverse β-oxidation in acidic conditions. However, no studies have investigated the effect of pH in reactor configurations suitable for syngas fermentation (i.e., allowing for cell retention and exhibiting high mass transfer rates at low operating costs), such as Trickle Bed Reactors, TBR. In this study, two TBR were used to study the pH effect on the fermentation of syngas to produce C4 and C6 acids, using undefined mixed cultures. Five pH values were tested in the range 4.5–7.5, and pH 6 was found to be the most favourable for simultaneous production of C4 & C6 acids from syngas, which agrees with what was found in suspended growth systems. In addition, the highest titers in literature so far were achieved in the TRB. 16S rRNA analysis was performed showing and to be the key genus for the efficient process at pH 6. Finally, the experimental methodology followed, and data collected proved the robustness of mixed culture biofilm reactors in respect to pH changes, as the same reactor performance and bacterial community were achieved regardless of the operation history.

中文翻译：

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pH 值对混合培养滴流床反应器中合成气转化为 C4 和 C6 酸的影响


合成气发酵可以将废物转化为有用的商品化学品。为了获得更高价值的产品，可以将条件调整为有利于产乙酸和反向 β-氧化途径，并在一个阶段中生产丁酸和己酸。 CSTR 的研究表明 pH 值的关键作用，pH 值必须足够低，以便在产乙酸步骤中产生乙醇，同时避免在酸性条件下抑制反向 β-氧化。然而，尚无研究调查适合合成气发酵的反应器配置（即允许细胞保留并以低运行成本表现出高传质率）（例如滴流床反应器，TBR）中 pH 值的影响。在本研究中，使用两个 TBR 使用未定义的混合培养物来研究 pH 对合成气发酵生产 C4 和 C6 酸的影响。测试了 4.5-7.5 范围内的五个 pH 值，发现 pH 6 最有利于从合成气同时生产 C4 和 C6 酸，这与悬浮生长系统中发现的结果一致。此外，迄今为止文献中的最高滴度是在 TRB 中实现的。进行的 16S rRNA 分析表明，它是 pH 6 下高效过程的关键。最后，遵循实验方法，收集的数据证明了混合培养生物膜反应器在 pH 变化方面的稳健性，因为相同的反应器性能和无论手术史如何，都实现了细菌群落。