Fernández-Naveira Ánxela, Abubackar Haris Nalakath, Veiga María C, Kennes Christian
Chemical Engineering Laboratory, Faculty of Sciences and Center for Advanced Scientific Research (CICA), University of La Coruña, Rúa da Fraga 10, 15008, La Coruña, Spain.
World J Microbiol Biotechnol. 2017 Mar;33(3):43. doi: 10.1007/s11274-016-2188-z. Epub 2017 Feb 3.
Bioprocesses in conventional second generation biorefineries are mainly based on the fermentation of sugars obtained from lignocellulosic biomass or agro-industrial wastes. An alternative to this process consists in gasifying those same feedstocks or even other carbon-containing materials to obtain syngas which can also be fermented by some anaerobic bacteria to produce chemicals or fuels. Carbon monoxide, carbon dioxide and hydrogen, which are the main components of syngas, are also found in some industrial waste gases, among others in steel industries. Clostridium carboxidivorans is able to metabolise such gases to produce ethanol and higher alcohols, i.e. butanol and hexanol, following the Wood-Ljungdahl pathway. This does simultaneously allow the removal of volatile pollutants involved in climate change. The bioconversion is a two step process in which organic acids (acetate, butyrate, hexanoate) are produced first, followed by the accumulation of alcohols; although partial overlap in time of acids and alcohols production may sometimes take place as well. Several parameters, among others pH, temperature, or gas-feed flow rates in bioreactors, affect the bioconversion process. Besides, the accumulation of high concentrations of alcohols in the fermentation broth inhibits the growth and metabolic activity of C. carboxidivorans.
传统第二代生物精炼厂中的生物过程主要基于对从木质纤维素生物质或农业工业废弃物中获得的糖类进行发酵。该过程的一种替代方法是将这些相同的原料甚至其他含碳材料气化以获得合成气，合成气也可被一些厌氧细菌发酵以生产化学品或燃料。合成气的主要成分一氧化碳、二氧化碳和氢气也存在于一些工业废气中，尤其是钢铁行业的废气。羧基还原梭菌能够按照伍德-龙格达尔途径代谢这些气体以生产乙醇和高级醇，即丁醇和己醇。这同时也能去除与气候变化相关的挥发性污染物。生物转化是一个两步过程，首先产生有机酸（乙酸、丁酸、己酸），随后是醇类的积累；不过有时酸和醇的产生时间也可能会有部分重叠。生物反应器中的几个参数，包括pH值、温度或气体进料流速等，都会影响生物转化过程。此外，发酵液中高浓度醇类的积累会抑制羧基还原梭菌的生长和代谢活性。
