Dhakal Nirpesh, Acharya Bishnu
Department of Chemical and Biological Engineering, 57 Drive, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada.
Polymers (Basel). 2021 Nov 12;13(22):3917. doi: 10.3390/polym13223917.
Increasing environmental awareness among the general public and legislators has driven this modern era to seek alternatives to fossil-derived products such as fuel and plastics. Addressing environmental issues through bio-based products driven from microbial fermentation of synthetic gas (syngas) could be a future endeavor, as this could result in both fuel and plastic in the form of bioethanol and polyhydroxyalkanoates (PHA). Abundant availability in the form of cellulosic, lignocellulosic, and other organic and inorganic wastes presents syngas catalysis as an interesting topic for commercialization. Fascination with syngas fermentation is trending, as it addresses the limitations of conventional technologies like direct biochemical conversion and Fischer-Tropsch's method for the utilization of lignocellulosic biomass. A plethora of microbial strains is available for syngas fermentation and PHA production, which could be exploited either in an axenic form or in a mixed culture. These microbes constitute diverse biochemical pathways supported by the activity of hydrogenase and carbon monoxide dehydrogenase (CODH), thus resulting in product diversity. There are always possibilities of enzymatic regulation and/or gene tailoring to enhance the process's effectiveness. PHA productivity drags the techno-economical perspective of syngas fermentation, and this is further influenced by syngas impurities, gas-liquid mass transfer (GLMT), substrate or product inhibition, downstream processing, etc. Product variation and valorization could improve the economical perspective and positively impact commercial sustainability. Moreover, choices of single-stage or multi-stage fermentation processes upon product specification followed by microbial selection could be perceptively optimized.
公众和立法者环境意识的提高推动了这个现代时代去寻找化石衍生产品（如燃料和塑料）的替代品。通过合成气（syngas）微生物发酵驱动的生物基产品来解决环境问题可能是未来的一项努力，因为这可能会产生生物乙醇和聚羟基脂肪酸酯（PHA）形式的燃料和塑料。以纤维素、木质纤维素以及其他有机和无机废物形式存在的丰富资源，使得合成气催化成为一个有趣的商业化课题。对合成气发酵的兴趣正在上升，因为它解决了传统技术（如直接生化转化和费托法）在利用木质纤维素生物质方面的局限性。有大量的微生物菌株可用于合成气发酵和PHA生产，这些菌株可以以无菌形式或混合培养的方式加以利用。这些微生物构成了由氢化酶和一氧化碳脱氢酶（CODH）的活性支持的多样生化途径，从而导致产品的多样性。总是有可能通过酶调控和/或基因定制来提高该过程的效率。PHA的生产率影响着合成气发酵的技术经济前景，而这又进一步受到合成气杂质、气液传质（GLMT）、底物或产物抑制、下游加工等因素的影响。产品的变化和增值可以改善经济前景，并对商业可持续性产生积极影响。此外，根据产品规格选择单阶段或多阶段发酵过程，然后进行微生物选择，可以显著优化。
