Isopropanol-butanol-ethanol production by cell-immobilized vacuum fermentation

Distillation for in situ recovery of volatile fermentation products

Many fermentation products inhibit their own microbial production, which complicates industrial-scale fermentation development for these products. When a product is volatile, this inhibition can be circumvented by removing product during fermentation through evaporation in a loop around the bioreactor. Microbes can survive this loop if its temperature is reduced using vacuum. Then, regrowing of microbes is not required. From a separation efficiency viewpoint, the evaporation loop should not use a single equilibrium stage, but a multistage vacuum distillation column. Such in situ product removal (ISPR) by vacuum distillation has hardly been recognized as an option, however. Costs for this product removal with subsequent purification are modest, even when product titers are low. A prerequisite is the use of advanced energy integration and heat pumping methods.

Biobutanol production from underutilized substrates using Clostridium: Unlocking untapped potential for sustainable energy development

The increasing demand for sustainable energy has brought biobutanol as a potential substitute for fossil fuels. The Clostridium genus is deemed essential for biobutanol synthesis due to its capability to utilize various substrates. However, challenges in maintaining fermentation continuity and achieving commercialization persist due to existing barriers, including butanol toxicity to Clostridium, low substrate utilization rates, and high production costs. Proper substrate selection significantly impacts fermentation efficiency, final product quality, and economic feasibility in Clostridium biobutanol production. This review examines underutilized substrates for biobutanol production by Clostridium, which offer opportunities for environmental sustainability and a green economy. Extensive research on Clostridium, focusing on strain development and genetic engineering, is essential to enhance biobutanol production. Additionally, critical suggestions for optimizing substrate selection to enhance Clostridium biobutanol production efficiency are also provided in this review. In the future, cost reduction and advancements in biotechnology may make biobutanol a viable alternative to fossil fuels.

Recovery and repurposing of waste isopropanol with CO2-switchable deep eutectic solvents

Large amounts of waste isopropanol (IPA) are generated in industry, rendering the recovery of IPA highly desirable due to the economic and environmental benefits. Because it forms an azeotropic mixture with water, IPA is difficult to separate from the waste stream. In the present work, a novel CO2-switchable monoethanolamine-butanol deep eutectic solvent (DES) ([MEA][BuOH]) was identified as a superior medium for separating IPA and water at ambient temperature by forming butanol-IPA mixtures. The switchable solvent system combines the advantages of homogeneous and heterogeneous systems, i.e., rapid mixing due to the low mass transfer limitations and facile product separation, respectively. The low viscosity of [MEA][BuOH], the similar physical features (polarity, dipole moment, and dielectric constant) of butanol and IPA, and the H-bonding interactions of [BuOH] with IPA are thought to enable effective IPA capture from water by the butanol. Recovery of the IPA and formation of a butanol-IPA mixture is appealing because the resultant mixture could serve as an additive or substitute for alternative fuels. The results suggest that the developed process will provide a low-cost, energy-saving, effective, and environmentally benign route to recycling and repurposing waste IPA, an environmental hazard, as a potential alternative fuel.

Methanotrophs: Metabolic versatility from utilization of methane to multi-carbon sources and perspectives on current and future applications

The development of biorefineries for a sustainable bioeconomy has been driven by the concept of utilizing environmentally friendly and cost-effective renewable energy sources. Methanotrophic bacteria with a unique capacity to utilize methane as a carbon and energy source can serve as outstanding biocatalysts to develop C1 bioconversion technology. By establishing the utilization of diverse multi-carbon sources, integrated biorefinery platforms can be created for the concept of the circular bioeconomy. An understanding of physiology and metabolism could help to overcome challenges for biomanufacturing. This review summaries fundamental gaps for methane oxidation and the capability to utilize multi-carbon sources in methanotrophic bacteria. Subsequently, breakthroughs and challenges in harnessing methanotrophs as robust microbial chassis for industrial biotechnology were compiled and overviewed. Finally, capabilities to exploit the inherent advantages of methanotrophs to synthesize various target products in higher titers are proposed.