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[Display omitted] • The harvesting efficiency achieved 99.2 % with the application of 60 g/L of FMT@DTAB. • PVDF integrated with extractants demonstrated enhanced butyric acid mass transfer. • Butyric acid showed improved mass transfer coefficient in PVDF with extractants. • PVDF-TDA achieved a 60 % recovery efficiency for butyric acid with 60 g/L of FMT@DTAB. Syngas fermentation utilizing acetogenic bacteria like Clostridium sp. provides a promising method for transforming CO and CO 2 -rich waste gases into valuable products such as short-chain fatty acids (SCFAs) and bio-alcohols, aiding in the reduction of greenhouse gas emissions and supporting carbon neutrality objectives. Magnetic nanoparticle-based coagulants, particularly Fe 3 O 4 @MIL-100(Fe)@TEOS@DTAB (FMT@DTAB), have recently attracted attention due to their efficient recovery and enhanced cell disruption capabilities enabled by cationic surfactant surface modifications. At a dosage of 60 g/L, FMT@DTAB has proven highly effective in achieving significant concentrations of acetic acid (7.06 g/L), butyric acid (6.27 g/L), ethanol (6.43 g/L), and butanol (5.24 g/L), along with notable harvesting efficiency (99.2 %) and intracellular ATP concentration (2.1 mM). Recent research on supported liquid membrane contactors highlights their cost-effective and environment-friendly properties, with an emphasis on minimal extractant usage. This study investigated the behavior of SCFAs using both virgin and supported liquid membrane contactors, focusing on factors such as organic extractant and membrane pore size. PVDF filled with tridodecylamine notably improved butyric acid recovery to around 60 %, with a mass flux of 14.95 ± 0.28 g/m2/h, outperforming virgin and other extractant-filled PVDF membranes. This study enhances resource efficiency and reduces industrial environmental impacts by optimizing the recovery and production of valuable chemicals from waste gases. It supports sustainable and economically viable biotechnology applications, aligning with global climate change mitigation efforts. [ABSTRACT FROM AUTHOR]

• A bulk-gas-to-atomized-liquid (BGAL) concept was developed for syngas fermentation. • Mass transfer rate of the BGAL system was 20 times of that in stirred tank reactors. • The BGAL system reduced 4-fold energy consumption compared to stir tank reactors. • BGAL system enhanced ethanol productivity by 2-fold compared to stir tank reactors. Syngas fermentation for fuels and chemicals is limited by the low rate of gas-to-liquid mass transfer. In this work, a unique bulk-gas-to-atomized-liquid (BGAL) contactor was developed to enhance mass transfer. In the BGAL system, liquid is atomized into discrete droplets, which significantly increases the interface between the liquid and bulk gas. Using oxygen as a model gas, the BGAL contactor achieved an oxygen transfer rate (OTR) of 569 mg·L−1·min−1 and a mass transfer coefficient (K L a) of 2.28 sec−1, which are values as much as 100-fold greater than achieved in other kinds of reactors. The BGAL contactor was then combined with a packed bed to implement syngas fermentation, with packing material supporting a biofilm upon which gas saturated liquid is dispersed. This combination avoids dispersing these gas-saturated droplets into the bulk liquid, which would significantly dilute the dissolved gas concentration. Although this combination reduced overall K L a to 0.45–1.0 sec−1, it is still nearly 20 times higher than achieved in a stirred tank reactor. The BGAL contactor/packed bed bioreactor was also more energy efficient in transferring gas to the liquid phase, requiring 8.63–26.32 J mg−1 O 2 dissolved, which is as much as four-fold reduction in energy requirement compared to a stirred tank reactor. Fermentation of syngas to ethanol was evaluated in the BGAL contactor/packed bed bioreactor using Clostridium carboxidivorans P7. Ethanol productivity reached 746 mg·L−1·h−1 with an ethanol/acetic acid molar ratio of 7.6. The ethanol productivity was two-fold high than the highest level previously reported. The exceptional capability of BGAL contactor to enhance mass transfer in these experiments suggests its utility in syngas fermentation as well as other gas-liquid contacting processes. [ABSTRACT FROM AUTHOR]

Implementation of biofuels as an alternative to fossil fuels has been established as an answer to climate change by limiting GHG emissions. Syngas fermentation has emerged as a promising process for the conversion of waste biomasses to valuable products with bioethanol being on the main focus. However, the bottleneck of the mass transfer of syngas compounds H 2 and CO along with low production yields has set barriers to the development of an industrial scale plant. Recent research indicates that many different methodologies spring up in order to face this important challenge. The aim of this review is to assemble all these techniques applied in syngas fermentation, focusing on the different bioreactor configurations operated in continuous mode for the production of liquid and gas biofuels. This article also outlines the so far entrepreneurial initiatives and the progress made towards the commercialization of the process. [ABSTRACT FROM AUTHOR]

[Display omitted] • The acetate production increased 20% by applying concentrated trace minerals. • The electrodialysis was used for recycling nutrients while extracting the acetate. • The acetate in the fermentation broth was extracted at a rate of 99.8%. • The recycled medium showed similar cell performances compared to the fresh medium. • The integration system saved 16.5–29.6% of medium costs with less carbon footprint. The current study proposes integrating syngas fermentation and electrodialysis (ED) systems to reduce operating costs of fermentation process by reusing nutrients required for biocatalyst growth as well as separating the ionized product, acetate. By reusing nutrients, the nutrient and mineral limitations that generally occur in high cell density conditions are resolved. Eubacterium callanderi KIST612, used as a biocatalyst, improved acetate titer by 25 % (264 mmol/L) in the ED-integrated process by avoiding nutrient and mineral limitations. A high extraction rate (>99.8 %) of acetate was also achieved, and divalent cations were maintained in the residual medium using mono-selective cation exchange membranes (CEMs) in the ED system. Cell growth was assessed using a residual medium, showing that this integrated system could be operated without any additional treatment of residual medium. A case study for cost and carbon footprint analyses demonstrated that reusing the residual medium can reduce medium cost (16.5 %–29.6 %) for syngas fermentation as well as reduce the carbon footprint. These results suggest that reusing the medium while extracting acetate in ED could potentially resolve issues of operational expenditure and carbon emissions in the industrial syngas fermentation process. [ABSTRACT FROM AUTHOR]

Abstract: Syngas fermentation is a promising technology for sustainable production of fuels and chemicals. Gas–liquid mass transfer of syngas, however, is regarded as a limiting step of the fermentation process. The authors designed an innovative external hollow fiber membrane (HFM) diffuser to remove this hurdle. In this study, the gas–liquid mass transfer of carbon monoxide, the major component of syngas, was optimized by implementing three operational factors, membrane surface area per working volume (A/v), water velocity (V L ), and specific gas flow rate (V g ). The maximum observed CO mass transfer coefficient (K L a) of 385.01/h in water, which is higher than that yielded by previous CO transfer methods, was achieved at an A/v of 0.561/cm, a V L of 2.20cm/s, and a V g of 1.021/min. At these conditions, the gas void fraction rate, the syngas supply rate per working volume, was lower than all reported values as well. The high volumetric mass transfer coefficient at low gas supply rate of the HFM diffuser would make syngas fermentation a feasible alternative industrial process. A three-factor quadratic model and a dimensionless model with high correlation coefficients were developed from the experimental data for a process scale-up. These two models verified that the membrane surface area is the most significant design factor with respect to the K L a. Three screen analyses also indicated that the membrane surface area had the highest positive impact on the K L a. As a result, the external HFM diffuser appears to be a feasible technology that can considerably increase the yield of syngas fermentation to fuels and chemicals. [Copyright &y& Elsevier]