This study explores key success factors for ethanol production via fermentation of gas streams, by assessing the effects of eight process variables driving the fermentation performance on the production costs and greenhouse gas emissions. Three fermentation feedstocks are assessed: off-gases from the steel industry, lignocellulosic biomass-derived syngas and a mixture of H2 and CO2. The analysis is done through a sequence of (i) sensitivity analyses based on stochastic simulations and (ii) multi-objective optimizations. In economic terms, the use of steel off-gas leads to the best performance and the highest robustness to low mass transfer coefficients, low microbial tolerance to ethanol, acetic-acid co-production and to dilution of the gas feed with CO2, due to the relatively high temperature at which the gas feedstock is available. The ethanol produced from the three feedstocks lead to lower greenhouse gas emissions than fossil-based gasoline and compete with first and second generation ethanol.@en

Background: Ethanol production through fermentation of gas mixtures containing CO, CO2 and H2 has just started operating at commercial scale. However, quantitative schemes for understanding and predicting productivities, yields, mass transfer rates, gas flow profiles and detailed energy requirements have been lacking in literature; such are invaluable tools for process improvements and better systems design. The present study describes the construction of a hybrid model for simulating ethanol production inside a 700 m3 bubble column bioreactor fed with gas of two possible compositions, i.e., pure CO and a 3:1 mixture of H2 and CO2. Results: Estimations made using the thermodynamics-based black-box model of microbial reactions on substrate threshold concentrations, biomass yields, as well as CO and H2 maximum specific uptake rates agreed reasonably well with data and observations reported in literature. According to the bioreactor simulation, there is a strong dependency of process performance on mass transfer rates. When mass transfer coefficients were estimated using a model developed from oxygen transfer to water, ethanol productivity reached 5.1 g L-1 h-1; when the H2/CO2 mixture is fed to the bioreactor, productivity of CO fermentation was 19% lower. Gas utilization reached 23 and 17% for H2/CO2 and CO fermentations, respectively. If mass transfer coefficients were 100% higher than those estimated, ethanol productivity and gas utilization may reach 9.4 g L-1 h-1 and 38% when feeding the H2/CO2 mixture at the same process conditions. The largest energetic requirements for a complete manufacturing plant were identified for gas compression and ethanol distillation, being higher for CO fermentation due to the production of CO2. Conclusions: The thermodynamics-based black-box model of microbial reactions may be used to quantitatively assess and consolidate the diversity of reported data on CO, CO2 and H2 threshold concentrations, biomass yields, maximum substrate uptake rates, and half-saturation constants for CO and H2 for syngas fermentations by acetogenic bacteria. The maximization of ethanol productivity in the bioreactor may come with a cost: low gas utilization. Exploiting the model flexibility, multi-objective optimizations of bioreactor performance might reveal how process conditions and configurations could be adjusted to guide further process development.@en

In this work, a model was developed to predict the performance of a bubble column reactor for syngas fermentation and the subsequent recovery of anhydrous ethanol. The model was embedded in an optimization framework which employs surrogate models (artificial neural networks) and multi-objective genetic algorithm to optimize different process conditions and design variables with objectives related to investment, minimum selling price, energy efficiency and bioreactor productivity. The results indicate the optimal trade-offs between these objectives while providing a range of solutions such that, if desired, a single solution can be picked, depending on the priority conferred to different process targets. The Pareto-optimal values of the decision variables were discussed for different case studies with and without the recovery unit. It was shown that enhancing the gas-liquid mass transfer coefficient is a key strategy toward sustainability improvement.@en

Syngas fermentation is one of the bets for the future sustainable biobased economies due to its potential as an intermediate step in the conversion of waste carbon to ethanol fuel and other chemicals. Integrated with gasification and suitable downstream processing, it may constitute an efficient and competitive route for the valorization of various waste materials, especially if systems engineering principles are employed targeting process optimization. In this study, a dynamic multi-response model is presented for syngas fermentation with acetogenic bacteria in a continuous stirred-tank reactor, accounting for gas–liquid mass transfer, substrate (CO, H2) uptake, biomass growth and death, acetic acid reassimilation, and product selectivity. The unknown parameters were estimated from literature data using the maximum likelihood principle with a multi-response nonlinear modeling framework and metaheuristic optimization, and model adequacy was verified with statistical analysis via generation of confidence intervals as well as parameter significance tests. The model was then used to study the effects of process conditions (gas composition, dilution rate, gas flow rates, and cell recycle) as well as the sensitivity of kinetic parameters, and multiobjective genetic algorithm was used to maximize ethanol productivity and CO conversion. It was observed that these two objectives were clearly conflicting when CO-rich gas was used, but increasing the content of H2 favored higher productivities while maintaining 100% CO conversion. The maximum productivity predicted with full conversion was 2 g·L−1·hr−1 with a feed gas composition of 54% CO and 46% H2 and a dilution rate of 0.06 hr−1 with roughly 90% of cell recycle.@en

Co-fermentation of mixed sugars to produce butanol is an attractive route in sucrochemical production chains. Herein, high-level mixed sugars from sugarcane bagasse hemicellulosic hydrolysate (HH) and molasses (SCM) were investigated as potential substrates for acetone-butanol-ethanol (ABE) production in batch fermentation by Clostridium saccharoperbutylacetonicum DSM 14923. HH produced after hydrothermal pretreatment was concentrated 5-fold and was called concentrated hemicellulosic hydrolysate (CHH). The fermentation media that were investigated consisted solely of CHH and SCM and three CHH-to-SCM ratios were used to provide 30 g/L initial sugar concentrations and furan derivatives lower than 0.1 g/L. For CHH50/SCM50 and CHH75/SCM25, diluting CHH to concentrations of 15 g/L sugars and 22.5 g/L sugars, respectively, which were supplemented with SCM and nutrients, suffered growth inhibition as a function of the concentration of undissociated acid in the medium. The best-performing medium, CHH25/SCM75 (7.5 g/L and 22.5 g/L sugars from CHH and SCM, respectively and about 0.017 g/L furan derivatives), showed 97 % sugar consumption, and in the pH range of 5.5–6.5, undissociated acetic acid was not an inhibitory molecular form to C. saccharoperbutylacetonicum. After 30 h of fermentation, 7.8 and 9.8 g/L butanol and ABE were produced, respectively, which yielded 0.28 and 0.36 g/g. Based on our findings, C. saccharoperbutylacetonicum exhibits its potential and effective application for renewable butanol production by co-fermenting mixed sugars.@en

Co-fermentation of mixed sugars to produce butanol is an attractive route in sucrochemical production chains. Herein, high-level mixed sugars from sugarcane bagasse hemicellulosic hydrolysate (HH) and molasses (SCM) were investigated as potential substrates for acetone-butanol-ethanol (ABE) production in batch fermentation by Clostridium saccharoperbutylacetonicum DSM 14923. HH produced after hydrothermal pretreatment was concentrated 5-fold and was called concentrated hemicellulosic hydrolysate (CHH). The fermentation media that were investigated consisted solely of CHH and SCM and three CHH-to-SCM ratios were used to provide 30 g/L initial sugar concentrations and furan derivatives lower than 0.1 g/L. For CHH50/SCM50 and CHH75/SCM25, diluting CHH to concentrations of 15 g/L sugars and 22.5 g/L sugars, respectively, which were supplemented with SCM and nutrients, suffered growth inhibition as a function of the concentration of undissociated acid in the medium. The best-performing medium, CHH25/SCM75 (7.5 g/L and 22.5 g/L sugars from CHH and SCM, respectively and about 0.017 g/L furan derivatives), showed 97 % sugar consumption, and in the pH range of 5.5–6.5, undissociated acetic acid was not an inhibitory molecular form to C. saccharoperbutylacetonicum. After 30 h of fermentation, 7.8 and 9.8 g/L butanol and ABE were produced, respectively, which yielded 0.28 and 0.36 g/g. Based on our findings, C. saccharoperbutylacetonicum exhibits its potential and effective application for renewable butanol production by co-fermenting mixed sugars.@en

The present study describes the procedure followed to construct, to quantitatively validate and the utilization of a mathematical model to simulate ethanol production inside a large-scale bubble column bioreactor fed by syngas of two possible compositions i.e., pure CO and a 3:1 mixture of H2 and CO2. The model is structured by i) a black-box model for catabolic ethanol production and biomass growth and ii) a mass transfer model of the bioreactor; both parts are combined through hyperbolic uptake kinetics for CO and H2. Thermodynamics are used to study the production of energy through catabolism and to estimate biomass yields and maximum specific CO and H2 uptake rates. The simulation identifies a strong dependence of bioreactor performance and mass transfer rate of CO and H2. When mass transfer rate is above the 90 % of the maximum estimated values, ethanol productivity would reach 4.7 g/L/h, gas utilization would be 22 % and, the fermentation process plus the distillation of the product would require 7 MW/kg of ethanol produced. H2/CO2 fermentation achieved 20 and 30 % higher productivity and gas utilization than CO fermentation, respectively. Moreover, gas compression and distillation of ethanol are the largest contributors to energetic costs.@en

The present study describes the procedure followed to construct, to quantitatively validate and the utilization of a mathematical model to simulate ethanol production inside a large-scale bubble column bioreactor fed by syngas of two possible compositions i.e., pure CO and a 3:1 mixture of H2 and CO2. The model is structured by i) a black-box model for catabolic ethanol production and biomass growth and ii) a mass transfer model of the bioreactor; both parts are combined through hyperbolic uptake kinetics for CO and H2. Thermodynamics are used to study the production of energy through catabolism and to estimate biomass yields and maximum specific CO and H2 uptake rates. The simulation identifies a strong dependence of bioreactor performance and mass transfer rate of CO and H2. When mass transfer rate is above the 90 % of the maximum estimated values, ethanol productivity would reach 4.7 g/L/h, gas utilization would be 22 % and, the fermentation process plus the distillation of the product would require 7 MW/kg of ethanol produced. H2/CO2 fermentation achieved 20 and 30 % higher productivity and gas utilization than CO fermentation, respectively. Moreover, gas compression and distillation of ethanol are the largest contributors to energetic costs.@en

Production of second generation ethanol can be accomplished with biomass gasification followed by syngas fermentation using acetogenic bacteria in a hybrid process. Using process simulation and financial analysis, this study evaluated the feasibility of producing hydrous ethanol from sugarcane bagasse in a conceptual hybrid plant designed to be energetically self-sufficient. The process was found to be competitive with other second generation routes, achieving an ethanol yield of 330 L per metric ton of dry biomass and an overall carbon conversion of 30%. The minimum ethanol selling price to achieve Net Present Value break-even with 10% Internal Rate of Return was estimated to be 706 US$/m3 after taxes in the base model. When accounting for uncertainties in the fixed capital investment and the cost of raw materials, the Net Present Value was found to be non-negative in 80% of the cases for a selling price of 783 US$/m3.@en

Production of second generation ethanol can be accomplished with biomass gasification followed by syngas fermentation using acetogenic bacteria in a hybrid process. Using process simulation and financial analysis, this study evaluated the feasibility of producing hydrous ethanol from sugarcane bagasse in a conceptual hybrid plant designed to be energetically self-sufficient. The process was found to be competitive with other second generation routes, achieving an ethanol yield of 330 L per metric ton of dry biomass and an overall carbon conversion of 30%. The minimum ethanol selling price to achieve Net Present Value break-even with 10% Internal Rate of Return was estimated to be 706 US$/m3 after taxes in the base model. When accounting for uncertainties in the fixed capital investment and the cost of raw materials, the Net Present Value was found to be non-negative in 80% of the cases for a selling price of 783 US$/m3.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

Robust strains are essential towards success of n-butanol production from lignocellulosic feedstock. To find a suitable strain to convert a non-detoxified hemicellulosic hydrolysate of sugarcane bagasse, we first assessed the performance of four wild-type butanol-producing Clostridium strains (C. acetobutylicum DSM 6228, C. beijerinckii DSM 6422, C. saccharobutylicum DSM 13864, and C. saccharoperbutylacetonicum DSM 14923)in batch fermentations containing either xylose or glucose at 30 g L−1 as sole carbon sources. C. saccharoperbutylacetonicum was selected after achieving butanol yields as high as 0.31 g g−1 on glucose and 0.25 g g−1 on xylose. In a 48-h fermentation containing a mixture of sugars (93% xylose and 7% glucose)that mimicked the hydrolysate, C. saccharoperbutylacetonicum delivered the highest butanol concentration (14.5 g L−1)when the initial sugar concentration was 50 g L−1. Moreover, the selected strain achieved the highest butanol yield (0.29 g g−1)on xylose-rich media reported so far. Meanwhile, C. saccharoperbutylacetonicum produced 5.8 g butanol L−1 (0.22 g g−1 butanol yield)when fermenting a non-detoxified sugarcane bagasse hemicellulosic hydrolysate enriched with xylose (30 g total sugars L−1). Although sugars were not exhausted (4.7 g residual sugars L−1)even after 72 h because of the presence of lignocellulose-derived microbial inhibitors, these results show that C. saccharoperbutylacetonicum is a robust wild-type strain. This microorganism with high butanol tolerance and yield on xylose can, therefore, serve as the basis for the development of improved biocatalysts for production of butanol from non-detoxified sugarcane bagasse hemicellulosic hydrolysate.@en

This study describes a methodological framework designed for the systematic processing of experimental syngas fermentation data for its use by metabolic models at pseudo-steady state and at transient state. The developed approach allows the use of not only own experimental data but also from experiments reported in literature which employ a wide range of gas feed compositions (from pure CO to a mixture between H2 and CO2), different pH values, two different bacterial strains and bioreactor configurations (stirred tanks and bubble columns). The developed data processing framework includes i) the smoothing of time-dependent concentrations data (using moving averages and statistical methods that reduce the relevance of outliers), ii) the reconciliation of net conversion rates such that mass balances are satisfied from a black-box perspective (using minimizations), and iii) the estimation of dissolved concentrations of the syngas components (CO, H2 and CO2) in the fermentation broth (using mass transfer models). Special care has been given such that the framework allows the estimation of missing or unreported net conversion data and metabolite concentrations at the intra or extracellular spaces (considering that there is availability of at least two replicate experiments) through the use of approximative kinetic equations.@en

This work presents a strategy for optimizing the production process of ethanol via integrated gasification and syngas fermentation, a conversion platform of growing interest for its contribution to carbon recycling. The objective functions (minimum ethanol selling price (MESP), energy efficiency, and carbon footprint) were evaluated for the combinations of different input variables in models of biomass gasification, energy production from syngas, fermentation, and ethanol distillation, and a multi-objective genetic algorithm was employed for the optimization of the integrated process. Two types of waste feedstocks were considered, wood residues and sugarcane bagasse, with the former leading to lower MESP and a carbon footprint of 0.93 USD/L and 3 g CO2eq/MJ compared to 1.00 USD/L and 10 g CO2eq/MJ for sugarcane bagasse. The energy efficiency was found to be 32% in both cases. An uncertainty analysis was conducted to determine critical decision variables, which were found to be the gasification zone temperature, the split fraction of the unreformed syngas sent to the combustion chamber, the dilution rate, and the gas residence time in the bioreactor. Apart from the abovementioned objectives, other aspects such as water footprint, ethanol yield, and energy self-sufficiency were also discussed.@en