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.

Understanding microbial syngas fermentation rates.

Syngas fermentation to ethanol has reached industrial production. Further improvement of this process would be aided by quantitative understanding of the influence of imposed reaction conditions on the fermentation performance. That requires a reliable model of the microbial kinetics.

Microbial electrosynthesis from CO reaches productivity of syngas and chain elongation fermentations.

Carbon-based products are essential to society, yet producing them from fossil fuels is unsustainable. Microorganisms have the ability to take up electrons from solid electrodes and convert carbon dioxide (CO) to valuable carbon-based chemicals. However, higher productivities and energy efficiencies are needed to reach a viability that can make the technology transformative.

Acetic acid, growth rate, and mass transfer govern shifts in CO metabolism of Clostridium autoethanogenum.

Syngas fermentation is a leading microbial process for the conversion of carbon monoxide, carbon dioxide, and hydrogen to valuable biochemicals. Clostridium autoethanogenum stands as a model organism for this process, showcasing its ability to convert syngas into ethanol industrially with simultaneous fixation of carbon and reduction of greenhouse gas emissions. A deep understanding on the metabolism of this microorganism and the influence of operational conditions on fermentation performance is key to advance the technology and enhancement of production yields.

Biomass-specific rates as key performance indicators: A nitrogen balancing method for biofilm-based electrochemical conversion.

Microbial electrochemical technologies (METs) employ microorganisms utilizing solid-state electrodes as either electron sink or electron source, such as in microbial electrosynthesis (MES). METs reaction rate is traditionally normalized to the electrode dimensions or to the electrolyte volume, but should also be normalized to biomass amount present in the system at any given time. In biofilm-based systems, a major challenge is to determine the biomass amount in a non-destructive manner, especially in systems operated in continuous mode and using 3D electrodes.

Membrane bioreactors for syngas permeation and fermentation.

Syngas fermentation to biofuels and chemicals is an emerging technology in the biobased economy. Mass transfer is usually limiting the syngas fermentation rate, due to the low aqueous solubilities of the gaseous substrates. Membrane bioreactors, as efficient gas-liquid contactors, are a promising configuration for overcoming this gas-to-liquid mass transfer limitation, so that sufficient productivity can be achieved.

A General Model for Biofilm-Driven Microbial Electrosynthesis of Carboxylates From CO.

Up to now, computational modeling of microbial electrosynthesis (MES) has been underexplored, but is necessary to achieve breakthrough understanding of the process-limiting steps. Here, a general framework for modeling microbial kinetics in a MES reactor is presented. A thermodynamic approach is used to link microbial metabolism to the electrochemical reduction of an intracellular mediator, allowing to predict cellular growth and current consumption.

Highly selective recovery of medium chain carboxylates from co-fermented organic wastes using anion exchange with carbon dioxide expanded methanol desorption.

The aim of this work was to recover a mixture of carboxylates ranging from 2 to 7 carbon atoms using a strong anion exchange resin, followed by desorption with CO-expanded methanol. Medium chain carboxylates hexanoate and heptanoate adsorbed better than acetate, and the corresponding medium chain carboxylic acids desorbed easier than acetic acid. Consequently, hexanoate and heptanoate were concentrated up to 14.

Downstream of the bioreactor: advancements in recovering fuels and commodity chemicals.

Downstream processing aims at recovering the target product at the required specifications from the bioreactor effluent. Research and development in this field relies on experimental and mathematical tools at the levels of chemical components, unit operations and processes. Recently, advances have been made in addressing the broth mixture complexity early on, in incorporating high-throughput experimentation for data generation and mechanistic understanding of the separation processes, in improving the materials and scalability of specific unit operations, as well as establishing the potential of process integration concepts.

Changes in root-exudate-induced respiration reveal a novel mechanism through which drought affects ecosystem carbon cycling.

Root exudates play an important role in ecosystem response to climate change, but the functional consequences of drought-induced changes in the quality of root exudates are unknown. Here, we addressed this knowledge gap in a unique experimental approach. We subjected two common grassland species that differ widely in their growth strategies and root systems, the grass Holcus lanatus and the forb Rumex acetosa, to 2 wk of drought.

Grand Research Challenges for Sustainable Industrial Biotechnology.

Future manufacturing will focus on new, improved products as well as on new and enhanced production methods. Recent biotechnological and scientific advances, such as CRISPR/Cas and various omic technologies, pave the way to exciting novel biotechnological research, development, and commercialization of new sustainable products. Rigorous mathematical descriptions of microbial cells and consortia thereof will enable deeper biological understanding and lead to powerful in silico cellular models.

Integrated Vacuum Stripping and Adsorption for the Efficient Recovery of (Biobased) 2-Butanol.

Biobased 2-butanol offers high potential as biofuel, but its toxicity toward microbial hosts calls for efficient techniques to alleviate product inhibition in fermentation processes. Aiming at the selective recovery of 2-butanol, the feasibility of a process combining vacuum stripping followed by vapor adsorption has been assessed using mimicked fermentation media. The experimental vacuum stripping of model solutions and corn stover hydrolysate closely aligned with mass transfer model predictions.

Perspectives for the microbial production of methyl propionate integrated with product recovery.

A new approach was studied for bio-based production of methyl propionate, a precursor of methyl methacrylate. Recombinant E. coli cells were used to perform a cascade reaction in which 2-butanol is reduced to butanone using alcohol dehydrogenase, and butanone is oxidized to methyl propionate and ethyl acetate using a Baeyer-Villiger monooxygenase (BVMO).

Detecting macroecological patterns in bacterial communities across independent studies of global soils.

The emergence of high-throughput DNA sequencing methods provides unprecedented opportunities to further unravel bacterial biodiversity and its worldwide role from human health to ecosystem functioning. However, despite the abundance of sequencing studies, combining data from multiple individual studies to address macroecological questions of bacterial diversity remains methodically challenging and plagued with biases. Here, using a machine-learning approach that accounts for differences among studies and complex interactions among taxa, we merge 30 independent bacterial data sets comprising 1,998 soil samples from 21 countries.

Microbial Hydrocarbon Formation from Biomass.

Fossil carbon sources mainly contain hydrocarbons, and these are used on a huge scale as fuel and chemicals. Producing hydrocarbons from biomass instead is receiving increased attention. Achievable yields are modest because oxygen atoms need to be removed from biomass, keeping only the lighter carbon and hydrogen atoms.

Prospects and challenges for the recovery of 2-butanol produced by vacuum fermentation - a techno-economic analysis.

The conceptual design of a bio-based process for 2-butanol production is presented for the first time. Considering a hypothetical efficient producing strain, a vacuum fermentation is proposed to alleviate product toxicity, but the main challenge is the energy-efficient product recovery from the vapor. Three downstream scenarios were examined for this purpose: 1) multi-stage vapor recompression; 2) temperature swing adsorption; and 3) vapor absorption.

Esters production via carboxylates from anaerobic paper mill wastewater treatment.

This paper describes a new option for integrated recovery and esterification of carboxylates produced by anaerobic digestion at a pH above the pK. The carboxylates (acetate, propionate, butyrate, valerate and lactate) are recovered using a strong anion exchange resin in the bicarbonate form, and the resin is regenerated using a CO-expanded alcohol technique, which allows for low chemicals consumption and direct esterification. Paper mill wastewater was used to study the effect of pH and the presence of other inorganic anions and cations on the adsorption and desorption with CO-expanded methanol.

Growth inhibition of S. cerevisiae, B. subtilis, and E. coli by lignocellulosic and fermentation products.

This paper describes the effect of several inhibiting components on three potential hosts for the bio-based production of methyl propionate, namely, wild-type Escherichia coli and Bacillus subtilis, and evolved Saccharomyces cerevisiae IMS0351. The inhibition by the lignocellulose-derived products 5-hydroxymethyl-2-furaldehyde, vanillin, and syringaldehyde and the fermentation products 2-butanol, 2-butanone, methyl propionate, and ethyl acetate has been assessed for these strains in defined medium. Multiple screenings were performed using small-scale cultures in both shake flasks and microtiter plates.

Input materials and processing conditions control compost dissolved organic carbon quality.

Dissolved organic carbon (DOC) has been proposed as an indicator of compost maturity and stability. Further fractionation of compost DOC may be useful for determining how particular composting conditions will influence DOC quality. Eleven composts ranging in input materials and processing techniques were analyzed; concentrations of DOC ranged from 428 mg kg(-1) to 7300 mg kg(-1).

Recovery of carboxylic acids produced by fermentation.

Carboxylic acids such as citric, lactic, succinic and itaconic acids are useful products and are obtained on large scale by fermentation. This review describes the options for recovering these and other fermentative carboxylic acids. After cell removal, often a primary recovery step is performed, using liquid-liquid extraction, adsorption, precipitation or conventional electrodialysis.

Pervaporation of ethanol from lignocellulosic fermentation broth.

Pervaporation can be applied in ethanol production from lignocellulosic biomass. Hydrophobic pervaporation, using a commercial PDMS membrane, was employed to concentrate the ethanol produced by fermentation of lignocellulosic hydrolysate. To our knowledge, this is the first report describing this.

Production of fumaric acid by fermentation.

Fermentative fumaric acid production from renewable resources may become competitive with petrochemical production. This will require very efficient processes. So far, using Rhizopus strains, the best fermentations reported have achieved a fumaric acid titer of 126 g/L with a productivity of 1.

Simultaneous Clostridial fermentation, lipase-catalyzed esterification, and ester extraction to enrich diesel with butyl butyrate.

The recovery of 1-butanol from fermentation broth is energy-intensive since typical concentrations in fermentation broth are below 20 g L(-1). To prevent butanol inhibition and high downstream processing costs, we aimed at producing butyl esters instead of 1-butanol. It is shown that it is possible to perform simultaneously clostridial fermentation, esterification of the formed butanol to butyl butyrate, and extraction of this ester by hexadecane.