Production of acetone butanol ethanol (ABE) by a hyper-producing mutant strain of Clostridium beijerinckii BA101 and recovery by pervaporation

The Influence of Sugar Composition and pH Regulation in Batch and Continuous Acetone–Butanol–Ethanol Fermentation

Acetone–butanol–ethanol (ABE) fermentation is influenced by external conditions. This work aimed to study the influence of pH regulation on monosaccharide composition in batch and continuous fermentation processes to determine butanol production and productivity. Batch fermentations with ammonium acetate or calcium carbonate combined with minimum pH control (pH ≥ 4.8 or 5.1) were assessed with pure xylose and glucose/xylose mixtures (ratios of 1:1 and 3:1). Continuous two-stage fermentation was developed using plastic rings to retain the biomass. Although batch fermentations with pure xylose performed better without active minimum pH control with both buffers, minimum pH control was necessary to metabolize xylose in the presence of glucose. Xylose uptake was favored by the use of calcium carbonate and pH ≥ 5.1 at a ratio of 1:1, while ammonium acetate and a pH ≥ 4.8 was the best option for a 3:1 ratio. The best butanol production and productivity values with sugar mixtures in batch reactors were 8.8 g L−1 and 0.61 g L−1 h−1 with an ammonium acetate pH ≥ 4.8 (ratio 3:1). The glucose/xylose ratio combined with pH regulation thus modulated xylose metabolism and solvent production in batch modes. Immobilized cells combined with operating at D = 0.333 h−1 and pH regulation increased butanol productivity almost fourfold up to 2.4 ± 0.2 g L−1 h−1.

Butanol Production by a Novel Efficient Method Using Mixed Cultures of Clostridium beijerinckii and Arthrobacter sp. in Stirred-Tank and Gas-Lift Bioreactors

Arthrobacter sp. BCC 72131, an obligate aerobic bacterium, was used to create anaerobic conditions, and Clostridium beijerinckii TISTR 1461 was used as a butanol producer in an acetone-butanol–ethanol (ABE) fermentation. Sweet sorghum juice (SSJ) medium containing 60 g/L of total sugar supplemented with 1.27 g/L of (NH4)2SO4 was used as a butanol production (BP) medium. Arthrobacter sp. was inoculated into the BP medium in 1-L screw-capped bottles. After 2, 4, 6 and 12 h of Arthrobacter sp. cultivation at 30 °C, C. beijerinckii was transferred into the BP medium to start butanol production at 37 °C. The results showed that C. beijerinckii inoculation after 6 h of Arthrobacter sp. cultivation gave the highest butanol titer (PB) at 12.56 g/L, with a butanol yield (YB/S) and volumetric butanol productivity (QB) of 0.34 g/g and 0.23 g/L·h, respectively. These values are approximately 10–27% higher than those of the control experiment using a single culture of C. beijerinckii TISTR 1461 and oxygen-free nitrogen (OFN) gas flushing to create anaerobic conditions. Field emission scanning electron microscopic (FE-SEM) images of Clostridium cells, as well as protein and free amino nitrogen concentrations in the broth during butanol fermentation were also studied to confirm the results. The butanol fermentation was then carried out in a 5.6-L stirred-tank and a 1.2-L low-cost gas-lift bioreactor by the mixed cultures using the optimal time of Clostridium inoculation. The PB, YB/S and QB values obtained were not significantly different from those in the 1-L screw-capped bottles. Hence, Arthrobacter sp. can be used as a novel method to create anaerobic conditions instead of a traditional method employing OFN gas flushing. Using mixed cultures of Arthrobacter sp. BCC 72131 and C. beijerinckii TISTR 1461 is a practical method to produce butanol on a large-scale, both in complex and low-cost bioreactors.

Addressing the energy crisis: using microbes to make biofuels

Much of the energy being used to power our lives comes from fossil fuels such as coal, natural gas and petroleum. These energy sources are non-renewable, are being exhausted and also pollute the air, water and soil with toxic chemicals. Their mining, transportation, refining and use are associated with a large carbon footprint that contributes significantly to global warming. In addition, the geopolitical complexities surrounding the main fossil fuel producers create risks and uncertainties around the world. Replacing fossil fuels with clean, renewable forms of energy is paramount to creating a sustainable and healthy future, and for laying the foundations for global political stability and prosperity. Using biomass from plants, microbes can produce biofuels that are identical to or perform as well as fossil fuels. In addition of creating sustainable energy, advancing the biofuel industry will create new, high-quality rural jobs whilst improving energy security.

Microbial biotechnological approaches: renewable bioprocessing for the future energy systems

The accelerating energy demands of the increasing global population and industrialization has become a matter of great concern all over the globe. In the present scenario, the world is witnessing a considerably huge energy crisis owing to the limited availability of conventional energy resources and rapid depletion of non-renewable fossil fuels. Therefore, there is a dire need to explore the alternative renewable fuels that can fulfil the energy requirements of the growing population and overcome the intimidating environmental issues like greenhouse gas emissions, global warming, air pollution etc. The use of microorganisms such as bacteria has captured significant interest in the recent era for the conversion of the chemical energy reserved in organic compounds into electrical energy. The versatility of the microorganisms to generate renewable energy fuels from multifarious biological and biomass substrates can abate these ominous concerns to a great extent. For instance, most of the microorganisms can easily transform the carbohydrates into alcohol. Establishing the microbial fuel technology as an alternative source for the generation of renewable energy sources can be a state of art technology owing to its reliability, high efficiency, cleanliness and production of minimally toxic or inclusively non-toxic byproducts. This review paper aims to highlight the key points and techniques used for the employment of bacteria to generate, biofuels and bioenergy, and their foremost benefits.

A comparative phenotypic and genomic analysis of Clostridium beijerinckii mutant with enhanced solvent production

The acetone-butanol-ethanol (ABE) fermentation by solventogenic clostridia has a long history of industrial butanol production. The Clostridium beijerinckii mutant BA101 has been widely studied for ABE fermentation owing to its enhanced butanol production capacity. Here, we characterized the BA101 mutant under controlled environmental conditions in parallel with the parental strain C. beijerinckii NCIMB 8052. To investigate the correlation between phenotype and genotype, we carried out the genome sequencing of BA101. Through comparative genomic analysis, several mutations in the genes encoding transcriptional regulator, sensor kinase, and phosphatase were identified in the BA101 genome as well as other sibling mutants. Among them, the SNP in the Cbei_3078 gene encoding PAS/PAC sensor hybrid histidine kinase was unique to the BA101 strain. The identified mutations relevant to the observed physiological behaviors of BA101 could be potential genetic targets for rational engineering of solventogenic clostridia toward desired phenotypes.

Impacts of Initial Sugar, Nitrogen and Calcium Carbonate on Butanol Fermentation from Sugarcane Molasses by Clostridium beijerinckii

Low-cost nitrogen sources, i.e., dried spent yeast (DSY), rice bran (RB), soybean meal (SM), urea and ammonium sulfate were used for batch butanol fermentation from sugarcane molasses by Clostridium beijerinckii TISTR 1461 under anaerobic conditions. Among these five low-cost nitrogen sources, DSY at 1.53 g/L (nitrogen content equal to that of 1 g/L of yeast extract) was found to be the most suitable. At an initial sugar level of 60 g/L, the maximum butanol concentration (PB), productivity (QB) and yield (YB/S) were 11.19 g/L, 0.23 g/L·h and 0.31 g/g, respectively. To improve the butanol production, the concentrations of initial sugar, DSY and calcium carbonate were varied using response surface methodology (RSM) based on Box–Behnken design. It was found that the optimal conditions for high butanol production were initial sugar, 50 g/L; DSY, 6 g/L and calcium carbonate, 6.6 g/L. Under these conditions, the highest experimental PB, QB and YB/S values were 11.38 g/L, 0.32 g/L·h and 0.40 g/g, respectively with 50% sugar consumption (SC). The PB with neither DSY nor CaCO3 was only 8.53 g/L. When an in situ gas stripping system was connected to the fermenter to remove butanol produced during the fermentation, the PB was increased to 15.33 g/L, whereas the YB/S (0.39 g/g) was not changed. However, the QB was decreased to 0.21 g/L·h with 75% SC.

Techno-Economic Analysis (TEA) of Different Pretreatment and Product Separation Technologies for Cellulosic Butanol Production from Oil Palm Frond

Among the driving factors for the high production cost of cellulosic butanol lies the pretreatment and product separation sections, which often demand high amounts of energy, chemicals, and water. In this study, techno-economic analysis of several pretreatments and product separation technologies were conducted and compared. Among the pretreatment technologies evaluated, low-moisture anhydrous ammonia (LMAA) pretreatment has shown notable potential with a pretreatment cost of $0.16/L butanol. Other pretreatment technologies evaluated were autohydrolysis, soaking in aqueous ammonia (SAA), and soaking in sodium hydroxide solution (NaOH) with pretreatment costs of $1.98/L, $3.77/L, and $0.61/L, respectively. Evaluation of different product separation technologies for acetone-butanol-ethanol (ABE) fermentation process have shown that in situ stripping has the lowest separation cost, which was $0.21/L. Other product separation technologies tested were dual extraction, adsorption, and membrane pervaporation, with the separation costs of $0.38/L, $2.25/L, and $0.45/L, respectively. The evaluations have shown that production of cellulosic butanol using combined LMAA pretreatment and in situ stripping or with dual extraction recorded among the lowest butanol production cost. However, dual extraction model has a total solvent productivity of approximately 6% higher than those of in situ stripping model.

Life-Cycle Assessment (LCA) of Different Pretreatment and Product Separation Technologies for Butanol Bioprocessing from Oil Palm Frond

Environmental impact assessment is a crucial aspect of biofuels production to ensure that the process generates emissions within the designated limits. In typical cellulosic biofuel production process, the pretreatment and downstream processing stages were reported to require a high amount of chemicals and energy, thus generating high emissions. Cellulosic butanol production while using low moisture anhydrous ammonia (LMAA) pretreatment was expected to have a low chemical, water, and energy footprint, especially when the process was combined with more efficient downstream processing technologies. In this study, the quantification of environmental impact potentials from cellulosic butanol production plants was conducted with modeled different pretreatment and product separation approaches. The results have shown that LMAA pretreatment possessed a potential for commercialization by having low energy requirements when compared to the other modeled pretreatments. With high safety measures that reduce the possibility of anhydrous ammonia leaking to the air, LMAA pretreatment resulted in GWP of 5.72 kg CO2 eq./L butanol, ecotoxicity potential of 2.84 × 10−6 CTU eco/L butanol, and eutrophication potential of 0.011 kg N eq./L butanol. The lowest energy requirement in biobutanol production (19.43 MJ/L), as well as better life-cycle energy metrics performances (NEV of 24.69 MJ/L and NER of 2.27) and environmental impacts potentials (GWP of 3.92 kg N eq./L butanol and ecotoxicity potential of 2.14 × 10−4 CTU eco/L butanol), were recorded when the LMAA pretreatment was combined with the membrane pervaporation process in the product separation stage.

Extraction of Natural Fragrance Ingredients: History Overview and Future Trends

For centuries, perfumes consisted in a combination of natural ingredients, mainly of plant origin. From the 19th century on, the advent of organic synthesis enabled the deployment of multiple synthetic olfactory notes, enriching significantly the perfumers' portfolio. Chemistry is ever since the foundation of modern perfumery. However, sustainable-minded consumers, massively rejecting synthetics for safety and ecological issues, engaged a global return to nature in numerous sectors, and the fragrance industry is not outdone. Sustainable extraction of natural products, making use of innovative technologies, process intensification and agro-based solvents, constitutes the answer to develop eco-conceived fragrant ingredients covering every olfactory family without endangering biodiversity any further. The objective of this review is to draw a clear picture of where those technological advances are today and to assess the ones that may be effectively transposed at the industrial scale tomorrow.

Chemical and bio-chemical reactions assisted by pervaporation technology

Since several decades ago, the application of pervaporation (PV) technology has been mainly aimed at the separation of different types of water-organic, organic-water and organic-organic mixtures, reaching its large-scale application in industry for the dehydration of organics. Today, the versatility and high selectivity toward specific compounds have led its consideration to other types of application such as the assisted chemical and bio-chemical reactions. The focus of this review is to provide a compelling overview on the recent developments of PV combined with chemical and bio-chemical reactions. After a general introduction of PV and its theoretical background, particular emphasis is given to the results obtained in the field for different reactions considered, identifying the key features and weak points of PV in such particular applications. Furthermore, future trends and perspectives are also addressed according to the latest literature reports.

Twenty-first-century chemical odyssey: fuels versus commodities and cell factories versus chemical plants

The harmful effects of pollution from the massive and widespread use of fossil fuels have led various organizations and governments to search for alternative energy sources. To address this, a new energy bioprocess is being developed that utilizes non-edible lignocellulose - the only sustainable source of organic carbon in nature. In this mini-review, we consider the potential use of synthetic biology to develop new-to-nature pathways for the biosynthesis of chemicals that are currently synthesized using classical industrial approaches. The number of industrial processes based on starch or lignocellulose is still very modest. Advances in the area require the development of more efficient approaches to deconstruct plant materials, better exploitation of the catalytic potential of prokaryotes and lower eukaryotes and the identification of new and useful genes for product synthesis. Further research and progress is urgently needed in order for government and industry to achieve the major milestone of transitioning 30% of the total industry to renewable sources by 2050.

Unravelling the influence of carbon dioxide on the adsorptive recovery of butanol from fermentation broth using ITQ-29 and ZIF-8

The presence of CO₂during the vapor phase adsorption of butanol from ABE fermentation at the head space of the fermenter has an important roll on the efficient recovery of biobutanol.

Genomic, Transcriptional, and Phenotypic Analysis of the Glucose Derepressed Clostridium beijerinckii Mutant Exhibiting Acid Crash Phenotype

Clostridium beijerinckii is a predominant solventogenic bacterium that is used for the ABE fermentation. Various C. beijerinckii mutants are constructed for desirable phenotypes. The C. beijerinckii mutant BA105 harboring a glucose derepression phenotype was previously isolated and demonstrated the enhanced amylolytic activity in the presence of glucose. Despite its potential use, BA105 is not further characterized and utilized. Therefore, the authors investigate fermentation phenotypes of BA105 in this study. Under the typical batch fermentation conditions, BA105 consistently exhibits acid crash phenotype resulting in limited glucose uptake and cell growth. However, when the culture pH is maintained above 5.5, BA105 exhibits the increased glucose uptake and butanol production than did the wild-type. To further analyze BA105, the authors perform genome sequencing and RNA sequencing. Genome analysis identifies two SNPs unique to BA105, in the upstream region of AbrB regulator (Cbei_4885) and the ROK family glucokinase (Cbei_4895) which are involved in catabolite repression and regulation of sugar metabolism. Transcriptional analysis of BA105 reveals significant differential expression of the genes associated with the PTS sugar transport system and acid production. This study improves understanding of the acid crash phenomenon and provides the genetic basis underlying the catabolite derepression phenotype of C. beijericnkii.

Conversion of Ethanol to 2-Ethylhexenal at Ambient Conditions Using Tandem, Biphasic Catalysis

Ethanol is a ubiquitous fermentation product well-tolerated by microbes, but purification from growth media requires multiple distillations or other energy intensive processes. Converting such metabolites to larger, hydrophobic products would both yield higher energy products and facilitate separation. Here, we demonstrate the conversion of C₂ ethanol to C₈ 2-ethylhexenal via a sequential oxidation-aldol-hydrogenation-aldol process with solar energy as the only required input. Photocatalysis was utilized to drive enzymatic oxidation of ethanol, while biphasic media in conjunction with aldol coupling and Pd assisted hydrogenation kept the oxidation and reduction processes physically and chemically separated. Using this process, 2-ethylhexenal was produced from ethanol in both buffer and diluted yeast media.

Light-Driven Catalytic Upgrading of Butanol in a Biohybrid Photoelectrochemical System

This paper reports the design and preparation of a biohybrid photoelectrochemical cell (PEC) that can drive the tandem enzymatic oxidation and aldol condensation of n-butanol (BuOH) to C8 2-ethylhexenal (2-EH). In this work, BuOH was first oxidized to n-butyraldehyde (BA) by the alcohol oxidase enzyme (AOx), concurrently generating hydrogen peroxide (H2O2). To preserve enzyme activity and increase kinetics nearly 2-fold, the H2O2 was removed by oxidation at a bismuth vanadate (BiVO4) photoanode. Organocatalyzed aldol condensation of C4 BA to C8 2-EH improved the overall BuOH conversion to 6.2 ± 0.1% in a biased PEC after 16 h. A purely light-driven, unbiased PEC showed 3.1 ± 0.1% BuOH conversion, or ~50% of that obtained from the biased system. Replacing AOx with the enzyme alcohol dehydrogenase (ADH), which requires the diffusional nicotinamide adenine dinucleotide cofactor (NAD+/NADH), resulted in only 0.2% BuOH conversion due to NAD+ dimerization at the photoanode. Lastly, the application of more positive biases with the biohybrid AOx PEC led to measurable production of H2 at the cathode, but at the cost of lower BA and 2-EH yields due to both product overoxidation and decreased enzyme activity.

Applied in situ product recovery in ABE fermentation

The production of biobutanol is hindered by the product's toxicity to the bacteria, which limits the productivity of the process. In situ product recovery of butanol can improve the productivity by removing the source of inhibition. This paper reviews in situ product recovery techniques applied to the acetone butanol ethanol fermentation in a stirred tank reactor. Methods of in situ recovery include gas stripping, vacuum fermentation, pervaporation, liquid–liquid extraction, perstraction, and adsorption, all of which have been investigated for the acetone, butanol, and ethanol fermentation. All techniques have shown an improvement in substrate utilization, yield, productivity or both. Different fermentation modes favored different techniques. For batch processing gas stripping and pervaporation were most favorable, but in fed‐batch fermentations gas stripping and adsorption were most promising. During continuous processing perstraction appeared to offer the best improvement. The use of hybrid techniques can increase the final product concentration beyond that of single‐stage techniques. Therefore, the selection of an in situ product recovery technique would require comparable information on the energy demand and economics of the process. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:563–579, 2017

Multicatalytic, Light-Driven Upgrading of Butanol to 2-Ethylhexenal and Hydrogen under Mild Aqueous Conditions

Microbes produce low-molecular-weight alcohols from sugar, but these metabolites are difficult to separate from water and possess relatively low heating values. A combination of photo-, organo-, and enzyme catalysis is shown here to convert C₄ butanol (BuOH) to C₈ 2-ethylhexenal (2-EH) using only solar energy to drive the process. First, alcohol dehydrogenase (ADH) catalyzed the oxidation of BuOH to butyraldehyde (BA), using NAD⁺ as a cofactor. To prevent back reaction, NAD+ was regenerated using a platinum-seeded cadmium sulfide (Pt@CdS) photocatalyst. An amine-based organocatalyst then upgraded BA to 2-EH under mild aqueous conditions rather than harsh basic conditions in order to preserve enzyme and photocatalyst stability. The process also simultaneously increased total BuOH conversion. Thus, three disparate types of catalysts synergistically generated C₈ products from C₄ alcohols under green chemistry conditions of neutral pH, low temperature, and pressure.

Development of Agave as a dedicated biomass source: production of biofuels from whole plants

BACKGROUND

Agave species can grow well in semi-arid marginal agricultural lands around the world. Selected Agave species are used largely for alcoholic beverage production in Mexico. There are expanding research efforts to use the plentiful residues (bagasse) for ethanol production as the beverage manufacturing process only uses the juice from the central core of mature plants. Here, we investigate the potential of over a dozen Agave species, including three from cold semi-arid regions of the United States, to produce biofuels using the whole plant.

RESULTS

Ethanol was readily produced by Saccharomyces cerevisiae from hydrolysate of ten whole Agaves with the use of a proper blend of biomass degrading enzymes including inulinase that overcomes inhibition of most of the species tested. As an example, US grown Agave neomexicana produced 119 ± 11 mg ethanol/g biomass. Unlike yeast fermentations, Clostridium beijerinckii produced n-butanol plus acetone from all species tested. Butyric acid, a precursor of n-butanol, was also present due to incomplete conversion during the screening process. Since Agave contains high levels of free and polyfructose which are readily destroyed by acidic pretreatment, a two-step procedure was developed to depolymerize polyfructose while maintaining its fermentability. The hydrolysate from before and after dilute acid processing was used in C. beijerinckii fermentations with selected Agave species with A. neomexicana producing 144 ± 4 mg fermentation products/g biomass.

CONCLUSIONS

Results showed Agave's potential to be a source of fermentable sugars beyond the existing beverage species to now include many species previously unfermentable by yeast, including cold-tolerant lines. This development should stimulate development of Agave as a dedicated feedstock for biofuels in semi-arid regions throughout the globe.

Enhancement of n-butanol production by in situ butanol removal using permeating-heating-gas stripping in acetone-butanol-ethanol fermentation

Butanol recovery from acetone-butanol-ethanol (ABE) fed-batch fermentation using permeating-heating-gas was determined in this study. Fermentation was performed with Clostridium acetobutylicum B3 in a fibrous bed bioreactor and permeating-heating-gas stripping was used to eliminate substrate and product inhibition, which normally restrict ABE production and sugar utilization to below 20 g/L and 60 g/L, respectively. In batch fermentation (without permeating-heating-gas stripping), C. acetobutylicum B3 utilized 60 g/L glucose and produced 19.9 g/L ABE and 12 g/L butanol, while in the integrated process 290 g/L glucose was utilized and 106.27 g/L ABE and 66.09 g/L butanol were produced. The intermittent gas stripping process generated a highly concentrated condensate containing approximately 15% (w/v) butanol, 4% (w/v) acetone, a small amount of ethanol (<1%), and almost no acids, resulting in a highly concentrated butanol solution [∼ 70% (w/v)] after phase separation. Butanol removal by permeating-heating-gas stripping has potential for commercial ABE production.

Investigation of gas stripping and pervaporation for improved feasibility of two-stage butanol production process

Gas stripping and pervaporation are investigated for butanol recovery in a two-stage acetone-butanol-ethanol (ABE) fermentation process. The first stage is operated in a continuous mode and the second stage as a fed-batch. Gas stripping coupled to the second stage and operated intermittently enabled additional glucose feeding in the second stage and up to 59 g/L butanol and 73 g/L total ABE solvents in the condensate. Concentration of 167 g/L butanol and 269 g/L ABE in the permeate was measured in ex situ pervaporation experiments using a PDMS membrane at temperature of 37 °C and pressure of 10mbars. The "operating window" tool is introduced to evaluate the feasibility of the existing ABE fermentations operated as continuous with cell recycle, as two-stages, with biomass immobilization or with integrated product removal. This tool enables the identification of the most favorable process configuration, which is the combination of cell immobilization and integrated product removal.