Impact of Furfural on Rapid Ethanol Production Using a Membrane Bioreactor

Ylitervo, Päivi; Franzén, Carl Johan; Taherzadeh, Mohammad J.

doi:10.3390/en6031604

Cited by 25 publications

(24 citation statements)

References 31 publications

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“…The inhibition constant for competitive inhibition of xylose uptake by glucose was assumed to be equal to the high affinity K M value for glucose. For furfural consumption, the maximum rate and saturation constant identified during steady state conditions at high cell density in a membrane bioreactor were used [31]. HMF is generally consumed at a lower rate than furfural.…”

Section: Methodsmentioning

confidence: 99%

Improved sugar co-utilisation by encapsulation of a recombinant Saccharomyces cerevisiae strain in alginate-chitosan capsules

Westman

Bonander

Taherzadeh

et al. 2014

Biotechnol Biofuels

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BackgroundTwo major hurdles for successful production of second-generation bioethanol are the presence of inhibitory compounds in lignocellulosic media, and the fact that Saccharomyces cerevisiae cannot naturally utilise pentoses. There are recombinant yeast strains that address both of these issues, but co-utilisation of glucose and xylose is still an issue that needs to be resolved. A non-recombinant way to increase yeast tolerance to hydrolysates is by encapsulation of the yeast. This can be explained by concentration gradients occuring in the cell pellet inside the capsule. In the current study, we hypothesised that encapsulation might also lead to improved simultaneous utilisation of hexoses and pentoses because of such sugar concentration gradients.ResultsIn silico simulations of encapsulated yeast showed that the presence of concentration gradients of inhibitors can explain the improved inhibitor tolerance of encapsulated yeast. Simulations also showed pronounced concentration gradients of sugars, which resulted in simultaneous xylose and glucose consumption and a steady state xylose consumption rate up to 220-fold higher than that found in suspension culture. To validate the results experimentally, a xylose-utilising S. cerevisiae strain, CEN.PK XXX, was constructed and encapsulated in semi-permeable alginate-chitosan liquid core gel capsules. In defined media, encapsulation not only increased the tolerance of the yeast to inhibitors, but also promoted simultaneous utilisation of glucose and xylose. Encapsulation of the yeast resulted in consumption of at least 50% more xylose compared with suspended cells over 96-hour fermentations in medium containing both sugars. The higher consumption of xylose led to final ethanol titres that were approximately 15% higher. In an inhibitory dilute acid spruce hydrolysate, freely suspended yeast cells consumed the sugars in a sequential manner after a long lag phase, whereas no lag phase was observed for the encapsulated yeast, and glucose, mannose, galactose and xylose were utilised in parallel from the beginning of the cultivation.ConclusionsEncapsulation of xylose-fermenting S. cerevisiae leads to improved simultaneous and efficient utilisation of several sugars, which are utilised sequentially by suspended cells. The greatest improvement is obtained in inhibitory media. These findings show that encapsulation is a promising option for production of second-generation bioethanol.

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Section: Methodsmentioning

confidence: 99%

Improved sugar co-utilisation by encapsulation of a recombinant Saccharomyces cerevisiae strain in alginate-chitosan capsules

Westman

Bonander

Taherzadeh

et al. 2014

Biotechnol Biofuels

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“…In the wide array of phenolic compounds there are both convertible and nonconvertible inhibitors (12). For in situ detoxification, it is necessary that the inhibitors are kept at a low level, at least relative to the amount of metabolically active cells: yeast at a high cell density using a membrane bioreactor could tolerate high concentrations of furfural (13). Other strategies to handle the toxicity of lignocellulosic hydrolysates involve, e.g., fed-batch processes, where the inhibitors can be kept at a low concentration inside the reactor (14).…”

mentioning

confidence: 99%

Flocculation Causes Inhibitor Tolerance in Saccharomyces cerevisiae for Second-Generation Bioethanol Production

Westman

Mapelli

Taherzadeh

et al. 2014

Appl Environ Microbiol

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bYeast has long been considered the microorganism of choice for second-generation bioethanol production due to its fermentative capacity and ethanol tolerance. However, tolerance toward inhibitors derived from lignocellulosic materials is still an issue. Flocculating yeast strains often perform relatively well in inhibitory media, but inhibitor tolerance has never been clearly linked to the actual flocculation ability per se. In this study, variants of the flocculation gene FLO1 were transformed into the genome of the nonflocculating laboratory yeast strain Saccharomyces cerevisiae CEN.PK 113-7D. Three mutants with distinct differences in flocculation properties were isolated and characterized. The degree of flocculation and hydrophobicity of the cells were correlated to the length of the gene variant. The effect of different strength of flocculation on the fermentation performance of the strains was studied in defined medium with or without fermentation inhibitors, as well as in media based on dilute acid spruce hydrolysate. Strong flocculation aided against the readily convertible inhibitor furfural but not against less convertible inhibitors such as carboxylic acids. During fermentation of dilute acid spruce hydrolysate, the most strongly flocculating mutant with dense cell flocs showed significantly faster sugar consumption. The modified strain with the weakest flocculation showed a hexose consumption profile similar to the untransformed strain. These findings may explain why flocculation has evolved as a stress response and can find application in fermentation-based biorefinery processes on lignocellulosic raw materials.

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“…MBR fermentation systems have significant advantages over conventional fermentation modes as they can provide high cell concentrations in the reactor that allow efficient conversion of substrates into products and also higher tolerance to cell inhibitory compounds [23]. Moreover, higher dilution rates can be achieved since undesired cell washout is prevented [24].…”

Section: Mbr Filtration Using Buffer As Feed Solutionmentioning

confidence: 99%

Removal of Bacterial Contamination from Bioethanol Fermentation System Using Membrane Bioreactor

et al. 2018

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A major issue hindering efficient industrial ethanol fermentation from sugar-based feedstock is excessive unwanted bacterial contamination. In industrial scale fermentation, reaching complete sterility is costly, laborious, and difficult to sustain in long-term operation. A physical selective separation of a co-culture of Saccharomyces cerevisiae and an Enterobacter cloacae complex from a buffer solution and fermentation media at dilution rates of 0.1-1 1/h were examined using an immersed membrane bioreactor (iMBR). The effect of the presence of yeast, inoculum size, membrane pore size, and surface area, backwashing and dilution rate on bacteria removal were assessed by evaluating changes in the filtration conditions, medium turbidity, and concentration of compounds and cell biomass. The results showed that using the iMBR with dilution rate of 0.5 1/h results in successful removal of 93% of contaminating bacteria in the single culture and nearly complete bacteria decontamination in yeast-bacteria co-culture. During continuous fermentation, application of lower permeate fluxes provided a stable filtration of the mixed culture with enhanced bacteria washout. This physical selective separation of bacteria from yeast can enhance final ethanol quality and yields, process profitability, yeast metabolic activity, and decrease downstream processing costs.

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Impact of Furfural on Rapid Ethanol Production Using a Membrane Bioreactor

Cited by 25 publications

References 31 publications

Improved sugar co-utilisation by encapsulation of a recombinant Saccharomyces cerevisiae strain in alginate-chitosan capsules

Improved sugar co-utilisation by encapsulation of a recombinant Saccharomyces cerevisiae strain in alginate-chitosan capsules

Flocculation Causes Inhibitor Tolerance in Saccharomyces cerevisiae for Second-Generation Bioethanol Production

Removal of Bacterial Contamination from Bioethanol Fermentation System Using Membrane Bioreactor

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