Chemical and structural changes of pretreated empty fruit bunch (EFB) in ionic liquid-cellulase compatible system for fermentability to bioethanol

The pretreatment of empty fruit bunch (EFB) was conducted using an integrated system of IL and cellulases (IL-E), with simultaneous fermentation in one vessel. The cellulase mixture (PKC-Cel) was derived from Trichoderma reesei by solid-state fermentation. Choline acetate [Cho]OAc was utilized for the pretreatment due to its biocompatibility and biodegradability. The treated EFB and its hydrolysate were characterized by the Fourier transform infrared spectroscopy, scanning electron microscopy, and chemical analysis. The results showed that there were significant structural changes in EFB after the treatment in IL-E system. The sugar yield after enzymatic hydrolysis by the PKC-Cel was increased from 0.058 g/g of EFB in the crude sample (untreated) to 0.283 and 0.62 ± 06 g/g in IL-E system after 24 and 48 h of treatment, respectively. The EFB hydrolysate showed the eligibility for ethanol production without any supplements where ethanol yield was 0.275 g ethanol/g EFB in the presence of the IL, while lower yield obtained without IL-pretreatment. Moreover, it was demonstrated that furfural and phenolic compounds were not at the level of suppressing the fermentation process

Concepts for improving ethanol productivity from lignocellulosic materials: Encapsulated yeast and membrane bioreactors

Lignocellulosic biomass is a potential feedstock for production of sugars, which can be fermented into ethanol. The work presented in this thesis proposes some solutions to overcome problems with suboptimal process performance due to elevated cultivation temperatures and inhibitors present during ethanol production from lignocellulosic materials. In particular, continuous processes operated at high dilution rates with high sugar utilisation are attractive for ethanol fermentation, as this can result in higher ethanol productivity. Both encapsulation and membrane bioreactors were studied and developed to achieve rapid fermentation at high yeast cell density.My studies showed that encapsulated yeast is more thermotolerant than suspended yeast. The encapsulated yeast could successfully ferment all glucose during five consecutive batches, 12 h each at 42 \ub0C. In contrast, freely suspended yeast was inactivated already in the second or third batch. One problem with encapsulation is, however, the mechanical robustness of the capsule membrane. If the capsules are exposed to e.g. high shear forces, the capsule membrane may break. Therefore, a method was developed to produce more robust capsules by treating alginate-chitosan-alginate (ACA) capsules with 3-aminopropyltriethoxysilane (APTES) to get polysiloxane-ACA capsules. Of the ACA-capsules treated with 1.5% APTES, only 0–2% of the capsules broke, while 25% of the untreated capsules ruptured within 6 h in a shear test. In this thesis membrane bioreactors (MBR), using either a cross-flow or a submerged membrane, could successfully be applied to retain the yeast inside the reactor. The cross-flow membrane was operated at a dilution rate of 0.5 h-1 whereas the submerged membrane was tested at several dilution rates, from 0.2 up to 0.8 h-1. Cultivations at high cell densities demonstrated an efficient in situ detoxification of very high furfural levels of up to 17 g L-1 in the feed medium when using a MBR. The maximum yeast density achieved in the MBR was more than 200 g L-1. Additionally, ethanol fermentation of nondetoxified spruce hydrolysate was possible at a high feeding rate of 0.8 h-1 by applying a submerged membrane bioreactor, resulting in ethanol productivities of up to 8 g L-1 h-1. In conclusion, this study suggests methods for rapid continuous ethanol production even at stressful elevated cultivation temperatures or inhibitory conditions by using encapsulation or membrane bioreactors and high cell density cultivations

Membrane bioreactors\u27 potential for ethanol and biogas production: a review

Companies developing and producing membranes for different separation purposes, as well as the market for these, have markedly increased in numbers over the last decade. Membrane and separation technology might well contribute to making fuel ethanol and biogas production from lignocellulosic materials more economically viable and productive. Combining biological processes with membrane separation techniques in a membrane bioreactor (MBR) increases cell concentrations extensively in the bioreactor. Such a combination furthermore reduces product inhibition during the biological process, increases product concentration and productivity, and simplifies the separation of product and/or cells. Various MBRs have been studied over the years, where the membrane is either submerged inside the liquid to be filtered, or placed in an external loop outside the bioreactor. All configurations have advantages and drawbacks, as reviewed in this paper. The current review presents an account of the membrane separation technologies, and the research performed on MBRs, focusing on ethanol and biogas production. The advantages and potentials of the technology are elucidated

Rapid ethanol production by Saccharomyces cerevisiae in a membrane bioreactor

Robust polysiloxane-ACA capsules for prolonged ethanol production from wood hydrolyzate by Saccharomyces cerevisiaeP\ue4ivi Ylitervo,a,b Carl Johan Franz\ue9n b and Mohammad J. Taherzadeh aa University of Bor\ue5s, School of Engineering, Swedenb Chalmers University of Technology, Industrial Biotechnology, SwedenThe recalcitrance of lignocellulose makes it difficult to hydrolyze and toxic inhibitors are formed during its decomposition. The formed inhibitors can severely affect the fermentability of the hydrolyzate. Encapsulating the fermenting yeast can be a potential option to make the cells more inhibitor and stress tolerant when compared with suspended yeast. In the encapsulation process the yeast is enclosed in a thin semi-permeable membrane surrounding the cells in the liquid core. To apply encapsulation for industrial applications the capsules need to be mechanically stable for long periods. Therefore, a new encapsulation method was developed were alginate-chitosan-alginate (ACA) capsules were treated with hydrolyzed 3-aminopropyltrietoxysilane (hAPTES) to reinforce capsules with polysiloxane (PS). PS-ACA-capsules treated with 1.5% and 3.0% hAPTES were very robust and only 0-1% capsules broke during the mechanical shear test performed after five batch cultivations. Of the untreated capsules, 25% burst within 6 h. The yeast in 3.0% hAPTES treated PS-ACA-capsules did not produce any ethanol during cultivations. However, capsules treated with 1.5% hAPTES were significantly stronger and showed similar ethanol production profile to untreated ACA-capsules cultivated in hydrolyzate. The produced PS-ACA-capsules were easily prepared and demonstrated high stability, reusability, and good ethanol production which are crucial features to make capsules the applicable at large scale for ethanol production

THERMOTOLERANCE OF ENCAPSULATED YEAST

There is a growing concern about the enhanced global warming caused by excessive CO2 emissions. Therefore alternative fuels are in focus today in order to replace fossil fuels. Production of bioethanol by fermentation can be a suitable substitute for fossil fuel, if it can be produced from lignocellulosic materials. However, there are still several problems to solve before second generation bioethanol can be produced in a stable and economically feasible way. One problem is e.g. the thermotolerance of Saccharomyces cerevisiae, which is the most commonly used yeast for ethanol production. Yeast with high thermotolerance is desirable especially in tropical countries where cooling is today necessary to keep the reactor at an appropriate temperature, and also in simultaneous saccharification and fermentation processes where the enzymes which work together with the yeast have an optimal temperature which is higher than the yeast can survive. Our group is investigating the effect encapsulation has on yeast. The yeast is enveloped inside spherical polyelectrolyte membranes, where the cells are kept close together in capsules of approximately 4 mm in diameter (Figure 1). Previous studies have shown that the encapsulated yeast is more tolerant against inhibitors and we have now also shown that the encapsulated yeast become more thermotolerant

Improving the stability and mechanical resistance of chitosan/alginate capsules for encapsulation of S. cerevisiae

IMPROVING THE STABILITY AND MECHANICAL RESISTANCE OF CHITOSAN/ALGINATE CAPSULES FOR ENCAPSULATION OF S. CEREVISIAEP\ue4ivi Ylitervo(a,b), Carl Johan Franz\ue9n(a) and Mohammad J. Taherzadeh(b)a,Industrial Biotechnology, Chalmers University of Technologyb,School of Engineering, University of Bor\ue5sNowadays, fuel ethanol is both used as a substitute and an additive to the conventional fossil fuels and the interest in converting lignocellulose to fuel ethanol has expanded in the last few decades. Lignocellulose is attractive as raw material due to its high abundance and low price.However, chemical hydrolysis or pre-treatment of lignocelluloses creates several components that are toxic to fermenting organisms and makes cultivation complicated. By using encapsulated yeast, one can overcome this problem. In encapsulation, the yeast cells are confined inside a capsule composed of an outer semi-permeable membrane and an inner liquid core. Encapsulation is an attractive method since it can improve the cell stability and inhibitor tolerance, increase the biomass concentration, and decrease the cost of cell recovery, recycling, downstream processing, and fermentation time. Mechanical resistance is a key parameter together with permeability for the success of an encapsulation system. In order to improve the robustness of the capsules we are testing different cross linkers to introduce covalent bonds to a chitosan-alginate matrix. By treating chitosan covered alginate capsules with glutaraldehyde the capsules became harder and less elastic. One big disadvantage in using crosslinking agent is, however, that they are toxic for the yeast. If the encapsulated yeast is treated at too harsh conditions they will die. Although, to improve the capsules mechanical strength the membrane have to be crosslinked to a satisfying degree. We have examined different capsule-treatments and found some encouraging results when applying repetitive treatments with crosslinking agent

Improving the stability and mechanical resistance of chitosan/alginate capsules for encapsulation of S. cerevisiae

IMPROVING THE STABILITY AND MECHANICAL RESISTANCE OF CHITOSAN/ALGINATE CAPSULES FOR ENCAPSULATION OF S. CEREVISIAEP\ue4ivi Ylitervo(a,b), Carl Johan Franz\ue9n(a) and Mohammad J. Taherzadeh(b)a,Industrial Biotechnology, Chalmers University of Technologyb,School of Engineering, University of Bor\ue5sNowadays, fuel ethanol is both used as a substitute and an additive to the conventional fossil fuels and the interest in converting lignocellulose to fuel ethanol has expanded in the last few decades. Lignocellulose is attractive as raw material due to its high abundance and low price.However, chemical hydrolysis or pre-treatment of lignocelluloses creates several components that are toxic to fermenting organisms and makes cultivation complicated. By using encapsulated yeast, one can overcome this problem. In encapsulation, the yeast cells are confined inside a capsule composed of an outer semi-permeable membrane and an inner liquid core. Encapsulation is an attractive method since it can improve the cell stability and inhibitor tolerance, increase the biomass concentration, and decrease the cost of cell recovery, recycling, downstream processing, and fermentation time. Mechanical resistance is a key parameter together with permeability for the success of an encapsulation system. In order to improve the robustness of the capsules we are testing different cross linkers to introduce covalent bonds to a chitosan-alginate matrix. By treating chitosan covered alginate capsules with glutaraldehyde the capsules became harder and less elastic. One big disadvantage in using crosslinking agent is, however, that they are toxic for the yeast. If the encapsulated yeast is treated at too harsh conditions they will die. Although, to improve the capsules mechanical strength the membrane have to be crosslinked to a satisfying degree. We have examined different capsule-treatments and found some encouraging results when applying repetitive treatments with crosslinking agent