| 1. |
- Erdei, Borbala
(author)
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Development of integrated cellulose- and starch-based ethanol production and process design for improved xylose conversion
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Transportation fuels from renewable resources such as ethanol are one of the alternatives to ensure energy security and decrease the net emission of carbon dioxide. First-generation ethanol production from sugar- and starch-based raw materials (1G) is today well established in many countries, and the focus of research has thus shifted to the development and demonstration of the production of second-generation bioethanol from lignocellulose (2G). This thesis deals with the development of process configurations for bioethanol production from wheat straw integrated with wheat starch-based ethanol production. One part of the work focused on integration in simultaneous saccharification and fermentation (SSF) of steam-pretreated wheat straw (SPWS) with pre-saccharified, completely saccharified or fermented wheat meal using baker’s yeast, Saccharomyces cerevisiae. Mixing wheat straw and pre-saccharified or saccharified wheat meal was shown to be beneficial for both 1G and 2G ethanol production. Not only the ethanol concentrations, but also the ethanol yields, increased when pre-saccharified wheat meal was mixed with SPWS. The highest ethanol yield achieved was higher than that obtained with SSF of either raw material alone. Ethanol yields above 80% of the theoretical (from the hexose sugars) and ethanol concentrations of about 6% (w/v) were achieved in batch SSF. Ethanol concentrations at such levels reduce the energy demand in distillation, thus lowering the production cost. Since wheat straw contains a large amount of xylose, integrated process configurations were developed and investigated in an attempt to improve xylose utilization by a xylose-fermenting, genetically modified strain, S. cerevisiae TMB3400, in the second part of the work. The most promising configuration for co-fermentation of glucose and xylose was separate hydrolysis and co-fermentation of SPWS, as this allowed the glucose concentration to be controlled by the wheat-starch hydrolysate feed. An ethanol yield of 92% was achieved after fermentation based on glucose and xylose, and almost complete xylose consumption was achieved. In the last part of the work, differences in the performance of two mutated strains of S. cerevisiae TMB3400 were revealed. It was shown that KE6-13i was more tolerant to inhibitors, while KE6-12 performed better in less inhibitory environments.
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| 2. |
- Erdei, Borbala, et al.
(author)
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Ethanol production from mixtures of wheat straw and wheat meal
- 2010
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In: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 3
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Journal article (peer-reviewed)abstract
- Background: Bioethanol can be produced from sugar-rich, starch-rich (first generation; 1G) or lignocellulosic (second generation; 2G) raw materials. Integration of 2G ethanol with 1G could facilitate the introduction of the 2G technology. The capital cost per ton of fuel produced would be diminished and better utilization of the biomass can be achieved. It would, furthermore, decrease the energy demand of 2G ethanol production and also provide both 1G and 2G plants with heat and electricity. In the current study, steam-pretreated wheat straw (SPWS) was mixed with presaccharified wheat meal (PWM) and converted to ethanol in simultaneous saccharification and fermentation (SSF). Results: Both the ethanol concentration and the ethanol yield increased with increasing amounts of PWM in mixtures with SPWS. The maximum ethanol yield (99% of the theoretical yield, based on the available C6 sugars) was obtained with a mixture of SPWS containing 2.5% water-insoluble solids (WIS) and PWM containing 2.5% WIS, resulting in an ethanol concentration of 56.5 g/L. This yield was higher than those obtained with SSF of either SPWS (68%) or PWM alone (91%). Conclusions: Mixing wheat straw with wheat meal would be beneficial for both 1G and 2G ethanol production. However, increasing the proportion of WIS as wheat straw and the possibility of consuming the xylose fraction with a pentose-fermenting yeast should be further investigated.
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| 3. |
- Erdei, Borbala, et al.
(author)
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Glucose and xylose co-fermentation of pretreated wheat straw using mutants of S. cerevisiae TMB3400.
- 2013
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In: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 164:1, s. 50-58
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Journal article (peer-reviewed)abstract
- Wheat straw was pretreated and fermented to ethanol. Two strains, which had been mutated from the genetically modified Saccharomyces cerevisiae TMB3400, KE6-12 and KE6-13i, have been used in this study and the results of performance were compared to that of the original strain. The glucose and xylose co-fermentation ability was investigated in batch fermentation of steam-pretreated wheat straw (SPWS) liquid (undiluted, and diluted 1.5 and 2 times). Both strains showed improved xylose uptake in diluted SPWS liquid, and increased ethanol yields compared with the original TMB3400 strain, although xylitol formation also increased slightly. In undiluted SPWS liquid, however, only KE6-13i performed better than the original strain regarding xylose utilization. Fed-batch fermentation of 1.5 and 2 times diluted liquid was performed by adding the glucose-rich hydrolysates from enzymatic hydrolysis of the solid fraction of SPWS at a constant feed rate after 5h of fermentation, when the glucose had been depleted. The modified strains showed improved xylose conversion; however, the ethanol yield was not significantly improved due to increased glycerol production. Fed-batch fermentation resulted in faster xylose utilization than in the batch cases.
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| 4. |
- Erdei, Borbala, et al.
(author)
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Separate hydrolysis and co-fermentation for improved xylose utilization in integrated ethanol production from wheat meal and wheat straw
- 2012
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In: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 5
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Journal article (peer-reviewed)abstract
- Background: The commercialization of second-generation bioethanol has not been realized due to several factors, including poor biomass utilization and high production cost. It is generally accepted that the most important parameters in reducing the production cost are the ethanol yield and the ethanol concentration in the fermentation broth. Agricultural residues contain large amounts of hemicellulose, and the utilization of xylose is thus a plausible way to improve the concentration and yield of ethanol during fermentation. Most naturally occurring ethanol-fermenting microorganisms do not utilize xylose, but a genetically modified yeast strain, TMB3400, has the ability to co-ferment glucose and xylose. However, the xylose uptake rate is only enhanced when the glucose concentration is low. Results: Separate hydrolysis and co-fermentation of steam-pretreated wheat straw (SPWS) combined with wheat-starch hydrolysate feed was performed in two separate processes. The average yield of ethanol and the xylose consumption reached 86% and 69%, respectively, when the hydrolysate of the enzymatically hydrolyzed (18.5% WIS) unwashed SPWS solid fraction and wheat-starch hydrolysate were fed to the fermentor after 1 h of fermentation of the SPWS liquid fraction. In the other configuration, fermentation of the SPWS hydrolysate (7.0% WIS), resulted in an average ethanol yield of 93% from fermentation based on glucose and xylose and complete xylose consumption when wheat-starch hydrolysate was included in the feed. Increased initial cell density in the fermentation (from 5 to 20 g/L) did not increase the ethanol yield, but improved and accelerated xylose consumption in both cases. Conclusions: Higher ethanol yield has been achieved in co-fermentation of xylose and glucose in SPWS hydrolysate when wheat-starch hydrolysate was used as feed, then in co-fermentation of the liquid fraction of SPWS fed with the mixed hydrolysates. Integration of first-generation and second-generation processes also increases the ethanol concentration, resulting in a reduction in the cost of the distillation step, thus improving the process economics.
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| 5. |
- Erdei, Borbala, et al.
(author)
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Simultaneous saccharification and co-fermentation of whole wheat in integrated ethanol production
- 2013
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In: Biomass & Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 56, s. 506-514
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Journal article (peer-reviewed)abstract
- Two of the most important ways of reducing the production cost of lignocellulosic ethanol are to increase the ethanol yield and the concentration in the fermentation broth. This can be facilitated by co-fermentation of glucose and xylose from agricultural residues such as wheat straw, due to the high amount of xylose in the hemicelluloses in these materials. Simultaneous saccharification and co-fermentation (SSCF) of steam-pretreated wheat straw (SPWS) with and without the addition of liquefied wheat meal (LWM) was performed using the pentose-fermenting yeast, TMB3400. The highest overall ethanol yield in batch operation, of around 70%, equivalent to an ethanol concentration of 43.7 g L-1, was achieved using SPWS with 7.5% water-insoluble solids (WIS) and addition of LWM with 1% WIS. Using SPWS with a higher WIS (10%) resulted in a decreased yield, 60%, although the concentration of ethanol increased to 53.0 g L-1. SSCF of 7.5% straw was also performed with a single (after 20 h) or fed-batch addition of 1% WIS LWM (after 20, 24 and 28 h) resulting in an increase in both ethanol yield and concentration compared to the reference, without wheat meal addition, but no significant difference compared to the batch experiments. The addition of wheat meal to SSCF did not improve xylose utilization significantly, probably due to the instant release of glucose from the liquefied meal, which hampers the uptake of xylose. The instant release of glucose was shown to be caused by the high amylase activity of the beta-glucosidase enzyme preparation. (C) 2013 Elsevier Ltd. All rights reserved.
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| 6. |
- Erdei, Borbala, et al.
(author)
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SSF of steam-pretreated wheat straw with the addition of saccharified or fermented wheat meal in integrated bioethanol production
- 2013
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In: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 6
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Journal article (peer-reviewed)abstract
- Background: Integration of second-generation (2G) bioethanol production with existing first-generation (1G) production may facilitate commercial production of ethanol from cellulosic material. Since 2G hydrolysates have a low sugar concentration and 1G streams often have to be diluted prior to fermentation, mixing of streams is beneficial. Improved ethanol concentrations in the 2G production process lowers energy demand in distillation, improves overall energy efficiency and thus lower production cost. There is also a potential to reach higher ethanol yields, which is required in economically feasible ethanol production. Integrated process scenarios with addition of saccharified wheat meal (SWM) or fermented wheat meal (FWM) were investigated in simultaneous saccharification and (co-)fermentation (SSF or SSCF) of steam-pretreated wheat straw, while the possibility of recovering the valuable protein-rich fibre residue from the wheat was also studied. Results: The addition of SWM to SSF of steam-pretreated wheat straw, using commercially used dried baker's yeast, S. cerevisiae, resulted in ethanol concentrations of about 60 g/L, equivalent to ethanol yields of about 90% of the theoretical. The addition of FWM in batch mode SSF was toxic to baker's yeast, due to the ethanol content of FWM, resulting in a very low yield and high accumulation of glucose. The addition of FWM in fed-batch mode still caused a slight accumulation of glucose, but the ethanol concentration was fairly high, 51.2 g/L, corresponding to an ethanol yield of 90%, based on the amount of glucose added. In batch mode of SSCF using the xylose-fermenting, genetically modified S. cerevisiae strain KE6-12, no improvement was observed in ethanol yield or concentration, compared with baker's yeast, despite the increased xylose utilization, probably due to the considerable increase in glycerol production. A slight increase in xylose consumption was seen when glucose from SWM was fed at a low feed rate, after 48 hours, compared with batch SSCF. However, the ethanol yield and concentration remained in the same range as in batch mode. Conclusion: Ethanol concentrations of about 6% (w/v) were obtained, which will result in a significant reduction in the cost of downstream processing, compared with SSF of the lignocellulosic substrate alone. As an additional benefit, it is also possible to recover the protein-rich residue from the SWM in the process configurations presented, providing a valuable co-product.
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| 7. |
- Joelsson, Elisabeth, et al.
(author)
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Techno-economic evaluation of integrated first- and second-generation ethanol production from grain and straw.
- 2016
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In: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 9
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Journal article (peer-reviewed)abstract
- Integration of first- and second-generation ethanol production can facilitate the introduction of second-generation lignocellulosic ethanol production. Consolidation of the second-generation with the first-generation process can potentially reduce the downstream processing cost for the second-generation process as well as providing the first-generation process with energy. This study presents novel experimental results from integrated first- and second-generation ethanol production from grain and wheat straw in a process development unit. The results were used in techno-economic evaluations to investigate the feasibility of the plant, in which the main co-products were distiller's dried grains with solubles and biogas.
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| 8. |
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| 9. |
- Sanchis Sebastia, Miguel, et al.
(author)
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Analysis of Animal Bedding Heterogeneity for Potential Use in Biorefineries Based on Farmyard Manure
- 2020
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In: Waste and Biomass Valorization. - : Springer Science and Business Media LLC. - 1877-2641 .- 1877-265X. ; 11:6, s. 2387-2395
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Journal article (peer-reviewed)abstract
- Animal bedding, a mixture of straw and manure, could be used as a feedstock for bioenergy production, but its heterogeneity poses new challenges in its use in biorefineries. We have investigated the origin of this heterogeneity and quantified it, and discuss its impact on bioenergy production. Samples were collected from the bedding at different points and depths and analysed by first separating the manure from the straw by means of washing with water, and then determining the chemical composition of the liquid and solid fractions. The results supported our hypothesis that animal bedding behaves as a combination of several layers at different stages of degradation. Analysis revealed that the layers with higher organic content in the manure exhibited a poorer performance during the washing, since the residence time in the barn alters the washing profile of the organic fraction in the manure. It was also found that the variability in the composition of animal bedding was much greater than in other agricultural feedstocks: the manure content in animal bedding varied from 26 to 41%, and the content of fermentable carbohydrates varied by 20%. Total carbon and total nitrogen analyses showed that these changes in composition also affected the C/N ratio of the material, and thus its suitability as a feedstock for anaerobic digestion. This implies that the residence time in the barn affects not only the heterogeneity of the properties of animal bedding, but also the best way to process it in a biorefinery.
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| 10. |
- Sanchis Sebastia, Miguel, et al.
(author)
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Introducing low-quality feedstocks in bioethanol production: efficient conversion of the lignocellulose fraction of animal bedding through steam pretreatment
- 2019
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In: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 12
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Journal article (peer-reviewed)abstract
- BackgroundAnimal bedding remains an underutilized source of raw material for bioethanol production, despite the economic and environmental benefits of its use. Further research concerning the optimization of the production process is needed, as previously tested pretreatment methods have not increased the conversion efficiency to the levels necessary for commercialization of the process.ResultsWe propose steam pretreatment of animal bedding, consisting of a mixture of straw and cow manure, to deliver higher ethanol yields. The temperature, residence time and pH were optimized through response-surface modeling, where pretreatment was evaluated based on the ethanol yield obtained through simultaneous saccharification and fermentation of the whole pretreated slurry. The results show that the best conditions for steam pretreatment are 200 °C, for 5 min at pH 2, at which an ethanol yield of about 70% was obtained. Moreover, the model also showed that the pH had the greatest influence on the ethanol yield, followed by the temperature and then the residence time.ConclusionsBased on these results, it appears that steam pretreatment could unlock the potential of animal bedding, as the same conversion efficiencies were achieved as for higher-quality feedstocks such as wheat straw.
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