| 1. |
- Erdei, Borbala, et al.
(författare)
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Glucose and xylose co-fermentation of pretreated wheat straw using mutants of S. cerevisiae TMB3400.
- 2013
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 164:1, s. 50-58
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Erdei, Borbala, et al.
(författare)
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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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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 5
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Frankó, Balázs, et al.
(författare)
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Bioethanol production from forestry residues : A comparative techno-economic analysis
- 2016
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 184, s. 727-736
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Tidskriftsartikel (refereegranskat)abstract
- A techno-economic analysis was conducted to assess the feasibility of using forestry residues with different bark contents for bioethanol production. A proposed cellulosic ethanol biorefinery in Sweden was simulated with Aspen Plus. The plant was assumed to convert different forestry assortments (sawdust and shavings, fuel logs, early thinnings, tops and branches, hog fuel and pulpwood) to ethanol, pellets, biogas and electricity. The intention was not to obtain absolute ethanol production costs for future facilities, but to assess and compare the future potential of utilizing different forestry residues for bioethanol production. The same plant design and operating conditions were assumed in all cases, and the effect of including bark on the whole conversion process, especially how it influenced the ethanol production cost, was studied. While the energy efficiency (not including district heating) obtained for the whole process was between 67 and 69% regardless of the raw material used, the ethanol production cost differed considerably; the minimum ethanol selling price ranging from 0.77 to 1.52 USD/L. Under the basic assumptions, all the forestry residues apart from sawdust and shavings exhibited a negative net present value at current market prices. The profitability decreased with increasing bark content of the raw material. Sensitivity analyses showed that, at current market prices, the utilization of bark-containing forestry residues will not provide significant cost improvement compared with pulpwood unless the conversion of cellulose and hemicellulose to monomeric sugars is improved.
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| 4. |
- Franko, Balazs
(författare)
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Implications of feedstock diversity on forest-based ethanol production
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The utilization of lignocellulosic biomass to produce biofuels, such as bioethanol, has the potential to provide a sustainable alternative to fossil fuels, and thus mitigate greenhouse gas emissions from the transportation sector.Forest biomass is expected to be a significant source of such biomass, as it can serve as an abundant and sustainable feedstock for bioethanol production. It is unlikely that white wood chips will be used as a sole commercial feedstock for the production of bioethanol, due to increasing feedstock competition and requirements to meet large scale. The high demand for biomass means that other forestry assortments, not traditionally utilized by the forest industry, such as harvesting residues, will have to be exploited. However, the presence of bark in these forest residues is expected to pose a challenge in the traditional wood-to-ethanol process and adversely affect the conversion efficiency. Ethanol production from softwoods was investigated with the main objective of assessing the potential of expanding the feedstock base of an ethanol plant to include not only white wood, but also other forestry residues from a process perspective. Bark was found to be significantly more difficult to hydrolyze to monomeric sugars than white wood. This could mainly be attributed to the condensation reactions of bark extractives during acid-catalyzed steam pretreatment, which rendered the otherwise water-soluble extractives insoluble, and altered the structure of the solid fraction, resulting in impaired enzymatic hydrolysis. Techno-economic evaluations showed decreasing profitability of ethanol production with increasing bark content in the feedstock. Thus, the utilization of bark-containing forestry residues will not lead to significant cost reductions compared to higher-value pulpwood at current market prices, unless the conversion of cellulose and hemicellulose to monomeric sugars is improved.Another alternative to increase the future biomass supply for large-scale bioethanol production is the use of fast-growing trees such as willow and poplar. Although the production of ethanol from these hardwood species is welldocumented, the inclusion of biomass from fast-growing tree species in a softwood feedstock base for bioethanol production has not previously been investigated. The structural differences between hardwood and softwood couldbe expected to reduce the pretreatment efficacy when treating a mixture of the two. However, it was found that the use of a mixture of poplar and spruce would presumably be constrained more by the performance of the fermenting microorganism, than the efficacy of steam pretreatment, and that the ethanol production process could be sufficiently robust to allow small amounts of hardwood in a softwood-to-ethanol process.
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| 5. |
- Franko, Balazs, et al.
(författare)
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Influence of bark on fuel ethanol production from steam-pretreated spruce.
- 2015
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Bark and bark-containing forest residues have the potential for utilization as raw material for lignocellulosic ethanol production due to their abundance and low cost. However, the different physical properties and chemical composition of bark compared to the conventionally used wood chips may influence the spruce-to-ethanol bioconversion process. This study assesses the impact of bark on the overall bioconversion in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), utilizing steam-pretreated spruce bark and wood mixtures.
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| 6. |
- Frankó, Balázs, et al.
(författare)
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Removal of Water-Soluble Extractives Improves the Enzymatic Digestibility of Steam-Pretreated Softwood Barks
- 2018
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Ingår i: Applied Biochemistry and Biotechnology. - : Springer Science and Business Media LLC. - 0273-2289 .- 1559-0291. ; 184:2, s. 599-615
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Tidskriftsartikel (refereegranskat)abstract
- Softwood bark contains a large amounts of extractives—i.e., soluble lipophilic (such as resin acids) and hydrophilic components (phenolic compounds, stilbenes). The effects of the partial removal of water-soluble extractives before acid-catalyzed steam pretreatment on enzymatic digestibility were assessed for two softwood barks—Norway spruce and Scots pine. A simple hot water extraction step removed more than half of the water-soluble extractives from the barks, which improved the enzymatic digestibility of both steam-pretreated materials. This effect was more pronounced for the spruce than the pine bark, as evidenced by the 30 and 11% glucose yield improvement, respectively, in the enzymatic digestibility. Furthermore, analysis of the chemical composition showed that the acid-insoluble lignin content of the pretreated materials decreased when water-soluble extractives were removed prior to steam pretreatment. This can be explained by a decreased formation of water-insoluble “pseudo-lignin” from water-soluble bark phenolics during the acid-catalyzed pretreatment, which otherwise results in distorted lignin analysis and may also contribute to the impaired enzymatic digestibility of the barks. Thus, this study advocates the removal of extractives as the first step in the processing of bark or bark-rich materials in a sugar platform biorefinery.
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| 7. |
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| 8. |
- Frankó, Balázs, et al.
(författare)
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The effect of blending spruce and poplar on acid-catalyzed steam pretreatment and enzymatic hydrolysis
- 2019
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Ingår i: Bioresource Technology Reports. - : Elsevier BV. - 2589-014X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to explore the possibility of mixed feedstocks utilization using acid-catalyzed steam pretreatment in the context of forest biomass. Three steam pretreatment conditions were applied to characterize the interactions between spruce (softwood) and poplar (hardwood) that were concurrently processed by SO2-catalyzed steam pretreatment and enzymatic hydrolysis. The effects of blending feedstocks were evaluated in terms of composition and enzymatic digestibility. The combined sugar yields after steam pretreatment and enzymatic hydrolysis ranged from 58% to 71%. No synergistic or antagonistic interactions were observed in the concurrent use of spruce and poplar—our linear interpolation model accurately predicted the overall sugar recovery after steam pretreatment and enzymatic hydrolysis for a 50:50 blend to within 3%, based on the results of the individual feedstocks.
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| 9. |
- Liu, Gangjin, et al.
(författare)
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Animal wastewater treatment with an improved combined Anaerobic-Aerobic System : Towards energy Self-Sufficiency
- 2022
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 323
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Tidskriftsartikel (refereegranskat)abstract
- A combined anaerobic–aerobic (CAO) system is a feasible animal wastewater treatment approach, and one of the prerequisites for its sustainable application is to realise energy self-sufficiency. Here, we built an energy balance model to calculate the probability of achieving energy self-sufficiency in three CAO systems with multiple uncertainties through Monte Carlo simulation. Upon comparison with the conventional combined anaerobic–aerobic (C-CAO) system and partial raw wastewater bypassed combined anaerobic–aerobic (PRB-CAO) system, the matters pre-captured combined anaerobic–aerobic (MPC-CAO) system displayed the highest probability (45.5%) and stability (with 10.9% coefficient of variation) in achieving energy self-sufficiency with the uniformly distributed input parameters. The uncontrollable factor of ambient temperature mainly contributed to the CAO system's net energy production among all input parameters. However, operating with the optimal control parameters of anaerobic digestion temperature (approximately 20 °C for C-CAO and PRB-CAO systems, 25–35 °C for MPC-CAO system) and organic loading rate (OLR) (50% of simulated maximum OLR) reduced the ambient temperature effect, thereby increasing the probability of energy self-sufficiency. And increasing the organic capture efficiency further reduced the effect of ambient temperature on net energy production of the MPC-CAO system. In addition, the probability of achieving energy self-sufficiency in the MPC-CAO system was more than 80%, with 30–50% of nitrogen captured simultaneously with organic matter and the direct use of anaerobic digestate (e.g., as fertilizer). These findings indicate that capturing more matter and increasing the capture efficiency is highly conducive for achieving energy self-sufficiency in CAO systems. Meanwhile, Monte Carlo simulation efficiently locates the key factors determining the CAO system's energy production performance from the different levels of uncertainty of multi-parameters, which is demonstrated as a time saving method for further system evaluation, design and upgrade. However, additional factors such as capital investment, social and environmental impacts should also be further considered for increasing the robustness of energy balance simulation model and providing a comprehensive assessment of CAO system for animal wastewater treatment.
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| 10. |
- Liu, Gangjin, et al.
(författare)
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Impact of atmospheric pressure variations on aerobic biodegradation test
- 2023
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Ingår i: Waste Management and Research. - 0734-242X. ; 41:10, s. 1559-1569
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Tidskriftsartikel (refereegranskat)abstract
- Biodegradation rate is an important index to evaluate the environmental risk of chemicals, which is usually determined by measuring oxygen consumption through respirometer in a biodegradation test. However, atmospheric pressure variations affect reactor oxygen concentration and oxygen volume recorded by respirometer in biodegradation test, and the parameters of reactor volume and test material amount amplify its effect. Atmospheric pressure variation >1 kPa could introduce >20% underestimation in biodegradation rate when a small amount of test material (0.04–0.2 g per 100 g of inoculum) and high reactor volume (2–4 L) were used according to the international standards. A 5 kPa drop in atmospheric pressure leads to a 6% decrease in headspace oxygen concentration in the reactor, which could subsequently inhibit biodegradation microbials and decrease the biodegradation rate by 30%. Moreover, the biodegradation process (oxygen consumption rate) could be accelerated/delayed several times by atmospheric pressure variations compared to the process without variations when the oxygen consumption rate was <5 mL h−1 in a 0.5 or 1 L reactor and <10 mL h−1 in a 2-L reactor. Mitigating the effects of atmospheric pressure variations on biodegradation test includes lowering the reactor volume, increasing the test material amount and recording atmospheric pressure for further modification.
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