| 1. |
- Anasontzis, George E, 1980, et al.
(författare)
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Rice straw hydrolysis using secretomes from novel fungal isolates from Vietnam
- 2017
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 99, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- With a production of 39 million metric tons each year, rice is one of the main agricultural products of Vietnam. Thus, rice straw is a significant by-product, whose use in a biorefinery process would contribute to the bio-based transformation of the Vietnamese and South East Asian economy. In order to find novel efficient enzyme mixtures for the hydrolysis of rice straw and other agricultural residues, we took advantage of the rapidly evolving biodiversity of Vietnam and screened 1100 new fungal isolates from soil and decaying plant tissues for their CMCase activity. We selected 36 strains and evaluated them for their cellulases, xylanases, and accessory enzymes activities. Most of these isolates belonged to the genera Aspergillus and Trichoderma. We identified a few promising isolates, such as A. brunneoviolaceus FEC 156, A. niger FEC 130 and FEC 705, and A. tubingensis FEC 98, FEC 110 and FEC 644, whose produced enzyme mixtures released a mass fraction of the sugar content of alkali-treated rice straw higher than 20%, compared to 10% for Trichoderma reesei RUT C-30. We verified that the black Aspergilli are particularly efficient in their saccharification ability. We also identified strains that although they produced low amounts of cellulases and xylanases, their enzyme mixtures had high saccharification efficiencies, indicating the importance of the synergy effect, rather than the amount of enzymes available. Our results highlight the intra-species variation, especially in the Trichoderma genus, regarding the biomass degradation characteristics and the associated range of enzymatic activities.
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| 2. |
- Panagiotou, G., et al.
(författare)
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Studying the ability of Fusarium oxysporum and recombinant Saccharomyces cerevisiae to efficiently cooperate in decomposition and ethanolic fermentation of wheat straw
- 2011
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 35:8, s. 3727-3732
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Tidskriftsartikel (refereegranskat)abstract
- Fusarium oxysporum F3 alone or in mixed culture with Saccharomyces cerevisiae F12 were used to ferment carbohydrates of wet exploded pre-treated wheat straw (PWS) directly to ethanol. Both microorganisms were first grown aerobically to produce cell mass and thereafter fermented PWS to ethanol under anaerobic conditions. During fermentation, soluble and insoluble carbohydrates were hydrolysed by the lignocellulolytic system of F. oxysporum. Mixed substrate fermentation using PWS and corn cobs (CC) in the ratio 1:2 was used to obtain an enzyme mixture with high cellulolytic and hemicellulolytic activities. Under these conditions, activities as high as 34300, 9100, 326, 24, 169, 27 and 254 U dm(-3) of xylanase, endoglucanase, beta-glucosidase, arabinofuranosidase, avicelase, feruloyl esterase and acetyl esterase, respectively, were obtained. The replacement of the enzyme production phase of F. oxysporum by the addition of commercially available enzymes Celluclast (R) 1.5 L FG and Novozym (R) 188 in 3:1 ratio for the treatment of PWS, resulted in a 3-fold increase in the volumetric ethanol productivity without increasing the ethanol production significantly. By direct bioconversion of 110 kg m(-3) dry matter of PWS, ethanol concentration (4.9 kg m(-3)) and yield (40 g kg(-1) of PWS) were similarly obtained by F. oxysporum and the mixed culture, while productivity rates as high as 34 g m(-3) h(-1) and 108 g m(-3) h(-1) were obtained by F. oxysporum and the mixed culture, respectively.
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| 3. |
- Quintela, Cesar, et al.
(författare)
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Effect of pH in syngas conversion to C4 & C6 acids in mixed-culture trickle bed reactors
- 2024
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Ingår i: Biomass and Bioenergy. - 1873-2909 .- 0961-9534. ; 187
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Tidskriftsartikel (refereegranskat)abstract
- Syngas fermentation allows for the conversion of wastes into useful commodity chemicals. To target higher value products, the conditions can be tuned to be favourable for both acetogenic and reverse beta-oxidation pathways and produce, in one stage, butyric and caproic acid. Studies in CSTR have shown the crucial role of pH, which must be low enough to allow for ethanol generation in the acetogenic step while avoiding the inhibition of reverse β-oxidation in acidic conditions. However, no studies have investigated the effect of pH in reactor configurations suitable for syngas fermentation (i.e., allowing for cell retention and exhibiting high mass transfer rates at low operating costs), such as Trickle Bed Reactors, TBR. In this study, two TBR were used to study the pH effect on the fermentation of syngas to produce C4 and C6 acids, using undefined mixed cultures. Five pH values were tested in the range 4.5–7.5, and pH 6 was found to be the most favourable for simultaneous production of C4 & C6 acids from syngas, which agrees with what was found in suspended growth systems. In addition, the highest titers in literature so far were achieved in the TRB. 16S rRNA analysis was performed showing Clostridium and Rummenliibacillus to be the key genus for the efficient process at pH 6. Finally, the experimental methodology followed, and data collected proved the robustness of mixed culture biofilm reactors in respect to pH changes, as the same reactor performance and bacterial community were achieved regardless of the operation history.
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| 4. |
- Xiros, Charilaos, 1973, et al.
(författare)
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Comparison of strategies to overcome the inhibitory effects in high-gravity fermentation of lignocellulosic hydrolysates
- 2014
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 65, s. 79-90
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Tidskriftsartikel (refereegranskat)abstract
- High-gravity (HG) technology aims at generating final ethanol concentrations above 50 kg m(-3) in order to reduce the cost of the distillation step. The generation of higher amounts of inhibitors during the pretreatment step is one of the challenges that accompany the increase in initial dry matter. Detoxification of spruce hydrolysate, adaptation of the cells before fermentation, supplementation with nutrients, and washing of solids were the strategies compared in this study. They represent different approaches to cope with the inhibitory effects, and we compared their efficiencies using a thermotolerant strain of Saccharomyces cereuisiae at temperatures from 30 degrees C up to 40 degrees C. The dilute acid-pretreated spruce used as substrate in this study was not fermentable under HG conditions (200 g kg(-1) water-insoluble solids) when no improvement method was applied. In HG simultaneous saccharification and fermentation at 30 degrees C combined with a 24 h pre-hydrolysis step, the detoxification of pretreated spruce with reducing agent (Na2S2O4) gave the best result with an ethanol yield of 57% (on total sugars) of the maximum theoretical and a volumetric productivity of 1.58 g dm(-3) h(-1). In HG separate hydrolysis and fermentation, nutrients supplementation gave better final ethanol yields than detoxification of the material, reaching an ethanol yield of about 60% of the theoretical (on total sugars). The results obtained, showed an increase in severity of inhibitory effects with temperature increase. Improved cell viability was observed when detoxified material was used and also when yeast extract addition was coupled with adaptation of the cells to the hydrolysate. (C) 2014 Published by Elsevier Ltd.
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