| 1. |
- Attié, David, et al.
(author)
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A time projection chamber with GEM-based readout
- 2017
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In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 856, s. 109-118
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Journal article (peer-reviewed)abstract
- For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1. T solenoidal field and read out with three independent Gas Electron Multiplier (GEM) based readout modules, are reported. The TPC was exposed to a 6. GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.
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| 2. |
- Cavka, Adnan, et al.
(author)
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Identification of Small Aliphatic Aldehydes in Pretreated Lignocellulosic Feedstocks and Evaluation of Their Inhibitory Effects on Yeast
- 2015
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In: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 63:44, s. 9747-9754
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Journal article (peer-reviewed)abstract
- Six lignocellulosic hydrolysates produced through acid pretreatment were analyzed for the occurrence of formaldehyde, acetaldehyde, and glycolaldehyde. Acetaldehyde was found in all six (0.3-1.6 mM) and formaldehyde in four (<= 4.4 mM), whereas glycolaldehyde was not detected. To assess the relevance of these findings, fermentations with yeast and formaldehyde or acetaldehyde were performed in the concentration interval 0.5-10 mM. Formaldehyde already inhibited at 1.0 mM, whereas 5.0 mM acetaldehyde was needed to obtain a clear inhibitory effect. After 24 h of fermentation, 1.5 mM formaldehyde reduced the glucose consumption by 85%, the balanced ethanol yield by 92%, and the volumetric productivity by 91%. The results show that formaldehyde and acetaldehyde are prevalent in pretreated lignocellulose and that formaldehyde in some cases could explain a large part of the inhibitory effects on yeast by lignocellulosic hydrolysates, as three of six hydrolysates contained >= 1.9 mM formaldehyde, which was shown to be strongly inhibitory.
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| 3. |
- Cavka, Adnan, et al.
(author)
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Ozone detoxification of steam-pretreated Norway spruce
- 2015
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In: Biotechnology for Biofuels. - : BioMed Central. - 1754-6834 .- 1754-6834. ; 8
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Journal article (peer-reviewed)abstract
- Background: Pretreatment of lignocellulose for biochemical conversion commonly results in formation of by-products that inhibit microorganisms and cellulolytic enzymes. To make bioconversion processes more efficient, inhibition problems can be alleviated through conditioning. Ozone is currently commercially employed in pulp and paper production for bleaching, as it offers the desirable capability to disrupt unsaturated bonds in lignin through an ionic reaction known as ozonolysis. Ozonolysis is more selective towards lignin than cellulose, for instance, when compared to other oxidative treatment methods, such as Fenton's reagent. Ozone may thus have desirable properties for conditioning of pretreated lignocellulose without concomitant degradation of cellulose or sugars. Ozone treatment of SO2- impregnated steam-pretreated Norway spruce was explored as a potential approach to decrease inhibition of yeast and cellulolytic enzymes. This novel approach was furthermore compared to some of the most effective methods for conditioning of pretreated lignocellulose, i.e., treatment with alkali and sodium dithionite. Results: Low dosages of ozone decreased the total contents of phenolics to about half of the initial value and improved the fermentability. Increasing ozone dosages led to almost proportional increase in the contents of total acids, including formic acid, which ultimately led to poor fermentability at higher ozone dosages. The decrease of the contents of furfural and 5-hydroxymethylfurfural was inversely proportional (R-2 > 0.99) to the duration of the ozone treatment, but exhibited no connection with the fermentability. Ozone detoxification was compared with other detoxification methods and was superior to treatment with Fenton's reagent, which exhibited no positive effect on fermentability. However, ozone detoxification was less efficient than treatment with alkali or sodium dithionite. High ozone dosages decreased the inhibition of cellulolytic enzymes as the glucose yield was improved with 13 % compared to that of an untreated control. Conclusions: Low dosages of ozone were beneficial for the fermentation of steam-pretreated Norway spruce, while high dosages decreased the inhibition of cellulolytic enzymes by soluble components in the pretreatment liquid. While clearly of interest for conditioning of lignocellulosic hydrolysates, future challenges include finding conditions that provide beneficial effects both with regard to enzymatic saccharification and microbial fermentation.
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| 4. |
- Cavka, Adnan, et al.
(author)
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Techno-economic evaluation of conditioning with sodium sulfite for bioethanol production from softwood
- 2015
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In: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 196, s. 129-135
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Journal article (peer-reviewed)abstract
- Conditioning with reducing agents allows alleviation of inhibition of biocatalytic processes by toxic by-products generated during biomass pretreatment, without necessitating the introduction of a separate process step. In this work, conditioning of steam-pretreated spruce with sodium sulfite made it possible to lower the yeast and enzyme dosages in simultaneous saccharification and fermentation (SSF) to 1 g/L and 5 FPU/g WIS, respectively. Techno-economic evaluation indicates that the cost of sodium sulfite can be offset by benefits resulting from a reduction of either the yeast load by 0.68 g/L or the enzyme load by 1 FPU/g WIS. As those thresholds were surpassed, inclusion of conditioning can be justified. Another potential benefit results from shortening the SSF time, which would allow reducing the bioreactor volume and result in capital savings. Sodium sulfite conditioning emerges as an opportunity to lower the financial uncertainty and compensate the overall investment risk for commercializing a softwood-to-ethanol process. (C) 2015 The Authors. Published by Elsevier Ltd.
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| 5. |
- Chen, Genqiang, et al.
(author)
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Bioconversion of waste fiber sludge to bacterial nanocellulose and use for reinforcement of CTMP paper sheets
- 2017
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In: Polymers. - : MDPI AG. - 2073-4360. ; 9:9
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Journal article (peer-reviewed)abstract
- Utilization of bacterial nanocellulose (BNC) for large-scale applications is restricted by low productivity in static cultures and by the high cost of the medium. Fiber sludge, a waste stream from pulp and paper mills, was enzymatically hydrolyzed to sugar, which was used for the production of BNC by the submerged cultivation of Komagataeibacter xylinus. Compared with a synthetic glucose-based medium, the productivity of purified BNC from the fiber sludge hydrolysate using shake-flasks was enhanced from 0.11 to 0.17 g/(L × d), although the average viscometric degree of polymerization (DPv) decreased from 6760 to 6050. The cultivation conditions used in stirred-tank reactors (STRs), including the stirring speed, the airflow, and the pH, were also investigated. Using STRs, the BNC productivity in fiber-sludge medium was increased to 0.32 g/(L × d) and the DPv was increased to 6650. BNC produced from the fiber sludge hydrolysate was used as an additive in papermaking based on the chemithermomechanical pulp (CTMP) of birch. The introduction of BNC resulted in a significant enhancement of the mechanical strength of the paper sheets. With 10% (w/w) BNC in the CTMP/BNC mixture, the tear resistance was enhanced by 140%. SEM images showed that the BNC cross-linked and covered the surface of the CTMP fibers, resulting in enhanced mechanical strength.
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| 6. |
- Chen, Genqiang, et al.
(author)
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Comparison of productivity and quality of bacterial nanocellulose synthesized using culture media based on seven sugars from biomass
- 2019
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In: Microbial Biotechnology. - : John Wiley & Sons. - 1751-7907 .- 1751-7915. ; 12:4, s. 677-687
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Journal article (peer-reviewed)abstract
- Komagataeibacter xylinus ATCC 23770 was statically cultivated in eight culture media based on different carbon sources, viz. seven biomass‐derived sugars and one sugar mixture. The productivity and quality of the bacterial nanocellulose (BNC) produced in the different media were compared. Highest volumetric productivity, yield on consumed sugar, viscometric degree of polymerization (DPv, 4350–4400) and thermal stability were achieved using media based on glucose or maltose. Growth in media based on xylose, mannose or galactose resulted in lower volumetric productivity and DPv, but in larger fibril diameter and higher crystallinity (76–78%). Growth in medium based on a synthetic sugar mixture resembling the composition of a lignocellulosic hydrolysate promoted BNC productivity and yield, but decreased fibril diameter, DPv, crystallinity and thermal stability. This work shows that volumetric productivity, yield and properties of BNC are highly affected by the carbon source, and indicates how industrially relevant sugar mixtures would affect these characteristics.
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| 7. |
- Chen, Genqiang, et al.
(author)
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Performance of nanocellulose-producing bacterial strains in static and agitated cultures with different starting pH
- 2019
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 215, s. 280-288
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Journal article (peer-reviewed)abstract
- The impact of strain selection and culture conditions on bacterial nanocellulose (BNC) productivity and quality was investigated by using four strains, static and agitated cultures, and an initial pH in the range 4-6. With agitation, strain DHU-ATCC-1 displayed highest productivity [1.14 g/(L x d)]. In static cultures, DHU-ZGD-1186 exhibited superior BNC yield on consumed glucose (0.79 g/g), and lowest by-product formation with respect to gluconic acids [<= 0.07 g/(L x d)]. By-product formation typically decreased in the order gluconic acid > 2-keto-gluconic acid > 5-keto-gluconic acid, and was lowest in cultures with high initial pH. The BNC from DHU-ZGD-1186 exhibited higher average viscometric degree of polymerization (DPv), higher crystallinity index, and higher tear index. In conclusion, both strain selection and cultivation conditions had an impact on BNC productivity and properties. Productivity, DPv, crystallinity, and mechanical strength of BNC from agitated cultures could be similar to or even higher than the corresponding values for static cultures.
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| 8. |
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| 9. |
- Chen, Genqiang, et al.
(author)
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Scale-up of production of bacterial nanocellulose using submerged cultivation
- 2018
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In: Journal of chemical technology and biotechnology (1986). - : Wiley. - 0268-2575 .- 1097-4660. ; 93:12, s. 3418-3427
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Journal article (peer-reviewed)abstract
- BACKGROUND: More extensive utilization of bacterial nanocellulose (BNC) is severely restricted by the low efficiency and small scale of the traditional static cultivation. Submerged fermentation in stirred-tank reactors (STRs) is potentially favourable for large-scale production of BNC, but scale-up of cultivation remains challenging. Even though the STR is most commonly used for submerged cultivation in the fermentation industry, there are few previous attempts to scale-up production of BNC to pilot scale using an STR. Furthermore, the question of how scale-up of submerged cultivation affects the properties of the BNC has received very little attention. RESULTS: Four strains were compared in 250-mL shake flasks. Strain DHU-ATCC-1 displayed the highest volumetric productivity, 0.56 g L−1 d−1, and was then cultivated in a 400-mL STR, showing a similar productivity of 0.55 g L−1 d−1. Scale-up using a 75-L STR pilot bioreactor resulted in enhancement of the BNC production rate from 0.056 g d−1 in the shake flasks to 17.3 g d−1 in the 75-L STR, although the productivity decreased to 0.43 g L−1 d−1. During scale-up from shake flasks to 400-mL STR and further on to 75-L STR, the BNC fibers formed more bundles, whereas the fiber diameter decreased from 25.6 to 21.7 nm. The BNC from the 75-L STR exhibited a higher degree of polymerization, specifically 3230, higher degree of crystallinity, specifically 83%, larger crystallites, and improved strength including higher tensile energy absorption index and superior stretch at break. CONCLUSION: It is possible to enhance BNC production, and maintain or improve its properties when scaling up submerged cultivation in STRs.
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| 10. |
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