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  • 1.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Noël, Maxime
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Aitomäki, Yvonne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Öman, Tommy
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Production potential of cellulose nanofibers from industrial residues: Efficiency and nanofiber characteristics2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 92, p. 84-92Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to evaluate the production potential of cellulose nanofibers from two different industrial bio-residues: wastes from the juice industry (carrot) and the beer brewing process (BSG). The mechanical separation of the cellulose nanofibers was by ultrafine grinding. X-ray diffraction (XRD) and Raman spectroscopy revealed that the materials were mechanically isolated without significantly affecting their crystallinity. The carrot residue was more easily bleached and consumed less energy during grinding, using only 0.9 kWh/kg compared to 21 kWh/kg for the BSG. The carrot residue also had a 10% higher yield than the BSG. Moreover, the dried nanofiber networks showed high mechanical properties, with an average modulus and strength of 12.9 GPa and 210 MPa, respectively, thus indicating a homogeneous nanosize distribution. The study showed that carrot residue has great potential for the industrial production of cellulose nanofibers due to its high quality, processing efficiency, and low raw material cost

  • 2.
    Hajlane, Abdelghani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kaddami, Hamid
    Laboratory of Organometallic and Macromolecular Chemistry-Composite Materials, Faculty of Sciences and Techniques, Cadi Ayyad University.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical modification of regenerated cellulose fibres by cellulose nano-crystals: Towards hierarchical structure for structural composites reinforcement2017In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 100, p. 41-50Article in journal (Refereed)
    Abstract [en]

    A simple and innovative new route, with less negative impact on the environment, for depositing and hope-grafting cellulose nano-crystals onto the surface of regenerated cellulose fibres (Cordenka 700 Super 3), using γ-methacryloxypropyltrimethoxysilane as coupling agent, is presented. Hierarchical cellulosic structure involving micro-scale fibres and nano-scale cellulose crystal network was created as verified by the scanning electron microscopy. The fibres were initially oxidised by optimized concentration of cerium ammonium nitrate to generate radicals on the cellulose backbone in order to polymerize the coupling agent at the surface. Infrared spectroscopy and scanning electron microscopy confirmed the chemical polymerisation of MPS onto regenerated cellulose fibres without enabling to show the chemical bonding between silane and nano-crystals. However, tensile test which was performed to study the impact of different treatments on mechanical properties of regenerated cellulose fibres, revealed that the modification by silane decreased the stiffness and strength of fibres (22% and 10% decrease, respectively) while the strain at failure was increased. These changes were attributed to the treatment conditions which may have induced the disorder and the misalignment of the structure of cellulose fibres (e.g. axial orientation of molecular chains and crystalline phase of the fibre has been reduced). This assumption is supported by the results from successive loading-unloading test of the fibre bundle. However, after depositing cellulose nano-crystals onto the fibre’s surface, the stiffness was recovered (20% increase in comparison to MPS treated fibres) while the strength and strain at failure remained at the same order of magnitude as for fibres treated only by the coupling agent.

  • 3.
    Jonoobi, Mehdi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Producing low-cost cellulose nanofiber from sludge as new source of raw materials2012In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 40, no 1, p. 232-238Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to isolate cellulose nanofibers by ultrafine grinding, from sludge (residue from dissolving cellulose production) and cellulose (dissolving cellulose) and to characterize their properties. The mechanical fibrillation was found to be more energy efficient at low rotor speed (1440) and was estimated to be 1.7 and 1.3 kWh/kg for cellulose (CF) and sludge fibers (SF), respectively. Sludge (SNF) and cellulose (CNF) nanofibers had diameter less than 100 nm, as measured from transmission electron microscopy images. The specific surface area ranged from approximately 84 to 112 m2/g for CNF and SNF respectively. The apparent networks density increased with fibrillation, being approximately 330 and 370 for CF and SF while 907 and 986 kg/m3 for the corresponding nanosized ones. The scanning electron microscopy (SEM) study exhibited considerably smoother surfaces for the nanofiber networks compared to microsized. Fibrillation to nanosized fibers had positive impact on modulus and strength of both raw materials and the improvement was more significant for sludge, indicating more efficient fibrillation. The study showed that the isolation of nanofibers from sludge could be considered an economic, energy efficient and viable alternative to generate value-added product from cellulose sludge while minimizing the sludge disposal issues.

  • 4.
    Korkut, Süleyman
    et al.
    Duzce University, Faculty of Forestry, Department of Forest Industrial Engineering.
    Korkut, Derya Sevim
    Department of Applied Sciences, University of Quebec at Chicoutimi.
    Kocaefe, Duygu
    Department of Applied Sciences, University of Quebec at Chicoutimi.
    Elustondo, Diego
    Bajraktari, Agron
    Prishtina University, Faculty of Technical Applied Sciences.
    çakicier, Nevzat
    Duzce University, Faculty of Forestry, Department of Forest Industrial Engineering.
    Effect of thermal modification on the properties of narrow-leaved ash and chestnut2012In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 35, no 1, p. 287-294Article in journal (Refereed)
    Abstract [en]

    The concept of thermal modification has evolved from a challenging research program to commercial reality in several European countries in recent years. The aim of this study is to determine the change of various physical properties (oven-dry density, air-dry density, weight loss, swelling and anti-swelling efficiency (ASE)), compression strength parallel to grain, colour difference (ΔE), glossiness and surface roughness of narrow-leaved ash (Fraxinus angustifolia Vahl.) and chestnut (Castanea sativa Mill.) woods after heat treatment under different temperatures and durations. For this study two different temperatures (160°C and 180°C) and two different durations (2h and 4h) were considered. A stylus method was employed to evaluate the surface characteristics of the samples. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Four main roughness parameters which are mean arithmetic deviation of profile (Ra), mean peak-to-valley height (Rz), root mean square roughness (Rq), and maximum roughness (Ry) obtained from the surface of wood were used to evaluate the effect of heat treatment on the surface characteristics of the specimens. The properties studied were significantly different (p=0.05) at two temperatures and two durations of heat treatment. Based on the findings of this study, the results showed that oven-dry density, air-dry density, swelling, compression strength parallel to grain and surface roughness decreases with increasing heat treatment temperature and time.

  • 5.
    Li, Muyang
    et al.
    Department of Biosystems & Agricultural Engineering, Michigan State University, East Lansing .
    Yan, Guilong
    School of Life Science, Huaiyin Normal University, Huaian, Jiangsu.
    Bhalla, Aditya
    DOE Great Lakes Bioenergy Research Center, Michigan State University.
    Maldonado-Pereira, Lisaura
    Department of Biosystems & Agricultural Engineering, Michigan State University, East Lansing .
    Russell, Petria R.
    Department of Chemical & Biological Engineering, Montana State University.
    Ding, Shi-You
    DOE Great Lakes Bioenergy Research Center, Michigan State University.
    Mullet, John E.
    DOE-Great Lakes Bioenergy Research Center, Michigan State University, East Lansing.
    Hodge, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Chemical & Biological Engineering, Montana State University, Bozeman, MT.
    Physical fractionation of sweet sorghum and forage/energy sorghum for optimal processing in a biorefinery2018In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 124, p. 607-616Article in journal (Refereed)
    Abstract [en]

    Sorghum offers enormous potential as a feedstock for the production of fuels and chemicals from both water-extractable sugars and the cell wall biopolymers, while its within-plant structural and compositional heterogeneity may allow for physical fractionations to tailor feedstock properties to a biorefining process. In this study, the stem internodes of two sorghum (Sorghum bicolor L. Moench) genotypes, a sweet sorghum (‘Della’) and a forage/energy sorghum (‘TX08001’), were first subjected to fractionation by manual classification by stem anatomy and internode proximity to the ground to yield 18 fractions. These fractions exhibited substantial differences in cell wall morphology, composition, and recalcitrance to mild alkaline pretreatment and enzymatic hydrolysis. While the sweet sorghum cultivar held nearly 70% more water-extractable sugar (sucrose, glucose, fructose, starch) in the stems than the forage/energy sorghum hybrid, both cultivars exhibited comparable diversity of composition and these compositions were remarkably similar in similar tissues and stem regions between the two cultivars. The fractions isolated from the pith parenchyma were the least recalcitrant to mild alkaline pretreatment and enzymatic hydrolysis and contained less lignin than fractions isolated from the epidermis, outer and inner rind, and internal vascular bundles. The pith samples isolated from the lowest region of the stem from both cultivars exhibited near-theoretical sugar hydrolysis yields when no pretreatment was employed and exhibited the lowest lignin contents of any of the fractions. Next, a physical fractionation approach approximating a commercial “de-pithing” process utilizing wet disintegration and sieving was applied to the forage/energy sorghum. A pith-rich fraction representing approximately 20% of the extractives-free mass of the stem could be isolated with this approach and, relative to the other fractions, was low in lignin, high in ash, highly hygroscopic, and showed an improved response to mild alkaline pretreatment and enzymatic hydrolysis at low enzyme loadings. Overall, these results demonstrate how heterogeneity within sorghum stems can be exploited using physical fractionation approaches to yield fractions enriched in desired properties that may allow for more streamlined processing.

  • 6.
    Mathew, Aji P.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Karim, Zoheb
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Liu, Peng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Khan, Saad Ahmad
    Naseri, Narges
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Process scale up and characterization of wood cellulose nanocrystals hydrolysed using bioethanol pilot plant2014In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 58, p. 212-219Article in journal (Refereed)
    Abstract [en]

    The paper discusses the isolation of cellulose nanocrystals (CNCBE) from wood resources by integrating the processing with pilot-scale bioethanol processing unit. The nanocrystals were isolated from cellulose obtained by acid pretreatment of wood chips in a bioethanol pilot-scale facility, followed by a series of chemical processes and subsequent homogenization using a lab-scale homogenizer. The isolated nanocrystals had diameters of 5-15 nm, cellulose I crystalline structure and formed a thick semi-transparent gel at low concentration (2 wt%). XPS data showed that these nanocrystals had predominantly O=C-O surface groups which also contributed to its high negative zeta potential. Casted CNCBE films showed excellent mechanical performance (200 MPa of strength, 16 GPa of modulus) and transparency and were also found to be cytocompatible. The developed process route resulted in high-quality nanocellulose crystals with a yield of 600 g/day.

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  • 7.
    Matsakas, Leonidas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Gerber, Milena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Yu, Liang
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Preparation of low carbon impact lignin nanoparticles with controllable size by using different strategies for particles recovery2020In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 147, article id 112243Article in journal (Refereed)
    Abstract [en]

    Lignin still remains an underutilized plentiful resource whose conversion to high-added value products is a cornerstone towards establishing a viable biomass biorefinery. Bio-materials in the form of nanoparticles represent promising high-value products with numerous downstream applications. The aim of the current work was to develop a method that would allow controlling the size of (birch and spruce) lignin nano- and micro-particles for their subsequent recovery into a solid product. We tested different two-step and one-step isolation processes and demonstrated that particle size could be easily controlled to meet different ranges (<100 nm, <500 nm, and>1 μm). In general, two-step isolation methods, i.e. a step of decrease of solvent concentration followed by isolation of lignin particles, were better for the isolation of well-defined spherical particles. In particular, the rate at which ethanol concentration was decreased played a significant role in determining the size of lignin particles. Moreover, when lignin concentration was increased from 1 % to 5 % and 10 % (w/v), particle size and homogeneity decreased slightly, but productivity augmented. The present study demonstrates that different isolation methods can be applied to obtain renewable, customarily sized, lignin spherical micro- and nano-particles.

  • 8.
    Matsakas, Leonidas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Sterioti, Aikaterini-Aithra
    Biotechnology Laboratory, School of Chemical Engineering, National Technical University of Athens.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Use of dried sweet sorghum for the efficient production of lipids by the yeast Lipomyces starkeyi CBS 18072014In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 62, p. 367-372Article in journal (Refereed)
    Abstract [en]

    The ability of the oleaginous yeast Lipomyces starkeyi to efficiently produce lipids when cultivated on saccharified sweet sorghum stalks juice was evaluated. Initially the production of lipids using synthetic media mimicking sweet sorghum stalks has been studied and optimized concerning the nitrogen source and the C:N ratio. Under optimum conditions (yeast extract as nitrogen source and C:N ratio of 190) the lipid production reached 5.81 g/L with a lipid content of 47.3% (w/w) from a mixture of sucrose, glucose and fructose, mimicking the sugar composition of sorghum. When cultivated on sweet sorghum stalks juice, it was observed that no external nitrogen addition was necessary which could result in substantial decrease of the initial C:N ratio. Moreover a distinct saccharification process prior to yeast cultivation improved the lipid production yield as it resulted in an increase of the C:N ratio. The highest lipid production, which was 6.40 g/L with a lipid content of 29.5% (w/w), was obtained when juice from saccharified sweet sorghum stalks at an initial sorghum content of 12% (w/w) was used as feedstock.

  • 9.
    Panagiotou, Gianni
    et al.
    National Technical University of Athens.
    Kekos, Dimitris
    National Technical University of Athens.
    Macris, Basil J.
    National Technical University of Athens.
    Christakopoulos, Paul
    Production of cellulolytic and xylanolytic enzymes by Fusarium oxysporum grown on corn stover in solid state fermentation2003In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 18, no 1, p. 35-47Article in journal (Refereed)
    Abstract [en]

    Corn stover is an abundant, potential fermentation substrate. Production of cellulolytic and xylanolytic enzymes by the mesophilic fungus Fusarium oxysporum under solid state culture (SSC) on corn stover was enhanced by optimization of the type of nitrogen source, initial moisture level, growth temperature and initial pH of the culture medium. Under these conditions, yields as high as 304, 4.1, 0.140, 1840 and 0.041 U/g of carbon source of endoglucanase, cellobiohydrolase, β-glucosidase, xylanase and β-xylosidase, respectively, were obtained. SCC in a laboratory horizontal bioreactor using the optimized medium allowed the large scale production of the multienzymic system in similar yields. Chromogenic (fluorogenic) 4-methylumbelliferyl β-glycosides of cellobiose and xylobiose were used to characterize the major activities of the multienzyme component, after separation by isoelectric focusing (IEF) electrophoresis. The zymograms indicated one major cellulase and four xylanase activities exhibiting pI values 5 and 5, 6, 7.3, 8.3, respectively.

  • 10.
    Paschos, Thomas
    et al.
    Biotechnology Laboratory, School of Chemical Engineering, National Technical University of Athens.
    Xiros, Charilaos
    National Technical University of Athens, Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Simultaneous saccharification and fermentation by co-cultures of Fusarium oxysporum and Saccharomyces cerevisiae enhances ethanol production from liquefied wheat straw at high solid content2015In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 76, p. 793-802Article in journal (Refereed)
    Abstract [en]

    A co-fermentation process involving Saccharomyces cerevisiae and Fusarium oxysporum was studied, using hydrothermally pretreated wheat straw as substrate. In the first step of the study, we examined liquefaction of the material in a free-fall reactor. Both the enzyme loading and the dry matter content affected severely the liquefaction efficiency. In the second step (simultaneous saccharification and fermentation (SSF) experiments), we found that the enzymatic system of F. oxysporum contributed significantly to substrate hydrolysis, while its metabolic system played a secondary role in fermentation. SSF in the presence of F. oxysporum cells and enzymes gave 62 g L−1 ethanol. In the third step of the study, a semi-consolidated bioprocess was designed in which F. oxysporum culture (submerged or solid-state) was added at the SSF stage along with S. cerevisiae. The addition of solid F. oxysporum culture increased ethanol production by 19%, leading to a final ethanol concentration of 58 g L−1. The present study proposes a semi-consolidated process combining two microorganisms for the fermentation at high solids concentration of a liquefied material using an in house free fall mixing reactor. The semi-consolidated process proposed not only increased the ethanol yields significantly, but could also lead to lower overall cost of the process by incorporating in-situ enzyme production.

  • 11.
    Salehpour, Shooboo
    et al.
    Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj.
    Rafieian, Fatemeh
    Food Science Department, Agriculture College, Isfahan University of Technology.
    Jonoobi, Mehdi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effects of molding temperature, pressure and time on polyvinyl alcohol nanocomposites properties produced by freeze drying technique2018In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 121, p. 1-9Article in journal (Refereed)
    Abstract [en]

    The main aim of this study was to develop a novel approach to incorporate high cellulose nanofiber (CNF) loadings into polyvinyl alcohol (PVA) nanocomposites. The nanocomposites were prepared by freezing via liquid nitrogen and consequent freeze drying combined with hot press molding. To investigate the effect of the molding parameters on the morphological, mechanical and thermal properties, chemical structure and transparency of the PVA + CNF nanocomposites, two different mold pressures, temperatures and holding times were used for fabrication of PVA + CNF nanocomposites. The maximum tensile strength of 121 MPa of the PVA + CNF 20% nanocomposites was obtained when they were molded at 130 °C and 50 kPa for 7 min. Dynamic mechanical analysis showed that the storage modulus of the composites prepared at 130 °C and 50 kPa for 7 min is about 20% higher than nanocomposites molded at 150 °C and 150 kPa for 10 min. Optical properties (absorption spectra) of the PVA and PVA + CNF nanocomposites were increased as the mold pressures, temperature and holding time increased. Micrographs showed more sough fracture surface with increasing pressure and temperature during hot press molding.

  • 12.
    Sarris, Dimitris
    et al.
    Agricultural University of Athens.
    Matsakas, Leonidas
    Agricultural University of Athens.
    Aggelis, George
    University of Patras.
    Koutinas, Apostolis
    Agricultural University of Athens.
    Papanikolaou, Seraphim
    Agricultural University of Athens.
    Aerated vs non-aerated conversions of molasses and olive mill wastewaters blends into bioethanol by Saccharomyces cerevisiae under non-aseptic conditions2014In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 56, p. 83-93Article in journal (Refereed)
    Abstract [en]

    The ability of Saccharomyces cerevisiae MAK-1 to convert blends of molasses and olive mill wastewaters (OMWs) into compounds of higher added-value under aerated and non-aerated conditions was studied in the current investigation. Noticeable decolorization (up to 60%) and moderate removal of phenolic compounds (up to 28%, w/w) was observed. Under aerated conditions in non-sterile shake-flask cultures, cultures in molasses-based media in which supplementation with OMWs had been performed did not significantly decrease ethanol and biomass production in comparison with control experiments (cultures in which no OMWs had been added). Ethanol of 34.3 g L−1 (with simultaneous yield of ethanol produced per sugar consumed of ∼0.40 g g−1) and biomass of 7.3 g L−1 (with yield of ∼0.08 g g−1) was observed. Under similar aerated bioreactor cultures, biomass production (up to 5.7 g L−1 with yield of biomass produced per sugar consumed of ∼0.07 g g−1) decreased while, on the other hand, ethanol biosynthesis was notably enhanced (up to 41.8 g L−1 with yield of ethanol produced of ∼0.49 g g−1 – value very close to the maximum theoretical one). Comparing non-sterile aerated with non-aerated bioreactor experiments, biomass production showed some slight increase and ethanol production slightly increased in the latter case. It is concluded that S. cerevisiae MAK-1 is a microorganism of importance amenable for simultaneous OMWs remediation and production of added-value compounds.

  • 13.
    Sjöblom, Magnus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Matsakas, Leonidas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Production of butyric acid by Clostridium tyrobutyricum (ATCC25755) using sweet sorghum stalks and beet molasses2015In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 74, p. 535-544Article in journal (Refereed)
    Abstract [en]

    Enzymatically liquefied sweet sorghum stalks and beet molasses were evaluated for butyrate production using Clostridium tyrobutyricum in 1 L scale fed-batch fermentations. The hydrolysates used for the fermentations were prepared separately by liquefying the sorghum stalks at 50 °C, pH 5.0 for 18 h, with 30% (w/v) DM content using the enzyme preparation Cellic® CTec2 at an activity of 26.5 FPU/g DM. To enhance sucrose consumption, the fermentations were supplemented with invertase at an activity equivalent to 8.3 U/g DM. With the hydrolysate as the feedstock, a butyrate concentration of 37.2 ± 0.8 g/L, a productivity of 0.86 ± 0.02 g/L h and a yield of 0.39 ± 0.02 g/g (p = 0.05) consumed sugars were obtained. Finally, a butyrate concentration of 58.8 g/L, a productivity of 1.9 g/L h, a butyrate yield of 0.52 g/g consumed sugars and a dry cell mass concentration of 15.7 g/L were obtained with fed-batch cultivation and a constant feed consisting of 64% sorghum hydrolysate juice and 36% molasses. Evidence for inducible saccharolytic activity was also proven, as the cellulase activity in the culture supernatant was found more than double during feed with limiting sugar concentrations. The present study clearly demonstrates that combinations of low cost raw materials can be used for efficient butyrate production, also without cell immobilization.

  • 14.
    Sjöblom, Magnus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Matsakas, Leonidas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Krige, Adolf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Direct electricity generation from sweet sorghum stalks and anaerobic sludge2017In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 108, p. 505-511Article in journal (Refereed)
    Abstract [en]

    Dried sweet sorghum stalks were valorized as a raw material for electricity generation in a two chamber microbial fuel cell using anaerobic sludge from a biogas plant as inoculum. The maximum voltage obtained on the sorghum stalks at an operating temperature of 35 °C was 546 mV with a maximum power- and current density of 131 mW/m2 and 543 mA/m2, respectively. The coulombic efficiency was 2.2%. Polarization data indicated that Ohmic resistances were dominant with an internal resistance of 182 Ω. The total electrical energy per gram of dried sorghum stalks was 165 J/g. Enzymatic treatment of the sorghum stalks did not improve the total electrical energy obtained. A metabolic study demonstrated that the sugars were quickly fermented to formate, acetate, propionate, lactate and butyrate with acetate and butyrate being the dominant acids during electricity generation

  • 15.
    Xiros, Charilaos
    et al.
    National Technical University of Athens.
    Topakas, Evangelos
    National Technical University of Athens.
    Katapodis, Petros
    National Technical University of Athens.
    Christakopoulos, Paul
    Evaluation of Fusarium oxysporum as an enzyme factory for the hydrolysis of brewer's spent grain with improved biodegradability for ethanol production2008In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 26, no 2, p. 213-224Article in journal (Refereed)
    Abstract [en]

    Brewer's spent grain (BG), the most abundant brewing by-product, is used in the present study as a low-cost feedstock for the production of ethanol by the mesophilic fungus Fusarium oxysporum using a consolidated bioconversion process. The production of required cellulolytic and hemicellulolytic enzymes was optimized under solid-state cultivation (SSC) concerning carbon source and initial moisture. The optimal medium contains BG and corn cobs (CC) in a ratio 7:3 while the optimal initial moisture is 66% (w/w). SSC in a laboratory horizontal bioreactor using the optimized medium allowed the large-scale production of a multienzymic system including endoglucanase, cellobiohydrolase, β-d-glucosidase, xylanase, feruloyl esterase, acetyl esterase, β-d-xylosidase and α-l-arabinofuranosidase. Chromogenic (fluorogenic) 4-methylumbelliferyl substrates were used to partially characterize the extracellular proteome of the microbe after the separation by isolectric focusing (IEF) electrophoresis. Alkali pretreatment of brewer's spent grain and different aeration levels were studied for the optimization of the ethanol production by F. oxysporum in a consecutive submerged fermentation. A yield about 65 g ethanol kg−1 of dry BG was obtained with alkali pretreated BG under microaerobic conditions (0.01 vvm) corresponding to 30% of the theoretical yield based on total glucose and xylose composition of BG.

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