Claes Niklasson - Academia.edu (original) (raw)

Papers by Claes Niklasson

Bioresources, Aug 15, 2008

The fungus Mucor indicus is able to produce ethanol from xylose as well as dilute-acid lignocellu... more The fungus Mucor indicus is able to produce ethanol from xylose as well as dilute-acid lignocellulosic hydrolyzates. The fungus completely assimilated 10 g/L xylose as the sole carbon and energy source within 32 to 65 h at an aeration rate of 0.1 to 1.0 vvm. The highest ethanol yield was 0.16 g/g at 0.1 vvm. Xylitol was formed intermediately with a maximum yield of 0.22 g/g at 0.5 vvm, but disappeared towards the end of experiments. During cultivation in a mixture of xylose and glucose, the fungus did not assimilate xylose as long as glucose was present in the medium. The anaerobic cultivation of the fungus in the hydrolyzate containing 20% xylose and 80% hexoses resulted in no assimilation of xylose but complete consumption of the hexoses in less than 15 h. The ethanol yield was 0.44 g/g. However, the xylose in the hydrolyzate was consumed when the media was aerated at 0.067 to 0.333 vvm. The best ethanol yield was 0.44 g/g at 0.067 vvm. The results of this study suggest that M. indicus hydrolyzate can be first fermented anaerobically for hexose assimilation and subsequently continued under oxygenlimited conditions for xylose fermentation.

Int J Engrg Education, 2005

has undergone a major curriculum reform. One of the driving motives behind the reform was that st... more has undergone a major curriculum reform. One of the driving motives behind the reform was that students should learn to use mathematics as a real tool for solving chemical problems. Mathematicians and chemists, with pedagogical help from an educational expert, changed the traditional course structure in terms of organization, content, and teaching and learning methods. This paper concentrates on the use of MATLAB in laboratory work and in individual and group assignments. It deals, in particular, with the pedagogical benefits that the designers of the new course saw in presenting real chemical problems that could be solved using applied mathematics and the MATLAB software. Student experience was evaluated both by the teachers and the educational consultant and responses are largely positive. Increased student learning can be seen through higher motivation and synergy effects of treating chemical problems in the MATLAB tutorials. The most serious problem is to give all students the necessary MATLAB skills and a risk is an overestimation of the MATLAB proficiency in subsequent courses leading to disproportional workloads on projects and little time for reading and study.

Mathematics that is taught at all engineering universities in Sweden and other countries has not ... more Mathematics that is taught at all engineering universities in Sweden and other countries has not been changed for a very long time. With the shift toward greater use of mathematical numerical tools in many engineering subjects, the content and manner of teaching in mathematics are undergoing profound changes. Since the mathematics often is taught early in a curriculum, it is of interest to investigate how the learning in mathematics will have an effect on the learning in chemistry and chemical engineering subjects. In the present work we discuss how changes in mathematics education might influence the way of teaching and learning for the following subjects in the chemical engineering programme at Chalmers. Furthermore, some thoughts are provided on how the changed mathematical knowledge and skills among students and also integration in the engineering subjects might affect and help in a deeper learning approach in particular chemical engineering subjects, such as fundamental chemistry, chemical reaction engineering and bioprocess engineering which are important subjects within the different Programs at the school of chemical engineering.

Thermochimica Acta, Oct 1, 2002

Product concentrations may be estimated from gas analysis or calorimetric measurements. These tec... more Product concentrations may be estimated from gas analysis or calorimetric measurements. These techniques of analysis are fast, simple, and provide a continuous output. To check the accuracy of these estimations, the anaerobic ethanol formation of an industrial strain of the yeast ...

Journal of Bioscience and Bioengineering, 1999

The effect of furfural on aerobic and anaerobic batch cultures of Saccharomyces cerevisiae CBS 80... more The effect of furfural on aerobic and anaerobic batch cultures of Saccharomyces cerevisiae CBS 8066 growing on glucose was investigated. Furfural was found to decrease both the specific growth rate and ethanol production rate after pulse additions in both anaerobic and aerobic batch cultures. The specific growth rate remained low until the furfural had been completely consumed, and then increased somewhat, but not to the initial value. The CO2 evolution rate decreased to about 35% of the value before the addition of 4 g-1-l furfural, in both aerobic and anaerobic fermentations. The decrease of the CO2 evolution rate was rapid at first, and then a more gradual decrease was observed. The furfural was converted mainly to furfuryl alcohol, with a specific conversion rate of 0.6 ( f 0.03) g (furfural) -g-l (biomass)-h-l by exponentially growing cells. However, the conversion rate of furfural by cells in the stationary phase was much lower. A previously unidentified compound was detected during the conversion of furfural. This compound was characterized by mass spectrometry and it is suggested that it is formed from furfural and pyruvate.

Yeast, 2000

The yeast Saccharomyces cerevisiae produces large amounts of glycerol as an osmoregulator during ... more The yeast Saccharomyces cerevisiae produces large amounts of glycerol as an osmoregulator during hyperosmotic stress and as a redox sink at low oxygen availability. NAD + -dependent glycerol-3-phosphate dehydrogenase in S. cerevisiae is present in two isoforms, coded for by two different genes, GPD1 and GPD2. Mutants for either one or both of these genes were investigated under carefully controlled static and dynamic conditions in continuous cultures at low oxygen transfer rates. Our results show that S. cerevisiae controls the production of glycerol in response to hypoxic conditions by regulating the expression of several genes. At high demand for NADH reoxidation, a strong induction was seen not only of the GPD2 gene, but also of GPP1, encoding one of the molecular forms of glycerol-3-phosphatase. Induction of the GPP1 gene appears to play a decisive role at elevated growth rates. At low demand for NADH reoxidation via glycerol formation, the GPD1, GPD2, GPP1, and GPP2 genes were all expressed at basal levels. The dynamics of the gene induction and the glycerol formation at low demand for NADH reoxidation point to an important role of the Gpd1p; deletion of the GPD1 gene strongly altered the expression patterns of the GPD2 and GPP1 genes under such conditions. Furthermore, our results indicate that GCY1 and DAK1, tentatively encoding glycerol dehydrogenase and dihydroxyacetone kinase, respectively, may be involved in the redox regulation of S. cerevisiae.

Industrial Engineering Chemistry Research, 1988

Thermo Chimica Acta, 2000

Microaerobic ethanol production by Saccharomyces cerevisiae CBS 8066 was investigated at differen... more Microaerobic ethanol production by Saccharomyces cerevisiae CBS 8066 was investigated at different growth rates in respiratory quotient (RQ)-controlled continuous culture. The RQ was controlled by changing the inlet gas composition by a feedback controller while keeping other parameters constant. The ethanol yield increased slightly from the anaerobic values with decreasing RQ, reaching a broad maximum at RQ 20 to 12. There was little or no glycerol production at RQ values below 17 over a wide range of dilution rates. Metabolic flux analysis revealed that a decrease in the ethanol yield at RQ 6 coincided with the cyclic, oxidative operation of the TCA cycle reactions. The model indicated that respiratory dissimilation of glucose only occurs when the oxygen uptake rate is high enough to completely substitute for glycerol formation. The cytosolic and the mitochondrial NADH balances were important for determining the flux distributions. The smallest deviations between estimated and measured product yields were obtained when the unknown co-factor requirements of a limited number of biosynthetic reactions were chosen so that the amount of excess NADH formed in biosynthesis was minimized. The biomass yield was positively correlated with the net amount of NADH reoxidized in respiration and glycerol formation, indicating that the turnover of excess NADH from biosynthesis is an important factor influencing the biomass yield under oxygen-limiting conditions.

Cellulose Chemistry and Technology, 2013

Applied Microbiology and Biotechnology, Aug 31, 1989

Batch growth of Saccharomyces cerevisiae was studied using a fluorescence probe as well as a micr... more Batch growth of Saccharomyces cerevisiae was studied using a fluorescence probe as well as a microcalorimeter. The biphasic growth pattern previously demonstrable by microcalorimetry was also seen using the fluorescence probe. Acid production rate changes in the transition phase could be detected by pH measurements. Qualitative similarities between calorimetric and fluorescence measurements are discussed.

Appl Biochem and Biotechnol, 1993

... ab 0.678 0.049 0.054 1.13 c 0.639 0.049 0.092 1.11 ac 0.574 0.069 0.090 1.03 bc 0.652 0.049 0... more ... ab 0.678 0.049 0.054 1.13 c 0.639 0.049 0.092 1.11 ac 0.574 0.069 0.090 1.03 bc 0.652 0.049 0.123 1.16 abc 0.587 0.059 0.081 1.03 bc* 0.639 0.039 0.093 1.10 abc* 0.639 0.069 0.043 1.08 * = Repeated experiments. "~xYx/s q'- "yEYE/s "F VxYL YxYL/S = VS (3) ...

Biotechnology and Bioengineering, 2005

... Talebnia, Farid, 1974-(author) Chalmers tekniska högskola, Institutionen för kemi-och biotekn... more ... Talebnia, Farid, 1974-(author) Chalmers tekniska högskola, Institutionen för kemi-och bioteknik Niklasson, Claes, 1957-(author) Chalmers tekniska högskola, Institutionen för kemi-och bioteknik Taherzadeh, Mohammad J., 1965-(author) Chalmers tekniska högskola ...

Minerva Biotecnologica, 2010

Mucor indicus was cultivated under aerobic and anaerobic conditions to study its tolerance agains... more Mucor indicus was cultivated under aerobic and anaerobic conditions to study its tolerance against high concentration of glucose up to 350 g/L and ethanol up to 120 g/L present in the medium. The fungus could grow well even in 350 g/L glucose and produce ethanol, but it was able to assimilate the entire glucose when its concentration was less than 200 g/L. On the other hand, M. indicus produced ethanol as the main product with yield and concentration up to 0.45 g/g and 73 g/L, respectively, while glycerol, its only major ...

Biomed Research International, 2014

Limonene is present in orange peel wastes and is known as an antimicrobial agent, which impedes b... more Limonene is present in orange peel wastes and is known as an antimicrobial agent, which impedes biogas production when digesting the peels. In this work, pretreatment of the peels to remove limonene under mild condition was proposed by leaching of limonene using hexane as solvent. The pretreatments were carried out with homogenized or chopped orange peel at 20-40 ∘ C with orange peel waste and hexane ratio (w/v) ranging from 1 : 2 to 1 : 12 for 10 to 300 min. The pretreated peels were then digested in batch reactors for 33 days. The highest biogas production was achieved by treating chopped orange peel waste and hexane ratio of 12 : 1 at 20 ∘ C for 10 min corresponding to more than threefold increase of biogas production from 0.061 to 0.217 m 3 methane/kg VS. The solvent recovery was 90% using vacuum filtration and needs further separation using evaporation. The hexane residue in the peel had a negative impact on biogas production as shown by 28.6% reduction of methane and lower methane production of pretreated orange peel waste in semicontinuous digestion system compared to that of untreated peel.