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- Talebnia, Farid
(author)
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Ethanol Production from Cellulosic Biomass by Encapsulated Saccharomyces cerevisiae
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Unstable oil markets with rising environmental concerns have revived widespread interest in production of fuel ethanol from renewable materials. Cellulosic materials are abundant and prominent feedstocks for cheap ethanol production. However, due to recalcitrant structure of these materials, pretreatment is a prerequisite. Depending on the biomass, pretreatment and hydrolysis conditions, a number of degradation products and/or toxic components may be released that show strong inhibitory effects on the fermenting microorganisms. This thesis deals with application of encapsulation technology to ferment the highly toxic hydrolyzates without further pretreatment. Free cells could not tolerate presence of 5 g/l furfural in defined medium, and inhibitors in wood and peel hydrolyzates in batch mode of operation and fermentation failed. Continuous cultivation of wood hydrolyzate was only successful at 0.1 h−1 and the majority of cells lost their viability after 5 retention times. Encapsulated cell system could successfully ferment the synthetic medium containing 5 g/l furfural during sequential batch cultivations with ethanol yield of 0.41-0.42 g/g. Cultivation of undetoxified hydrolyzates was also carried out, where glucose and mannose were converted within 10 h without significant lag phase. However, a gradual decrease in cell activity was observed in sequential batches. Continuous cultivation was more successful, and wood hydrolyzate was fermented to ethanol by encapsulated S. cerevisiae at dilution rates up to 0.5 h−1. More than 75% of the encapsulated cells were viable in the worst conditions. Ethanol was produced with yield 0.44 g/g and specific productivity 0.14–0.17 g/g•h at all dilution rates. Contrary to wood hydrolyzate, where there is no preference for permeation of sugars or inhibitors through the capsules’ membrane, encapsulation technology was applied to eliminate inhibition of limonene in fermentation of orange wastes to ethanol. The capsules’ membrane, of hydrophilic nature, is practically impermeable to hydrophobic compounds such as limonene while allowing penetration of nutrients and products. While presence of 0.1% v/v limonene in the medium results in strong inhibition or even failure of cultivation with free cells, using this technique allowed fermentation of a medium containing 1.5% v/v limonene. The impact of encapsulation on the anaerobic growth pattern, morphological and physiological changes of S. cerevisiae over long-term application was investigated. The growth rate, total RNA and protein content of the encapsulated cells decreased gradually over repeated batch cultivations, while stored carbohydrates content increased. Within 20 batch cultivations, total RNA and protein content of encapsulated cells decreased by 39% and 24%, whereas glycogen and trehalose content increased by factors of 4.5 and 4, respectively.
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| 2. |
- Talebnia Rowshan, Farid, 1974, et al.
(author)
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Ethanol production from glucose and dilute-acid hydrolyzates by encapsulated S-cerevisiae
- 2005
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In: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 90:3, s. 345-353
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Journal article (peer-reviewed)abstract
- The performance of encapsulated Saccharomyces cerevisiae CBS 8066 in anaerobic cultivation of glucose, in the presence and absence of furfural as well as in dilute-acid hydrolyzates, was investigated. The cultivation of encapsulated cells in 10 sequential batches in synthetic media resulted in linear increase of biomass up to 106 g/L of capsule volume, while the ethanol productivity remained constant at 5.15 (+/- 0.17) g/L(.)h (for batches 6-10). The cells had average ethanol and glycerol yields of 0.464 and 0.056 g/g in these 10 batches. Addition of 5 g/L furfural decreased the ethanol productivity to a value of 1.31 (+/- 0.10) g/L(.)h with the encapsulated cells, but it was stable in this range for five consecutive batches. On the other hand, the furfural decreased the ethanol yield to 0.41-0.42 g/g and increased the yield of acetic acid drastically up to 0.068 g/g. No significant lag phase was observed in any of these experiments. The encapsulated cells were also used to cultivate two different types of dilute-acid hydrolyzates. While the free cells were not able to ferment the hydrolyzates within at least 24 h, the encapsulated yeast successfully converted glucose and mannose in both of the hydrolyzates in less than 10 h with no significant lag phase. However, since the hydrolyzates were too toxic, the encapsulated cells lost their activity gradually in sequential batches. (c) 2005 Wiley Periodicals, Inc.
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| 3. |
- Talebnia Rowshan, Farid, 1974, et al.
(author)
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In situ detoxification and continuous cultivation of dilute-acid hydrolyzate to ethanol by encapsulated S. cerevisiae
- 2006
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In: Journal of Biotechnology. - : Elsevier. - 0168-1656 .- 1873-4863. ; 125:3, s. 377-384
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Journal article (peer-reviewed)abstract
- Dilute-acid lignocellulosic hydrolyzate was successfully fermented to ethanol by encapsulated Saccharomyces cerevisiae at dilution rates up to 0.5 h-1. The hydrolyzate was so toxic that freely suspended yeast cells could ferment it continuously just up to dilution rate 0.1 h-1, where the cells lost 75% of their viability measured by colony forming unit (CFU). However, encapsulation increased their capacity for in situ detoxification of the hydrolyzate and protected the cells against the inhibitors present in the hydrolyzate. While the cells were encapsulated, they could successfully ferment the hydrolyzate at tested dilution rates 0.1-0.5 h-1, and keep more than 75% cell viability in the worst conditions. They produced ethanol with yield 0.44 ± 0.01 g/g and specific productivity 0.14-0.17 g/(g h) at all dilution rates. Glycerol was the main by-product of the cultivations, which yielded 0.039-0.052 g/g. HMF present in the hydrolyzate was converted 48-71% by the encapsulated yeast, while furfural was totally converted at dilution rates 0.1 and 0.2 h-1 and partly at the higher rates. Continuous cultivation of encapsulated yeast was also investigated on glucose in synthetic medium up to dilution rate 1.0 h-1. At this highest rate, ethanol and glycerol were also the major products with yields 0.43 and 0.076 g/g, respectively. The experiments lasted for 18-21 days, and no damage in the capsules was detected.
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| 4. |
- Talebnia Rowshan, Farid, 1974, et al.
(author)
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Physiological and morphological study of encapsulated Saccharomyces cerevisiae
- 2007
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In: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 41:6-7, s. 683-688
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Journal article (peer-reviewed)abstract
- The impact of encapsulation on the anaerobic growth pattern of S. cerevisiae CBS 8066 in a defined synthetic medium over 20 consecutive batch cultivations was investigated. In this period, the ethanol yield increased from 0.43 to 0.46 g/g, while the biomass and glycerol yields decreased by 5 8 and 23%, respectively. The growth rate of the encapsulated cells in the first batch was 0.13 h(-1), but decreased gradually to 0.01 h(-1) within the 20 sequential batch cultivations. Total RNA content of these yeast cells decreased by 39% from 90.3 to 55 mg/g, while the total protein content decreased by 24% from 460 to 350 mg/g. On the other hand, the stored carbohydrates, that is, glycogen and trehalose content, increased by factors of 4.5 and 4 within 20 batch cultivations, respectively. Higher biomass concentrations inside capsules led to a lower glucose diffusion rate through the membrane, and volumetric mass transfer coefficient for glucose was drastically decreased from 6.28 to 1.24 (cm(3)/min) by continuing the experiments. Most of the encapsulated yeast existed in the form of single and non-budding cells after long-term application. (C) 2007 Elsevier Inc. All rights reserved.
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