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- Johnsson, Ola, et al.
(författare)
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A novel feeding strategy for industrial fed-batch processes based on frequency content analysis
- 2012
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Ingår i: New Biotechnology. - : Elsevier BV. - 1876-4347 .- 1871-6784. ; 29:Supplement, s. 11-11
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Konferensbidrag (refereegranskat)abstract
- Overflow metabolism, i.e. the production of metabolic by-products at a high glycolytic flux, is a recurring problem in fed-batch processes with many types of microorganisms. In the current study, a novel feeding strategy aimed at avoiding process failures due to overflow by-product formation was designed and implemented in a pilot-scale reactor (0.5 m3). The basic principle behind the strategy was to analyze the effects on the dissolved oxygen concentration by periodic variations in the inlet feed rate. The frequency spectrum of the dissolved oxygen signal was used to estimate the proximity of the system to the region where overflow metabolism occurs by examining the content in the relevant frequency range. A control variable based on the measured frequency content was subsequently used to control the feed rate. The only measurement required for this strategy is the dissolved oxygen level in the broth, for which robust, fast and precise probes are widely available in industrial fermentors today. The strategy was successfully implemented in pilot-scale processes for industrial enzyme production using Bacillus licheniformis. It was shown possible to run the process close to the optimal feed rate, indicated by very low amounts of acetate (the overflow metabolite) in the broth. In comparison to a reference strategy the new control strategy resulted in over 10% higher biomass yields.
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- Ishola, Mofoluwake M., et al.
(författare)
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Minimization of Bacterial Contamination with High Solid Loading during Ethanol Production from Lignocellulosic Materials
- 2014
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Ingår i: New Biotechnology. - : New Biotechnology. - 1871-6784.
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Konferensbidrag (refereegranskat)abstract
- Ethanol is the most important renewable fuel in the transportation sector. Its production from lignocellulosic materials, commonly referred to as second generation ethanol, is considered more attractive than production from starch and sugar crops. Bacterial contamination by lactic acid-producing bacteria is still a major problem during ethanol production processes. Bacteria compete with the yeast by consuming the sugars and the nutrients required by the yeast for efficient ethanol production. This often causes substantial economic losses at industrial fermentations. In this study, without any sterilization of the substrate, simultaneous saccharification and fermentation (SSF) was performed using cellulase Cellic® Ctec2 enzyme for hydrolysis and Baker’s yeast, Saccharomyces cerevisiae, was used as the fermenting organism with different loads of suspended solids - 8%, 10% and 12%. With8%and 10% SS, there was a significant contamination, which caused consumption of both hexoses pentose sugars in the fermentation medium, this resulted in lactic acid concentrations of 43 g/L and 36 g/L from 10% SS and 8% SS respectively. In contrast, only 2.9 g/L lactic acid was observed with 12% SS. An ethanol concentration of 47 g/L was produced from high solid loading of 12% SS while just 26 g/L and 23 g/L were produced from 10% and 8% SS respectively. Our results show that SSF with 12% SS has an increased concentration of inhibitors, particularly acetic acid which selectively inhibited the bacterial growth without affecting the metabolic activities of the yeast during the fermentation.
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