COMPARISON OF VACUUM AND HIGH PRESSURE EVAPORATED WOOD HYDROLYZATE FOR ETHANOL PRODUCTION BY REPEATED FED-BATCH USING FLOCCULATING SACCHAROMYCES CEREVISIAE

With the aim of increasing the sugars concentration in dilute-acid ligno-cellulosic hydrolyzate to more than 100 g/l for industrial applications, the hydrolyzate from spruce was concentrated about threefold by high-pressure or vacuum evaporations. It was then fermented by repeated fed-batch cultivation using flocculating Saccharomyces cerevisiae with no prior detoxification. The sugars and inhibitors concentrations in the hydrolyzates were compared after the evaporations and also fermenta-tion. The evaporations were carried out either under vacuum (VEH) at 0.5 bar and 80°C or with 1.3 bar pressure (HPEH) at 107.5°C, which resulted in 153.3 and 164.6 g/l total sugars, respectively. No sugar decomposition occurred during either of the evaporations, while more than 96% of furfural and to a lesser extent formic and acetic acids disappeared from the hydrolyzates. However, HMF and levulinic acid remained in the hydrolyzates and were concentrated proportionally. The concentrated hydrolyzates were then fermented in a 4 l bioreactor with 12-22 g/l yeast and 0.14-0.22 h-1 initial dilute rates (ID). More than 84% of the fermentable sugars present in the VEH were fermented by fed-batch cultivation using 12 g/l yeast and initial dilution rate (ID) of 0.22 h-1, and resulted in 0.40±0.01 g/g ethanol from the fermentable sugars in one cycle of fermentation. Fermentation of HPEH was as successful as VEH and resulted in more than 86% of the sugar consumption under the corresponding conditions. By lowering the initial dilution rate to 0.14 h-1, more than 97% of the total fermentable sugars were consumed, and ethanol yield was 0.44±0.01 g/g in one cycle of fermentation. The yeast was able to convert or assimilate HMF, levulinic, acetic, and formic acids by 96, 30, 43, and 74%, respectively

Fermentation of undetoxified dilute acid lignocellulose hydrolysate for fuel ethanol production

Important aspects of ethanol production from undetoxified dilute acid lignocellulose hydrolysate are covered in this thesis, which primarily focuses on the use of Saccharomyces cerevisiae (Baker\u27s yeast) as the biocatalyst. Nine different strains of S. cerevisiae were compared for fermentation of dilute acid lignocellulose hydrolysate with batch and fed-batch methodology and the one found to be best, ATCC 96581, was used in further studies involving S. cerevisiae. Cultures of this strain could stay viable during extended continuous cultivations with low cell growth, achieved with cell recirculation, and consumed more than 99% of the available glucose. However, the ethanol yield was not significantly affected neither by excessive nitrogen limitation nor microaerobic conditions. Importantly, microaerobicity stabilised cell survival during these cumbersome conditions. Cell retention was also applied to ferment dilute acid lignocellulose hydrolysate in a continuous reactor, which increased the cell concentration and improved both the utilisation of hexoses and the intracellular conversion of at least one inhibitory compound in the hydrolysate (5-hydroxymethyl furfural). Cell retention by filtration, as a method to improve fermentation of lignocellulose hydrolysate supplemented with wheat hydrolysate, ammonium sulphate and biotin, was furthermore compared to alternative methods of cell retention: immobilisation and sedimentation. All cell retention methods were useful for improving hexose utilisation at a dilution rate of 0.10 h-1, but washout occurred in all systems except for the immobilised system when the dilution rate was increased to 0.20 h-1. In a study on M. indicus, an \u27alternative\u27 fermenting organism, which can ferment also pentoses, it was shown that this organism is suitable for fed-batch fermentation of dilute acid lignocellulose hydrolysate. With an initial dilution rate of 0.20 h-1, the sugar consumption and the ethanol yield were satisfactory. Moreover, the troublesome filamentous growth of M. indicus was circumvented

Fermentation of undetoxified dilute acid lignocellulose hydrolysate for fuel ethanol production

Important aspects of ethanol production from undetoxified dilute acid lignocellulose hydrolysate are covered in this thesis, which primarily focuses on the use of Saccharomyces cerevisiae (Baker\u27s yeast) as the biocatalyst. Nine different strains of S. cerevisiae were compared for fermentation of dilute acid lignocellulose hydrolysate with batch and fed-batch methodology and the one found to be best, ATCC 96581, was used in further studies involving S. cerevisiae. Cultures of this strain could stay viable during extended continuous cultivations with low cell growth, achieved with cell recirculation, and consumed more than 99% of the available glucose. However, the ethanol yield was not significantly affected neither by excessive nitrogen limitation nor microaerobic conditions. Importantly, microaerobicity stabilised cell survival during these cumbersome conditions. Cell retention was also applied to ferment dilute acid lignocellulose hydrolysate in a continuous reactor, which increased the cell concentration and improved both the utilisation of hexoses and the intracellular conversion of at least one inhibitory compound in the hydrolysate (5-hydroxymethyl furfural). Cell retention by filtration, as a method to improve fermentation of lignocellulose hydrolysate supplemented with wheat hydrolysate, ammonium sulphate and biotin, was furthermore compared to alternative methods of cell retention: immobilisation and sedimentation. All cell retention methods were useful for improving hexose utilisation at a dilution rate of 0.10 h-1, but washout occurred in all systems except for the immobilised system when the dilution rate was increased to 0.20 h-1. In a study on M. indicus, an \u27alternative\u27 fermenting organism, which can ferment also pentoses, it was shown that this organism is suitable for fed-batch fermentation of dilute acid lignocellulose hydrolysate. With an initial dilution rate of 0.20 h-1, the sugar consumption and the ethanol yield were satisfactory. Moreover, the troublesome filamentous growth of M. indicus was circumvented

Influence of cultivation procedure for Saccharomyces cerevisiae used as pitching agent in industrial spent sulphite liquor fermentations

The cell viability and fermentation performance often deteriorate in fermentations of spent sulphite liquor (SSL). This investigation therefore addresses the question of how different cultivation conditions for yeast cells influence their ability to survive and boost the ethanol production capacity in an SSL-based fermentation process. The strains used as pitching agents were an industrially harvested Saccharomyces cerevisiae and commercial dry baker\u27s yeast. This study therefore suggests that exposure to SSL in combination with nutrients, prior to the fermentation step, is crucial for the performance of the yeast. Supplying 0.5 g/l fresh yeast cultivated under appropriate cultivation conditions may increase ethanol concentration more than 200%

The impact of severe nitrogen limitation and microaerobic conditions on extended continuous cultivations of Saccharomyces cerevisiae with cell recirculation

Continuous cultivations of Sacchaivinyces certvisiae ATCC 96581 with severe nitrogen limitation (C/N ratios 200 and 400g g(-1)) and cell recirculation were carried out under anaerobic and microaerobic conditions for more than 300h. With a dilution rate of 0.06 h(-1) and 90% recirculation in combination with an estimated 70% biomass sedimentation rate in the bleed flow, specific growth rates of 0.002-0.006 h(-1) were obtained. Under these conditions, ethanol yields of 0.46-0.48g g(-1) were achieved. The biomass yields on ATP were only 1.6-2.9gmol(-1), indicating metabolic uncoupling or high maintenance energy requirements. Viability levels, measured by FUNO staining and fluorescence microscopy, usually varied between 100 and 80%. However, under anaerobic conditions at C/N ratio 400, a reproducible drop to 25 % viability occurred between 250 and 300h of fermentation, after which the culture recovered again. Under anaerobic conditions, an increase in the C/N ratio from 200 to 400 resulted in a three-fold higher specific glycerol production, in spite of lower biomass formation and lower cellular protein and RNA content. A low oxygen addition eliminated the large drop in viability and the increased glycerol production observed at C/N 400, and caused viability and glycerol levels similar to the anaerobic C/N 200 case. A S. certvisiae W303-1A gpdI Delta gpd2 Delta mutant, completely deficient in glycerol production, could ferment a nitrogen-limited medium under RQ-controlled microaerobic conditions with an ethanol yield of 0.45 g g(-1), indicating that the increased glycerol production under nitrogen limitation is not necessary, as long as there is sufficient oxygen transferred to the culture. (c) 2006 Elsevier Inc. All fights reserved

Development and dissemination strategies for accelerating biogas production in Nigeria

Following the worsening energy crisis of unreliable electricity and unaffordable petroleum products coupled with the increase number of poverty-stricken people in Nigeria, the populace is desperately in need of cheap alternative energy supplies that will replace or complement the existing energy sources. Previous efforts by the government in tackling the challenge by citizenship sensitization of the need for introduction of biofuel into the country’s energy mix have not yielded the expected results because of a lack of sustained government effort. In light of the shortcomings, this study assesses the current potential of available biomass feedstock for biogas production in Nigeria, and further proposes appropriate biogas plants, depending on feedstock type and quantity, for the six geopolitical zones in Nigeria. Besides, the study proposes government-driven biogas development systems that could be effectively used to harness, using biogas technology, the estimated 270 TWh of potential electrical energy from 181 million tonnes of available biomass, in the advancement of electricity generation and consequent improvement of welfare in Nigeria.Sponsorship:Swedish Energy Agency, Sweden and Lagos State University, Nigeria</p

Fed-batch cultivation of Mucor indicus in dilute-acid lignocellulosic hydrolyzate for ethanol production

Mucor indicus fermented dilute-acid lignocellulosic hydrolyzates to ethanol in fed-batch cultivation with complete hexose utilization and partial uptake of xylose. The fungus was tolerant to the inhibitors present in the hydrolyzates. It grew in media containing furfural (1 g/l), hydroxymethylfurfural (1 g/l), vanillin (1 g/l), or acetic acid (7 g/l), but did not germinate directly in the hydrolyzate. However, with fed-batch methodology, after initial growth of M. indicus in 500 ml enzymatic wheat hydrolyzate, lignocellulosic hydrolyzate was fermented with feeding rates 55 and 100 ml/h. The fungus consumed more than 46% of the initial xylose, while less than half of this xylose was excreted in the form of xylitol. The ethanol yield was 0.43 g/g total consumed sugar, and reached the maximum concentration of 19.6 g ethanol/l at the end of feeding phase. Filamentous growth, which is regarded as the main obstacle to large-scale cultivation of M. indicus, was avoided in the fed-batch experiments