Effects of furfural on ethanol fermentation bySaccharomyces cerevisiae: Mathematical models

Different inocula with high yeast concentration were investigated as a means of overcoming the inhibitory effect of furfural in ethanol fermentation. In order to verify the toxicity of the furfural, a series of fermentation runs were made with 0.25, 5.50, and 9.00 g/L (dry weight) ofSaccharomyces cerevisiae inoculum and 1, 3, and 5 g/L of furfural. The extent of cell death occurring in the early phase of fermentation was dependent on the initial cell concentration. With high initial yeast concentration, the effect of furfural is canceled, because it is depleted at an early stage of fermentation. The ethanol weight yield averaged 0.45 on the basis of sugar consumed. The ethanol productivity and specific growth rate decreased with the increase of furfural concentration, and the inhibitory effect almost disappeared with high cell concentration (9 g/L). Mathematical models were developed that relate productivity and growth rate with furfural and cell concentration.     

流加发酵对重组Bacillus subtilis发酵生产角质酶的影响

为实现基因工程菌Bacillus subtilis WSHB06-07生产角质酶的高产,在3L发酵罐中考察了不同初糖浓度对菌体生长和产酶的影响,并在选择38 g/L初始蔗糖浓度的基础上,进行碳源的分批流加和恒速流加,结果表明发酵16 h开始流加碳源,采用总补糖量60g/L,蔗糖平均流速为4g/(L·h)的恒速补料方式,角质酶酶活在31h可达到最大545.87U/ml,比分批发酵酶活提高67.8%,并获得较高的角质酶生产强度,满足工业化生产要求。     

Use of response surface method for the determination of demineralization efficiency in fermented shrimp shells

A Box-Behnken design with three variables (sucrose concentration, initial pH value and soaking time) and three levels were used for studying the demineralization efficiency in fermented shrimp shells by Pediococcus sp. L1/2. First, the bacterial cells were inoculated into the media with various concentrations of sucrose and initial pH values, and fermentation took place under static conditions at 37 degrees C for 24h. Significant differences in the levels of total titratable acid were observed. This was followed by adding shrimp shells and soaking them in the fermentation media for 12, 24 and 36 h. The results showed that when the sucrose concentration was 50 g/L, and the initial pH value was 6.00, soaking for 36 h gave a demineralization efficiency of 68.38%. By solving the equation and also analyzing the response surface contour plots, optimum conditions occurred when the sucrose concentration was 50 g/L, the initial pH value was 7.00 and the soaking time was 36 h with a predicted value of demineralization of 83.03% whereas our experiment gave 83.47%.     

Systematic simulation of a tubular recycle reactor on the basis of pilot plant experiments

Systematic simulation may decisively help in development and optimization of bioprocesses. By applying simulation techniques, optimal use can be made of experimental data, decreasing development costs and increasing the accuracy in predicting the behavior of an industrial scale plant.The procedure of the dialogue between simulation and experimental efforts will be exemplified in a case study. Alcoholic fermentation of glucose by zymomonas mobilis bacteria in a gasified tubular recycle reactor was studied first by systematic simulation, using a computer model based solely on literature data. On the base of the results of this simulation, a 0.013 m³ pilot plant reactor was constructed. The pilot plant experiments, too, were based on the results of the systematic simulation.Simulated and experimental data were well in agreement. The pilot plant experiments reiterated the trends and limits of the process as shown by the simulation results. Data from the pilot plant runs were then used to improve the simulation model. This improved model was subsequently used to simulate the performances of an industrial scale plant. The results of this simulation are presented. They show that the alcohol fermentation in a tubular recycle reactor is potentially advantageous to other reactor configurations, especially to continuous stirred tanks.List of Symbols CPFR Continous plug flow reactor - CST R Continous stirred tank reactor - CTR Continous tubular reactor - FMC Fermentation micro computer - P kg/m³ Product concentration - S kg/m³ Glucose concentration - S _o kg/m³ Glucose concentration in the feed - X kg/m³ Biomass concentration - z Cell damage     

Kissiris: A mineral support for the promotion of ethanol fermentation by Saccharomyces cerevisiae

Ethanol production using Saccharomyces cerevisiae, promoted by the mineral kissiris, is reported on. A three-fold increase of ethanol productivity in the fermentation of molasses was achieved. An ethanol yield factor 0.43 g/g and conversion of 93.3% at an initial sugar concentration (ISC) 208.5 g/l were obtained in the presence of this mineral in molasses fermentation, compared to 0.21 g/g and 44.2% in its absence. It is also shown that the fermentation of molasses takes place even at relatively higher ethanol levels, with kissiris contributing to a 35% reduction of the energy demand in grade-fuel and potable ethanol production. The proposed mineral was shown to have a smaller effect in fermentations carried out in synthetic media containing glucose or saccharose.     

A bioethanol process development unit: initial operating experiences and results with a corn fiber feedstock

Interest in bioethanol production from lignocellulosic feedstocks for use as an alternative fuel is increasing, but near-term commercialization will require a low cost feedstock. One such feedstock, corn fiber, was tested in the US Department of Energy (DOE)/National Renewable Energy Laboratory (NREL) bioethanol pilot plant for the purpose of testing integrated equipment operation and generating performance data. During initial runs in 1995, the plant was operated for two runs lasting 10 and 15 days each and utilized unit operations for feedstock handling, pretreatment by dilute sulfuric-acid hydrolysis, yeast inoculum production, and simultaneous saccharification and fermentation using a commercially available cellulase enzyme. Although significant operational problems were encountered, as would be expected with the startup of any new plant, operating experience was gained and preliminary data were generated on corn fiber pretreatment and subsequent fermentation of the pretreated material. Bacterial contamination was a significant problem during these fermentations.     

Oxalic acid production by Aspergillus niger

Aspergillus niger is able to produce a quite high concentration of oxalic acid using sucrose as carbon and energy source. Operating at pH higher than 6 and an enriched N and P medium is necessary in order to conduct the fermentation towards oxalic acid production. A pH?shift technique, operating at acid pH?in the first two days and then setting pH?to 6, allowed the productivity to slightly increase in shaking flasks cultures up to 3.0?kg/m³?·?d, with a final oxalic acid concentration of 29?kg/m³. When operating at more controlled conditions, in a stirred tank, both productivity and oxalic acid concentration were improved (4.1?kg/m³?·?d and 33.8?kg/m³, respectively). However the main drawback of this fermentation is the low yield attained (about 0.3?kg oxalic acid/kg sucrose) because most of glucose, resulting from the hydrolysis of sucrose by the extracellular enzymes secreted at the beginning of the fermentation, is very quickly oxidised to gluconic acid, a process which is favoured at a pH?close to 6. Milk whey was proved to be a very good substrate as it allows oxalic acid to be produced with a similar productivity (2.5?kg/m³?·?d in shaking flasks) giving excellent yields of almost 0.6?kg oxalic acid/kg lactose.     

Enhanced Formation of β-Glucosidase by Aspergillus niger VKMF-2092 in Fed-Batch Operation with Frequently Intermittent Glucose Addition

The wild strain Aspergillus niger VKMF-2092 forms β-glucosidase on the basis of glucose as the sole carbon source. The formation of β-glucosidase is initiated after the glucose concentration in the medium has reached a low level since the formation is subjected to catabolite repression. The β-glucosidase is mainly cell-bound and only released after a longer period. Under non-repressed conditions the total formation of β-glucosidase is not associated with growth. By supplying glucose in a fed-batch-technique, maintaining a low actual glucose concentration in the medium, the formation of β-glucosidase is enhanced in comparison to simple batch fermentation. Using a fed-batch-technique with a frequently intermittent addition of glucose it is possible to increase the formation of β-glucosidase with regard to both productivity and the activity related to the mycelium and the fermentation broth as well. The increase of productivity is about two to four times greater than at constant feed rate of the same overall amount of glucose. The reason for this increase will be discussed below. A method is presented which permits to investigate the influence of the substrate concentration and other parameters on the enzyme formation in short periods of one and the same fermentation run.     

Influence of sucrose concentration and phosphate limitation on citric acid production by immobilized cells of Aspergillus niger

Summary Immobilized cells of Aspergillus niger needed a lower initial sucrose concentration than free cells in order to obtain maximal yields of citric acid production. High sucrose concentrations led to reduced yields and increased polyol formation (glycerol, erythritol, arabitol). Continuous fermentation with media containing low sugar concentrations prevented the formation of polyols. The change from nitrogen-limited to phosphate-limited precultivation of immobilized spores significantly increased the productivity of the mycelium. The ratio of citric acid to residual sugar in the effluent distinctly lay in the direction of citric acid. Inside the alginate beads mainly large bulbous cells were observed.     

Increase of xylitol production rate by controlling redox potential in Candida parapsilosis

The effect of redox potential on xylitol production by Candida parapsilosis was investigated. The redox potential was found to be useful for monitoring the dissolved oxygen (DO) level in culture media, especially when the DO level was low. An increase in the agitation speed in a 5 L fermentor resulted in an increased culture redox potential as well as enhanced cell growth. Production of xylitol was maximized at a redox potential of 100 mV. As the initial cell concentration increased from 8 g/L to 30 g/L, the volumetric productivity of xylitol increased from 1.38 g/L. h to 4.62 g/L. h. A two-stage xylitol production strategy was devised, with stage 1 involving rapid production of cells under well-aerated conditions, and stage 2 involving cultivation with reduced aeration such that the culture redox potential was 100 mV. Using this technique, a final xylitol concentration of 180 g/L was obtained from a culture medium totally containing 254.5 g/L xylose in a 3,000 L pilot scale fermentor after 77 h fermentation. The volumetric productivity of xylitol during the fermentation was 2.34 g/L. h.     

Effects of glycerol on alcohol fermentation. Inhibition mechanism and diffusion limitations

Batch alcohol fermentations have been carried out varying the starting level of glycerol in the broth and keeping constant all the other fermentation parameters, in order to study the effect of the accumulation of this metabolite on the fermentation kinetics. A linear slow decrease of the maximum specific ethanol productivity with increasing glycerol level has been followed by a sharp fall of this parameter over a glycerol concentration threshold. A kinetic study through unstructured integrated models demonstrates that, at low concentrations, glycerol behaves as a non competitive inhibitor of fermentation, while, over a concentration threshold (105 kg/m³), an additional effect takes place, likely ascribable to diffusion limitations provoked by excess viscosity of the broth.     

Unsteady-state operation of continuous fermentor for enhancement of cell mass production

The transient behavior of continuous fermentation is studied concentrating on the time scale intrinsic to the system. The time scale is the time required for the fermentorto reach a stable steady state after the disturbance of cell mass is introduced. When the cell concentration is disturbed from the steady-state value, in particular, at the dilution rate near washout, the transient period becomes extended significantly, and the steady state is resumed sluggishly. This sluggish transient behavior could be turned to an advantage for enhancing the cell mass output rate. The proposed transient operation is a continuous fermentation whereby a positive disturbance in the cell mass is introduced, so that the cell concentration is higher than the steady-state value for an extended transient period. It is shown that a significantly higher cell mass production than that from the steady-state continuous fermentation can be achieved. Simple experiments were performed to demonstrate the improvement of cell (Candida utilis) productivity.     

Optimization of an industrial microalgae fermentation

Optimization of cellular productivity of an industrial microalgae fermentation was investigated. The fermentation was carried out at Coors Biotech Products Company, Fort Collins, Colorado. A mathematical model was developed based on the data collected from pilot plant test runs at different operating conditions. Pontryagin's maximum principle was used for determining the optimal feed policy. A feedback control algorithm was also studied for maximizing the cellular productivity. During continuous operation, the optimum dilution rate was determined by an adaptive optimization scheme based on the steepest descent technique and a recursive least squares estimation of model parameters. A direct search algorithm was also applied to determine the optimum feed rate. Comparison of the theoretical results of the different optimization schemes revealed that the direct search algorithm was preferable because of its simplicity. The experimental results of real time application of the feedback algorithm agreed fairly well with those of the theoretical analyses. (c) 1994 John Wiley & Sons, Inc.     

Pilot-scale semisolid fermentation of straw.

Semisolid fermentation of ryegrass straw to increase its animal feed value was successfully performed on a pilot scale. The pilot plant, which could handle 100 kg of straw per batch, was designed so that all major operations could take place in one vessel. The straw was hydrolyzed at 121 degrees C for 30 min with 0.5 N H2SO4 (7:3 liquid:solid), treated with ammonia to raise the pH to 5.0, inoculated with Candida utilis, and fermented in a semisolid state (70% moisture). During fermentation the straw was held stationary with air blown up through it. Batch fermentation times were 12 to 29 h. Semisolid fermentation did not require agitation and supported abundant growth at 20 to 40 degrees C even at near zero oxygen tensions. Fermentation increased the protein content, crude fat content, and in vitro rumen digestibility of the straw.     

Pilot-scale semisolid fermentation of straw

Semisolid fermentation of ryegrass straw to increase its animal feed value was successfully performed on a pilot scale. The pilot plant, which could handle 100 kg of straw per batch, was designed so that all major operations could take place in one vessel. The straw was hydrolyzed at 121 degrees C for 30 min with 0.5 N H2SO4 (7:3 liquid:solid), treated with ammonia to raise the pH to 5.0, inoculated with Candida utilis, and fermented in a semisolid state (70% moisture). During fermentation the straw was held stationary with air blown up through it. Batch fermentation times were 12 to 29 h. Semisolid fermentation did not require agitation and supported abundant growth at 20 to 40 degrees C even at near zero oxygen tensions. Fermentation increased the protein content, crude fat content, and in vitro rumen digestibility of the straw.     

Influence of alginate properties and gel reinforcement on fermentation characteristics of immobilized yeast cells

The effect of alginate composition, gel concentration, gelation method, cell loading and surface area on fermentation characteristics of immobilized yeast cells have been investigated. Molecular weight and G/M ratio had only little effect on fermentation velocity and gel strength, while increasing the alginate concentration caused a sizeable decrease in fermentation velocity and an increase in gel strength. The internally gelled immobilizates generally showed a higher fermentation velocity for the same gel strength and no decrease in gel strength was seen during fermentation. With high initial cell loadings, the fermentation velocity per g of immobilizate was higher, but the productivity per cell was lower than with low initial cell loadings. The difference decreased with time. Specific surface area (surface/volume) was shown to be an important factor for the observed productivity per gram of immobilizate, with high S/V ratios giving the highest productivity. Gel shape had no influence on fermentation velocity for a given S/V ratio. Gelation behaviour of externally gelled beads was determined by estimating the amount of cells liberated during gel formation through measurement of invertase activity (yeast-bound) in the gelling solution. A method for reinforcement of internally gelled alginate slabs with a nylon mesh was developed and utilized for production of a continuous fermentation reactor with reinforced gels.     

Recent vegetation changes at the high‐latitude tree line ecotone are controlled by geomorphological disturbance,productivity and diversity

Aim We test how productivity, disturbance rate, plant functional composition and species richness gradients control changes in the composition of high‐latitude vegetation during recent climatic warming. Location Northern Fennoscandia, Europe. Methods We resampled tree line ecotone vegetation sites sampled 26 years earlier. To quantify compositional changes, we used generalized linear models to test relationships between compositional changes and environmental gradients. Results Compositional changes in species abundances are positively related to the normalized difference vegetation index (NDVI)‐based estimate of productivity gradient and to geomorphological disturbance. Competitive species in fertile sites show the greatest changes in abundance, opposed to negligible changes in infertile sites. Change in species richness is negatively related to initial richness, whereas geomorphological disturbance has positive effects on change in richness. Few lowland species have moved towards higher elevations. Main conclusions The sensitivity of vegetation to climate change depends on a complex interplay between productivity, physical and biotic disturbances, plant functional composition and richness. Our results suggest that vegetation on productive sites, such as herb‐rich deciduous forests at low altitudes, is more sensitive to climate warming than alpine tundra vegetation where grazing may have strong buffering effects. Geomorphological disturbance promotes vegetation change under climatic warming, whereas high diversity has a stabilizing effect.     

Influence of experimental soil disturbances on the diversity of plants in agricultural grasslands

Aims and Methods Disturbance is supposed to play an important role for biodiversity and ecosystem stability as described by the intermediate disturbance hypothesis (IDH), which predicts highest species richness at intermediate levels of disturbances. In this study, we tested the effects of artificial soil disturbances on diversity of annual and perennial vascular plants and bryophytes in a field experiment in 86 agricultural grasslands differing in land use in two regions of Germany. On each grassland, we implemented four treatments: three treatments differing in application time of soil disturbances and one control. One year after experimental disturbance, we recorded vegetation and measured biomass productivity and bare ground. We analysed the disturbance response taking effects of region and land-use-accompanied disturbance regimes into account.Important findings Region and land-use type strongly determined plant species richness. Experimental disturbances had small positive effects on the species richness of annuals, but none on perennials or bryophytes. Bare ground was positively related to species richness of bryophytes. However, exceeding the creation of 12% bare ground further disturbance had a detrimental effect on bryophyte species richness, which corresponds to the IDH. As biomass productivity was unaffected by disturbance our results indicate that the disturbance effect on species richness of annuals was not due to decreased overall productivity, but rather due to short-term lowered inter- and intraspecific competition at the newly created microsites. Generally, our results highlight the importance of soil disturbances for species richness of annual plants and bryophytes in agricultural grasslands. However, most grasslands were disturbed naturally or by land-use practices and our additional experimental soil disturbances only had a small short-term effect. Overall, total plant diversity in grasslands seemed to be more limited by the availability of propagules rather than by suitable microsites for germination. Thus, nature conservation efforts to increase grassland diversity should focus on overcoming propagule limitation, for instance by additional sowing of seeds, while the creation of additional open patches by disturbance might only be appropriate where natural disturbances are scarce.     

An assessment of seed quality and its influence on productivity estimation in an industrial antibiotic fermentation

This study investigates the benefits of including seed quality information into data-based models for final productivity estimation in an industrial antibiotic fermentation process. Multiway principal component analysis is applied to assess the seed quality using routinely gathered plant data. Multiway partial least-squares regression is then used to estimate the final productivity using data from the main fermentation only. The issue of selecting appropriate process variables as inputs is investigated. Subsequently, seed characteristics are included into the estimation models to assess the benefits of including information from this stage for productivity estimation. It is shown that it is possible to extract seed fermentation features related to the final productivity both at pilot and production scales. It is postulated that significant influential variations are mirrored in monitored variables during the main fermentation, and therefore seed quality is implicitly accounted for.     

Regional productivity mediates the effects of grazing disturbance on plant cover and patch‐size distribution in arid and semi‐arid communities

Patch‐size distribution and plant cover are strongly associated to arid ecosystem functioning and may be a warning signal for the onset of desertification under changes in disturbance regimes. However, the interaction between regional productivity level and human‐induced disturbance regime as drivers for vegetation structure and dynamics remain poorly studied. We studied grazing disturbance effects on plant cover and patchiness in three plant communities located along a regional productivity gradient in Patagonia (Argentina): a semi‐desert (low‐productivity community), a shrub‐grass steppe (intermediate‐productivity community) and a grass steppe (high‐productivity community). We sampled paddocks with different sheep grazing pressure (continuous disturbance gradients) in all three communities. In each paddock, the presence or absence of perennial vegetation was recorded every 10 cm along a 50 m transect. Grazing effects on vegetation structure depended on the community and its association to the regional productivity. Grazing decreased total plant cover while increasing both the frequency of small patches and the inter‐patch distance in all communities. However, the size of these effects was the greatest in the high‐productivity community. Dominant species responses to grazing explained vegetation patch‐ and inter‐patch‐size distribution patterns. As productivity decreases, dominant species showed a higher degree of grazing resistance, probably because traits of species adapted to high aridity allow them to resist herbivore disturbance. In conclusion, our findings suggest that regional productivity mediates grazing disturbance impacts on vegetation mosaic. The changes within the same range of grazing pressure have higher effects on communities found in environments with higher productivity, markedly promoting their desertification. Understanding the complex interactions between environmental aridity and human‐induced disturbances is a key aspect for maintaining patchiness structure and dynamics, which has important implications for drylands management.