A rapid and internally consistent technique has been developed to measure the volumetric oxygen transfer coefficient, k~a , i n fermentation systems. The method consists of tracing the dissolved 0 2 concentration of the fermentation broth during a short interruption of the aeration. The O2 concentration trace thus obtained can be analyzed to determine the values of k~a . Additional experiments on prolonged 0 2 starvation, carried out to find the limitation of the technique, suggest that 0 2 uptake rate will vary if a prolonged 12-10 min.) 0 2 starvation occurs.
Initially the concern on scale‐up of fermentation processes was with oxygen transfer. Strain stability on scale‐up was thought to be sufficiently established by serial transfer in shake flasks where conditions were homogeneous. Unfortunately, we now know that there are often mixing problems in large‐scale fermentors. The conditions within the vessel can be highly non‐homogeneous even on a macro‐scale. These non‐homogeneous variations include temperature, dissolved oxygen, and fluid shear. Such variations can cause strain degredation and failure of a strain to perform satisfactorily over long fermentation times in large‐scale vessels. Also, the highly mutated industrial strains often have hidden auxotrophy that only may be exposed in non‐homogeneous conditions. For this reason scale‐up is still an art not an exact science. We need to learn how to achieve better mixing in large‐scale fermentors.
Four key cellular metabolic fluorophores--tryptophan, pyridoxine, NAD(P)H, and riboflavin--were monitored on-line by a multiple excitation fluorometric system (MEFS) and a modified SLM 8000C scanning spectrofluorometer in three model yeast fermentation systems--bakers' yeast growing on glucose, Candida utilis growing on ethanol, and Saccharomyces cerevisiae RTY110/pRB58 growing on glucose. The measured fluorescence signals were compared with cell concentration, protein concentration, and cellular activity. The results indicate that the behavior and fluorescence intensity of various fluorophores differ in the various fermentation systems. Tryptophan fluorescence is the best signal for the monitoring of cell concentration in bakers' yeast and C. utilis fermentations. Pyridoxine fluoresce is the best signal for the monitoring of cell concentration in the S. cerevisiae RTY110/pRB58 fermentation. In bakers' yeast fermentations the pyridoxine fluorescence signal can be used to monitor cellular activity. The NAD(P)H fluorescence signal is a good indicator of cellular activity in the C. utilis fermentation. For this fermentation NAD(P)H fluorescence can be used to control ethanol feeding in a fed-batch process.
The purpose of this work was to determine the effect of surface aeration on scaleup procedures based on maintaining a constant volumetric oxygen transfer coefficient, (Klo). Oxygen mass transfer rates were measured both with and without air-sparging
The energy requirements associated with conventional mechanical size reduction of poplar and aspen wood are compared to a new method of size reduction employing a wood planer. Although the planer requires about 2.3 times less energy to achieve the same size reduction as conventional methods, large-scale equipment to implement this approach does not currently exist. Explosive depressurization was also compared to conventional mechanical size reduction. The conventional mechanical methods require roughly 70% more energy to achieve the same size reduction as explosive depressurization. Thus, explosive depressurization appears to be the preferred method and has the added benefit of altering the chemical structure of the wood to enhance the enzymatic hydrolysis of the cellulose fraction.
A new fluorescent bioreactor monitoring probe-multiple excitation fluorometric system (MEFS)-has been developed. This probe was compared to the commercially available BioChem Technology FluroMeasure system (NADH probe). In this task the fluorescence behavior of three model fermentation systems, ethanol fermentation by Candida utilis, phenol fermentation by Pseudomonas putida, and glucose fermentation by Saccharomyces cerevisiae, were examined. The results indicated that the fluorescence intensity and behavior of various cellular fluorophors vary significantly between the different fermentation systems. Monitoring a fermentation process using only NAD(P)H fluorescence provided limited information. The NAD(P)H fluorescence was found not to be the best fluorescence signal for monitoring cell concentrations. The best way of monitoring a bioreactor by fluorometry may be to monitor several fluorophors in the whole culture broth simultaneously and to relate these fluorescence signals to various biological parameters.
SummaryWhen two organisms compete for a given substrate without preying on one another, the possible steady states depend on the relative disposition of the two growth curves and the position of the point (Z,O), whose coordinates are the nutrient feed concentration and dilution rate. It is shown how the stability of each steady state can be understood and qualitative phase portraits can be drawn for each of the 31 distinct types of situations.
EQUATIONS FOR A SYSTEM OF TWO ORGANISMSTwo organisms, whose concentrat.ions are denoted by Xl and Xz, respectively, are growing in a chemostat on a common substrate whose concentration is S. If the dilution rate is D we may, following the generally accepted notation used by Yang and Humphrey,' write the balance equation asHere Y l and Yz are the yield coefficients and SR is the feed concentration of nutrient. The specific growth rates pl and pz take the form : Pj = Pj,rnax(l + Ksj/S + S/Krj)-' j = 1, 2 (4) 1375
The use of alcohollwaterlcatalyst mixtures to delignify wood allows the lignin to be recovered in a usable form while leaving the carbohydrate fraction relatively intact. The effects of temperature, reaction time, and the type of solvent and catalyst on the delignification of milled poplar wood were investigated. The lignin, cellulose, and hemicellulose composition of the pretreated material was measured for each treatment condition. In addition, the pretreated samples were subjected to enzymatic hydrolysis using the cellulases produced by the thermophilic bacterium Thermomonospora sp. YX. The extent of enzymatic hydrolysis was characterized using an empirical model, and the results were used to examine the effectiveness of the pretreatment.
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