Bioreactors dilution rate

Index Entries ABE fermentation butanol Clostridium acetobutylicum fibrous bed bioreactor dilution rate. 

In the case of mcf-PHAs, Pseudomonas oleovorans was cultivated on octane with a volumetric PHA productivity of 1.06 g L h and PHA content of 63% in the second bioreactor. Dilution rates of D = 0.21 h in the first stage and 0.16 h in the second stage were reported to result in the highest PHA productivity [136]. 

Dilution rate 0.4 h"1 gives highest productivity, but 25% of the substrate remains unused. Dilution rate 0.3 h"Y gives better substrate utilisation but with reduced productivity. Both these dilution rates require minimum OTRs greater than the bioreactor can supply. This means that such biomass concentrations could not be produced in practice. 

Dilution rate is defined as the number of tank volume pass through per unit time, D = F/V. The residence time is defined as the tune required for one unit volume of reactor to be replaced by the flow rate, t = VIv. When feed is sterile, there is no cell entering the bioreactor, which means x0 = 0, the rate may be simplified and reduced to ... 

Fig. E.9.1. Substrate concentration versus dilution rate in a CSTR bioreactor.

The Monod rate model is valid for a CSTR bioreactor with maximum specific growth rate of 0.5 li 1 and K, 2 g-1. What would be a suitable dilution rate at steady-state condition, where there is no cell death if initial substrate concentration is 50g-l-1 and yield of biomass on substrate is 100%. 

At time t=212 h the continuous feeding was initiated at 5 L/d corresponding to a dilution rate of 0.45 d . Soon after continuous feeding started, a sharp increase in the viability was observed as a result of physically removing dead cells that had accumulated in the bioreactor. The viable cell density also increased as a result of the initiation of direct feeding. At time t 550 h a steady state appeared to have been reached as judged by the stability of the viable cell density and viability for a period of at least 4 days. Linardos et al. (1992) used the steady state measurements to analyze the dialyzed chemostat. Our objective here is to use the techniques developed in Chapter 7 to determine the specific monoclonal antibody production rate in the period 212 to 570 h where an oscillatory behavior of the MAb titer is observed and examine whether it differs from the value computed during the start-up phase. 

To run it under automated conditions, the bioreactor was equipped with two temperature sensors, two pH electrodes, a water level detector, a manometer and a computer-controlled electric valve. Control of key parameters (pH, temperature, dilution rates) has allowed to define the culture conditions producing maximal amounts of molecular hydrogen. 

Figure 2 show the schematic diagram of both heat exchanger and wastewater digester and the interconnection. As was mentioned in previous subsections, if the bioreactor and heat exchanger are separately operated (i.e., uncoupled system), then they do not exhibit oscillatory behavior for the nominal value of the parameter vector and any value of the dilution rate 0 < urr < u < 00. Now, since the bioreactor and the heat exchanger are coupled by the recycle streams and controlled by specific control laws, we need to re-write the models (1) and (3) under recycle and feedback. Figure 2 shows (a) the schematic... 

We explored the influence of dilution rate and pH in continuous cultures of Clostridium acetobutylicum. A 200-mL fibrous bed bioreactor was used to produce high cell density and butyrate concentrations at pH 5.4 and 35°C. By feeding glucose and butyrate as a cosubstrate, the fermentation was maintained in the solventogenesis phase, and the optimal butanol productivity of 4.6 g/(L h) and a yield of 0.42 g/g were obtained at a dilution rate of 0.9 h1 and pH 4.3. Compared to the conventional acetone-butanol-ethanol fermentation, the new fermentation process greatly improved butanol yield, making butanol production from corn an attractive alternative to ethanol fermentation. 

The present study on butanol fermentation has been focused primarily on the effects of pH and dilution rate (D) in continuous cultures of the mutant strain from C. acetobutylicum ATCC 55025. To overcome the problems of low productivity and yield of butanol, cell immobilization in a convoluted fibrous bed bioreactor (FBB) and feeding with dextrose and butyric acid as cosubstrates to produce butanol and reduce production of ancillary byproducts were used in the fermentation. By changing the dilution rate from 0.1 to 1.2 h 1 at pH 4.3 and varying the pH from 3.5 to 5.5 at the dilution rate of 0.6 hr1, the optimal conditions for high productivity and butanol yield were investigated. 

Figure 9.16A shows a typical operational configuration of a continuous bioreactor culture. In Figure 9.16B, the cell concentration data of a real continuous culture, operated at three different dilution rates, are presented. The rectangles indicate the different steady states observed, whereas the arrows show the moment of change in dilution rate. Furthermore, a guide line has been included in Figure 9.16B to help interpretation of the cell concentration profile. 

A limiting condition when carrying out continuous culture is the situation known as bioreactor wash-out. This condition is characterized by a cell removal rate at the bioreactor outlet that is equal to or higher than the cell growth rate, such as that shown in Figure 9.16B after D has been increased to 0.8 d 1. The wash-out condition occurs when the dilution rate is increased to a threshold value called Dwash-out which can be derived from Equation 7, considering steady state and adopting Pmax for p. 

Dilution rate values higher than Dwask 0ut cause a progressive decrease in cell concentration, until no more cells are found inside the bioreactor. Thus, Dwash-out is the upper limit that should not be exceeded in a continuous culture. Since the Pmax values for animal cells are between 0.02 and 0.04 h-1 (0.5-1 d 1), the maximum cell concentration usually does not surpass 2 X 106 cell mL"1. Considering that productivity in a contin-... 

In this section we return to mass equations on the cells [Equation If (7-117)] and substrate [Equation (7-118)] and consider the case where the vol- umetric flow rates in and out are the same and that no live (i.e., viable) cells enter the chemostat. We next define a parameter common to bioreactors called the dilution rate, D. The dilution rate is... 

Theoretical considerations show that, with a methanol concentration of 701 m in the incoming medium to ffie bioreactor, the biomass concentration and residual methanol concentration (in outgoing medium) would vary with dilution rate as outlined below. 

Transfer 1500 ml of cell suspension containing 7-8 x 10 cells ml from the KLF 2000 to the NLF 22 bioreactor. The dilution rate of spent to fresh medium should be 1 8 and the cell density after inoculation should be about 1 x 10 cells mH. 

A batch experiment takes 3-5 days to grow cells to confluency, up to 5 more days to investigate antibody production during decline phase and 1-2 days for cleaning and sterilizing. Optimization of parameters in chemostat experiments requires 5-12 days per selected value. The time required depends essentially on the dilution rate. Provided that the 12-1 NLF 22 bioreactor is the final scale for production. 

We found that an inclined overflow tube would allow most of the cellulose to settle back so that clarified liquid could be passed through an analytical system. When the dilution rate was too slow to provide sufficient sample, the sample stream plus small amounts of salt (formed from neutralization in the analytical system) could be recycled to the bioreactor. Cellulose was withdrawn separately with a smaller tube that allowed no settling. Independent removal of clarified liquid and cellulose slurry could be controlled to hold a setpoint for cellulose concentration, but we have not used this other than to carry out some manual adjustments. 

Dilution rate is a major factor in design, operation and profitablity of a continuous bioreactor. When the main nutrient is a solid, dilution rate and detention time of the solids are two separate but interrelated issues. Hydrolysis of the cellulose continues as long as it is in the bioreactor, but the rates should change as the amorphous regions react more quickly leaving a higher proportion of the... 

From these data select the optimum working dilution rate for the bioreactor. 

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