Recycling of cells

Receptor-specific antibodies can be used to analyze morphologically the cellular distribution of chemokine receptors, following ligand treatment. If the anti-receptor antibodies do not interfere with chemokine binding the protocols can be adapted to follow endocytosis and recycling of cell surface receptors (see Notes 4 and 5). 

Figure 13.9 also contains plots of the productivity of the CSTBR as a function of the dilution rate for operation with and without recycle of cells. The recycled cells enable one to operate at dilution rates considerably above those characteristic of the close-to-washout conditions that would prevail in the absence of recycle. The higher density of cells leads to very substantial increases in reactor productivity. The recycle mode of operation is particularly important in the use of microorganisms for the treatment of wastewaters (see Section 13.3.1). 

Because activated sludge facilities have been utilized successfully for decades in the treatment of industrial wastewaters, and because of the similarity of the analysis of the peaformance of the constituent bioreactor to that for an individual CSTR operating with partial recycle of cells (see Section 13.2.4), we first consider how to develop steady state models of these bioreactors. We then proceed to matters related to the use of bioreactors for cultivation of animal and plant cells, including information pertinent to their susceptibility to damage in shear fields. We conclude with discussions of aspects of two interesting evolving... 

Figure P13.15 Continuous culture of yeast in a CSTBR with recycle of cells using a membrane separation device from which the retentate is returned to the CSTBR.

Added productivity of lactic acid fermentations can be achieved by combining continuous systems with mechanisms that allow higher bacterial cell concentrationsResearch is concentrated on two mechanisms (1) membrane recycle bioreactors (MRBs) and (2) immobilized cell systems (ICSs). The MRB consists of a continuous stirred-tank reactor in a semiclosed loop with a hollow fiber, tubular, flat, or cross flow membrane unit that allows cell and lactic acid separation and recycle of cells back to the bioreactor. The results of a number of laboratory studies with various MRB systems demonstrate the effect of high cell concentrations on raising lactic acid productivity (Litchfield 1996). O Table 1.12 lists examples of published results employing various MRB systems. 

Direct Methane Conversion, Methanol Fuel Cell, and Chemical Recycling of Carbon Dioxide... 

Water from screens, cleaners, washers, thickeners, and flotation cells contain relatively high levels of ink. These waters also contain valuable chemicals, ie, sodium hydroxide and surfactants. Recycle of this water can save up to 10% ia chemical costs. 

For a profitable electrochemical process some general factors for success might be Hsted as high product yield and selectivity current efficiency >50%, electrolysis energy <8 kWh/kg product electrode, and membrane ia divided cells, lifetime >1000 hours simple recycle of electrolyte having >10% concentration of product simple isolation of end product and the product should be a key material and/or the company should be comfortable with the electroorganic method. 

There have been a number of cell designs tested for this reaction. Undivided cells using sodium bromide electrolyte have been tried (see, for example. Ref. 29). These have had electrode shapes for in-ceU propylene absorption into the electrolyte. The chief advantages of the electrochemical route to propylene oxide are elimination of the need for chlorine and lime, as well as avoidance of calcium chloride disposal (see Calcium compounds, calcium CHLORIDE Lime and limestone). An indirect electrochemical approach meeting these same objectives employs the chlorine produced at the anode of a membrane cell for preparing the propylene chlorohydrin external to the electrolysis system. The caustic made at the cathode is used to convert the chlorohydrin to propylene oxide, reforming a NaCl solution which is recycled. Attractive economics are claimed for this combined chlor-alkali electrolysis and propylene oxide manufacture (135). 

Without recycle, washout occurs when D is greater than flmax, but recycle permits operation with D far greater than flmax- A family of curves is shown in Fig. 24-24 for concentrations of cell mass and nutrient at different recycle ratios. The distinct differences from Fig. 24-22 with no recycle are obvious. 

FIG. 24-24 Effect of recycle on steady-state concentrations of cell mass and limiting nutrient. 5-fold increase in cell concentration in separator. SiiLscripts denote fraction of cell concentrate recycled. 

In the living cells of luminous bacteria, FMNH2 is produced by the reduction of FMN with NADH catalyzed by FMN-reductase. This process is, in effect, the recycling of FMN. In the cells, a long-chain aldehyde is produced by the reduction of the corresponding long-chain acid, which is also a recycling process. 

The activated sludge process for wastewater treatment uses recycle of live cells. The goal is to oxidize organics without generating too much sludge (i.e., biomass). 

FIGURE 12.6 Continuous fermentor with recycle of live cells. 

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