CSTBR concentration factor

Figure 13.8 Schematic flow sheet for a process coupling use of a CSTBR and a generic unit operation for separation and concentration of a suspension of cells for recycle to enhance reactor productivity. The concentration factor /=X2/Xj.

In addition to the variables we have used previously in our analysis of the behavior of a CSTBR, we employ the recycle ratio (R) to represent the ratio of the volumetric flow rate of the suspension of cells leaving the separation device to the volumetric flow rate of the net product stream. The symbol / represents the ratio of the concentration of biomass in the recycle stream to that in the gross product stream so /=X2/jCi. This concentration factor characterizes the degree to which the separation operation increases the amount of biomass present in the recycle stream beyond... 

Because the concentration factor vp must exceed unity to render operation in a recycle mode viable, the quantity 1 (1 - /) must be negative and the dilution rate D must exceed mef Consequently, the use of separation and recycle of a portion of the cells permits one to operate with a steady-state dilution rate that exceeds the net biomass specific growth rate in the CSTBR. 

For purposes of the analysis, you may assume that cell death and cell maintenance metabolism effects are negligible, as is formation of any products other than biomass. The concentration of substrate in the feed is 25 g/L and the yield coefficient x/s is 0.52 g cells (dry weight)/g substrate. The kinetics of cell growth are characterized by a rate law of the Monod form with = 0.6 h" and Kg = 0.5 g/L. The dilution rate for the CSTBR is 0.95 h" and the concentration factor / is 2.5. 

The subscripts on the usual process parameters indicate the positions in the process to which these parameters refer. The kinetics of yeast growth can be described by a Monod rate expression with = 0.625 h and Kg = 2 g/L. Cell death and cell maintenance effects are negligible, as is formation of products other than yeast cells. The yield coefficient x/s is 0.44. The effluent from the bioreactor flows directly to a membrane filtration apparams. The membrane is completely permeable to the substrate, so the concentrations of the substrate in the CSTBR, the effluent from the bioreactor, and the permeate from the membrane and in the recycle stream are all identical. The membrane rejects a substantial proportion of the yeast cells so that the ratio of the concentration of yeast in the recycle stream is a factor of 4 larger than that in the effluent from the CSTBR. Volumetric expansion and contraction effects may be considered negligible. 

---

See also in sourсe #XX -- [ , ]

---