Membrane dialysis fermenter

The limitations of dialysis fermentation are evident, since the inherently slow process of diffusion of both nutrients and metabolic products through the membrane is the rate-determining step. Inhibitory and/or toxic substances can accumulate and limit maximum cell concentration. 

There have been a number of membrane-based culture units developed (24), many based on dialysis tubing (1), and even available as large fermenters (Bioengineering AG Membrane Laboratory Fermenter with a Cuphron dialysis membrane of 10 000 dalton molecular weight cut-off forming an inner chamber). One of the more successful and currently available systems is described here—the miniPerm Bioreactor (Heraeus Instruments). 

While it is easy to add materials to a fermentation, removal is difficult. Membrane devices have been placed in the fermenter or in external recycle loops to dialyze away a soluble component. Cells release wastes or metabolites that can be inhibitory these are sometimes referred to as staling factors. Their removal bv dialysis has allowed cell concentrations to reach ten to one hundred times that of control cultures. 

DOE has cofunded lactic acid separations technology involving the use of electro dialysis, advanced membranes, and reactive separations capable of converting the lactic acid salts made during fermentation directly into ethyl lactate. 

Electro- dialysis Cation- and anion—exchang e membrane Electrical potential difference Electric charges of particle Removing salts, acids, and bases from fermentation broths, separation of amino acids, etc. 

Viable cells can also be confined within the shell of a hollow fiber membrane module85 (Figure 7.41) or in a cell circuit separated with a dialysis membrane from a dialysate circuit, where water or substrate solution is kept flowing86 (Figure 7.42). When kinetic models for the growth and fermentation of a specific kind of cell or microbe on the corresponding substrate medium are avail-... 

Figure 6.47. Typical experimental setup of dialysis culture using a reservoir for substrate feed S, a fermenter for bioconversion, and a chamber with a semipermeable membrane M to retain biomass X.

Mathematical analysis always consists of the writing of suitable balance equations by the insertion of kinetic terms. In the case of dialysis culture, balances must be made either on the reservoir chamber or the fermenter chamber. With use of Equ. 6.146a for membrane permeation, the basic balance equations for dialysis culture are as follows ... 

Figure 6.49. Expected changes in cell mass concentrations for dialysis culture systems operated with batch fermenter and batch reservoir (x2 and Sres,2) or batch fermenter and continuous reservoir (xj and Sres,i)- The critical time when substrate diffusion through the membrane becomes limiting is indicated as tcrit- Exponential, linear, and asymtotic growth can be observed. (Adapted from Schultz and Gerhardt, 1969.)...

The case (c) of batch fermenter/continuous reservoir dialysis culture can be evaluated similarly. The behavior is also shown in Fig. 6.49, and the properties are analogous to those in case (b). Linear growth can be maintained, because Sres is constant due to membrane diffusion. 

A number of alternative approaches are available as technical solutions for the above-mentioned problems (e.g., Hamer, 1982 Lilly, 1982 Meiorella et al., 1981) vacuum membrane retractive and extractive fermentation, and biphasic processing (Mattiasson, 1983 Reisinger et al., 1987) and ion-exchange resin culture techniques. Experimental tests of dialysis culture processes are described in the literature for ammonium-lactate fermentation of whey (Stieber et al., 1977), and an improved mathematical model was later developed (Stieber and Gerhardt, 1979) incorporating P inhibition. Recently,... 

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