DIALYSIS CULTURES

Dialysis techniques are discussed as a means for effective removal of low-molecular-mass components from fermentation broth to reach high ce ll density. Reactor systems and process strategies, the relevant prope rties of membranes and examples for high-density fermentation with dia lysis, and problems related to scale-up are addressed. The dialysis te chnique has turned out to be very efficient and reliable for obtaining high cell densities. As in dialysis processes the membranes are not p erfused, membrane clogging is not a problem as it is for micro- and ul trafiltration. By applying a ''nutrient-split'' feeding strategy, the loss of nutrients can be avoided and the medium is used very efficient ly. The potential of dialysis cultures is demonstrated on the laborato ry scale in a membrane dialysis reactor with an integrated membrane an d in reactor systems with an external dialysis loop. In dialysis cultu res with different microorganisms (Staphylococci, Escherichia coli, ex tremophilic microorganisms, Lactobacilli) the cell densities achieved were up to 30 times higher than those of other fermentation methods. T he technique enables high cell densities to be attained without time-c onsuming medium optimization. For animal cell cultures the concept of a fixed bed coupled with dialysis proved to be very effective.