Advances in Biochemical Engineering/
Biotechnology, Vol. 68
Managing Editor: Th. Scheper
© Springer-Verlag Berlin Heidelberg 2000
Recovery of Proteins and Microorganisms from
Cultivation Media by Foam Flotation
Karl Schügerl
Institute for Technical Chemistry, University of Hannover, Callinstrasse 3, D-30167 Hannover,
Germany
E-mail: Schuegerl@mbox.iftc.uni-hannover.de
Foaming is often present in aerated bioreactors. It is undesired, because it removes the cells
and the cultivation medium from the reactor and blocks the sterile filter. However, it can be
used for the recovery of proteins and microorganisms from the cultivation medium.
The present review deals with the characterization of model protein foams and foams of
various cultivation media. The suppression of foaming by antifoam agents and their effect on
the oxygen transfer rate, microbial cell growth and product formation are discussed. The
influence of process variables on the recovery of proteins by flotation without and with
surfactants and mathematical models for protein flotation are presented. The effect of cultivation conditions, flotation equipment and operational parameters on foam flotation of
microorganisms is reviewed. Floatable and non-floatable microorganisms are characterized
by their surface envelope properties. A mathematical model for cell recovery by flotation is
presented. Possible application areas of cell recovery by flotation are discussed.
Keywords. Foaminess, Protein foams, Flotation of proteins, Flotation of microorganisms, Foam
suppression, Antifoam agents, Characterization of cell surface
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
2
Characterization of Biological Foams . . . . . . . . . . . . . . . . . 194
2.1 Protein Foams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
2.1.1 Definition of Foaminess . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.1.2 Investigations with Bovine Serum Albumin . . . . . . . . . . . . . . 196
2.1.3 Influence of Protein Structure . . . . . . . . . . . . . . . . . . . . . 196
2.1.4 Influence of Protein Environment . . . . . . . . . . . . . . . . . . . 196
2.1.5 Influence of Foam Stability . . . . . . . . . . . . . . . . . . . . . . . 197
2.2 Foams of Cultivation Media . . . . . . . . . . . . . . . . . . . . . . . 197
2.2.1 Foaminess of Components of Cultivation Media . . . . . . . . . . . 198
2.2.2 Foaminess of Microbial Cell Cultivation Systems . . . . . . . . . . . 198
2.3 Prevention, Breaking and Suppression of Foams . . . . . . . . . . . 199
2.3.1 Foam Suppression by Chemical Antifoam Agents . . . . . . . . . . . 200
2.3.2 Influence of Antifoam Agents on Oxygen Transfer Rate . . . . . . . 200
2.3.3 Influence of Antifoam Agents on Fluid Dynamics,
Cell Growth and Product Formation . . . . . . . . . . . . . . . . . . 203
3
Protein Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
3.1 Continuous Flotation of Proteins . . . . . . . . . . . . . . . . . . . . 212
3.1.1 Characterization of Process Performance . . . . . . . . . . . . . . . 214
Biotechnology, Vol. 68
Managing Editor: Th. Scheper
© Springer-Verlag Berlin Heidelberg 2000
Recovery of Proteins and Microorganisms from
Cultivation Media by Foam Flotation
Karl Schügerl
Institute for Technical Chemistry, University of Hannover, Callinstrasse 3, D-30167 Hannover,
Germany
E-mail: Schuegerl@mbox.iftc.uni-hannover.de
Foaming is often present in aerated bioreactors. It is undesired, because it removes the cells
and the cultivation medium from the reactor and blocks the sterile filter. However, it can be
used for the recovery of proteins and microorganisms from the cultivation medium.
The present review deals with the characterization of model protein foams and foams of
various cultivation media. The suppression of foaming by antifoam agents and their effect on
the oxygen transfer rate, microbial cell growth and product formation are discussed. The
influence of process variables on the recovery of proteins by flotation without and with
surfactants and mathematical models for protein flotation are presented. The effect of cultivation conditions, flotation equipment and operational parameters on foam flotation of
microorganisms is reviewed. Floatable and non-floatable microorganisms are characterized
by their surface envelope properties. A mathematical model for cell recovery by flotation is
presented. Possible application areas of cell recovery by flotation are discussed.
Keywords. Foaminess, Protein foams, Flotation of proteins, Flotation of microorganisms, Foam
suppression, Antifoam agents, Characterization of cell surface
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
2
Characterization of Biological Foams . . . . . . . . . . . . . . . . . 194
2.1 Protein Foams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
2.1.1 Definition of Foaminess . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.1.2 Investigations with Bovine Serum Albumin . . . . . . . . . . . . . . 196
2.1.3 Influence of Protein Structure . . . . . . . . . . . . . . . . . . . . . 196
2.1.4 Influence of Protein Environment . . . . . . . . . . . . . . . . . . . 196
2.1.5 Influence of Foam Stability . . . . . . . . . . . . . . . . . . . . . . . 197
2.2 Foams of Cultivation Media . . . . . . . . . . . . . . . . . . . . . . . 197
2.2.1 Foaminess of Components of Cultivation Media . . . . . . . . . . . 198
2.2.2 Foaminess of Microbial Cell Cultivation Systems . . . . . . . . . . . 198
2.3 Prevention, Breaking and Suppression of Foams . . . . . . . . . . . 199
2.3.1 Foam Suppression by Chemical Antifoam Agents . . . . . . . . . . . 200
2.3.2 Influence of Antifoam Agents on Oxygen Transfer Rate . . . . . . . 200
2.3.3 Influence of Antifoam Agents on Fluid Dynamics,
Cell Growth and Product Formation . . . . . . . . . . . . . . . . . . 203
3
Protein Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
3.1 Continuous Flotation of Proteins . . . . . . . . . . . . . . . . . . . . 212
3.1.1 Characterization of Process Performance . . . . . . . . . . . . . . . 214