where G is the surface concentration of protein, q P the residence time of the
bubble in the liquid pool, G formation the protein concentration at the end of the
dG
bubble formation, 5 the rate of protein adsorption onto the bubble during
dt pool
its travel through the liquid pool, and z is the axial distance from the foam/
liquid interface (m).
The film thickness and area of the Plateau border at the foam/liquid interface
were obtained from the knowledge of the gas velocity and bubble size. The
coupled partial differential equations of the balances were solved using a differential equation solving package. The surface concentration of the protein at
the film interface is calculated by assuming a diffusion-controlled adsorption
rate. From the mass balance the bottom flow rate and the liquid pool concentration were evaluated. Using these data the enrichment and recovery were
calculated. This model predicts the enhancement of protein enrichment with
increasing liquid pool height, decreasing gas velocities, increasing bubble size
due to coalescence, high feed flow rates and low feed concentrations in good
agreement with the measurements with BSA solution. The extension and application of this mathematical model for complex cultivation media is still to be
achieved.
4
Flotation of Microorganisms
Centrifugal separators are applied in industry for the recovery of microbial cells
from cultivation media. In waste water engineering a combination of flocculation and sedimentation is practiced. In the laboratory, cross-flow membrane separation is often used for retention of the cells. Some microorganisms
and cells are enriched in the foam; therefore, flotation is suited for the recovery
of particular microbial cells from cultivation medium.
Dognon and Dumonte [97] and Dognon [98] were the first to observe the
enrichment of microorganisms in foam. To enhance the separation quaternary
ammonium ions [99–101] or flocculants [102] were applied. Cell recovery without additives (collectors) was seldom used [103–107]. All of these investigations
were performed in batch operation.
Several investigations were carried out to remove toxic heavy metal ions
from waste water by biosorption. Microbial cells loaded with heavy metals were
recovered by flotation, e.g. Streptomyces griseus and S clavuligerus loaded with
Pb [108] and Streptomyces pilosus loaded with Cd [109]. In these flotation processes the microbial cells were dead; therefore, they are not considered here.
The removal of pyritic sulfur from coal slurries such as coal/water mixtures by
Thiobacillus ferrooxidans and recovery of this iron-oxidizing bacterium by
flotation is a special technique in the presence of high concentrations of solid
particles (see e.g. [110]). The flotation of colloid gas aphrons was used for the
recovery of yeast in continuous operation [111] for the recovery of micro algae,
and in the presence of flocculants in batch operation [112]. These special
techniques are not discussed here.
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
219
bubble in the liquid pool, G formation the protein concentration at the end of the
dG
bubble formation, 5 the rate of protein adsorption onto the bubble during
dt pool
its travel through the liquid pool, and z is the axial distance from the foam/
liquid interface (m).
The film thickness and area of the Plateau border at the foam/liquid interface
were obtained from the knowledge of the gas velocity and bubble size. The
coupled partial differential equations of the balances were solved using a differential equation solving package. The surface concentration of the protein at
the film interface is calculated by assuming a diffusion-controlled adsorption
rate. From the mass balance the bottom flow rate and the liquid pool concentration were evaluated. Using these data the enrichment and recovery were
calculated. This model predicts the enhancement of protein enrichment with
increasing liquid pool height, decreasing gas velocities, increasing bubble size
due to coalescence, high feed flow rates and low feed concentrations in good
agreement with the measurements with BSA solution. The extension and application of this mathematical model for complex cultivation media is still to be
achieved.
4
Flotation of Microorganisms
Centrifugal separators are applied in industry for the recovery of microbial cells
from cultivation media. In waste water engineering a combination of flocculation and sedimentation is practiced. In the laboratory, cross-flow membrane separation is often used for retention of the cells. Some microorganisms
and cells are enriched in the foam; therefore, flotation is suited for the recovery
of particular microbial cells from cultivation medium.
Dognon and Dumonte [97] and Dognon [98] were the first to observe the
enrichment of microorganisms in foam. To enhance the separation quaternary
ammonium ions [99–101] or flocculants [102] were applied. Cell recovery without additives (collectors) was seldom used [103–107]. All of these investigations
were performed in batch operation.
Several investigations were carried out to remove toxic heavy metal ions
from waste water by biosorption. Microbial cells loaded with heavy metals were
recovered by flotation, e.g. Streptomyces griseus and S clavuligerus loaded with
Pb [108] and Streptomyces pilosus loaded with Cd [109]. In these flotation processes the microbial cells were dead; therefore, they are not considered here.
The removal of pyritic sulfur from coal slurries such as coal/water mixtures by
Thiobacillus ferrooxidans and recovery of this iron-oxidizing bacterium by
flotation is a special technique in the presence of high concentrations of solid
particles (see e.g. [110]). The flotation of colloid gas aphrons was used for the
recovery of yeast in continuous operation [111] for the recovery of micro algae,
and in the presence of flocculants in batch operation [112]. These special
techniques are not discussed here.
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
219