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Crossflow filtration of yeast broth cultivated in molasses
T Tanaka1, R Kamimura, R Fujiwara
1Department of Biotechnology, Faculty of Engineering, Okayama University, Tsushima-Naka, Okayama 700, Japan.
Abstract:
A broth of yeast cells cultivated in molasses was crossfiltered with a thin-channel module. The permeation flux gradually decreased at a constant cell concentration. The flux was much lower than that obtained for yeast broth cultivated in yeast extract, polypeptone, and dextrose (YPD) medium during the filtration. The flux did not depend on the membrane pore size (0.45 to 5 mum). The steady-state flux was one-twentieth that calculated for a cake filtration mode from the amount of cake per unit filtration area and the specific resistance of the cake measured in a dead-end filtration apparatus. The lower flux was due to small particles (most of which were less than 1 mum in diameter) in the molasses. The mehanism of crossflow filtration of broths of yeast cells cultivated in molasses was clarified by analysis of the change in flux with time and observations with scanning electron microscopy. At the initial stage of crossflow filtration the yeast cells and particles from the molasses were deposited on the membrane to form the molasses were deposited on the membrane to form a cake in a similar way to dead-end filtration. After the deposition of cells onto the membrane ceased, the fine particles from molasses formed a thin layer, which had higher resistance than the cake formed next to the membrane. The backwashing method was effective to increase the flux. The flux increased low when the pore size was 0.45 to 0.08 mum, but using larger pores of 3 to 5 mum it returned almost to the bases line. (c) 1994 John Wiley & Sons, Inc.
Insights
Yeast cell filtration in molasses broth is significantly hindered by fine molasses particles, forming a resistant layer on the membrane. Backwashing partially restores flux, with larger pores showing better recovery.
Area of Science:
- Biochemical Engineering
- Separation Science
- Membrane Technology
Background:
- Crossflow filtration is a key separation technique for biological broths.
- Molasses-based media present unique challenges in yeast cell separation due to inherent particulate matter.
- Previous filtration studies often utilized simpler media like yeast extract, polypeptone, and dextrose (YPD) medium.
Purpose of the Study:
- To investigate the mechanism of crossflow filtration of yeast cells cultivated in molasses.
- To understand the factors contributing to reduced permeation flux during this process.
- To evaluate the effectiveness of backwashing and membrane pore size on filtration performance.
Main Methods:
- Crossflow filtration of yeast broth cultivated in molasses using a thin-channel module.
- Analysis of permeation flux over time at constant cell concentration.
- Scanning electron microscopy (SEM) for visualizing membrane surface and cake structure.
- Comparison with dead-end filtration for cake resistance measurements.
- Evaluation of backwashing effectiveness and impact of varying membrane pore sizes (0.08–5 µm).
Main Results:
- Permeation flux decreased significantly over time, much lower than with YPD medium.
- Flux was independent of membrane pore size (0.45–5 µm), indicating a fouling mechanism beyond simple pore blocking.
- SEM revealed a dual-layer cake: yeast cells near the membrane and a more resistant layer of fine molasses particles on top.
- Steady-state flux was substantially lower than predicted by cake filtration models.
- Backwashing improved flux, with larger pores (3–5 µm) showing near-complete recovery, while smaller pores (0.08–0.45 µm) had limited improvement.
Conclusions:
- Fine particles in molasses are the primary cause of reduced flux in crossflow filtration of yeast broth.
- A cake layer formed by these fine particles, distinct from the yeast cell cake, significantly increases filtration resistance.
- Backwashing is an effective strategy for flux recovery, and larger membrane pore sizes enhance this recovery.
