Microfiltration: Filtration above and below the critical flux with a vibrating hollow fiber module
Advancing the chemical engineering fundamentals
Filtration (T2-11P)
Keywords: Vibrating microfiltration, Critical flux, Yeast cell suspensions, Extracellular polymeric substances, Membrane bioreactor
Introduction:
A vibrating microfiltration membrane module consisting of hollow fibers has been tested in filtrations above and below the critical flux. Filtrations of yeast cell suspensions have been conducted and the influence of extracellular polymeric substances (EPS) from the yeast cells has been investigated. The critical flux for this system has earlier been determined in the filtration of yeast suspensions [1] and in the separation of yeast cell from macromolecules [2] and the critical flux depends on the surface shear rate which then is dependent of the vibration frequency and amplitude. The system is operated in a similar manner as many membrane bioreactors (MBR) described in the literature. It is very important to gain knowledge about how to operate such a system in order to avoid membrane fouling since it has to run for a very long time at constant flux without membrane cleaning in order to keep the running costs low.
Experimental:
The membrane module consists of 54 hollow fibers placed vertically in a bundle. The membrane material is polyethersulfone (PES) with pore sizes from 0.36 to 0.50 m. The module is vibrated at 25 Hz with an amplitude of 0.7 mm. Feed suspensions contained 4 g/L of dry bakers yeast cells.
Results:
It is shown that the permeability drop of the membrane module during filtration above the critical flux for 5 hour is larger than when the filtration is conducted below the critical flux for 5 hours. Furthermore it is shown that the “washing out mechanism” of EPS from the yeast cells during filtration is dependent on whether the flux is above or below the critical flux.
Conclusion:
In order to avoid or keep the membrane fouling low it is advantageous to operate slightly below the critical flux since this flux seems to be a good compromise between acceptable flux level and acceptable transmembrane pressure. At the same time the fouling of EPS is kept low. These conditions are all required in order to make the system work for long period of constant flux filtration without membrane cleaning.
References:
[1] S.P. Beier, M. Guerra, A. Garde, G. Jonsson, Dynamic microfiltration with a vibrating hollow fiber membrane module: Filtration of yeast suspensions, Journal of Membrane Science, 281 (2006) 281-287.
[2] S.P. Beier, G. Jonsson, Separation of enzymes and yeast cells with a vibrating hollow fiber membrane module, Separation & Purification Technology, In press (2006).
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 13:30 to 15:00, in session Filtration (T2-11P).
