The dead-end ultrafiltration experiments of BSA protein and alumina colloid solution were carried out to investigate on the effect of membrane fouling control by natural convection instability flow (NCIF) induced in the membrane module. Ultrafiltration experiments were carried out by measuring the flux enhancements according to the change of the inclined angles (from 0° to 180°) with respect to the gravity direction of the membrane module. The flux results were interpreted using the blocking filtration model and the following conclusions were obtained.
NCIF induced in the membrane module by changing the inclined angles make a results of the flux enhancement because the occurrence of the membrane fouling are more controlled as the inclined angle is turned toward the opposite direction of gravity (180°). That is because the induced NCIF promotes the transfer of the solute from the membrane surface to the bulk solution, thereby the flux is maximized at the inclined angle of 180°. In the ultrafiltration of BSA protein solution, the flux enhancement of is increased about 5 times in the short-term operation (2 hours) and about 17 times in the long-term operation (20 hours). In the ultrafiltration of alumina colloid solution, the flux enhancement of is increased about 3 times in the short-term operation (2 hours).
As a result of applying the blocking filtration model to those flux results, it could not be analyzed by using any one of the four blocking filtration models. But it is more appropriate to analyze those flux results with the intermediate blocking model at the beginning of the operation and then the cake filtration model. In the ultrafiltration of BSA solution, the membrane fouling with intermediate blocking is reduced to about 67% at the beginning of the operation, and thereafter the membrane fouling with cake formation is reduced to about 98% at the inclined angle of 180°. Also in the ultrafiltration of alumina colloid solution, the fouling with intermediate blocking is reduced to about 52% at the beginning of the operation, and thereafter the fouling with cake formation is reduced to about 93%. NCIF induced in the membrane module by simply changing the inclined angles of module with gravity, has a large effect on the control of membrane fouling.
The induction of NCIF in the membrane module is expected to increase the flux, the membrane cleaning cycle and the productivity of membrane module thereby reducing the operating cost of the membrane filtration process.