The effect of shear rate on controlling the concentration polarization and membrane fouling

This paper deals with the results from experiments concerning the effects of an increasing shear rate at the edge of the membrane on reducing concentration polarization and on controlling membrane fouling during filtration of river water. Concentration polarization of humic substances in NF and MF membranes can be reduced by increasing the shear rate. The concentration polarization model can predict the removal efficiency of humic substances successfully. The high removal efficiency of humic substances in NF membrane filtration processes can be sustained even when the water recovery rate reaches to 96%, if the membranes are vibrated with the maximum vibratory amplitude of 1″. A cake layer formation on the NF membrane surface due to deposition of suspended colloids and humic substances dominates NF membrane fouling. NF membrane fouling can be evaluated by the cake filtration model and controlled by increasing the shear rate. Humic substances with molecular weight of more than 6,000 Da are transported away from the membrane surface by the shear-induced diffusion. Humic substances with molecular weight of 2,000 Da and with molecular weight of less than 500 Da are transported away from the membrane surface not only by the shear-induced diffusion, but also by Brownian diffusion.