USE OF HYDRODYNAMIC METHODS FOR PRESSURE-DRIVEN MEMBRANE OPERATIONS

Membrane separation is one of the most used processes at present but i ts long term application is still limited because of concentration pol arization and fouling caused by particles which are retained by the me mbrane. These retained particles accumulate on the membrane surface or /and in the pores and result in reducing the membrane porosity and inc reasing the overall membrane resistance. The net effect is decrease in the permeation rate with process time. In case where the treatment of the feed or the membrane is not feasible or advisable, hydrodynamic m ethods can be used for controlling the concentration polarization and membrane fouling. In this paper, various hydrodynamic systems develope d and tested for the control of permeate flux decrease or for its enha ncement have been reviewed. Using polypropylene and polyamide hollow f ibre filters for plasma separation, it is shown that appropriate pulsa tions applied to the inlet blood flow could enhance the filtration rat e by about 45% compared to nonpulsatile conditions. When a rotating me mbrane device equipped with polycarbonate membrane for separating plas ma from whole blood was used, it has been found that the filtration ve locities were 10-20 times higher than those obtained with steady flow. With tubular mineral membranes (ceramic and carbon) for raw apple jui ce and raw wine clarification, when pressure and flow pulsations have been superimposed on the inlet flow of the filtration module, that the permeate flux increased up to 45% at 1 Hz frequency and with stroke v olumes smaller than the internal volume of the membrane. Carefully cho sen pulsations wave form decreased the hydraulic power dissipated in t he retentate per unit volume of permeate up to 30%. The use of a helic al shape baffle in a mineral membrane for microfiltration of bakers ye ast solution (5% dry weight) and dodecane-water emulsion (0.1% by weig ht) provided an increase of more than 50% in permeate flux compared to that obtained without a baffle at the same hydraulic dissipated power .