Energy saving pulsatile mode cross flow filtration

Abstract

In this paper, we investigate a new mode of cross flow filtration in which the steady flow pump is replaced by a piston-in-cylinder which produces periodic bursts of velocity and pressure along the membrane at frequencies between 0.5 and 1.5 Hz. This technique has been tested on red wine clarification using zirconium oxide membranes on carbon support. Since the flow is intermittent, the time-mean velocity can be reduced to 0.6–1.2 m/s while obtaining permeate fluxes equal to or higher than those (35 l/m 2 h) observed in steady flow filtration at velocities of 3 m/s. As a result, the specific energy per unit volume of permeate is lower (3 to 4 MJ/m 3) than for steady flow filtration (6 MJ/m 3). In addition, by increasing the piston stroke volume above the internal volume of the membranes, high permeate fluxes, in excess of 100 l/m 2 h, are obtained with a small increase in specific energy (4.5 MJ/m 3) at a frequency of 1 Hz. Observation of pressure and flow recordings shows that the permeate flux time variation follows closely that of the transmembrane pressure, confirming that the membrane is able to respond to transient pressure changes without being penalized by concentration polarization build-up. These data suggest that this new technique is more energy efficient than our previous technique in which pulsations were superimposed on a steady flow produced by pumps.