MEMBRANE ULTRAFILTRATION IN MULTIPASS HOLLOW-FIBER MODULES

Rising fluid velocity in the fiber tubes of a hollow-fiber module has two conflicting effects. One, the decrease in resistance to permeation due to reduction in concentration polarization, is good for ultrafilt ration, while the other, the decrease in average transmembrane pressur e due to increase in frictional pressure loss, is bad for ultrafiltrat ion. It appears, therefore, that proper adjustment of fluid velocity a s well as proper arrangement of the number of fiber passes in a hollow -fiber module of fixed total hollow fibers, might effectively suppress the undesirable resistance to permeation while still preserving an ef fective transmembrane pressure and thereby lead to improved performanc e of membrane ultrafiltration. It was found that considerable improvem ent in ultrafiltration is obtainable by employing a multipass hollow-f iber membrane module rather than using the one with only single fiber pass and with the same total fibers, especially for a dilute solution ultrafiltered with low volumetric flow rate and under high transmembra ne pressure. (C) 1998 Elsevier Science B.V.