EFFECT OF AN ELECTRIC-FIELD ON THE ULTRAFILTRATION OF MILK

Ultrafiltration of reconstituted skim-milk was performed on tubular alumina membranes in the presence of a transmembrane electric field under static and dynamic conditions. By a method for deposit formation and extraction described here, we distinguished 3 different and independent layers in the deposit. Furthermore, we showed that a correctly oriented field of 300 V.m-1 could slow down the fouling. Under dynamic conditions when a field of 100 V.m-1 was applied before introduction of the milk, we observed a 30% decrease in clogging and a marked increase in the flux rate. At 200 V.m-1 this effect reached 50%. One limitation of the method was electrolysis of the medium; this phenomenon became important at 400 V.m-1 under our working conditions and led to coagulation of the milk at the cathode. Based on the results of assays of calcium and total nitrogen and electrophoretic analysis of the proteins in the different fractions of the deposit, we propose a mechanism for deposit formation under static and dynamic conditions as well as a mode of action of the electric field involving polarization of molecules in the deposit.