Electrolysis products formed at the electrodes were rinsed away with Na2SO4 solution with the same conductivity as the xanthan dispersion. Furthermore, like a heat exchanger
the flush liquid dissipates heat out of the filter chamber, thus preventing heating of the filter cake by the electric current. The filtrate mass was measured with an electronic balance and recorded by a PC. The pH value in the liquid, the voltage
and the current were recorded online with the PC. The applied electric field strength (DC) was kept constant at 4 V=mm. In order to determine the xanthan concentration
gradient within the electric field, samples were taken out of the filtration chamber with a volume of 35 cm3. By cannulas, which were built into the chamber and sealed with
overcoats made of latex. The sample volume was 300 l and the xanthan concentration in the samples and the filtrate was determined by the Alcian Blue test (Ramus, 1977;
Hofmann & Posten, 2002).
Calculation of the specific filter cake resistance. The specific filter cake resistances of the pressure filtration experiments in the Nutsch filter were calculated from Eq. (4) and the slope of the tf=VL versus VL plots.