STUDIES ON THE ADSORPTION OF MEMBRANE-ACT IVE SURFACTANTS BY ALTERNATING-CURRENT POLAROGRAPHY

The major problem encountered in the recycling of highly contaminated wastewater is the covering of the membrane surface by feed impurities (organic fouling, biofouling). Some earlier experiments have indicated that surfactants affect this layer in different ways. An octyl phenol ethoxylate (OPE9/10) with 10 EO units showed an increase of layer for mation with a consequent decrease in flux, while with lecithin the flu x at the end of the experiments showed a significant higher level. The se differences result from the various structures of the adsorption la yers. The adsorption coefficient, interaction coefficient of the Frumk in isotherm and the area per molecule were determined by a.c. polarogr aphy. In addition the adsorption of both surfactants was examined on m embrane material. It was found that the Frumkin isotherm characterises this adsorption on mercury and on the membrane surface. The lateral i nteraction forces within the lecithin layer are lower than the OPE9/10 ones. The loosely packed lecithin adsorption layers do not lead to an increase of the hydrodynamic resistance, but have a positive effect o n the flux behaviour.