Influence of sodium dodecyl sulfate on colloidal fouling potential during ultrafiltration

The influence of sodium dodecyl sulfate (SDS) on colloidal interactions in the cake layer on a membrane surface was investigated with colloidal fouling tests. Fouling experiments of silica colloids were carried out in a bench scale ultrafiltration (UF) device under various SDS concentrations in waters of different ionic strengths. Addition of small amounts of SDS (0.3 mM) was found to reduce the colloidal fouling potential by 15–18.5%. This reduction was brought about by masking of heterogeneities on the colloidal silica surface thus increasing their repulsion in the cake layer and thereby resulting in a more porous cake layer. At intermediate concentrations of SDS, the colloidal fouling potential of the feed water increased with the SDS concentration and reached a peak at the critical micelle concentration (CMC). SDS additions in this range were shown to function similar to indifferent electrolytes that compress the electric double layer around the colloidal particles to form a tighter cake layer. Concentrations of SDS beyond the CMC resulted in a decline of the colloidal fouling potential. Co-deposition of micelles with colloidal particles on the membrane surface resulted in an additional structural interaction energy to the Derjaguin–Landau–Verway–Overbeek (DLVO) interaction energy between the silica particles. The structuring of micelles between silica particles facilitated a more porous cake layer. The same general trends were observed in all waters tested.