The effect of a polyelectrolyte on the efficiency of dye-surfactant solution treatment by ultrafiltration

The effect of a cationic polyelectrolyte (PE) on the dye and surfactant removal from aqueous mixtures by lowpressure membrane process was assessed. Flat ultrafiltration (UF) membranes made of regenerated cellulose and polyethersulfone, and characterized by different cut-off values (5, 10, and 30 kDa) were used in the experiments. The UF process involved a pressure of 0.1 and 0.2 MPa. Permeation measurements were carried out with aqueous solutions of different anionic dyes (methyl orange, indigo carmine, amido black, and direct black) and dye solutions containing an anionic surfactant – sodium dodecyl sulfate (SDS), and/or a cationic PE. Dye, surfactant, and PE concentrations in the experimental solutions amounted to 100, 100, and 0.5 g/m3, respectively. It was found that when a cationic PE was present in the dye-surfactant mixture, this was concomitant with a decrease in membrane permeability and an increase in dye and surfactant retention. This relationship was more pronounced for polyetersulfone membranes than for membranes made of regenerated cellulose, as well as for membranes of high cut-off values.

(1) An improvement of the membrane separation properties toward anionic dyes and SDS in the presence of a cationic PE was observed. Polyethersulfone membranes exhibited a slight better separation properties than membranes made of regenerated cellulose. (2) An essential drop in membrane permeability occurred when a cationic polyelectrolyte was added to the dye-surfactant aqueous mixture. (3) The adsorptive fouling tendency was more pronounced for polyethersulfone membranes than for regenerated cellulose membranes, as well as for more hydrophobic dyes and more open membranes.