Adsorption of non-ionic surfactant from aqueous solution onto various ultrafiltration membranes

Ultrafiltration of aqueous surfactant solutions shows in this study a high micelle retention and the permeability decline below, as well as above the critical micelle concentration (cmc). The trajectory of concentration-dependent permeability gives comparable patterns for various membranes under similar filtration conditions. This phenomenon is analysed by applying the two following models: (1) constant pressure blocking filtration laws established by Hermia; (2) adsorption model proposed by Zhu and Gu. From experimental flux data, all Hermia's models fail to explain flux decline during stepwise increasing the surfactant concentration covering a range from (a) 0 to cmc and (b) cmc to 4·cmc. In contrast, the adsorption model is proven to be a helpful method to identify the responsible process causing the flux decline. Applying the two-step model with S-shape, we determined the equilibrium adsorption constant K and hemimicelle aggregation number n from permeability decline in dependence of surfactant concentration. This study contributes a qualitative and quantitative comparison of adsorption behaviours regarding the hydrophilicity of the membrane surface, the MWCO and the polarity of the feed solution. Moreover, the difference in the filtration performance between MEUF and reverse MEUF is systematically investigated here to explain the reason for the technical infeasibility of reverse MEUF.