Surfactant Fouling of Nanofiltration Membranes: Measurements and Mechanisms

Abstract

Fouling of nanofiltration membranes is studied during filtration of aqueous surfactant solutions under different conditions. To this purpose, four typical nanofiltration membranes (Desal51HL, NF270, NTR7450 and NFPES10) and three typical surfactants (nonionic neodol, anionic SDBS and cationic cetrimide) are selected. Fouling is studied as a function of the surfactant concentration, with and without addition of an electrolyte (NaCl), at different pH and when filtering a mixture of surfactants. Adsorption experiments and hydrophobicity measurements (to study the orientation of the surfactants on the membrane surface) are also performed under the different conditions. The least membrane fouling is found for the anionic surfactant SDBS, while for the cationic surfactant cetrimide very low relative fluxes are observed. Neodol shows an intermediate degree of fouling. Both hydrophobic and electrostatic interactions (in the case of ionic surfactants) between the membrane surface and the surfactant explain the degree of adsorption and hence fouling, as membrane fouling is correlated with the amount of adsorbed surfactant. The difference between cetrimide and SDBS becomes especially visible when changing the pH: increasing the pH leads not only to an opposite orientation of the adsorbed surfactants, but also to an opposite trend in adsorbed amount and membrane fouling. This study permits selection of an optimal nanofiltration membrane to recycle wastewater containing surfactants in the carwash industry. The optimal choice would be a hydrophilic membrane with a low molecular weight cut-off and a small negative surface charge at neutral pH. Cationic surfactants in the wastewater should also be avoided as much as possible.

Positively charged aromatic polyamide reverse osmosis membrane with high anti-fouling property prepared by polyethylenimine grafting

“…The more hydrophilic the membrane is, the tighter the hydrophobic end group of cation surfactant adsorbed on the membrane surface. Similar process can be found in other literatures [36].…”

Nanofiltration regeneration of contaminated single-phase detergents used in the dairy industry

“…However, above the CMC, concentration polarization by retained micelles causes permeate flux reduction. Kaya et al (2006) and Boussu et al (2007) demonstrated that the adsorption of anionic surfactants on the surface of negatively charged membranes is due to hydrophobic attraction, which is stronger than electrostatic repulsion. Due to the negative membrane charge, the hydrophobic tails are oriented towards the membrane surface and the hydrophilic heads towards the aqueous 3.0 Â 10 À5 4.8 Â 10 À5 40 3.5 Â 10 À5 6.4 Â 10 À5 60 4.3 Â 10 À5 7.9 Â 10 À5 70 4.6 Â 10 À5 9.0 Â 10 À5 80 9.9 Â 10 À5 phase, which results in a more hydrophilic membrane.…”

“…Therefore, at the pH values considered in this work they have a weak negative surface charge. A few authors (Cornelis et al, 2005;Boussu et al, 2007;Kaya et al, 2006Kaya et al, , 2009 investigated the nanofiltration of solutions containing surfactants and they concluded that permeability is strongly influenced by the membrane material and the feed conditions (pH, concentration, etc.). The best results in terms of permeability were obtained with hydrophilic membranes.…”

“…There are also a few works where membrane technology has been used to recover surfactants or surfactant-based detergents (Forstmeier et al, 2003;Boussu et al, 2007;Kaya et al, 2006;Kaya et al, 2009). Nanofiltration has been successfully used for this purpose.…”

Membrane Separation Process in Wastewater Treatment of Food Industry

“…If surfactants are below their critical micelle concentration (CMC) they will not be retained by any of these techniques, but if they are above CMC, MF and UF techniques retain these components and the permeate stream will lose its cleaning properties. Some works based on NF processes with the aim of surfactants recovery in the permeate stream have been published in the last years (Boussu et al, 2007, Forstmeier et al, 2002Kaya et al, 2006Kaya et al, , 2009. In those cases permeate flux and surfactant rejection are strongly dependent on the membrane material (membrane isoelectric point -IEP) and feed conditions (pH, concentration, etc.)…”