The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C12(EO)5 and C12(EO)8] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

Surfactants toxicity has induced a worldwide alert followed by various regulations. There are still concerns about the biodegradability and ecofriendliness of surfactants. Reviews on surfactants are available, but a concise manuscript covering surfactant types, primary and secondary toxicity of surfactants, evaluating the level of surfactant pollution worldwide, is needed. We review here the safety of surfactants in the aquatic system, in terrestrial ecosystems and for humans. We discuss strategies to solve surfactant contamination. Remediation methods include ozonation, UV radiation and catalyst-coupled auto-oxidation. We focus on the biodegradation of the anionic detergents sodium dodecyl sulfate and linear alkyl benzene sulfonate. Finally, the relevance and role of biosurfactants as alternatives to synthetic detergents are also described.

Surfactants: toxicity, remediation and green surfactants

The role of surfactants in wastewater treatment: Impact, removal and future techniques: A critical review.

Anionic and cationic surfactant recovery from water using a multistage foam fractionator

A comparative economic analysis of copper removal from water by ligand-modified micellar-enhanced ultrafiltration and by conventional solvent extraction

The purpose of this study was to investigate the use of foam fractionation to recover surfactant from water A simple continuous mode foam fractionation was used and three surfactants were studied (two anionic and one cationic) The effects of air flow rate, foam height, liquid height, liquid feed surfactant concentration, and sparger porosity were studied This technique was shown to be effective in either surfactant recovery or the reduction of surfactant concentration in water to acceptable levels As an example of the effectiveness of this technique, the cetylpyridinium chloride concentration in water can be reduced by 90% in one stage with a liquid residence time of 375 minutes The surfactant concentration in the collapsed foam is 215 times the feed concentration This cationic surfactant was easier to remove from water by foam fractionation than the anionic surfactants studied

Nopparat Tharapiwattananon

Papers

Surfactant Recovery from Water Using Foam Fractionation