Removal of cadmium ions using micellar-enhanced ultrafiltration with mixed anionic-nonionic surfactants

Application of saponin biosurfactant and its recovery in the MEUF process for removal of methyl violet from wastewater

The potential of saponin, a biosurfactant, in the micellar enhanced ultrafiltration (MEUF) process was tested systematically for removal of methyl violet from wastewater. For this, the aqueous extract of reetha (Sapindus mukorossi) pericarp which contains saponin was used as the biosurfactant. First, the micellar solubilization of methyl violet in saponin micelles was investigated in terms of molar solubilization power (SP) of saponin. It was observed that the adsorption of methyl violet on the agglomerates of saponin micelles was mainly responsible for the enhanced solubilization. The Gibbs free energy of solubilization (calculated as -29.63 kJ mol^-1) suggested that process was feasible and spontaneous. The MEUF experiments were performed in batch as well as continuous mode using saponin biosurfactant, and the effect of operating parameters on permeate flux and solute retention were evaluated. The removal of methyl violet in MEUF process was >99% achieved with 10 kDa polyethersulfone (PES) membrane for feed dye concentration of 250 mg L^-1 at studied conditions. Finally, the saponin in permeate was recovered using n-heptane and n-butanol by solvent extraction process. The solvent n-butanol showed better extraction efficiency as compared to n-heptane for saponin extraction.

Micelles as Soil and Water Decontamination Agents

Contaminated soil and water pose a serious threat to human health and ecosystem. For the treatment of industrial effluents or minimizing their detrimental effects, preventive and remedial approaches must be adopted prior to the occurrence of any severe environmental, health, or safety hazard. Conventional treatment methods of wastewater are insufficient, complicated, and expensive. Therefore, a method that could use environmentally friendly surfactants for the simultaneous removal of both organic and inorganic contaminants from wastewater is deemed a smart approach. Surfactants containing potential donor ligands can coordinate with metal ions, and thus such compounds can be used for the removal of toxic metals and organometallic compounds from aqueous systems. Surfactants form host-guest complexes with the hydrophobic contaminants of water and soil by a mechanism involving the encapsulation of hydrophobes into the self-assembled aggregates (micelles) of surfactants. However, because undefined amounts of surfactants may be released into the aqueous systems, attention must be paid to their own environmental risks as well. Moreover, surfactant remediation methods must be carefully analyzed in the laboratory before field implementation. The use of biosurfactants is the best choice for the removal of water toxins as such surfactants are associated with the characteristics of biodegradability, versatility, recovery, and reuse. This Review is focused on the currently employed surfactant-based soil and wastewater treatment technologies owing to their critical role in the implementation of certain solutions for controlling pollution level, which is necessary to protect human health and ensure the quality standard of the aquatic environment.

Removal of heavy metals from wastewater using micellar enhanced ultrafiltration technique: a review

Application of Micellar enhanced ultrafiltration (MEUF) for the removal of different heavy metals has been reviewed. It is considered an economical alternative available to the conventional membrane separation process, because it reduces the requirement of higher pressure and high membrane costs. MEUF is a separation processes which uses surfactants and ultrafiltration membranes to remove multivalent ions from wastewater with high percent rejection using electrostatic attraction between metals and micelles.

This review seeks to define the effect of the operating parameters, i.e., applied pressure, surfactant concentration, feed temperature, metal ion concentration, feed flow rate, operating time etc. on the removal of metal ions. Emphasis is given to the application of MEUF for the removal of single metal ions, multiple metal ions and different metals along with other organic materials. Also, this review focuses on studies related to micelle formation, attraction between metal ions and micelles, and recovery of surfactants for future research.

Micellar-enhanced ultrafiltration of cadmium and methylene blue in synthetic wastewater using SDS

Single and simultaneous removal of Cd(2+) and methylene blue (MB) with sodium dodecyl sulfate (SDS) by micellar-enhanced ultrafiltration under different experimental conditions was investigated. In single removal process, with initial SDS concentration increasing, the removal efficiency of Cd(2+) and MB kept increasing and then decreased. When the initial concentrations of SDS and Cd(2+) were 1.0 cmc and 50 mg L(-1), respectively, the maximum removal efficiency of Cd(2+) was obtained as 99.2%. Removal efficiency of MB could achieve more than 99.9% with initial SDS concentration below 2.0 cmc. As compared with single Cd(2+) removal, the removal efficiency of Cd(2+) in the presence of MB was slightly higher with initial SDS concentration below 1.0 cmc, while decreased with the SDS concentration above 1.0 cmc. The maximum removal efficiency of Cd(2+) was 98.8% when initial concentrations of SDS and MB were 1.0 cmc and 4 mg L(-1), respectively. The removal efficiency of MB in the presence of Cd(2+) could achieve higher than 96.5%, which was only 3.4% less than the optimum result of the single removal. Meanwhile, effect of pH on removal efficiency of Cd(2+) was more significant than that of MB.

Micellar-enhanced ultrafiltration of zinc in synthetic wastewater using spiral-wound membrane

In the present study, micellar-enhanced ultrafiltration (MEUF) was used to remove Zn(2+) from synthetic wastewater by the spiral-wound ultrafiltration membrane. The effects of different operating conditions on the separation performance of membrane were investigated. It was found that the transmembrane pressure has the largest influence on the permeate flux, but it has negligible effect on the rejection coefficient. Furthermore, sodium dodecyl sulfate (SDS) feed concentrations, SDS-Brij35 mixed micelles concentration and solution pH have a major influence on the rejection coefficient and negative effect on the permeate flux due to concentration polarization layer formation. Also, the results showed that the permeate flux and removal efficiency of zinc by anionic surfactant (SDS)-MEUF depends on the ligand-to-Zn(2+) ratio extremely. In general, MEUF by spiral-wound ultrafiltration membrane has good rejection of Zn(2+)under different operating conditions, as the rejections were higher than 98.0%. However, application of single anionic surfactant at relatively low concentration is more efficient than mixed surfactants and MEUF was not practical when the wastewater is intensively acidic.

Adsorption of surfactant micelles and Cd2+/Zn2+ in micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a powerful treatment developed to remove heavy metals from wastewater. Efficient removal of Cd(2+)/Zn(2+) from wastewater was performed by MEUF using a polysulfone hollow ultrafiltration membrane, with sodium dodecyl sulfate (SDS) as the surfactant. The adsorption of surfactant micelles and Cd(2+)/Zn(2+) in MEUF was studied by changing the surfactant dosage and the Cd(2+)/Zn(2+) concentration in the feed. In addition, kinetics, adsorption isotherms, and thermodynamic rules were analyzed, and X-ray photoelectron spectroscopy (XPS) was conducted. It was found that when the Cd(2+)/Zn(2+) feed concentration was 50 mg/L, and the SDS dosage reached 2.15 g/L, the concentration of heavy metal ions in the permeate stabilized at around 1-4 mg/L, and the adsorption of Cd(2+)/Zn(2+) on SDS micelles followed second-order kinetics and the Langmuir isotherm laws. Adsorption is a spontaneous endothermic process in which the adsorption force is principally the attraction of opposite electrical charges.