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

Micellar-enhanced ultrafiltration (MEUF) was used to remove cadmium ions from wastewater efficiently. In this study the nonionic surfactants polyoxyethyleneglycol dodecyl ether (Brij35) and polyoxyethylene octyl phenyl ether (TritonX-100) were for micellar-enhanced ultrafiltration to lower the dosage of the anionic surfactant sodium dodecyl sulfate (SDS). The surfactant critical micelle concentration (CMC) and the degree of micelle counterion binding were investigated. The effects of nonionic surfactant addition on the efficiency of cadmium removal, the residual quantities of surfactant, the permeate flux and the secondary membrane resistance were investigated. A comparison between MEUF with SDS and MEUF with mixed anionic–nonionic surfactants was undertaken. The results show that the addition of Brij35 or TritonX-100 reduced the CMC of SDS and the degree of counterion binding for the micelles. Due to these variations the Cd²⁺ rejection efficiency was at a maximum when the Brij35:SDS and the TritonX-100:SDS molar ratio was 0.5. The Cd²⁺ rejection efficiency in MEUF with SDS is higher than for MEUF with mixed surfactants when the total dose of surfactant is constant. The permeate flux of MEUF with SDS is higher than that for MEUF with mixed surfactants while the secondary resistance of MEUF with SDS is less than that of MEUF with mixed surfactants.     

Micellar Enhanced Ultrafiltration of Reactive Black 5 from Aqueous Solution by Cationic Surfactants

Reactive black 5 (RB-5) dye was removed from a water stream using two cationic surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), via micellar enhanced ultrafiltration. Three membranes with different pore size were used for the determination of rejection coefficient and permeate flux of the solution at 1.5 bar trans-membrane pressure (TMP). The two surfactants (CPC and CTAB) played an almost negligible role in rejection efficiency with 5000 and 10,000 molecular weight cut-off membrane (MWCO), respectively. In this case, high rejection and low permeate flux was the result of a larger molecular size of RB-5 DYE being retained by comparatively smaller sized pores of membrane via ultrafiltration. However, CPC and CTAB surfactants showed 83% and 98% rejection coefficient, respectively, at a concentration greater than their CMC values against 30,000 MWCO. Permeate flux remained low and constant in presence of 5000 and 10,000 MWCO with a small variation against 30,000 MWCO for the two surfactants, thereby no appreciable effect on both surfactant concentrations on concentration polarization was estimated. Thus, RB-5 dye alone was determined to be responsible for membrane plugging or concentration polarization and ultimately for low permeate flux. The effect of trans-membrane pressure was also investigated during this study.     

Determination of equilibrium distribution constants of phenol between surfactant micelles and water using ultrafiltering centrifuge tubes

Equilibrium distribution constants, K_s, of phenol between surfactant micelles and water have been determined by micellar enhanced ultrafiltration (MEUF) using commercial ultrafiltering centrifuge tubes. Three surfactants: sodium dodecyl sulphate (SDS), polyoxyethylene 20 cetyl ether (C16E20) and cetylpiridinium chloride (CPC) were tested with a 10 000 molecular weight cut off (MWCO) membrane. Additionally, membranes of 5000 and 30 000 MWCO were used for CPC. A phenomenological mathematical model has been proposed for the batch MEUF process and checked with the experimental permeate or retentate composition. The model is based on two assumptions: monomeric molecules are not rejected by the membrane and the rejection of micelles is independent of the retentate concentration. The measured micelles rejections for different surfactants and the equivalent molecular weight of the micelles are correlated and they are not significantly affected by the addition of phenol. The estimates of K_s for SDS and CPC agree with previously reported values determined by other methods. K_s values for CPC, calculated using 5000, 10 000 and 30 000 MWCO membranes, have not been significantly different. K_s estimate has allowed to predict the phenol permeate concentration measured in continuous tangential MEUF experiments.     

Micellar enhanced ultrafiltration of phenol in synthetic wastewater using polysulfone spiral membrane

The micellar enhanced ultrafiltration (MEUF) of phenol in synthetic wastewater using two polysulfone spiral membranes of 6- and 10-kDa molecule weight cut-off (MWCO) and cetylpyridinium chloride (CPC) as cationic surfactant was studied. The effects on the permeate flux, permeate and retentate concentrations of phenol and CPC of various factors in the practical application of MEUF were studied, including surfactant and phenol concentrations, retentate flux, operating pressure, temperature and electrolyte. It was found that these two membranes could adsorb free phenol so the concentration of permeate phenol was lower than that of free phenol. The retentate phenol concentration kept increasing, then decreased slightly with the increase of the feed CPC concentration. Retentate flux and temperature had great effect on the performance of MEUF, and operating pressure did not. The addition of sodium carbonate (Na₂CO₃) could increase the retentate phenol concentration and decrease the permeate concentrations of phenol and CPC significantly.     

Micellar-enhanced ultrafiltration of cadmium ions with anionic–nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF), a surfactant-based separation process, is promising in removing multivalent metal ions from aqueous solutions. The micellar-enhanced ultrafiltration of cadmium from aqueous solution was studied in systems of anionic surfactant and mixed anionic/nonionic surfactants. The micelle sizes and zeta potentials were investigated by dynamic light scattering measurements. The effects of feed surfactant concentration, cadmium concentration and the molar ratio of nonionic surfactants to sodium dodecyl sulfate (SDS) on the cadmium removal efficiency, the rejection of SDS and nonionic surfactants and the permeate flux were investigated. The rejection efficiencies of cadmium in the MEUF operation were enhanced with higher SDS concentration and moderate Cd concentration. When SDS concentration was fixed at 3 mM, the optimal ranges of the molar ratios of nonionic surfactants to SDS for the removal of cadmium were 0.4–0.7 for Brij 35 and 0.5–0.7 for Triton X-100, respectively. With the addition of nonionic surfactants, the SDS dosage and the SDS concentration in the permeate were reduced efficiently.     

Comparison of polysulfone and ceramic membranes for the separation of phenol in micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) of phenol and a cationic surfactant, cetylpyridinium chloride (CPC), is studied using two polysulfone membranes of 5- and 50-kDa molecular weight cutoff (MWCO) and two ceramic membranes of 15- and 50-kDa MWCO. Filtrations are run under laminar cross-flow and steady-state conditions. The effect of operation variables (pressure and retentate flux) and membrane properties (nature and MWCO) on permeate flux, surfactant, and phenol rejections is analyzed. The permeate flux depends, among other variables, on the fouling favored by membrane-micelle interactions, which are strongest in the 50-kDa MWCO ceramic membrane. On the other hand, surfactant rejection is mainly determined by the pore size and influenced by the pressure for both 50-kDa MWCO membranes. An equilibrium distribution constant, K(s), of phenol between surfactant micelles and water is calculated. Its value is not significantly affected by operation conditions and membrane type. K(s) is also approximately 20% lower than the value determined in a previous work with batch dead-end ultrafiltration.     

Nonlinear two-phase equilibrium model for the binding of arsenic anions to cationic micelles

The binding of arsenic ions to cationic cetylpyridinium chloride (CPC) micelles has been investigated using the semiequilibrium dialysis (SED) technique. In SED experiments, it has been shown that CPC micelles are very effective in binding arsenic ions in the retentate. At the studied pH (pH 8), the unbound and bound arsenic exists primarily as divalent anions (HAsO₄²⁻) while CPC molecules exist as monovalent cations. Therefore, arsenic ions are bound electrostatically to the cationic micelle. The resultant colloid is large enough not to pass through the dialysis membrane, producing a rejection greater than 99.59%. The concentration of the unbound arsenic anions passing through the dialysis membrane is practically the same as the permeate concentration of these species in the analogous micellar-enhanced ultrafiltration (MEUF) experiments. Therefore, a nonlinear equilibrium model which combines thermodynamic relations, charge balance equations, and material balance equations with the Oosawa two-phase polyelectrolyte theory has been developed to correlate the binding of arsenic to CPC micelles in SED and MEUF. It was shown that the equilibrium model successfully accounts for the experimental data in both SED and MEUF in the absence and presence of monovalent (HCO₃¹⁻) and divalent co-ions (HPO₄²⁻). Because of their small sizes (less than 10 nm), micelles should retain their equilibrium shapes in the presence of hydrodynamic shear typically attained in most dynamic processes. Therefore, the equilibrium model can be used to predict separation efficiencies in other ultrafiltration units such as in crossflow ultrafiltration processes.     

Separation of aromatic alcohols using micellar-enhanced ultrafiltration and recovery of surfactant

The removals of single aromatic alcohols, including para nitro phenol (PNP), meta nitro phenol (MNP), phenol (P), catechol (CC), beta napthol (BN) and ortho chloro phenol (OCP) from aqueous solution have been studied using micellar-enhanced ultrafiltration (MEUF). Cetyl (hexadecyl) pyridinium chloride (CPC) has been taken as the cationic surfactant. An organic polyamide membrane of molecular weight cut-off 1000 is used in the MEUF experiments. Experiments are conducted using unstirred batch cell and a continuous cross flow cell. The effects of surfactant-to-solute concentration ratio in the feed, transmembrane pressure drop and cross flow rate on the permeate flux and observed retention of each solute have been studied in detail. The retention of solutes without using surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m³. However, under the same operating pressure (345 kPa), retention increases to about 66–98% depending on the nature of solute at the end of 30 min of experiment in the batch cell using surfactant micelles (10 kg/m³). The maximum retention of solute is obtained at surfactant-to-solute concentration ratio of 110. Free surfactant molecules present in the permeate and retentate are then recovered by a two-step chemical treatment process. In the first step, the surfactant is precipitated by potassium iodide and in the second step, the surfactant is recovered from the precipitate by the addition of cupric chloride. Optimum consumptions of potassium iodide and cupric chloride are also obtained experimentally.     

Effects of membrane hydrophilicity on the removal of a trihalomethane via micellar-enhanced ultrafiltration process

Micellar-enhanced ultrafiltration (MEUF) process was explored for obtaining pure water from an aqueous solution containing small amount of trihalomethanes (THMs). A homologous series of polyethylene glycol alkylether was used as nonionic surfactant. To understand effects of membrane hydrophilicity on the performance of MEUF process, membranes for the ultrafiltration were prepared from polysulfone blends containing various amount of a hydrophilic copolymer, poly(1-vinylpyrrolidone-co-acrylonitrile) (P(VP-AN)). An increase in the permeate flux was observed with an increase of the membrane hydrophilicity. The performance of MEUF process in removing THM and surfactant was shown to depend on the membrane characteristics, surfactant characteristics, and operating pressure. The rejections of THM and surfactant were increased with increasing hydrophobicity of surfactant and hydrophilicity of membrane. The rejections of THM examined with hydrophilic membranes were increased with increasing operating pressure, while those examined with hydrophobic membranes were decreased with increasing operating pressure. THM included in water could be removed up to 99% via MEUF process. The performance of MEUF examined with hydrophilic membranes could be explained with the rejection of micelles containing THM, while that examined with hydrophobic membranes could be explained with hydrophobic interactions between surfactant and membrane materials.     

Micellar enhanced ultrafiltration of phenolic derivatives from their mixtures

Micellar enhanced ultrafiltration (MEUF) of different phenolic derivatives including meta-nitrophenol (MNP), catechol (CC), para-nitrophenol (PNP), and beta-napthol (BN) in their binary mixture has been studied. A 1:1 ratio of the mixture of (i) MNP with CC and (ii) PNP with BN is taken for the MEUF experiments using a cationic surfactant, namely, cetyl(hexadecyl)pyridinium chloride (CPC). An organic polyamide membrane with molecular weight cutoff of 1000 is used. Experiments are conducted using an unstirred batch cell and a continuous cross-flow cell. The effects of various operating conditions, e.g., concentrations of surfactant and solute in the feed, transmembrane pressure drop, and cross-flow rate (for cross-flow experiments) on the permeate flux and the observed retention of each solute have been studied in detail. The retention of solutes without using the surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m3, whereas, under the same operating pressure (345 kPa), retention at the end of the experiment increases to about 66 to 99.8% depending on the nature of solute in the batch cell using surfactant micelles (10 kg/m3). Retention of solutes is less in the case of the two-component feed solution compared to the single-component feed solution. An increase in flux to the range of 9 to 16% is realized in cross-flow experiments compared to batch cell flux after one hour of operation.     

Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

Reverse osmosis filtration for space mission wastewater: membrane properties and operating conditions

Reverse osmosis (RO) is a compact process that has potential for the removal of ionic and organic pollutants for recycling space mission wastewater. Seven candidate RO membranes were compared using a batch stirred cell to determine the membrane flux and the solute rejection for synthetic space mission wastewaters. Even though the urea molecule is larger than ions such as Na+, Cl-, and NH4+, the rejection of urea is lower. This indicates that the chemical interaction between solutes and the membrane is more important than the size exclusion effect. Low pressure reverse osmosis (LPRO) membranes appear to be most desirable because of their high permeate flux and rejection. Solute rejection is dependent on the shear rate, indicating the importance of concentration polarization. A simple transport model based on the solution-diffusion model incorporating concentration polarization is used to interpret the experimental results and predict rejection over a range of operating conditions. Grant numbers: NAG 9-1053.     

Solubilization and Separation of Dicarboxylic Acids by Surfactant Micelles and Polyelectrolytes

Semi‐equilibrium dialysis (SED) and micellar enhanced ultra filtration (MEUF) methods are used to determine the extent of solubilization of water‐insoluble compounds by surfactant and polyelectrolyte. In this study, solubilization of ortho‐, meta‐ and para‐phthalic acids (OPA, MPA and TPA), 1,4‐ and 2,6‐naphthalene dicarboxylic acids (1,4‐NDCA and 2,6‐NDCA) into hexadecylpyridinium chloride (CPC), and the behavior of these acids to bind to the polyelectrolyte ionizable groups were investigated at 25 °C, using SED and MEUF methods. Polydimethyldiallylammonium chloride (PDMDAAC) is used in this study. It was found that the solubilization of organic acids decreases with increasing the solute mole fractions in micelles. Also, the best separation occurs at the lowest concentration of the phthalate ions and high concentrations of either CPC or PDMDAAC. The results support the idea of charge interaction between the anionic dicarboxylate groups and cationic surfactant or polyelectrolyte. The results also show that the presence of a second phenyl ring does not greatly affect the solubilization behavior of the acids.     

Hydrophobic modification of poly(phthalazinone ether sulfone ketone) hollow fiber membrane for vacuum membrane distillation

New hydrophobic poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber composite membranes coated with silicone rubber and with sol–gel polytrifluoropropylsiloxane were obtained by surface-coated modification method. The effects of coating time, coating temperature and the concentration of silicone rubber solution on the vacuum membrane distillation (VMD) properties of silicone rubber coated membranes were investigated. It was found that high water permeate flux could be gotten in low temperature and low concentration of silicone rubber solution. When the coating temperature is 60 °C, the coating time is 9 h and the concentration of silicone rubber solution is 5 g L⁻¹ the water permeate flux of the silicone rubber coated membrane is 3.5 L m⁻² h⁻¹. The prepolymerization time influence the performance of polytrifluoropropylsiloxane coated membranes, and higher prepolymerization time decrease the water permeate flux of the membrane. The water permeate flux and the salt rejection was 3.7 L m⁻² h⁻¹ and 94.6%, respectively in 30 min prepolymerization period. The VMD performances of two composite membranes during long-term operation were studied, and the results indicated that the VMD performances of two composite membranes are quite stable. The salt rejection of silicone rubber coated membrane decreased from 99 to 95% and the water permeate flux fluctuated between 2.0 and 2.5 L m⁻² h⁻¹. The salt rejection of polytrifluoropropylsiloxane coated membrane decreased from 98 to 94% and the water permeate flux fluctuated in 1 L m⁻² h⁻¹ range.     

Evaluation of PTMSP membranes in achieving enhanced ethanol removal from fermentations by pervaporation

The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years. Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne] (PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance in operation with cell-containing fermentation broths.     

Binding of ionic surfactants to purified humic acid

The binding of organic contaminants to dissolved humic acids reduces the free concentration of the contaminants in the environment and also may cause changes to the solution properties of humic acids. Surfactants are a special class of contaminants that are introduced into the environment either through wastewater or by site-specific contamination. The amphiphilic nature of both surfactants and humic acids can easily lead to their mutual attraction and consequently affect the solution behavior of the humics. Binding of an anionic surfactant (sodium dodecyl sulfate, SDS) and two cationic surfactants (dodecyl- and cetylpyridinium chloride, DPC and CPC) to purified Aldrich humic acid (PAHA) is studied at pH values of 5, 7, and 10 in solutions with a 0.025 M ionic strength (I). Monomer concentrations of the surfactants are measured with a surfactant-selective electrode. At I = 0.025 M, no significant binding is observed between the anionic surfactant (SDS) and PAHA, whereas the two cationic surfactants (DPC, CPC) bind strongly to PAHA over the pH range investigated. The binding is due both to electrostatic and hydrophobic attraction. The initial affinity increases with increasing pH (i.e., negative charge of PAHA) and tail length of the surfactant. Binding reaches a pseudo-plateau value (2-5 mmol/g) when the charge associated with PAHA is neutralized by that of the bound surfactant molecules. The pseudo-plateau values for DPC and CPC are very similar and depend on the solution pH. The cationic surfactant-PAHA complexes precipitate when the charge neutralization point is reached. This occurs at approximately 10% of the critical micelle concentration or CMC. This type of phase separation commonly occurs during surfactant binding to oppositely charged polyelectrolytes. For CPC, the precipitation is complete, but in the case of DPC, a noticeable fraction of PAHA remains in solution. At very low CPC concentrations (less than 0.1% of the CMC), CPC binding to PAHA is cooperative. The investigated range of concentrations for DPC was too limited to reach a similar conclusion. The results of this study demonstrate that the fate of humic acids will be strongly affected by the presence of low cationic surfactant concentrations in aqueous environmental systems.     

Removal of 17β-estradiol by powdered activated carbon—Microfiltraion hybrid process: The effect of PAC deposition on membrane surface

The removal of 17β-estradiol (E2) was investigated in a powdered activated carbon-submerged microfiltration (PAC-MF) hybrid system to better understand the effect on the system performance of PAC deposition on the membrane. A series of experiments were carried out under various operating conditions. Although the rejection or adsorption of E2 by MF membrane itself was almost negligible, the concentration of E2 in the permeate was always lower than it was in the reactor. This is because E2 was further removed as it passed through the PAC layer deposited on the membrane. As the E2 removal efficiency by the deposited PAC was lower than that by the PAC in the bulk phase, the overall E2 removal was largely dependent on the fraction of the deposited PAC on the membrane which were influenced by operating parameters such as permeate flux, hydraulic retention time (HRT) and mixing intensity in a PAC-MF system. The effect of these parameters on the overall E2 removal rate were also determined quantitatively using model equations developed in this study.     

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.     

Modelling of the pore size distribution of ultrafiltration membranes

A dilute aqueous solution of polydisperse neutral dextrans was used to determine the sieving properties (flux and rejection) of porous polyacrylonitrile membranes. Gel ermeation chromatography was used to measure the solute mole and concentration in the permeate. From these data, rejection coefficients were calculated as a function of solute molecular size. A mathematical model was then developed to relate the flux and solute rejection to pore size distribution and the total number of pores, based upon the assumption that solute rejection was the result of purely geometric considerations. As a first approximation, a solute molecule was considered either too large to enter a membrane pore, or if it entered, its concentration in the permeate from that pore, as well as the solvent flux through the pore, were not affected. This model also considered the effects of steric hindrance and hydrodynamic lag on the convection of solute through a membrane. The shape and sharpness of pore size distributions were found to be useful in comparisons of ultrafiltration membranes.     

Influence of operating conditions on performance of ceramic membrane used for water treatment

The removal of natural organic matter (NOM) is a critical aspect of potable water treatment because NOM compounds are precursors of harmful disinfection by-products, hence should be removed from water intended for human consumption. Ultrafiltration using ceramic membranes can be a suitable process for removal of natural substances. Previously reported experiments were dedicated to evaluating the suitability of ultrafiltration through ceramic membrane for water treatment with a focus on the separation of natural organic matter. The effects of the membrane operating time and linear flow velocity on transport and separation properties were also examined. The experiments, using a 7-channel 300 kDa MWCO ceramic membrane, were carried out with model solutions and surface water at trans-membrane pressure of 0.2–0.5 MPa. The results revealed that a loose UF ceramic membrane can successfully eliminate natural organic matter from water. The permeability of the membrane was strongly affected by the composition of the feed stream, i.e. the permeate flux decreased with an increase in the NOM concentration. The permeate flux also decreased over the period of the operation, while this parameter did not influence the effectiveness of separation, i.e. the removal of NOM. It was observed that the increased cross-flow velocity resulted in the decrease in the membrane-fouling intensity and slightly improved the retention of contaminants.