Polyelectrolyte-enhanced Ultrafiltration Research Articles

An integrated membrane distillation, photocatalysis and polyelectrolyte-enhanced ultrafiltration process for arsenic remediation at point-of-use

Arsenic contamination of drinking water is a result of natural and/or anthropogenic activities, causing undesirable detrimental effects on the environment and the human health. Herein, an integrated process based on Membrane Distillation (MD), photocatalysis and Polymer-enhanced Ultrafiltration (PEUF) was developed for an effective remediation of arsenic (As). This approach, whose effectiveness was demonstrated by experimental tests on artificial solution mimicking As-contaminated water in the area of Sila Massif (Italy), ensured a near total water recovery and a rational management of residual contaminants.MD allowed to produce high-quality freshwater from contaminated feedwater containing As in the range of 0.059-5 mg·L-1, without deterioration of the transmembrane flux up to a recovery factor of 98.8%. Furthermore, a photocatalytic step was applied on MD retentate to convert arsenite As (III) into arsenate As(V), the latter subsequently removed by PEUF with efficiency of 98.2%. Speciation analysis demonstrated the necessity to reduce the feed pH to 5.6 in order to avoid the risk of scaling in MD stage, whereas Na2CO3 softening at pH 9 before the photocatalytic stage ensured both the reactive precipitation of Ca and Mg ions and the depletion of bicarbonate ions.

Porous Gelatin Membranes Obtained from Pickering Emulsions Stabilized with h-BNNS: Application for Polyelectrolyte-Enhanced Ultrafiltration.

In recent years, numerous studies have been conducted to develop biopolymer-based membranes, highlighting the challenges to prepare porous structures with control porosity. In this paper an innovative method that relies on the generation of Pickering emulsions was developed to prepare porous membranes from gelatin for filtration purpose. Hexagonal boron nitride nanosheets (h-BNNS) were used to stabilize micro-droplets of castor oil in a continuous homogeneous gelatin solution. Two steps in the membrane preparation process strongly influenced the porous structure. Specifically, the duration of the drying time after emulsion casting and the duration of the cross-linking step affected membrane pore size, hydrophobicity, water swelling, and water permeability. By controlling these two steps, membranes could be designed with pore size between 0.39 and 1.60 μm and display pure water permeability between 150 and 506 L h−1 m−2 bar−1. These membranes have been tested for complexation–ultrafiltration experiments in which iron ions were removed from aqueous solutions with/without poly (acrylic acid) (PAA). Without PAA, the removal of free iron (II) ions was low (not more than 14%). The addition of PAA (200 ppm) allowed obtaining high removal rates (97%) at pH ≥ 5 with 3 bars of transmembrane pressure.

Comparison of positively charged polymer species and cationic surfactants for methyl orange removal via polyelectrolyte and micellar enhanced ultrafiltration

Cationic charged polymer species were synthesized via emulsion polymerization and used as polyelectrolytes in polyelectrolyte enhanced ultrafiltration (PEUF) for the removal of the anionic dye methyl orange (MO). A cellulose membrane with a 30 kDa molecular weight cut-off (MWCO) was used for the separation process showing almost complete MO removal for a polymer concentration of 1 g L−1 and a dye concentration up to 50 mg L−1. Four cationic surfactants from the CTAB family (DeTAB, DTAB, TTAB, and CTAB) have been investigated in a comparable micellar enhanced ultrafiltration (MEUF) process. The MO removal efficiency was lower, and only TTAB and CTAB showed removal efficiencies above 90 %. The flux for the polymer species is slightly lower as for the surfactants, but the removal efficiency is higher, and carbon leaching into the purified stream is much lower.

Copper recovery via polyelectrolyte enhanced ultrafiltration followed by dithionite based chemical reduction: Effects of solution pH and polyelectrolyte type

Abstract A chemical reduction process was proposed to recover copper from the retentate of polyelectrolyte enhanced ultrafiltration (PEUF). Three polyelectrolytes (PSS, PAA, and PEI) containing various functional groups and molecular weights were studied to explore their effects on the copper removal in PEUF and on the copper recovery by chemical reduction under various pH conditions. With PSS which contains sulfonic group, copper was removed reasonably well (ca. 75%) by PEUF even under acidic pH value of 3. With PAA which contains carboxylic group, copper removal was a bit low (∼60%) under pH 3.0 but increased substantially at pH 4.0. A branched PEI having amine group achieved the highest Cu removal of 94% at pH 3. The copper removal efficiency decreased slightly with increasing pH due to the high permeation of PEI through membrane. Chemical reduction achieved the complete copper recovery for solution containing PSS. The copper recovery efficiencies were more than 95% for PAA solution with pH values ranging from 3 to 9 at reaction time of one hour. For PEI, the recovery efficiencies ranged from 20 to 96% and were pH dependent. Aggregated and settled readily copper particles were produced by chemical reduction in PSS solution. XRD analysis identified cuprous oxide in all of the samples. Dependent of pH and polyelectrolytes, additional peaks matching those of elemental copper were identified. TGA analysis showed that solids produced from PSS and PAA systems contained no polyelectrolytes while solid collected from PEI system contained 32% of polyelectrolyte.

Comparison of low-pressure reverse osmosis filtration and polyelectrolyte-enhanced ultrafiltration for the removal of Co and Sr from nuclear plant wastewater

Abstract Volume reduction and the concentration of long-lived radioactive species are critical issues for the management of liquid low-level radioactive waste. This study investigated and compared the performances of low-pressure reverse osmosis (LPRO) and polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of target metals (Co and Sr) from simulated low-level radioactive waste. The effects of dosage and types of chelating polymers, such as polyacrylic acid (PAA) and polyethylenimine (PEI), were evaluated at acidic and neutral pH levels. The metal removal efficiencies by precipitation at acidic pH (4.5) and neutral pH (6.5) were marginal. The addition of PAA to LPRO had no effect on metal removal, but had a negative impact on membrane permeability, particularly at acidic pH levels. The LPRO itself already achieved sufficient metal rejection; therefore, the addition of PAA only caused fouling. In contrast, the PAA dosage and solution pH governed the metal rejection in PEUF. Deprotonated PAA molecules bound to metal ions, but the distribution of PAA species had no significant impact on flux decline. The PEUF with PEI exhibited almost no pH dependency in metal removal, but showed metal-specific removal behaviors. The PEUF with PAA achieved metal removal as high as LPRO, with relatively high water permeability.

Integration of polyelectrolyte enhanced ultrafiltration and chemical reduction for metal-containing wastewater treatment and metal recovery.

Chemical reduction was firstly employed to treat synthetic wastewaters of various compositions prepared to simulate the retentate stream of polyelectrolyte enhanced ultrafiltration (PEUF). With fixed Cu:polyethylenimine (PEI) monomer:dithionite molar ratio, increasing copper concentration increases copper removal efficiency. Under fixed Cu:dithionite molar ratio and fixed Cu concentration, increasing PEI monomer:copper molar ratio decreases copper removal efficiency. The formation of nano-sized copper particles, which readily pass through 0.45 μm filter used for sample pretreatment before residual copper analysis, might be the reason behind the decreasing copper removal efficiency observed. Particle size analysis shows that the size of copper particles, which are formed through reduction reaction, increases with decreasing pH value and increasing reaction time. As ultrafiltration is capable of removing these nano-sized particles, integration of chemical reduction and PEUF is proposed to simultaneously achieve regeneration of polyelectrolyte and recovery of copper in one process. Results show that the proposed process could achieve almost complete copper removal without being affected by reaction pH.

Removal of arsenic from contaminated water by coagulation followed by polyelectrolyte enhanced ultrafiltration

AbstractIn this work, removal of arsenic from contaminated water was carried out using coagulation followed by polyelectrolyte enhanced ultrafiltration (PEUF). Ferric chloride and polydiallyldimethylammonium chloride (polyDADMAC) were used as coagulant and cationic polyelectrolyte, respectively. In the first step, effect of coagulant concentration on removal of arsenic was studied and coagulant dosage was optimized. In the second set of study, a combination of low dose of coagulant and polyelectrolyte solution was used for treatment of arsenic contaminated water. The supernatant collected following coagulation was subjected to PEUF so as to remove the residual arsenate ions. Ultrafiltration (UF) was carried out in a tangential flow module fitted with 5 kD polyethersulfone (PES) membrane. During UF, influence of polyelectrolyte dosage and transmembrane pressure (TMP) on permeate flux and arsenic rejection were investigated and optimum values were reported. It was observed that small dose [1 mL PE (polyelec...

Removal of heavy metals from aqueous solution by polyacrylic acid enhanced ultrafiltration

One of the recently developed water treatment processes is the polyelectrolyte-enhanced ultrafiltration (PEUF). This technique combines a membrane filtration process (ultratfiltration) and a cation–polyectrolyte complexation technique. PEUF is shown to be an efficient technology for the removal of heavy metals from liquid effluents even at low concentrations. In this proposal, the removal of three heavy metals (cadmium, copper and zinc) from aqueous solutions by PEUF process was investigated. The poly(acrylic acid) (PAA) with an average molecular weight 100 kDa was used as complexing agent. The ultrafiltration experiments were performed using a tangential cell system equipped with a polyethersulphone membrane having a 10.000 molecular weight cut-off (MWCO). To improve the retention of the heavy metal ions, the effect of some operating parameters and solution characteristics were studied. For different PAA concentrations, this study showed that all permeate fluxes increased linearly by increasing transmembrane pressure. For the three studied metals, the best retentions were observed at 2 × 10–3 mol L–1 PAA concentration, 3 bar transmembrane pressure and pH above 5. The removal of cadmium, copper and zinc exceeded, respectively, 80, 93 and 70%.

Retention of samarium ions from aqueous solutions by poly(acrylic acid)-enhanced ultrafiltration

Rare earth elements (REE) are widely used in variety of commercial applications, which results in public exposure to them, and it is a matter of concern. Recent studies have demonstrated that the toxicity of (REE) as a group is similar to the toxicity of heavy metals. Many methods were used to remove lanthanides from wastewaters generated from their commercial use. Samarium, a REE, which may be removed from the aqueous solution by polyelectrolyte-enhanced ultrafiltration process, was investigated using poly(acrylic acid) (PAA) with average molecular weight 100,000 Da. The ultrafiltration studies were carried out using a tangential cell system. Polyethersulfone membrane with molecular weight cutoff of 5,000 Da and an effective filtration area of 50 cm2 were used (PES-5). Several parameters, such as transmembrane pressure, PAA concentrations, and pH, have been optimized to improve the retention of the Sm(III) ions. Results shows that the permeate flux increases linearly with increasing transmembrane pressure. It can be seen that with the increase in the concentration of PAA, the Sm(III) ions retention also increases until reaching 80%. A better retention was observed at 2 × 10−4 mol L−1 PAA concentration and 3 bar transmembrane pressure. The pH effect study on samarium ions revealed a maximum retention around 70% for pH 5.

The effect of operating conditions on the retention of Toluidine blue by polyelectrolyte-enhanced ultrafiltration

In the present work, we study the effect of experimental conditions on the performance of polyelectrolyte-enhanced ultrafiltration for the removal of Toluidine blue from aqueous solution. The dye solution was processed by ultrafiltration using a regenerate cellulose membrane with pore sizes small enough to block the passage of the polymer and then the complexed dye ions. The experiments showed that retentions as high as 99% and 97% were obtained for PAA and PANH4, respectively, due to the strong electrostatic interaction between anionic polyelectrolytes and cationic dye. The increase of retention was linked to the complexation of the dye by polyelectrolyte while the decrease of the permeate flux was attributed to the accumulated macromolecular complex near the membrane.

The effect of surfactant on dye removal by polyelectrolyte enhanced ultrafiltration

AbstractPolyelectrolyte-based separation of toxic dyes is studied to estimate the potential of polyelectrolyte enhanced ultrafiltration (PEUF) using polyethylene glycol (PEG). Removal of methyl orange (MO) an azo dye from aqueous solutions, by continuous polymer enhanced ultrafiltration (PEUF) was investigated. The permeate flux profile and obtained retention of MO were studied as a function of polyelectrolyte concentrations, transmembrane pressure, ionic strength and pH in the absence and in the presence of surfactant (CTAB). The experiments showed that retention of MO in the presence of PEG of different concentrations was 65%. This may be due to that the PEG polyelectrolyte cannot bind MO to form aggregates to enhance UF process. However, when the CTAB was applied at a fixed concentration below CMC, MO decolourization increased and reached a limiting value of 99%. The high rejection for MO dye is due to the formation of H aggregates in the aqueous solution. This result was confirmed by the change of the...

Modification of polyethersulfone using sericin and polyvinylpyrrolidone for cadmium ion removal by polyelectrolyte-enhanced ultrafiltration

The present study deals with the synthesis of polyethersulfone (PES)-based membrane using a biopolymer sericin and polyvinylpyrrolidone (PVP) by phase inversion process. The synthesized membranes were characterized for hydrophilicity, pure water permeability (PWP), membrane stability, and surface functional group analysis. The synthesized membranes were used to study the effective removal of cadmium ions using poly(diallyldimethylammoniumchloride) and polyethyleneimine (PEI) by polyelectrolyte-enhanced ultrafiltration. PVP-sericin-incorporated PES membrane resulted in the highest average pore radius (22 nm) and PWP (34.11 L m−2 h−1 bar−1). It also showed that higher antifouling resistance of 10 folds than neat PES membrane retained the higher flux rate. Overall, PES/sericin/PVP membrane has better characteristics, and maximum percentage of cadmium removal was obtained when added with PEI ligand.

Removal of methylene blue from aqueous solutions by poly(acrylic acid) and poly(ammonium acrylate) assisted ultrafiltration

Despite the numerous works dealing with the application of polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of micropollutants, its application for the treatment of dye effluent is very scarce. In the present study we investigated the recovery of methylene blue (MB), a phenothiazine cationic dye, by ultrafiltration with two anionic polyelectrolytes used as complexing agents. The ultrafiltration experiments were operated in batch mode with stirred cell equipped with 10,000 MWCO regenerated cellulose. Effects of operating conditions, e.g., transmembrane pressure, feed polyelectrolyte, feed dye solution, NaCl concentration, and pH on dye retention and permeate flux have been analyzed. High retention rate of dye in the order of 98% was obtained as a result of complexation between anionic polyelectrolyte and cationic dye. However the retention of the dye decreases as the salt concentration increases and pH decreases.

Neural network model prediction of chromium separation in polyelectrolyte-enhanced ultrafiltration

Effectiveness of polyelectrolyte-enhanced ultrafiltration in chromium recovery from its aqueous solutions was tested experimentally. Two chromium species, Cr(III) and Cr(VI) ions, were the subject of ultrafiltration processes enhanced with two water-soluble, ion-exchanging polyelectrolytes. These were: poly(sodium 4-styrenesulfonate) - PSSS (for Cr(III) ions recovery) and poly(diallyldimethylammonium chloride) - PDDAC (for Cr(VI) ions recovery). Experimental ultrafiltration tests with two different membranes and model solutions of appropriate chromium ions (5 and 50 mg dm -3 ), at different pH and with various polyelectrolyte doses, provided numerical data for the artificial neural networks training procedure. Numerical neural network models made prediction of chromium retention coefficient (R) under different process conditions (pH, polymer dose, concentration of selected Cr form) possible. Strongly nonlinear dependences of retention coefficient (R) on pH and polymer : metal concentration ratio for both chromium species, represented by experimental data, were identified and modeled by neural networks correctly. Good compatibility between experimental data and neural network predictions was observed.

Copper and Zinc removal from aqueous solutions by polyacrylic acid assisted-ultrafiltration

Copper and Zinc removal from aqueous solution by polyelectrolyte enhanced ultrafiltration (PEUF) process was investigated using poly(acrylic acid) (PAA) with average molecular weight 100kDa. The ultrafiltration studies were carried out using a tangential cell system, equipped with 10,000 MWCO regenerated cellulose. Several parameters have been studied such as: transmembrane pressure, PAA concentration, pH and ionic strength to improve the retention of the metal ions. The removal of Zn2+ and Cu2+ is respectively more than 70% and 93%. A better retention was observed at 2·10−3molL−1 PAA concentration and 3bar transmembrane pressure. The pH effect on the Zinc and Copper recovery revealed a maximum retention around 75% and 97%, respectively, for pH=5. The study of the ionic strength effect has shown a retention decrease with the salt concentration increase. Selectivity was studied using a solution containing the two metal ions. Zinc retention decreases compared to single metal solutions, and this is more significant in the case of Copper ions.

Polyelectrolyte-Enhanced Ultrafiltration (PEUF) Process for Low Level Arsenic Removal: Recovery of Polyelectrolyte from Retentate Stream

Removal of low levels of arsenic from contaminated water using the polyelectrolyte-enhanced ultrafiltration or PEUF process technology has been studied. The cationic polyelectrolyte poly (diallyldimethyl ammonium chloride), PDADMAC, was utilized to bind arsenic (in the form of arsenate anion) in contaminated water and the polyelectrolyte-arsenate complex solution was then filtered off (as retentate) by ultrafiltration. The 99-99.9% arsenic removal from synthetic low level arsenic (100 ppb) contaminated water demonstrates that the technology can easily achieve the relatively new international arsenic maximum concentration level of 10 ppb. To make the PEUF process more economical and environmentally friendly, the PDADMAC in the retentate must be recovered. Precipitation of PDADMAC-arsenate solutions with divalent cations has been studied to separate out metal-arsenate compounds leaving free PDADMAC to reuse in the process. The metal-arsenate compound precipitation is strongly affected by divalent metal:As molar ratio, and pH of the solution. The precipitation results also suggest that polyelectrolyte retards formation of the metal-arsenate compounds and affects the size and morphology of the particles formed, thus directly affecting the sedimentation rate of the resulting precipitate.

Application of Polyelectrolyte‐Enhanced Ultrafiltration for Rhenium Recovery from Aqueous Solutions

AbstractPolyelectrolyte‐enhanced ultrafiltration was investigated for rhenium(VII) recovery from aqueous solutions by using polyquaternium‐6 (PQ6) as a complexing agent. The effects of the operating parameters on the permeate flux (J) and the rhenium rejection coefficient (R) were studied. In the process of concentration, J declines slowly and R is about 1. The concentrated solution was used for the decomplexation. It takes 10 min to achieve the decomplexation equilibrium at a chloride ion concentration of 100 mg L–1. The decomplexation percentage reaches 45.6 %. In the diafiltration process, rhenium is extracted effectively, and the purification of the regenerated PQ6 is satisfactory. The regenerated PQ6 was used to bind rhenium(VII). The binding capacity of the regenerated PQ6 is close to that of fresh PQ6.

A physico-chemical model for polyelectrolyte enhanced ultrafiltration

A physico-chemical model for the polyelectrolyte enhanced ultrafiltration (PEUF) was developed. Experimental data available for removal of cadmium using poly-ammonium acrylate (PAmA) was used to validate the model. The model was based on counter ion condensation theory of Oosawa. Intensity of binding of cadmium to polyelectrolyte was estimated. Solution osmotic pressure was quantified by computing the activity of the polyelectrolyte–counter ion complex. Using osmotic pressure controlling model, the permeate flux was quantified. Variation of polyelectrolyte diffusivity and viscosity with concentration within the mass transfer boundary layer was included in the calculation. Various parameters of the model were estimated by comparing the experimental data with the calculated ones. The model was also extended and developed for PEUF system in presence of monovalent salt, variation of pH and for pure polyelectrolyte solution.

Comparative study of the uses of poly(4-vinylpyridine) and poly(diallyldimethylammonium) chloride for the removal of perchlorate from aqueous solution by polyelectrolyte-enhanced ultrafiltration

An application of polyelectrolyte-enhanced ultrafiltration utilizes cationic polyelectrolytes to electrostatically bind anionic species. The colloid and target anion are then concentrated using an ultrafilter, producing a filtrate with a lower concentration of the target. This study compared the performances of poly(4-vinylpyridine) (P4VP) and poly(diallyldimethylammonium) chloride (PDADMAC) for the removal of perchlorate. Potentiometric titration data revealed that the ionization properties of P4VP in aqueous solution vary as functions of titrant utilized, degree of protonation, and counterion concentration. The greater affinity of perchlorate over chloride for the protonated pyridine residues of P4VP provided up to 95.8% retention of perchlorate under the solution conditions investigated. Through ultrafiltration experiments, the effects solution pH, counterion concentration, and polymer concentration were examined for both P4VP and PDADMAC. In addition, the effectiveness of P4VP recovery and reuse was also assessed.

Removal of dyes from wastewater using polyelectrolyte enhanced ultrafiltration (PEUF)

Polyelectrolyte-based separation of toxic dyes is studied to estimate the potential of polyelectroyte enhanced ultrafiltration (PEUF) using poly(ammonium-acrylate) as anionic polymer. PEUF experiments are conducted to study the retention characteristics of two model dyes (Safranin T (ST) and Eriochrome Blue Black R (EBBR) in the continuous cross flow system. Effects of the operating conditions, e.g., transmembrane pressure, feed polyelectrolyte concentration, feed dye concentration, ionic strength and pH on the permeate flux profile and observed retention have been investigated. The results show that the highest rejection for ST and EBBR dyes are 99% and 90% respectively. The enhancement is primarily due to the formation of complexes between the anionic polymer and dye molecules. The retention of ST decreases with ionic strength. High retention was obtained at pH range 4–10 in the case of ST; this effect was attributed to the increase of electrostatic interaction. The ionic strength and pH have no effect on the removal of EBBR.