Polyelectrolyte-enhanced Ultrafiltration Research Articles

Retention of Cadmium and Zinc from Aqueous Solutions by Poly(acrylic Acid)-Assisted Ultrafiltration

Cadmium and zinc removal from aqueous solution by polyelectrolyte enhanced ultrafiltration (PEUF) process was investigated using poly(acrylic acid) (PAA) with an average molecular weight of 100 kDa. The ultrafiltration studies were carried out using a tangential cell system equipped with 10.000 MWCO regenerated cellulose. Several parameters, such as transmembrane pressure, PAA concentration, pH and ionic strength, have been optimized to improve the retention of the metal ions. The removal of Cd2+ and Zn2+ is more than 96% and 94%, respectively, when each ion was studied separately. The study of pH effect on the cadmium and zinc recovery reveals retentions almost around 85% and 78% respectively at pH 5. Selectivity was studied using a solution containing the two metal ions. It was found that zinc retention decreases compared to single metal solutions, which is more significant in the case of cadmium ions.

Removal of Cr(III) and Cr(VI) ions from aqueous solutions by means of polyelectrolyte-enhanced ultrafiltration

The possibility of applying polyelectrolyte-enhanced ultrafiltration to the removal of chromium ions from aqueous solutions has been discussed. Two water-soluble polyelectrolytes containing weak ion-exchange groups were chosen to bind metal ions and enable chromium retention on ultrafiltration membranes. These were sodium polyacrylate to bind Cr(III) ions and polyethylenimine for Cr(VI) ions. These two forms of chromium ions, Cr(III) and Cr(VI), were tested in separate solutions. The main parameters which determine the effectiveness of chromium retention (the polyelectrolyte quantity and solution pH) were examined. Ultrafiltration concentration of Cr(III) and Cr(VI) solutions (initial concentrations of 5 and 50 mg Cr/dm 3) were carried out according to the previously determined polymer : metal concentration ratios, and at optimum pH. The volume reduction factor (VRF) of 50 was obtained. The retention coefficient for chromium observed during the process fell within the range of 0.82–1.

Retention of cadmium ions from aqueous solutions by poly(ammonium acrylate) enhanced ultrafiltration

Cadmium removal from aqueous solution by polyelectrolyte enhanced ultrafiltration (PEUF) with relatively low transmembrane pressure was investigated at varying conditions of polyelectrolyte and cadmium concentrations, transmembrane pressure, ionic strength and pH. The poly(ammonium acrylate), with two average molecular weights (8000 and 15 000 Da) were used as polyelectrolyte. Flux declines during ultrafiltration of polyelectrolyte solutions. An effort has been made to evaluate these resistances independently at different operating conditions. The hydraulic membrane resistance is higher for processing solutions of PAmA 8 than solutions of PAmA 15. The study of ionic strength effect demonstrates that it decreases the retention of cadmium ions and increases the permeate flux. More than 99% of cadmium was retained for a NaNO 3 feed concentration less than 5 × 10 −2 mol L −1. The pH effect study on the cadmium recovery revealed a maximum retention around 98% for pH 4.

Polyelectrolyte enhanced ultrafiltration (PEUF) for the removal of Cd(II): Effects of organic ligands and solution pH

This study focused on the effects of pH and organic ligands, namely ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and citric acids, on the removal and recovery of Cd(II) in polyelectrolyte enhanced ultrafiltration (PEUF). Polyethylenimine (PEI), which can bind with both positively charged metal ions by coordination bonding and negatively charged ligand–metal complexes by charge attraction, was employed as a chelating polymer. The removal and recovery of Cd species was greatly dependent on the chemistry of organic ligands according to solution pH, particularly being related to the distribution of Cd-ligand complexes at different pH levels. In the presence of EDTA, the dominant Cd species are negatively charged Cd(EDTA) 2− and CdH(EDTA) − over the range of pH levels investigated, interacting with PEI via electrostatic attraction and being less pH dependent. On the other hand, the pH effects of both NTA and citric acid systems are similar to that for the system without organic ligands. This was associated with the fact that free Cd ions were predominant at the acidic pH range in both NTA and citric acid systems.

Removal of Chromate Ions from Water using the Polyelectrolyte‐Enhanced Ultrafiltration Process

Polysulfone (PSf) asymmetric hollow fiber membranes with the molecular weight cut‐off (MWCO) of 13,000 Dalton were prepared by the dry‐wet phase inversion method, with which negatively charged chromate ions, CrO4 2− was removed form aqueous solutions using the polyelectrolyte‐enhanced ultrafiltration (PEUF) process. Parameters relating to the chromate removal such as the type of polyelectrolyte, the loading ratio, and the pH value of the aqueous solution were studied. Poly (dially dimethylammonium chloride) (PDADMAC) was found to be the most effective polyelectrolyte. Under the optimal conditions, that is, the polyelectrolyte‐metal loading ratio of 20 and the pH value 8.0 respectively, up to 100% of the chromate rejection was achieved. The used polyelectrolyte may be recovered about 70% by the acidified decomplexation combined with ultrafiltration. The concentration polarization was present but imposed limited effect on the PEUF process in the long‐term operation.

Preliminary design and optimisation of a PEUF process for Cr(VI) removal

The main purpose of this work is the study of the viability of a polyelectrolyte enhanced ultrafiltration (PEUF) process for the chromate recovery using poly(diallyldimethylammonium chloride) (PDADMAC) as water-soluble polymer. First of all, the interaction between PDADMAC and chromate ions was studied by potentiometric titrations of different poly(acrylic acid) (PAA) solutions in which its acidity constant (p K a) was determined using the Henderson–Hasselbach equation. This interaction is linked to the influence of the presence of PDADMAC and chromate in the PAA p K a value. Next, the operation conditions (pH, temperature and transmembrane pressure) that optimize the membrane hydrodynamic behaviour were studied with ultrafiltration runs in mode operation of total recirculation. Furthermore, working at the operation conditions determined in the previous stage and with solutions of PDADMAC and chromate, the influence of ionic strength on design parameters was studied. Finally, the viability of a chemical method to regenerate the polyelectrolyte, based on the addition of NaCl and subsequent ultrafiltration, was checked. We conclude that this method is not suitable, mainly because of the great amount of water spent in the diafiltration stage necessary to reduce the polyelectrolyte solution chloride concentration.

Equilibrium dialysis and ultrafiltration investigations of perchlorate removal from aqueous solution using poly(diallyldimethylammonium) chloride

Use of perchlorate salts in military activities and the aerospace industry is widespread. These salts are highly water-soluble and are, to a large extent, kinetically inert as aqueous species. As a groundwater contaminant, perchlorate is now being detected in an increasing number of locations and is believed to interfere with the uptake of iodide by the thyroid, which can result in decreased hormone production. The United States Environmental Protection Agency (US EPA) has established a reference dose for perchlorate of 0.0007 mg/kg/day, which translates to a drinking water equivalent level of 24.5 ppb. This study investigated the application of polyelectrolyte-enhanced ultrafiltration (PEUF) for the selective removal of perchlorate from aqueous solution through equilibrium dialysis and ultrafiltration experiments. Using poly(diallyldimethylammonium) chloride, the effectiveness and efficiency of PEUF in the removal of perchlorate from other aqueous solution components was investigated by testing parameters such as polyelectrolyte concentration, pH, and ionic strength. Removal of perchlorate from synthetic groundwater initially containing 10.3 ppm perchlorate and also containing chloride, sulfate, and carbonate was also examined. Perchlorate separations of greater than 95% were achieved, even in the presence of 10-fold excesses of competing ions.

Removal of perchlorate from groundwater by the polyelectolyte-enhanced ultrafiltration process

The polyelectrolyte enhanced ultrafiltration (PEUF) process for perchlorate removal from groundwater containing common co-contaminants like nitrate and sulfate was investigated. Existing processes such as ion exchange can remove perchlorate but with greater complexity, especially when applied in the presence of high nitrate and sulfate concentration. The effect of cationic polyelectrolyte, poly(diallyldimethyl ammonium chloride) (PDADMAC) concentration and the effect of nitrate and sulfate in a broader concentration range were observed. In the absence of other anions, a lower amount of PDADMAC (0.5–1 mM) can remove more than 90% of perchlorate from the aqueous phase. However, in the presence of 5 mM nitrate, perchlorate removal decreases as the available binding sites of PDADMAC for perchlorate are reduced. In the presence of both 1 mM to 10 mM nitrate and sulfate, 60–80% perchlorate was removed with 30 mM PDADMAC. The removal of sulfate and nitrate in this case was nearly 75% and 65%, respectively. The effect of other parameters such as relative flux, membrane material and pore size were also observed to study the feasibility of PEUF for perchlorate removal. Consequently, PEUF proved to be an effective perchlorate removal process owing to the high removal efficiency and suitability in groundwater remediation containing other contaminants.

Nitrate removal from contaminated water using polyelectrolyte-enhanced ultrafiltration

The removal of nitrate from contaminated groundwater via polyelectrolyte-enhanced ultrafiltration (UF) was investigated using different chelating polymers and membrane pore sizes. Although the percentage polymer rejection by membranes slightly decreased with higher chelating polyelectrolyte dosages, the nitrate rejection efficiency continued to increase while retaining a larger amount of polymers. Substantial nitrate removal up to >90% at high molar ratios of quaternary amine groups to nitrate was achieved depending on the types of chelating polymers and UF membranes used. The branched polymers removed nitrate better than the linear polymers, whereas the UF membrane with higher molecular weight cut-offs (MWCOs) removed more nitrate than that with smaller ones in the presence of polymers. Greater nitrate rejection using the branched chelating polymer and the membrane with higher MWCO was associated with the sorption of polyelectrolytes onto membrane pores and thereby better removal of nitrate by chelation. The flux decline became severe with increasing the dosage of polymers and the MWCO of the UF membranes, but it had no direct correlation with the molecular weight (MW) of chelating polymers. The regeneration of chelating polymers was successfully carried out with a NaCl solution and greater nitrate rejection was achieved with regenerated chelating polymers. This could be attributed to the irreversible attachment of polymers at the membrane surface during the first UF run. The polymers attached might offer an additional sorption capacity for nitrate.

Decolorization of dye-containing aqueous solutions by the polyelectrolyte-enhanced ultrafiltration (PEUF) process using a hollow fiber membrane module

Polysulfone (PSf) asymmetric hollow fiber membranes with molecular weight cut-off (MWCO) of 13,000 Da have been prepared and employed for removal of the triphenylmethane dyes including malachite green (MG), brilliant green (BG) and new fuchsin (NF) from aqueous solutions. Several water-soluble polymers such as poly(diallydimethyl ammonium chloride) (PDADMAC), poly(sodium-4-styrenesulfonate) (PSS) and polyvinyl alcohol (PVA) have been examined for the polyelectrolyte-enhanced ultrafiltration (PEUF). The experimental results indicate that all the three triphenylmethane-type dyes can be removed effectively using the PSf hollow fiber ultrafiltration membrane with the aid of the anionic PSS polymer. The enhancement is primarily due to the formation of complexes between the anionic polymer and the cationic dye molecules through electrostatic attraction. The cationic and nonionic polymers such as PDADMAC and PVA are not suitable for the decolorization of MG, BG and NF aqueous solutions. The decolorization performances of the PSf membrane module can be fully restored by the back-washing operation using alcohol after each experiment.

Pilot‐scale study of Polyelectrolyte‐Enhanced UF for arsenic removal

The removal of arsenic (As) from dilute aqueous solutions has become of greater interest as lower drinking standards are implemented. In polyelectrolyte‐enhanced ultrafiltration (PEUF), a cationic water‐soluble polyelectrolyte (poly‐diallyldimethylammonium chloride [QUAT]) binds the anionic arsenate species and is rejected by the membrane, which has a 10 kDa molecular weight cutoff (MWCO). In the research presented in this article, PEUF was used to treat water with As concentrations of 50–100 μg/L. The results demonstrated that PEUF was able to produce treated water that meets the proposed US Environmental Protection Agency maximum contaminant level of 10 μg/L. In this study, the PEUF process was scaled up with a spiral‐wound ultrafiltration module operated under steady‐state continuous flow conditions (i.e., permeate flux of 80 L/m2‐h, and a pressure drop of 60 psi, which is typical for large‐volume applications). The main process parameters considered in this study were the QUAT‐to‐As ratio, pH, and the presence of background electrolytes (i.e., sulfate). The As removal efficiency improved with increasing pH, which is an advantage when the As‐tainted water is at an elevated pH since most adsorption‐based As removal methods perform better at lower pH levels.

Improvement and modelling of a batch polyelectrolyte enhanced ultrafiltration process for the recovery of copper

A batch Polyelectrolyte Enhanced Ultrafiltration (PEUF) process with Poly(acrylic acid) sodium salt (PAASS) for the recovery of Cu(II) from industrial wastewaters has been studied. In contrast to previous researches, insertion of an internal steel rod inside tubular ceramic membrane, which implies a decrease of hydraulic diameter, enables to minimize pumping energy (lower feed flow rates are required) and provides high tangential velocities in order to avoid concentration polarization and to lessen fouling. Simultaneously, working at higher temperature improves turbulence conditions over the membrane and makes possible to increase operating polyelectrolyte concentration (maintaining high permeate fluxes) and, subsequently, metal ion concentration in waste stream to treat. Temporal decrease of permeate fluxes has been reproduced with an in-series resistance model. Evolution of metal rejection coefficients is estimated with a model taking into account chemical equilibriums in solution and mass conservation equations. Furthermore, replacement of a polyelectrolyte of analytical grade by an analogous polymer of industrial grade reduces significantly raw material costs.

Humic substance-enhanced ultrafiltration for removal of cobalt

It is well known that the membrane separation process combined with surfactant micelle (micellar-enhanced ultrafiltration) or polyelectrolyte (polyelectrolyte-enhanced ultrafiltration) can remove heavy metal ions or radionuclides effectively. However, the complexing agent, surfactant or polyelectrolyte remained in effluent is a serious disadvantage of these methods. In this study, humic substances (HS) were used as complexing agents instead of synthetic chemicals. The HS are sorts of natural organic matters and their functional groups such as carboxyl and phenyl groups can bind with the cation and form complexes. The effects of HS concentration and pH on the removal of cobalt were investigated. At the HS concentration of 3 g/L and pH of 6, over 95% of cobalt was removed by regenerated cellulose membrane with molecular weight cut-off (MWCO) of 3000. As the HS concentration increased, the removal of cobalt was also enhanced because of the increase in binding sites (functional groups). The removal of cobalt increased from 72.5% to 97.5% as pH increased from 4 to 8 at the HS concentration of 3 g/L. It resulted from the more deprotonation of functional groups in humic acid at higher pH.

Removal of Arsenic Anions from Water Using Polyelectrolyte‐Enhanced Ultrafiltration

Polyelectrolyte‐enhanced ultrafiltration (PEUF), using cationic poly(diallyldimethyl ammonium chloride) polyelectrolyte, was used to investigate the removal of arsenic(V) from dilute aqueous solutions. In PEUF a water‐soluble polyelectrolyte of opposite charge to that of the target ion binds the charged arsenate complex. The solution is then treated by ultrafiltration with membrane pore sizes small enough to block the polymer. Only the residual unbound arsenate at the concentration in the retentate (solution not passing through membrane) is present in the permeate solution passing through the membrane. Arsenic rejections as high as 99.95% are obtained and increase with increasing polymer concentration and decrease with increasing ionic strength (added salt concentration). Arsenic rejection increases with increasing pH (pH of 6.5–8.5) as the HAsO4 2−/H2AsO4 − ratio in solution increases, improving arsenate binding to the polymer. Gel point concentration (polymer concentration at which flux becomes zero) was found to be 655–665 mM (approximately 5.98–6.07 wt%), consistent with previous PEUF studies. These high gel points mean that high water recoveries (>99%) are achievable in this separation process.

Aqueous Dispersion Behavior of Barium Chromate Crystals: Effect of Cationic Polyelectrolyte

In polyelectrolyte-enhanced ultrafiltration (PEUF), a cationic polyelectrolyte binds to chromate and is ultrafiltered from solution. The permeate passing through the membrane can contain a very low chromate concentration; the retentate solution not passing through the membrane must be treated to recover a large fraction of the polymer for reuse for economical operation. In the regeneration step, barium chloride can be added to the retentate to precipitate chromate anion as a compact barium chromate solid waste. The solution containing the polymer can be directly recycled after the solid barium chromate is separated from the solution. Gravity settling is much less expensive than filtration or centrifugation, so this investigation studies the ability to separate solid from solution in a settling unit. Unfortunately, the polyelectrolyte can act as a dispersing agent that stabilizes the dispersion of barium chromate particles, resulting in poor separation efficiency in the settler. The adsorption of cationic ...

Analysis of the variation in the permeate flux and of the efficiency of the recovery of mercury by polyelectrolyte enhanced ultrafiltration (PE-UF)

Enhanced ultrafiltration by the addition of polymers soluble in water is a promising technique for the recuperation of heavy metals in wastewater streams. In this work an analysis is made of the influence of the molecular weight (inferior and superior to the molecular weight of the polymer) cut-off of the membrane and the quantity of the polymer on the permeate flux and the recovery of mercury. The results show that with a membrane with a cut-off inferior to that of the combination metal polymer, the polymer concentration has no influence on the permeate flux, whereas for the membrane with a superior cut-off, there appears restrictions to the passing of water in accordance with the hydrodynamic model, and there is decreased efficiency in the recuperation of metal.

Polyelectrolyte-enhanced ultrafiltration of chromate, sulfate, and nitrate

Polyelectrolyte-enhanced ultrafiltration (PEUF) involves addition of a polyelectrolyte of opposite charge to that of the multivalent ions to be removed from the contaminated water. In this study, a water-soluble polyelectrolyte, poly(diallyldimethyl ammonium chloride) or QUAT is added to the aqueous solutions containing divalent anions chromate or sulfate. Removal of monovalent anion nitrate is also studied to probe the effect of valence. The water is then passed through an ultrafiltration membrane with pore size small enough to reject the polyelectrolyte with the bound target ions. The rejection of anions increases with increasing concentration ratio of QUAT to anion. A high QUAT concentration in the retentate decreases relative flux due to accumulation of polyelectrolyte near the membrane surface (hydrodynamic boundary layer). Rejections of chromate and sulfate are similar and >98% at reasonable operating conditions. Rejection of nitrate is substantially below that of the divalent anions, but can be as high as 97% under feasible operating conditions. The gel concentration (where flux approaches zero) of the QUAT varied from 5.1 to 8.1 wt%.

Use of Poly electrolyte-Enhanced Ultra filtration to Remove Chromate from Water

Abstract Poly electrolyte-enhanced ultra filtration (PEUF) is a process which can be used to remove multivalent ions from water. In PEUF a poly electrolyte of opposite charge to the target ion is added to the water to bind the ion to be removed. The solution is then treated using ultra filtration with membrane pore sizes small enough to reject the polymer and bound ion. In this study, chromate (CrO2 4 −) is removed from water using poly(diallyldimethyl ammonium chloride) with an average molecular weight of 240K as the poly electrolyte. In the absence of other added electrolytes, chromate rejections of up to 99.8% were observed. The presence of added NaCl reduces the chromate rejection substantially. A study of the flux of the system yielded a gel concentration of 0.55 M cationic poly electrolyte. This high gel concentration and high rejection mean that the ultra filtration can produce a concentrated, low-volume waste stream, and a purified stream containing chromate at low concentration.

Retention of copper(II)—EDTA chelates from dilute aqueous solutions by a polyelectrolyte-enhanced ultrafiltration process

The retention behavior of copper(II)—ethylenediaminetetraacetic acid (EDTA) chelates in dilute aqueous solutions ([Cu 2+] = 0.5–4 mM) by ultrafiltration was studied with the help of a basic polyelectrolyte, polyethylenimine (PEI). The regenerated cellulose Amicon YM10 and YM30 were used as ultrafilters. Experiments were performed in a stirred batch cell as a function of aqueous pH (2–10), the concentration ratios of EDTA to copper ions (0.5–4) and of PEI to copper ions (2.5–20), and the applied pressure (0.68–3.40 atm). The best conditions for rejection coefficient greater than 97% equivalent to 7 ppm copper chelates were obtained. The effect of inorganic salts such as NaCl, CaCl 2, and Na 2SO 4 on the retention was also examined. In addition, the membrane fouling during ultrafiltration was analyzed by modified fouling index. The regeneration method of PEI from the retentate is finally discussed.

Economic feasibility study of polyelectrolyte-enhanced ultrafiltration (PEUF) for water softening

In polyelectrolyte-enhanced ultrafiltration (PEUF), a water-soluble anionic polyelectrolyte (in this study sodium polystyrene sulfonate or PSS) is added to hard water. The calcium and magnesium bind to the polymer which has a high enough molecular weight to be rejected by an ultrafiltration membrane. The permeate is softened water. Economically, the PSS needs to be recovered from the retentate for reuse. Three methods of recovery developed in this study were addition of NaCl, Na 2CO 3 or HCl to PEUF to regenerate PSS. Of the three PEUF processes considered, NaCl/PEUF as compared to Na 2CO 3/PEUF and HCl/PEUF provided the best scheme for the water softening process. PEUF is shown in this study to be competitive with lime softening at low flow rates. The PEUF process is more expensive than ion exchange for a stream containing only hardness ions. However, PEUF becomes nearly comparable with ion exchange for a stream containing hardness ions as well as bacteria, viruses and pyrogen. The cost comparisons are based on fully continuous operations and include treatment of waste streams from each process.