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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 3g/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 3g/L. It resulted from the more deprotonation of functional groups in humic acid at higher pH.

Feasibility of micellar-enhanced ultrafiltration for the mixed waste that is consisted of chlorinated aromatic hydrocarbons, nitrate, and chromate was investigated using a cationic surfactant. The co-presence of nitrate and chromate did not significantly affect the removal of chlorobenzenes, and the co-presence of chlorobenzenes did not affect the removal of nitrate and chromate because chlorobenzenes were solubilized at the hydrophobic interior of the micelles by hydrophobic interaction, but nitrate and chromate were bound to the outer shell by electrostatic interaction. Micellar-enhanced ultrafiltration can be applied to treat the mixed wastes. [Copyright &y& Elsevier]

The feasibility of micellar-enhanced ultrafiltration (MEUF) for the removal of nitrate, chromate, and ferric-cyanide was investigated because of ionic competition to bind on the cetylpyridinium chloride micelles. In a single pollutants system, the order of removal efficiency was nitrate

Simultaneous removal of chromate and nitrate, major anionic pollutants in subsurface water system, was investigated using micellar-enhanced ultrafiltration (MEUF) with cetylpyridinium chloride as a cationic surfactant. Rejection of nitrate and chromate was expressed as a function of molar ratio of surfactant to pollutants. With the molar ratio of 1:1:10 (chromate: nitrate: surfactant), rejection of nitrate and chromate reached 80% and 98%, respectively. Rejection of surfactant was observed to be >95% under the same conditions. The rejection of nitrate was inhibited by co-existence of chromate. It was due to the differences in binding power between ionic micelles and counter ions, which is proportional to the valence of counter ions; the valence of chromate was higher than that of nitrate. [Copyright &y& Elsevier]

Feasibility of cross-flow micellar-enhanced ultrafiltration was investigated to remove chromate and nitrate from water system using a cationic surfactant, cetylpyridinium chloride (CPC). Removal of chromate with −2 as valence was higher than that of nitrate with −1 as valence in the conditions of co-existence of chromate and nitrate. Removal of nitrate was significantly inhibited by co-existence of chromate because of competitive binding to CPC micelles between chromate and nitrate, while that of chromate was only slightly inhibited by nitrate. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Ultrafiltration has been used as an effective process to remove heavy metals and organic pollutants from contaminated-groundwater and wastewater or as a part of surfactant-enhanced aquifer remediation (SEAR) process to concentrate and reuse the surfactant. The objective of this study was to investigate the effects of surfactant types, hydrophile–lipophile balance (HLB), salt amount, humic acid, and clay on the ultrafiltration: permeate concentration and flux. The regenerated cellulose membrane of 10K MWCO was used throughout the experiment. The flux was dependent on the viscosity of surfactant solution and water solubility of surfactant. Higher viscosity and lower water solubility caused the decrease of flux. The permeate concentration of surfactant was a function of the critical micelle concentration of surfactant. In the case of anionic surfactants, the permeate concentration decreased as salts concentration increased. The lower of HLB value caused the flux decline and higher concentration of permeate. Humic acid and clay decreased the flux. The permeate concentration of surfactant was not significantly influenced by the existence of humic acid and clay. [Copyright &y& Elsevier]

Feasibility of micellar-enhanced ultrafiltration was investigated to study simultaneous removal of ferric cyanide and nitrate with a cationic surfactant, cetylpyridinium chloride (CPC). The removal of ferricyanide and nitrate was studied as a function of surfactant to ferricyanide/nitrate molar ratios. In the ferricyanide/CPC and nitrate/CPC systems, the removal of ferricyanide and nitrate increased gradually as the molar ratio of CPC to ferricyanide or nitrate increased. With a 10 molar ratio of CPC, the removal of ferricyanide and nitrate increased to >99.9% and 93%, respectively. In the ferricyanide/nitrate/CPC system, the removal of ferricyanide increased from 62% to 72% and to 99.9%, while that of nitrate from <2% to <2% and to 27% as the molar ratio of ferricyanide:nitrate:CPC increased from 1:1:1 to 1:1:2 and to 1:1:4, respectively. With the molar ratio of 1:1:10, the removals were >99.9% and 78% for ferricyanide and nitrate, respectively. Ferricyanide ions were more easily bound to CPC micelles because the binding power of ferricyanide was greater than that of nitrate. With the difference of binding power, selective removal of ferricyanide using micellar-enhanced ultrafiltration could be achieved. [Copyright &y& Elsevier]

The feasibility of micellar-enhanced ultrafiltration to remove nutrients, nitrate and phosphate, was investigated with a cationic surfactant, cetlypyridinium chloride (CPC). The effects of surfactant molar ratios on the rejection of nitrate and phosphate and flux decline were studied. In the nitrate/phosphate/CPC system, as the molar ratio of nitrate: phosphate:CPCincreasedfrom 1:0.06:1.06to 1:0.06:3.18andto 1:0.06:5.30,therejectionofnitrateincreased from 77% to 84% andto 92%, while phosphate rejection increased from 83% to 87% and 95%, respectively. The rejection ofCPC increased as the molar ratio increased, and the concentration of CPC in the permeate was negligible because the size of the CPC micelle was lager than the pore size of the membrane, which indicated that the secondary pollution by surfactants might be insignificant. The reduction of permeate flux induced by the addition of a surfactant was due to the gel layer formed on the surface of the membrane. [Copyright &y& Elsevier]

Abstract: A variety of inorganic contaminants may form toxic oxyanions in aqueous systems which pose significant hazard to human health and the ecosystem. In order to remove the oxyanions from aqueous stream effectively, surfactant-modified powdered activated carbon (SM-PAC) combined with ultrafiltration (UF) was proposed in this study. As the cationic surfactant, cetylpyridinium chloride (CPC), adsorbs on the surface of PAC, the zeta potential of PAC increases to +40mV. Oxyanions such as chromate, ferricyanide and arsenate bind on SM-PAC by electrostatic interaction, then the contaminants bound with SM-PAC can be separated by UF membrane. 0.3mM of chromate and ferricyanide are removed completely with 4.0g/L of SM-PAC. In case of arsenate, the removal efficiency was lower than chromate and ferricyanide. It is considered that the competition occurs among anionic pollutants on the limited binding sites of SM-PAC and lower valence of arsenate results in the lower removal efficiency. High permeate flux is maintained during filtration. The spent SM-PAC was regenerated by the concentrated Cl− solutions. NaCl solution whose molar Cl− concentration is 1.4 times higher than the contaminants bound on SM-PAC was optimal for the regeneration. Regenerated SM-PAC exhibited similar adsorption capacity to fresh SM-PAC. SM-PAC combined with UF can effectively remove anionic contaminants. Moreover, the simple and efficient regeneration process is proposed. [Copyright &y& Elsevier]

Abstract: Heavy metals are the major pollutants in the soil and groundwater. They are not only toxic but also nonbiodegradable. In field application of heavy metal remediation, soil washing is the most prevalent technology due to its low cost and wide applicability for various pollutants. However, a drawback of soil washing is the treatment of effluent which contains heavy metals and chelating agent used to enhance the extraction capacity. To treat soil washing effluent with conventional technologies such as precipitation are not appropriate. Because chelating agents disturb to extract or precipitate heavy metals from the wastewater. Therefore in this study micellar-enhanced ultrafiltration (MEUF) was suggested as an alternative technology to treat heavy metals from washing effluent. Through centrifugal MEUF and conventional dead-end MEUF tests, the conditions were optimized. When complexing agent and metal ratio was around 1, metal complexation reached the maximum at pH 8. In addition the value of surfactant over metals was 10, the removal efficiency showed 97% for all metals. The feasibility of MEUF for washing effluent was determined with removal efficiency, flux and COD reduction during the treatment of lab-scale soil washing effluent. In the effluent from soil washing, total metal concentration and complexing agent was 10.14 and 9.03 mM respectively and the pH was 6.34. When the optimized conditions were employed to treat washing effluent, the removal efficiency and COD reduction reached over 92% and 80%, respectively. However the flux decline was severe, but this can be improved by introducing cross-flow filtration. [Copyright &y& Elsevier]

Abstract: The feasibility of cationic starch-enhanced ultrafiltration (CSEUF) was investigated to remove chromate from the aqueous stream. Cationic starch is a modified starch with cationic functional groups, which interact with anionic pollutants. For CSEUF, a cationic starch was synthesized, whose degree of substitution was 0.2 and water-insoluble. Chromate was bound spontaneously to cationic starch, after that the binding was saturated. As the concentration of cationic starch increased from 0.5 to 1.0, to 1.5, to 2.0, and to 2.5 g/l, the removal of chromate increased from 33% to 62%, to 82%, to 95% and to 98%, respectively. Based on the high removal, high flux, and biodegradability of cationic starch, CSEUF is a feasible process to remove chromate from the aqueous stream. [Copyright &y& Elsevier]

Abstract: The removal characteristics of arsenate using micellar-enhanced ultrafiltration (MEUF) were investigated. Among four different cationic surfactants used, hexadecylpyridinium chloride (CPC) showed the highest removal efficiency of arsenic (96%), and the removal efficiency with hexadecyltrimethylammonium bromide (CTAB) was 94%. But the removal efficiency with benzalkonium chloride (BC) was the lowest (57%) due to higher critical micelle concentration (CMC) of BC than those of other surfactants. Over 80% of arsenic was removed with octadecylamine acetate (ODA). On the effect of solution pH on the arsenic removal, since the valance of arsenate decreases from trivalent to monovalent as pH decreases, the removal was reduced at lower pH. The presence of 0.45mM of nitrate and 0.01mM of phosphate reduced the removal efficiency by 5–8%. This decrease was because of the competition between the arsenate, nitrate and phosphate for the binding sites of the surfactant micelle. Similar decrease in the removal of arsenate was observed with CPC, CTAB and ODA in the presence of these anions. In cross-flow filtration, the removal efficiency of arsenic was similar to that in the dead-end system. However, the decline in flux was less than that in dead-end filtration. In order to lower the concentration of the surfactant in the effluent, the effluent was treated with powdered activated carbon (PAC) before discharging to the environment. Over 98% surfactant was removed with 1gl−1 of PAC. In conclusions, the MEUF is considered as a feasible process using CPC or CTAB to remove the arsenate from groundwater compared with the other solid based adsorbent processes. [Copyright &y& Elsevier]

Abstract: A surfactant-based membrane process, micellar-enhanced ultrafiltration (MEUF), was studied in order to remove heavy metal ions from groundwater or wastewater. Retentate is the concentrated solution of surfactants and heavy metals retained by the membrane. Because surfactant accounts for a large portion of operating costs, it is essential to recover and reuse the surfactant from the retentate stream as economically as possible. Three methods were tested for the separation of metal ions from simulated retentate of MEUF: (1) acidification followed by ultrafiltration (UF), (2) use of a chelating agent followed by UF, and (3) precipitation by ferric- and ferrocyanide followed by centrifugation. Copper and cadmium were completely separated from the surfactant solution by acidification (lowering pH to strong acidic region) followed by UF. By adding ethylenediaminetetraacetic acid (EDTA) followed by UF, the separation efficiency of copper and cadmium was 100% and 75.5%, respectively. As pH increased, iminodiacetic acid and citric acid also showed high separation efficiency due to the deprotonation of the carboxylic group. Ferricyanide precipitated with copper and cadmium, and most of surfactants were recovered after centrifugation. In terms of the recovery of surfactant, at least 84% was in acidification and addition of EDTA. In the case of centrifugation after complexation, almost 100% of surfactant recovery was achieved. In general use, it is considered that acidification is the simplest and most efficient process for surfactant recovery. However, ferricyanide has a potential applicability because of the rapid precipitation with metal ions and selectivity. [Copyright &y& Elsevier]

Abstract: Micellar-enhanced ultrafiltration (MEUF)is a promising technology to separate organic and inorganic contaminants simultaneously under mild conditions. Organic compounds are solubilized into the core of micelle and inorganic pollutants can be bound on the surface of oppositely charged micelle. Trichloroethylene (TCE) and chromate were selected as an organic and inorganic contaminant, respectively. In this study, mixed surfactants were used to minimize the permeate surfactant concentration and enhance solubilization capacity. The feasibility of simultaneous removal of TCE and chromate by MEUF in the mixed surfactants was investigated, especially focused on the following aspects: the removal efficiency of each contaminant, the rejection of surfactants and relative flux. Cetylpyridinium chloride (CPC) as a cationic surfactant and Tween 80 as a nonionic surfactant were used to form mixed micelles. The removal of each pollutant was not hindered by co-presence of TCE and chromate, because the dominant removal mechanisms for each compound were different. Both CPC and Tween 80 were rejected effectively and the permeate concentration of each surfactant was maintained near the critical micelle concentration of the mixed surfactants system. The flux decline observed during filtration was mainly caused by the concentration polarization and high viscosity of Tween 80. [Copyright &y& Elsevier]

Surfactant-based separation of Fe(CN)63− and CrO42− using regenerated cellulose membrane was studied in order to assess the potential of micellar-enhanced ultrafiltration for the remediation of wastewater or groundwater polluted with ferriccyanide and chromate. In the ferriccyanide/octadecylamine acetate (ODA) and chromate/ODA systems, removal of ferriccyanide increased from 73 to 92% and to 98%, and that of chromate from 64 to 97% and to >99.9% as the molar ratio of ODA to ferriccyanide and to chromate increased from 1 to 2 and to 3, respectively. In the ferriccyanide/chromate/ODA system, while the removal of ferriccyanide increased from 62 to 72% and to 93%, the removal of chromate from 20 to 38% and to 68% as the molar ratio of ferriccyanide:chromate:ODA increased from 1:1:1 to 1:1:2 and to 1:1:4, respectively. With the molar ratio of 1:1:6, the removal was >99.9 and 98% for chromate and ferriccyanide, respectively. Ferriccyanide ions were more easily bound to ODA micelles because the binding power of ferriccyanide was greater than that of chromate. [Copyright &y& Elsevier]