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Abstract: Removal characteristics of polycyclic aromatic hydrocarbons (PAHs) from low-permeable soil using a surfactant-enhanced electrokinetic (EK) process were investigated. Phenanthrene and kaolinite were selected as a representative PAH and a model soil. A nonionic surfactant, alkyl polyglucosides (APG), and an anionic surfactant, Calfax 16L-35, were used to enhance the solubility of phenanthrene. The two surfactants showed similar solubilization capacities for phenanthrene, while only APG was affected by sorption. When surfactants were applied to EK process, the electrical potential gradient was lower than that of water. The electroosmotic flow (EOF) decreased as the concentration of surfactant increased. In the case of APG, the removal efficiency of phenanthrene increased with the surfactant concentration. The APG micelles containing phenanthrene easily migrated to the cathode reservoir by EOF. On the other hand, Calfax 16L-35 did not enhance the removal efficiency even at the highest concentration, because most of Calfax 16L-35 remained in soil, and only small amount existed in effluent. It was thought that, during electrokinetic process, Calfax 16L-35 was adsorbed onto soil and the migration of the surfactant from cathode to anode was superior to EOF due to anionic charges of Calfax 16L-35. A nonionic surfactant, APG, seems to be suitable for surfactant-enhanced electrokinetic remediation. [Copyright &y& Elsevier]

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]

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]

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: In this study, surfactant-modified powdered activated carbon (PAC) was used to remove anionic contaminants from water. The conventional modification method of PAC with surfactants produced large quantity of unbound surfactant in aqueous phase (3.0–3.5 mM). However, the revised modification method — filtration followed by centrifugation — released negligible amount of residual surfactant (<0.01 mM). Adsorption characteristics were investigated with arsenate (H2AsO4 −), chromate (CrO4 2−) and ferricyanide (Fe(CN)6 3−). The adsorption isotherm followed Langmuir model, and it suggested that the anions bind on the monolayer of the modified PAC by the electrostatic attraction. The order of maximum adsorbed amount was chromate (0.234 mmol/g) > arsenate (0.087 mmol/g) ≈ ferricyanide (0.085 mmol/g). On the other hand, the order changed to ferricyanide > chromate > arsenate in multi-contaminant system. Anions competed with each other for limited binding sites in the multicontaminant system, hence the order of maximum adsorbed amount followed the valence of each anion. With 2 g/L of modified PAC, it was possible to treat 0.001 mM of arsenate, 0.5 mM of chromate and 0.2 mM of ferricyanide completely. [Copyright &y& Elsevier]

Abstract: Surfactants are widely used for the remediation of groundwater contaminated with chlorinated solvents. The reuse of surfactants is quite important for the economic feasibility of the remediation process. Pervaporation with a polydimethylsiloxane membrane was conducted to simultaneously separate trichloroethylene (TCE) and tetra-chloroethylene (PCE) from waste solution of the non-ionic surfactant Tween 80. The effects of key process variables on the removal efficiency were investigated. Membrane thickness between 200 µm and 300 µm did not affect the pervaporation performance. Organic flux did not increase above the flow rate of 100 mL/min. The increase of feed concentration and temperature led to large organic flux. Selectivity was reduced significantly with temperature due to the increase in thermal motion of polymer. The reduction of flux was small below 1.0 wt% surfactant (Tween 80) in feed solution. Flux and selectivity of TCE were higher than those of PCE because an extramicellar portion of TCE was higher than that of PCE. In simultaneous pervaporation of TCE and PCE, flux and selectivity declined due to the competitive sorption of TCE and PCE. However, the reduction percentage in flux and selectivity was less than 10% with 1:1 ratio of TCE/PCE. With operation during 100 h, over 95% of TCE and 90% of PCE were simultaneously removed from 0.5 wt% of Tween 80 solution with TCE and PCE of 1,000 ppm. From the present results, which gave a high efficiency in the simultaneous removal of chlorinated solvents, this process could be a practical alternative for surfactant reuse. [Copyright &y& Elsevier]

Removal of hydrophobic organic contaminants (HOCs) using surfactant-enhanced electrokinetic (EK) method was studied in a model system. Kaolinite and phenanthrene were selected as a model clay soil and a representative HOC, respectively. Three different types of surfactants: APG (alkyl polyglucoside), Brij30 (polyoxyethylene-4-lauryl ether), and SDS (sodium dodecyl sulfate), were used to enhance the solubility of HOC. Characteristics of surfactants, such as surface tension, HOC solubility, and biodegradability were measured. In the case of Brij30 solution, phenanthrene solubility was higher than that of others. After 4 days, APG and Brij30 were degraded by 65% and 26% of the initial amount, respectively. However, degradation of SDS was hardly detected. Electroosmotic flow (EOF) of Brij30 solution was lower than others when the 0.1M NaCl was used as electrolyte. Addition of the acetate buffer solution increased the EOF of Brij30 solution and enhanced removal of phenanthrene. Among three different surfactants tested, APG showed the highest removal efficiency. [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]

Abstract: Chitosan-based polymeric surfactants (CBPSs) were prepared by N-acylation of chitosans (chitosan 10 and 500) with several acid anhydrides such as hexanoic (C6), lauric (C12), and palmitic (C16) anhydrides. Among the CBPS samples, CBPSs having a good solubility at pH 4.0 were selected and observed for viscosity, surface tension, and adsorption of heavy metals (Cd2+, Co2+, Cr2O7 2−, and Pb2+) as well as the fatty acid (n-octanoic acid). The 1H NMR spectrum of chitosan 10 modified with C16 at the substitution ratio of 0.4 (CBPS10–C16,0.4) showed 85% of acylation in 1% DCl/D2O solutions. CBPS10 with the substitution ratio less than 0.4 showed a good solubility because of shorter repeating units and lesser amounts of hydrophobic substituents. The intrinsic viscosity of CBPS10 was slightly increased, while that of CBPS500 was decreased. As the substitution ratio and length of the carbon chain increased, the surface tension of CBPS10 tended to decrease. CBPS10–C16,0.2 had high adsorption ability for cationic metal ions such as Cd2+, Co2+, and Pb2+ comparable to chitosan. Interestingly, CBPS10–C16,0.2 showed a unique pH optimum for the anionic metal ion such as Cr2O7 2−. In addition, CBPS10–C16,0.2 exhibited the highest adsorption ability for n-octanoic acid among the tested CBPS10 with different carbon chains. [Copyright &y& Elsevier]