Innovation in Draw Solute for Practical Zero Salt Reverse in Forward

May 26, 2015 - In forward osmosis (FO), reverse salt diffusion not only reduces water flux but also increases the requirement of draw solute replenish...
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Innovation in Draw Solute for Practical Zero Salt Reverse in Forward Osmosis Desalination Hau Thi Nguyen,† Nguyen Cong Nguyen,† Shiao-Shing Chen,*,† Chi-Wang Li,‡ Hung-Te Hsu,§ and Shu-Ying Wu† †

Institute of Environmental Engineering and Management, National Taipei University of Technology, No. 1, Sec. 3, Chung−Hsiao E. Rd., Taipei 106, Taiwan, ROC ‡ Department of Water Resources and Environmental Engineering, TamKang University, 151 Yingzhuan Road, Tamsui District, New Taipei City 25137, Taiwan, ROC § Department of Environmental Engineering, Chung Yuan Christian University, Chung Li 32023, Taiwan, ROC ABSTRACT: In forward osmosis (FO), reverse salt diffusion not only reduces water flux but also increases the requirement of draw solute replenishment. FO would be very desirable if there was no draw solute leakage and the recovery of draw solutes was easy. In this study, a novel draw solute, ethylenediaminetetraacetic acid (EDTA)-2Na coupled with Triton X-100 was explored with the aim of minimizing reverse salt diffusion. The results indicated that reverse salt diffusion achieved zero the first time when using 0.1 M EDTA-2Na coupled with 0.5 mM Triton X-100 as draw solution and DI water as feed solution. A water flux of 4.6 L/m2 h was reached when 35 g/L NaCl of model seawater was used as the feed solution and 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 was used as the draw solute. Moreover, a nanofiltration (NF) membrane was employed to recover the draw solute, achieving a high rejection of 95% due to the high charge and large size of the draw solute. but monovalent Na+ and Cl− resulted in a high reverse salt flux of 7.2 g/m2 h leading to water flux decline.7 In another study, the highly soluble NH4HCO3(0.7 M) was used generating huge osmotic pressure and yielding a high water flux;22,23 however, a reverse salt flux of 18.2 g/m2 h was recorded.21 To mitigate the high reverse salt flux caused by the presence of monovalent ions in the draw solution, some studies have used divalent salts instead but the success is rather marginal. For example, 0.5 M MgCl2 yielded the highest reverse salt flux of 5.6 g/m2 h, followed by 0.6 M K2SO4 (3.7 g/m2 h) and 0.6 M MgSO4 (0.9 g/m2 h).21 Recently, synthetic draw solutes such as magnetic nanoparticles, ferric and cobaltous hydroacid complexes, switchable polarity solvents, and 2-methylimidazole-based compounds have been explored, showing promise in terms of negligible reverse solute fluxes or low-energy consumption during regeneration.25−29 Nevertheless, most novel draw solutes undergo complicated synthesis procedures; some have problems of particle aggregation, and others require rather complicated recycling processes. Therefore, new draw solutes must be developed further. In 2015, polyacrylamide (PAM; MW ∼3 000 000) and polymer hydrogels have been applied as new draw solutes in the FO process, in which the reverse salt diffusion can be avoided.30,31 In addition, the diluted PAM solution would maintain the high viscosity and be used directly for polymer flooding in many oilfields to increase oil yield.30 In this study, a novel draw solute, coupling nonionic surfactant (polyethylene glycoltert-octylphenyl ether, Triton

1. INTRODUCTION The growing demand for fresh water is a substantial challenge in this century.1 Although reverse osmosis (RO) is frequently used, it requires a high amount of energy, 3−7 kWh/m3.2−5 Therefore, developing other technologies with a much lower amount of energy consumption is essential. Forward osmosis (FO) is an emerging membrane process that has recently gained considerable attention.6−11 Its application has been studied in various fields such as seawater desalination,12 wastewater treatment,3 and energy generation.10 Not only does it achieve high rejection of contaminants but also results in lower fouling because of no hydraulic pressure involved.3,13,14 However, FO still faces the challenges of the unavailability of high performance FO membranes and appropriate draw solutes. Some FO membranes have recently been developed with high water fluxes and low reverse solute fluxes,15,16 while exploring a suitable draw solute is still challenging. In general, an ideal FO draw solute not only has a high water flux and low reverse salt diffusion but also must be easily recoverable.17,18 So far, there have been many great studies focusing on the development of different draw solutes for FO process, including inorganic substances, highly charged compounds, nutrient-rich substances, and thermolytic draw solutes.19−21 Among these draw solutes, inorganic substance solutions are the most frequently used because of their high solubility, low cost, and high osmotic pressure potential. However, reverse salt diffusion from draw solute into feed solution is one of the most notable problems. Reverse salt diffusion not only reduces the water flux in FO but also contaminates the feed solution and eventually leads to a high cost of draw solute replenishment in a closedloop system.24 A high initial water flux of 9.6 L/m2 h was achieved when 0.6 M NaCl was used as the draw solute in FO, © XXXX American Chemical Society

Received: February 5, 2015 Revised: May 16, 2015 Accepted: May 26, 2015

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DOI: 10.1021/acs.iecr.5b00519 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research X-100) to a highly charged EDTA, for minimizing the salt leakage of ions during FO desalination was explored. It is hypothesized that the hydrophobic interactions between tail groups of Triton X-100 with the membrane would form an additional layer on the membrane surface, preventing ions from escaping through membrane pores, thus reducing reverse salt flux. Moreover, above the critical micelle concentrations (CMC > 0.4 mM), Triton X-100 in solution aggregates to form micelles that can form complexes with the highly charged EDTA to enlarge the molecular size of the draw solute. The micelle/EDTA complexes could be easily recovered by nanofiltration (NF) instead of reverse osmosis (RO).32−34 Therefore, the objectives of this study were to systematically investigate the FO performance using the Triton X-100/EDTA mixture as draw solution. The effect of Triton X-100/ membrane interaction on the reverse salt flux reduction is explored by comparing the draw solution using an anionic surfactant, sodium dodecyl sulfate (SDS). NF-TS80 membrane was used to evaluate recovery efficiency of the diluted draw solution. Moreover, the membrane fouling characteristics were also investigated using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM−EDS).

Table 2. Properties of Synthetic Brackish Water and Seawater as Feed Solutions at 25° C

abbreviation

polyethylene glycol tert-octylphenyl ether sodium dodecyl sulfate

nonionic

646

Triton X100

0.4

anionic

288

SDS

8

TDS, g/L viscosity, cp osmotic pressure, bar

10 1.08 6.12

35 1.12 26.38

ΔV AΔt

where ΔV (L) is the volume change of the feed solution over a predetermined time Δt (h) and A is the effective FO membrane area (m2). Since EDTA-2Na coupled with surfactants was conductive in their aqueous solutions, a calibrated conductivity meter (Oakton Instruments, Vernon Hills, IL) was used to measure the conductivity in the feed tank. A standard curve indicating the relationship of conductivity and concentration was built from a series of single solutions. All the conductivities measured from the feed solution were converted in the range of this standard curve. The concentration of the draw solution transported to the feed solution was thereafter obtained directly from the standard curve. The reverse salt flux of draw solute (J s , g/m 2 h) was determined from the concentration increase of the feed solution following equation.

CMC (mM)38

mol. wt.(g/mol)

seawater

Jw =

Table 1. Summary of the Surfactant Properties type

brackish water

2.2. Experiment Setup. Figure 1 shows the experiment setup. The feed and draw solutions on both sides of the FO membrane (effective membrane area of 41.40 cm2) were circulated by two peristaltic pumps (Master Flux L/S Drive, Model 7518-00) with a cross-flow rate of 6.4 cm/s. Two water baths were used to maintain the temperature at 25 ± 0.5 °C during the experiment. Conductivity and pH sensors were installed in the containers to monitor any changes in the feed and draw solutions. A 2 L feed solution tank was placed on a weighing scale (BW12KH, Shimadzu, Japan) that was connected to a computer data logging system to monitor weight and volume changes at regular time intervals. All FO experiments were conducted with the membrane orientation of the active layer facing the feed solution, and all data were obtained from three repeated tests. The experimental water flux (Jw, L/m2 h) was calculated by measuring the mass change in the feed container with time as follows:

2. MATERIALS AND METHODS 2.1. Materials. Commercially available asymmetric cellulose triacetate with an embedded support cartridge-type membrane was supplied by Hydration Technology Inc., Albany, OR, USA, and used for all FO experiments. The contact angle of the FO membrane was measured by CAM 100 and determined to be 78° in the active layer and 71° in the support layer. This result is in agreement with Cartinella et al. and Jin et al., who observed that the FO membrane is moderately hydrophobic with a contact angle of approximately 70°.35,36 The FO membrane has a negative charge, a mean pore radius of 0.37 nm,37 and a water permeation coefficient of 3.07 × 10−12 ms−1 Pa−1.7 Laboratory-grade EDTA-2Na (99.0% purity) was purchased from Sigma-Aldrich Co., Germany. Table 1 lists

surfactant

feed solution

Js =

VtCt − V0C0 At

where Ct (g/L) and Vt (L) are the concentration and volume of feed solution measured at time t and C0 (g/L) and V0 (L) are the initial concentration and volume of feed solution. Specific reverse salt flux (Js/Jw, g/L) defined as the ratio of the salt flux (Js, g/m2 h) in the reverse direction to the water flux (Jw, L/m2 h) in the forward direction is used to estimate the amount of the draw solute lost per liter of the water produced during FO. This ratio is related to the water−salt selectivity of the membrane. Specific reverse salt flux was quantified through experiments using DI water as the feed solution with the concentration of the draw solute being varied. After FO, the diluted draw solution was recovered through the NF membrane for reuse by using a cross-flow module (CF042 Delrin Acetal Cross Flow Cell, USA) under hydraulic pressures of 8 bar. All experimental data were collected after 1 h to avoid the influence of adsorption of ions on the membrane surface.

the names, chemical formulas, and properties of two surfactants (Triton X-100 and SDS) used in this study. The draw solute was prepared using laboratory-grade EDTA-2Na coupled with surfactants in various mole ratios at room temperature. These mixtures were maintained at pH 8 and then continuously stirred for 24 h before performing FO tests. In FO experiments, deionized (DI) water, synthetic brackish water, and seawater were used as feed solutions. The synthetic brackish water and seawater were prepared with total dissolved solid (TDS) of 10 000 and 35 000 ppm by adding NaCl salt to DI water as shown in Table 2. In this study, the NF-TS80 membrane was supplied by TriSep company and used to effectively recover the draw solution (EDTA-2Na coupled with Triton X-100). The properties of the NF-TS80 membrane were followed by molecular weight cutoff of 150 g/mol, typical flux/psi of 34/ 110 LMH/psi, and contact angle of 48 ± 2 °C. B

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Figure 1. Experimental setup of lab-scale FO/NF hybrid system using EDTA-2Na coupled with Triton X-100 as draw solute.

Figure 2. Variation of reverse salt flux and water flux (a) from coupling anionic surfactants SDS with EDTA-2Na and (b) from coupling nonionic surfactants Triton X-100 with EDTA-2Na (active layer facing the feed solution, cross-flow rate of 6.4 cm/s, temperature of 25 ± 0.5 °C, pH of 8, using DI water as feed solution, and all experiments were run in 1 h). Error bars were based on the standard deviation of three replicate tests.

The filtration experiments were repeated at least three times using fresh NF membranes. 2.3. Analytical Methods. The concentration of Na+ and Cl− ions were analyzed using Ion Chromatography (a DionexICS-90). The osmolality was measured by an Osmometer (Model 3320, Advanced Instruments, INC, USA) based on the freezing-point depression method.39 The viscosity and the conductivity were determined by a Vibro Viscometer (AD Company, Japan) and a conductivity meter (Sension156, Hach, China), respectively. The particle size of draw solution was measured using a Nano Particle Analyzer SZ100 (HORIBA, Japan). The particle size and distribution width was measured by dynamic light scattering (DLS) (SZ-100 series) with a measurement range of 0.3 nm to 8 μm. Before measuring, the mixtures of surfactant and draw solution were stirred for 15 min. The sample was put into the cuvettes and measured in approximately 2 min under ordinary conditions (from the start of measurement to the display of results for

particle size measurement). The contact angle of the FO membrane was measured by CAM 100 (Opto-Mechatronics P Ltd., India). The fouled membranes were observed by SEM− EDS with a Philips XL30 system operating with an accelerating voltage of 10 kV.

3. RESULTS AND DISCUSSION 3.1. Effect of Various Surfactants Concentrations. The effect of surfactant concentration on FO performance was conducted using DI water as the feed solution. SDS and Triton X-100 in a wide range of concentrations (0.2, 0.8, 2, 5, 10, 30, and 40 mM; 0.1, 0.2, 0.5, 0.8, 2, 5, and 20 mM, respectively) were mixed with EDTA-2Na (0.1 M) as draw solutes. Figure 2a,b indicates that the reverse salt flux is reduced significantly with increasing surfactant concentration. Figure 2a shows that coupling 0.2−40 mM SDS with 0.1 M EDTA-2Na considerably reduced the reverse salt flux from 0.19 to 0.10 g/m2 h. The reverse salt flux dropped to approximately zero when 0.5−20 C

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Figure 3. Schematic illustration of reducing back diffusion of ions with the presence of surfactant in the FO process.

Figure 4. Effect of coupling various concentrations of surfactants into EDTA-2Na on osmolality and viscosity (a) anionic surfactants SDS and (b) nonionic surfactants Triton X-100.

basis of the steric effect, free Na+ (hydrated radius of 0.178 nm) easily passes through the FO membrane (pore radius of 0.37 nm) without coupling with the surfactant, increasing reverse salt diffusion. Therefore, the results showed that the highest reverse salt flux of 0.24 g/m2 h was observed when only 0.1 M EDTA-2Na was used as the draw solute. However, when the surfactant was coupled with EDTA-2Na, adsorption of the surfactant on the membrane through a hydrophobic interaction between the hydrophobic tail of the surfactant and the membrane constricted membrane pores, reducing the reverse

mM Triton X-100 was coupled with EDTA-2Na (Figure 2b). To date, no study has demonstrated that the reverse salt flux can be reduced to zero by using a dissolved salt as the draw solute. The mechanism through which the back diffusion of ions is reduced in the presence of surfactants in FO is described in Figure 3. At pH 8, the main composition of EDTA-2Na is free Na + , trivalent H[EDTA] 3− , and complex Na[EDTA] 3− (reproduced from the data of Mineql+ based on the chemical equilibrium model from the thermodynamic database). On the D

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Figure 5. (a) Effect of various EDTA-2Na concentrations coupled with 0.5 mM Triton X-100 on reverse salt flux and water flux and (b) relation between water flux and TDS with the addition of 0.5 mM Triton X-100 into various concentration of EDTA-2Na draw solute (draw solution facing the support layer, cross-flow rate of 6.4 cm/s, temperature of 25 ± 0.5 °C, pH of 8, using DI water as feed solution, all experiments were run in 1 h). Error bars were based on the standard deviation of three replicate tests.

Figure 6. (a) Membrane fouling in FO process using 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 as draw solute, DI water as feed solution; (b) SEM image of the support layer of original FO membrane; (c) SEM image of the support layer of used FO membrane (draw solution facing the support layer, cross-flow rate of 6.4 cm/s, temperature of 25 ± 0.5 °C, pH of 8, using DI water as feed solution, the experiment was run in 16 h).

(Figure 3). Thus, the reduction of reverse salt flux by SDS addition is not as significant as that by Triton X-100. Moreover, Figure 4a,b shows the effect of increasing the surfactant concentration on the osmolality and viscosity of the draw solution. The osmolality gradually increased from 285 to 310 mOsm/kg with increasing SDS concentration from 0.2 to 40 mM; however, the osmolality slightly increased from 285 to 288 mOsm/kg with increasing Triton X-100 concentration from 0.1 to 20 mM. As shown in Figure 4, the viscosity of the draw solution increased rapidly as the SDS and Triton X-100 concentrations were increased. This decrease in the water flux as the surfactant concentration increases is due to the increases in the viscosity of the draw solution and formation of thicker layer of surfactants on the FO membrane surface. 3.2. Effect of Various EDTA-2Na Concentrations on Water Flux and Reverse Salt Flux. Figure 5a shows the

salt diffusion of Na+, H[EDTA]3−, and Na[EDTA]3−.40 This phenomenon is in agreement with Kiso and Jin et al., who observed that the hydrophobic interactions between selected pharmaceuticals and CTA FO membranes were the dominant removal mechanism, and the hydrophobicity of the pharmaceuticals exhibited a strong influence on their rejection.41,36 The reduction of reverse salt diffusion by Triton X-100 outperformed that by SDS because the neutral charge of Triton X-100 prevented repulsion of the surfactant by the negatively charged membrane; therefore, secondary filtration layers easily formed on the FO membrane surface, resulting in constriction of the membrane pores. On the other hand, the negatively charged SDS head groups were electrostatically repelled by the negatively charged membrane, limiting the hydrophobic interaction and adsorption of SDS on the membrane surface E

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Figure 7. (a) Water flux of the FO process using 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 as draw solute, DI water, brackish water (10 g/ L NaCl), and seawater (35 g/L NaCl) as feed solution; (b) SEM image of the active layer of original FO membrane; (c) SEM image of the active layer of used FO membrane; (d) EDS graph of used membrane; (e) SEM image of the cross section of the used membrane (draw solution facing the support layer, cross-flow rate of 6.4 cm/s, temperature of 25 ± 0.5 °C, pH of 8).

Figure 8. (a) The speciation of complex and charged EDTA in draw solution at different pH values of 0.07 M EDTA sodium (reproduced from the data of Mineql+). (b) Size distribution of 0.07 M EDTA-2Na coupled with 0.5 mM Triton X-100 at pH 8.

3.3. Adsorption Effect of Surfactant on Water Flux. To further investigate the effect of adsorption of surfactant on the water flux, 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 as draw solute was used during a 16 h experiment and then used FO membranes were taken out from the membrane cell and analyzed by SEM-EDS. Figure 6a shows a slight decrease of water flux from 9.6 to 8.1 L/m2 h because of the low osmotic pressure of the draw solution which was diluted with time throughout the FO experiment. This SEM images show that the presence of Triton X-100 in draw solute does not contribute to membrane fouling as the membrane surface of the original and used membranes were not significantly different (Figure 6b,c). 3.4. Desalination Processes. Furthermore, 1 M EDTA2Na coupled with 0.5 mM Triton X-100 was used as the draw solute to study brackish water and seawater desalination. As shown in Figure 7a, higher water flux (6.7 L/m2 h) was obtained with brackish water (TDS of 10 g/L) as feedwater compared to that with seawater (4.6 L/m2 h). The water flux

effect of EDTA-2Na concentrations (0.1−1 M) in the draw solution with fixed Triton X-100 concentration of 0.5 mM at pH 8 on the water and reverse salt flux. Again, in the experiment, DI water was used as the feed solution. The results showed that the water flux increased rapidly from 3.0 to 9.6 L/ m2 h when the EDTA-2Na concentration was increased from 0.1 to 1 M because of the increase in the total dissolved solids (TDS) in the draw solution (Figure 5b). Moreover, the flux increases were nonlinear because the EDTA-2Na concentration increased 10 times; however, the water flux increased only 3.2 times because of the internal concentration polarization (ICP) of the membrane. According to Alnaizy et al., the experimental water flux was observed to be 7 times lower than the ideal water flux.42 Furthermore, the reverse salt flux was approximately zero when the EDTA-2Na concentration was increased from 0.1 to 1 M (Figure 5a). 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 was determined to be the optimal draw solute for the FO process because it yielded the highest water flux and minimal reverse salt flux. F

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decreased considerably when brackish water and seawater replaced DI water as the feed solution because the osmotic pressure exerted by the brackish water and seawater reduced the net driving force across the membrane as well as concentration polarization effect (some tiny white crystals (NaCl) exist on the active layer of the FO membrane in Figure 7c−e).22,43,44 3.5. Recovery of Draw Solution Using NF-TS80 Membrane. After the FO process, the draw solutes have to be recovered and reconcentrated from the diluted draw solution which is one of the significant challenges in FO processes.45 In this work, 0.07 M EDTA-2Na coupled with 0.5 mM Triton X-100 was prepared as diluted draw solution and the NF-TS80 membrane was selected for recovery of the draw solutes under operation pressure of 8 bar to demonstrate the applicably of NF technology. The results show that the removal efficiency of EDTA-2Na and Triton X-100 was more than 95% (TDS of permeate stream of 418 mg/L) because of electrostatic repulsion and a steric-hindrance effect. An average permeate water flux of 3.51 L/m2 h was achieved during the 2 h operation. At pH 8, 95% of EDTA is in the form of trivalent H[EDTA]3− and 4% of EDTA is in the complex formation of Na[EDTA]3− (Figure 8a). The negatively charged H[EDTA]3− and Na[EDTA]3− were repelled by the negatively charged NFTS80 membrane, resulting in an increase in the solute rejection efficiency. Moreover, the micelle size distribution of aqueous solutions containing 0.07 M EDTA-2Na and 0.5 mM Triton X100 surfactants as depicted in Figure 8b indicates the formation of the large micellar particles with mean size of 18.4 nm, which is much bigger than the measured micelle sizes of 8.5 nm for Triton X-100 reported by others.46,47 Therefore, it is clearly seen that coupling Triton X-100 into EDTA-2Na draw solute can increase the particle size and improves the efficiency of recovery draw solution.

REFERENCES

(1) Crow, J. M. Keeping the tap on. Chem. World 2012, 9 (0), 44− 47. (2) Bamaga, O. A.; Yokochi, A.; Zabara, B.; Babaqi, A. S. Hybrid FO/ RO desalination system: Preliminary assessment of osmotic energy recovery and designs of new FO membrane module configurations. Desalination 2011, 268 (1−3), 163−169. (3) Cath, T. Y.; Childress, A. E.; Elimelech, M. Forward osmosis: Principles, applications, and recent developments. J. Membr. Sci. 2006, 281 (1−2), 70−87. (4) Lee, K. P.; Arnot, T. C.; Mattia, D. A review of reverse osmosis membrane materials for desalination-Development to date and future potential. J. Membr. Sci. 2011, 370 (1−2), 1−22. (5) Zhang, T. C.; Surampalli, R. Y.; Vigneswaran, S.; Tyagi, R. D.; Ong, S. L.; Kao, C. M. Membrane Technology and Environmental Applications; American Society of Civil Engineers: Reston, VA, 2012; 224 pages. (6) Petrotos, K. B.; Quantick, P.; Petropakis, H. A study of the direct osmotic concentration of tomato juice in tubular membrane - module configuration. I. The effect of certain basic process parameters on the process performance. J. Membr. Sci. 1998, 150 (1), 99−110. (7) Achilli, A.; Cath, T. Y.; Marchand, E. A.; Childress, A. E. The forward osmosis membrane bioreactor: A low fouling alternative to MBR processes. Desalination 2009, 239 (1−3), 10−21. (8) Jiao, B.; Cassano, A.; Drioli, E. Recent advances on membrane processes for the concentration of fruit juices: A review. J. Food Eng. 2004, 63 (3), 303−324. (9) Kessler, J. O.; Moody, C. D. Drinking water from sea water by forward osmosis. Desalination 1976, 18 (3), 297−306. (10) Lee, K. L.; Baker, R. W.; Lonsdale, H. K. Membranes for power generation by pressure-retarded osmosis. J. Membr. Sci. 1981, 8 (2), 141−171. (11) Seppala, A.; Lampinen, M. J. Thermodynamic optimizing of pressure-retarded osmosis power generation systems. J. Membr. Sci. 1999, 161 (1−2), 115−138. (12) Ling, M. M.; Chung, T. S. Desalination process using super hydrophilic nanoparticles via forward osmosis integrated with ultrafiltration regeneration. Desalination 2011, 278 (1−3), 194−202. (13) Nguyen, N. C.; Chen, S. S.; Yang, H. Y.; Hau, N. T. Application of forward osmosis on dewatering of high nutrient sludge. Bioresour. Technol. 2013, 132, 224−229. (14) Lutchmiah, K.; Cornelissen, E. R.; Harmsen, D. J. H.; Post, J. W.; Lampi, K.; Ramaekers, H.; Rietveld, L. C.; Roest, K. Water recovery from sewage using forward osmosis. Water Sci. Technol. 2011, 64 (7), 1443−1449. (15) Song, X.; Liu, Z.; Sun, D. D. Nano gives the answer: Breaking the bottleneck of internal concentration polarization with a nanofiber composite forward osmosis membrane for a high water production rate. Adv. Mater. 2011, 23 (29), 3256−3260. (16) Sukitpaneenit, P.; Chung, T. S. High performance thin-film composite forward osmosis hollow fiber membranes with macrovoidfree and highly porous structure for sustainable water production. Environ. Sci. Technol. 2012, 46 (13), 7358−7365. (17) Ge, Q.; Ling, M.; Chung, T.-S. Draw solutions for forward osmosis processes: Developments, challenges, and prospects for the future. J. Membr. Sci. 2013, 442 (0), 225−237. (18) Chekli, L.; Phuntsho, S.; Shon, H. K.; Vigneswaran, S.; Kandasamy, J.; Chanan, A. A review of draw solutes in forward osmosis process and their use in modern applications. Desalin. Water Treat. 2012, 43 (1−3), 167−184. (19) Kravath, R. E.; Davis, J. A. Desalination of sea water by direct osmosis. Desalination 1975, 16 (2), 151−155. (20) Stache, K. Apparatus for transforming sea water, brackish water, polluted water or the like into a nutritious drink by means of osmosis. US Patent No. 4879030, 1989. (21) Achilli, A.; Cath, T. Y.; Childress, A. E. Selection of inorganicbased draw solutions for forward osmosis applications. J. Membr. Sci. 2010, 364 (1−2), 233−241.

4. CONCLUSION EDTA-2Na coupled with Triton X-100 has been explored and used as a novel draw solute in FO. The high charge and satisfactory solubility of EDTA produced a high osmotic pressure, and the interaction force between the hydrophobic tails of Triton X-100 and the hydrophobic FO membrane minimized reverse salt diffusion. The results of FO tests indicated that using 1 M EDTA-2Na coupled with 0.5 mM Triton X-100 and DI water as the feed solution yielded the highest water flux of 9.6 L/m2 h and zero reverse salt flux. Moreover, the NF-TS80 membrane was used to recover the draw solution and enabled one to achieve a high recovery efficiency of 95%. This investigation of using EDTA-2Na coupled with Triton X-100 as the draw solute in FO provides a new promising method for future application.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to acknowledge the sponsor of the Ministry of Science and Technology, Taiwan, ROC under the grant number of 101-2221-E-027-061-MY3. G

DOI: 10.1021/acs.iecr.5b00519 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.5b00519 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX