Polyelectrolyte-Promoted Forward Osmosis–Membrane Distillation

Article pubs.acs.org/est

Polyelectrolyte-Promoted Forward Osmosis−Membrane Distillation (FO−MD) Hybrid Process for Dye Wastewater Treatment Qingchun Ge, Peng Wang, Chunfeng Wan, and Tai-Shung Chung* Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore S Supporting Information *

ABSTRACT: Polyelectrolytes have proven their advantages as draw solutes in forward osmosis process in terms of high water flux, minimum reverse flux, and ease of recovery. In this work, the concept of a polyelectrolyte-promoted forward osmosis− membrane distillation (FO−MD) hybrid system was demonstrated and applied to recycle the wastewater containing an acid dye. A poly(acrylic acid) sodium (PAA-Na) salt was used as the draw solute of the FO to dehydrate the wastewater, while the MD was employed to reconcentrate the PAA-Na draw solution. With the integration of these two processes, a continuous wastewater treatment process was established. To optimize the FO−MD hybrid process, the effects of PAA-Na concentration, experimental duration, and temperature were investigated. Almost a complete rejection of PAA-Na solute was observed by both FO and MD membranes. Under the conditions of 0.48 g mL−1 PAA-Na and 66 °C, the wastewater was most efficiently dehydrated yet with a stabilized PAA-Na concentration around 0.48 g mL−1. The practicality of PAA-Na-promoted FO−MD hybrid technology demonstrates not only its suitability in wastewater reclamation, but also its potential in other membrane-based separations, such as protein or pharmaceutical product enrichment. This study may provide the insights of exploring novel draw solutes and their applications in FO related processes.

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INTRODUCTION Water-soluble acid dyes are extensively used as coloring agents in manufacturing industries of textiles, paper, and food stuff. Waste effluents containing these coloring agents may cause severe environmental pollution1,2 and serious threat to human health due to their toxic and carcinogenic properties. Over the past decades, extensive physical and chemical or electrochemical technologies have been developed for the reclamation of wastewater containing acid dyes.1−6 Unfortunately, the nonbiodegradable characteristics of dye-contained wastewater make it difficult to clean the wastewater thoroughly.7 Most of the current technologies are costly and technically complicated to be applied. Hence, there is an urgent need for the development of more economic and efficient technologies for the dye-contained wastewater treatment. Compared with the traditional separation and purification technologies, membrane-based separation is a relatively new technology, which possesses the merits of high rejection, low energy cost, ease of scale-up, etc.8−12 Research has been carried out on the application of membrane technology in wastewater reclamation for both removal and recovery of textile effluents13−15 and has proven to be a greatly capable method.15−19 The forward osmosis−membrane distillation (FO−MD) integrated system is a newly developed membrane-based hybrid © 2012 American Chemical Society

technology. It consists of an FO and an MD where the FO process draws clean water from the wastewater feed solution while the MD process continuously reconcentrates the diluted draw solution for the FO process and simultaneously produces high-purity water from its permeate side. The integration of FO and MD processes combines the strengths of both processes, including high product water quality, low fouling tendency, and potential utilization of industrial waste heat. So far only a very limited number of works aimed to explore these advantages. Yen et al. utilized the FO−MD process to recycle draw solutes and produce clean water,20 while Wang et al. started to study the FO−MD process for protein concentration.21 However, similar to the individual FO process, the current FO−MD hybrid process is highly constrained by high reverse draw solute flux (i.e., draw solute leakage) of commonly used draw solutions such as NaCl, MgCl2, and NH4HCO3, etc.22 Recently, a series of novel draw solutes based on polyelectrolytes of PAA-Na salts have been developed by Ge et al.23 Their characteristics of high solubility in water and flexibility in structural configuration enable them to generate high water Received: Revised: Accepted: Published: 6236

February April 25, April 26, April 26,

27, 2012 2012 2012 2012

dx.doi.org/10.1021/es300784h | Environ. Sci. Technol. 2012, 46, 6236−6243

Environmental Science & Technology

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Figure 1. Schematic diagram of the lab-scale FO−MD hybrid system.

fluxes yet with insignificant reverse salt fluxes when being used as draw solutes in the FO process. Such properties not only ensure the high efficiency in water reclamation and the quality of product water, but also lower the replenishment cost of the draw solutes. Meanwhile, different from other newly developed draw solutes,24 PAA-Na salts have high stability which makes their performance repeatable after many recycles. In view of these favorable characteristics, the polyelectrolyte of PAA-Na with an average molecular weight of 1200 is selected as the draw solute in this FO−MD study,23 while the dye of acid orange 8-contained water is employed as the feed solution of model wastewater. A continuous dehydration process is achieved in the FO process when the PAA-Na solution draws clean water from the dye-contained water while is reconcentrated simultaneously by the MD process. In addition to high purity water that is produced from the distillate of MD, the reconcentrated dye from the retentate of FO is also a valuable product. It is envisioned that the polyelectrolyte-promoted FO−MD technology is promising not only in dye-contained wastewater treatment, but also in other separations, such as protein and pharmaceutical enrichment.

measured by a DMA 35 potable density meter, and t0 (s) and ρ0 (g mL−1) are the elution time and density of DI water, respectively. Acid Orange 8 Analyses. Since acid orange 8 contains azo and naphthalene groups, its aqueous solution exhibits the maximum absorption at 490 nm.26 Therefore, the concentrations of acid orange 8 solutions can be obtained through the conversion of their absorbance measured by an ultraviolet (UV) visible spectrophotometer (Biochrom Libra S32) at the wavelength of 490 nm. The relationship between the concentration of acid orange 8 solutions and their absorbance was given in Figure S1. FO−MD Processes. FO−MD experiments were carried out through a lab-scale FO−MD hybrid setup as depicted in Figure 1. Individual FO and MD experiments were also conducted through this hybrid setup. In the FO process, cellulose acetate (CA) hollow fiber membranes fabricated by our group27 were used. The feed and draw solutions flowed concurrently through the lumen and shell sides at the respective flow rates of 100 and 500 mL min−1. A mode of draw solution against the active layer (AL-DS) and feed solution against the support layer (SL-FS) was employed in all FO experiments. The pressures at the two channel inlets were below 0.07 bar (1.0 psi). Performance at temperatures of 50 ± 0.5 °C, 60 ± 0.5 °C, 70 ± 0.5 °C, and 80 ± 0.5 °C was measured. In all FO-involved experiments, the draw solutions were prepared from PAA-Na with the volume of 300 mL, while the feed solutions were 50 ppm of acid orange 8 solutions with the initial volume of 500 mL. For the MD process, high-performance PVDF composite hollow fiber membranes were employed. The membranes were spun by a dry-jet wet spinning process documented elsewhere.28 The spinning conditions and their characteristics were given in Supporting Information (Table S1). PAA-Na solutions at the same temperatures as the FO process were circulated through the shell-side of the MD module at the flow rate of 500 mL min−1, while cold DI water (20 ± 0.5 °C) as the permeate solution was concurrently flowing through the lumen side of the PVDF hollow fiber at the flow rate of 200 mL min−1. The water fluxes of the FO and MD processes, Jv (L m−2 h−1, abbreviated as LMH), were calculated, respectively, from the volume changes of the acid orange 8 solutions and cold DI water using eq 2

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MATERIALS AND METHODS Materials. PAA-Na (45 wt %, Mw ∼ 1200) and acid orange 8 were acquired from Sigma-Aldrich and used as received. Polyvinylidene fluoride (PVDF) HSV#900 was purchased from Arkema Inc. N-Methyl-1-pyrrolidone (NMP, >99.5%), ethylene glycol (EG, >99.5%), and isopropanol (IPA, >99.5%) used in the PVDF hollow fiber fabrication were purchased from Merck, Germany. Hydrophobic POSS particles (FL0583) were supplied by Hybrid Plastics (Hattiesburge). DI water from a Milli-Q (Millipore) system was used in all experiments. Purification and Characterization of PAA-Na. PAA-Na was purified by using the method reported previously.23 Briefly, the commercially available PAA-Na solution with pH ∼ 9.2 at 45 wt % was purified through a dialysis process until the pH of the solution was neutral. Then, the final product of PAA-Na was dried under vacuum before performance measurements. The relative viscosity of PAA-Na at different temperatures and concentrations, ηr, compared to DI water is calculated using eq 125 η tρ = ηr = η0 t0ρ0 (1)

Jv = ΔV /(AΔt )

where t (s) is the elution time of the aqueous polyelectrolyte solution measured by an AVS 360 inherent viscosity meter, ρ (g mL−1) is the density of the aqueous polyelectrolyte solution

(2)

where ΔV (L) is the volume change over a predetermined time Δt (h) and A is the effective membrane surface area (m2). 6237



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flux and reverse solute flux increase with temperature as a result of enhanced osmotic pressure and solution fluidity.21 In contrast, FO systems employing polyelectrolyte solutes show higher water flux and negligible reverse solute flux due to the expanded structural configuration. To optimize the FO−MD hybrid experimental conditions and make the dehydration of acid orange 8 solutions more efficient, individual FO and MD processes were studied first. FO Processes Using CA Hollow Fiber Membranes. As the FO−MD hybrid process is performed at temperatures higher than typical FO operations, the effects of temperature and experiment duration on FO performance of PAA-Na at concentrations of 0.24, 0.36, 0.48, and 0.60 g mL−1 are investigated. The water fluxes, together with the concentration evolution of the draw and feed solutions, are shown in Figure 3a−c at a representative draw solution concentration of 0.48 g mL−1. In the 2 h experiments, it is observed that the water flux decreases significantly with the progress of time at 50 °C (Figure 3a). This is mainly due to the dilution effect of the draw solution, as indicated in Figure 3c. However, the variation of water flux is not linear with time due to the dynamic dilution process. Concentration polarization and/or fouling may also contribute to the nonlinear decline of water flux. Figure 3b shows the dependence of water flux on temperature. Better performance is observed at a higher temperature. This phenomenon may be attributed to the greater decline of viscosity at higher temperatures at a certain draw solution concentration, as illustrated in Figure 2. The evolution of the acid orange 8 concentration in the feed solution is also reflected in Figure 3c. The dehydration process is more efficient at the early stage when the draw solution is relatively more concentrated than the late stage of the experiments. After the 2 h experiments, the concentration of acid orange 8 in the feed solution increases to 81.9 ppm from its initial 50 ppm. As anticipated, when PAA-Na solutions at concentrations of 0.24, 0.36, and 0.60 g mL−1 are used as draw solutions, the variations of FO performance and the concentration evolution of draw solution and feed solution follow similar trends. Compared with the 0.48 g mL−1 PAA-Na solution, lower water fluxes are observed when 0.24 and 0.36 g mL−1 PAA-Na solutions are used. In contrast, a better performance is achieved when 0.60 g mL−1 PAA-Na is employed as the draw solution. A comparison of water flux and the evolution of acid orange 8 solution concentration at different temperatures and PAA-Na concentrations after 2 h experiments are shown in Figure 4a,b. It is found that temperature and PAA-Na concentration have notable impact on water flux and the final acid orange 8 concentration in the feed side (Figure 4b). A higher temperature and/or a higher PAA-Na solution concentration lead to better performance and more efficient dehydration of acid orange 8 solution. It is noteworthy that (i) reverse PAA-Na flux, (ii) ratio of reverse PAA-Na flux (Js) to water flux (Jv), Js/Jv, and (iii) reverse diffusion of acid orange 8 to the draw solution are also considered for the purpose of selecting optimum conditions for the FO−MD hybrid processes. No obvious reverse diffusion of acid orange 8 is found under all circumstances. The Js/Jv ratio, which gives the loss of PAA-Na in recovering 1 L of clean water, is an important parameter in monitoring the system performance and estimating the replenishment amount of draw solutes. Figure 5a,b shows the effects of temperature and PAANa concentration on Js and Js/Jv.

Due to the dissociation and conductive properties exhibited by PAA-Na in its aqueous solution, the concentration of PAANa draw solutes diffusing to the feed solution was obtained by the conversion of its electrical conductivity measured using a calibrated conductivity meter (Oakton Instruments, Vernon Hills, IL). The reverse PAA-Na flux, Js (g m−2 h−1, abbreviated as gMH), was obtained by this way. Since the acid orange 8 feed solution used in this study was very dilute (50 ppm), DI water was used as the feed solution instead of acid orange 8 solution when reverse PAA-Na fluxes were measured. As stated in our previous work,23 using mass concentration is a more practical representation of a polymer’s actual amount; hence, in this study, mass concentration of PAA-Na solution was employed for the analyses of the performance across the CA and PVDF hollow fiber membranes. The osmolality of PAA-Na draw solutions, which can be converted to osmotic pressure, was measured using a model 3250 osmometer (Advanced Instruments, Inc.). The relationship of PAA-Na solution concentration and its osmotic pressure was given in Figure S2. The osmotic pressure of acid orange 8 solution could not be detected by the osmometer instrument when the concentration is below 500 ppm.

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RESULTS AND DISCUSSION Effects of Temperature and Concentration on the Relative Viscosity of PAA-Na. As a polyelectrolyte’s viscosity has significant influence on its performance when being used as a draw solute in the FO process,23 the effects of temperature and concentration on the relative viscosity of PAA-Na are first evaluated and shown in Figure 2.

Figure 2. Effects of temperature and concentration on the relative viscosity of PAA-Na.

It is found that an increase in PAA-Na solution concentration results in a simultaneous increase in its relative viscosity. A temperature increase, however, leads to a significant decline in its relative viscosity, especially when temperature increases from room temperature to higher than 50 °C at higher solute concentrations. Considering the operation of the FO−MD process at a higher temperature, this viscosity-lowering phenomenon implies that the application of polyelectrolyte in the FO−MD hybrid system is more conducive and meaningful than those conventional draw solutes, such as NH4HCO3, NaCl, and MgCl2. For these conventional solutes, both water 6238



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Figure 3. (a) Effect of time on water flux at 50 °C. (b) Effect of temperature on water flux after 30-min experiments. (c) Effect of time on PAA-Na and acid orange 8 concentrations at 50 °C. Initial conditions: 0.48 g mL−1 PAA-Na draw solution operated in AL-DS in the FO process.

Figure 4. Effects of temperature and PAA-Na concentration on (a) water flux and (b) acid orange 8 feed solution concentration. Operation mode: AL-DS in the FO process. Experimental duration: 30 min.

The reverse PAA-Na flux, Js, increases slightly with an increase in temperature and/or PAA-Na solution concen-

tration. Nevertheless, the reverse flux variation is in the range 0.09−0.14 gMH in spite of the temperature and PAA-Na 6239



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Figure 5. Effects of temperature and PAA-Na concentration on (a) reverse PAA-Na flux when DI water as feed solution and (b) the ratio of reverse PAA-Na flux to water flux Js/Jv. Operation mode: AL-DS in the FO process. Experimental duration: 2 h.

Figure 6. (a) Effects of temperature and PAA-Na concentration on water flux. (b) Effects of temperature and experimental duration on water flux at 0.48 g mL−1 PAA-Na. Operation process: MD process.

in Supporting Information (Table S1 and Figure S3, respectively). Due to the use of highly hydrophobic HSV#900 PVDF polymer and hydrophobic group functionalized POSS particles, the membrane shows a large contact angle over 110°. The membrane has a suitable average pore size of 0.28 μm with an interconnected pore structure. Hence, the vapor transfer in the membrane pores is maximized by the combined mechanism of both Knudsen and molecular diffusions.29,30 By employing weaker coagulants and a poreforming agent, the membrane has a high porosity of 78.8%. This indicates the membrane has improved thermal conductivity and therefore less thermal loss and reduced temperature polarization.28 With the excellent hydrophobicity, suitable pore structure, and high porosity, the spun hollow fiber membrane ensures the excellent resistance toward membrane wetting, maximized thermal efficiency, and enhanced permeation flux. Hence, it is suitable to be used in the hybrid FO− MD process. The effects of temperature, PAA-Na concentration, and experimental duration on water flux in the MD process were investigated and shown in Figure 6a,b.

concentration adopted in this study. Such a small variation range indicates that the effects of temperature and concentration on reverse PAA-Na flux are negligible. This observation demonstrates the superiority of PAA-Na draw solutes over NaCl where much higher reverse salt flux is found, and an elevated NaCl concentration leads to a significant increase in reverse salt flux.21 According to the Js/Jv values shown in Figure 5b, the loss of PAA-Na in recovering each liter of water from the acid orange 8 solution is lower than 0.01 g under all circumstances of this work. This indicates that such a negligible loss would not contaminate the feed stream of the acid orange 8 solution and the replenishment cost of the PAA-Na draw solute would be extremely low, which reveal additional advantages of using polyelectrolytes as draw solutes. Given the insignificant influence of temperature and PAA-Na concentration on reverse draw solute flux and the combined aforementioned analyses, a high temperature and a high PAANa solution concentration are preferable to the FO process. MD Processes Using PVDF Hollow Fiber Membranes. The spinning conditions, characteristics, and microstructure of the spun PVDF composite hollow fiber membranes were given 6240



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Figure 7. Effect of time on (a) water transfer rate and (b) acid orange 8 concentrations. Operation process: FO−MD hybrid process.

chosen as experimental conditions for the FO−MD hybrid system. A comparison of water transfer rate calculated from Figures 4a and 6a shows that the water transfer rate of 0.60 g mL−1 PAA-Na solution in the FO process consistently outperforms that in the MD process at temperatures lower than 72 °C even in a dynamic dilution process. In contrast, the water transfer rates of 0.36 and 0.48 g mL−1 PAA-Na solutions in the FO process at the respective temperatures of 58 and 63 °C are comparable to those of the same concentration solutions in the MD process. Therefore, experimental conditions of 0.36 and 0.48 g mL−1 PAA-Na solutions at the respective temperatures of 58 and 63 °C or 0.60 g mL−1 PAA-Na solution at 72 °C seem suitable to balance the water transfer rates between the FO and MD subsystems simultaneously. Considering the efficiency of the acid orange 8 solution dehydration and the alleviation of concentration polarization as well as the economy and practicability, the 0.48 g mL−1 PAANa solution at 63 °C is chosen for the initial conditions for testing the FO−MD hybrid system. The time-dependent variations of water transfer rates of the individual FO and MD subsystems and acid orange 8 concentration are shown in Figure 7a,b. An obvious decline in water transfer rate of the FO subsystem can be observed in the initial stage. This is within the expectation since the selected conditions of 0.48 g mL−1 PAA-Na at 63 °C are based on a comparison of water transfer rate calculated from Figures 4a and 6a where FO and MD run independently. The initial 0.48 g mL−1 PAA-Na solution in Figure 4a is in a dynamic dilution FO process without draw solute regeneration; hence, the water transfer rate in the FO− MD system should be larger than that calculated from Figure 4a when the MD process is incorporated to recover the diluted PAA-Na solution (Figure 7a). The concentration evolution of acid orange 8 solution shown in Figure 7b demonstrates that the FO−MD hybrid process is more efficient than the individual FO process (Figure 4b) in concentrating the acid orange 8 dye. Since the water transfer rate of the MD process is slightly lower than that of the FO process within the 2 h experiments, a higher temperature may match the water transfer rates better because the effect of temperature on the MD process is larger than that on the FO process. In view of this, conditions of 0.48 g mL−1 PAA-Na solution at 66 °C

Unlike in the FO process (Figure 4), temperature has a dominant effect on water flux in the MD process since MD is a thermal driven process.31 The driving force for water vapor transport through hydrophobic membrane pores is the temperature difference across the membrane. Therefore, when temperature increases, an accelerated increment of water flux can be observed as the water vapor pressure follows an exponential function of temperature.32 On the other hand, when PAA-Na concentration is elevated, a slight decline of water flux is noticed. This is possibly attributed to the decreased water activity and more severe temperature polarization. As the solute concentration increases, the water activity of the feed solution of MD decreases, and hence, effective vapor pressure is sacrificed.33 Besides the reduced water activity, the viscous characteristics of the PAA-Na solution also reduce the heat and mass transfer efficiencies at the feed side boundary, which results in more severe temperature polarization and reduced water flux.34 The insignificant variation of water flux with time at 0.48 g mL−1 PAA-Na also shows that it is temperature, instead of experimental duration, that plays an important role in the performance of the MD process (Figure 6b). Given the unique vapor transfer mechanism of MD, no variation of conductivity can be detected at the permeate side of MD under all operation conditions. This means an almost complete rejection of PAA-Na in the MD process. FO−MD Hybrid Processes. As discussed above, a high temperature is preferred for both FO and MD processes, while the effect of PAA-Na concentration is small on the MD process but great on the FO process. Hence, operating the FO−MD hybrid system at high temperatures and high PAA-Na concentrations is favorable. Since a steady water transfer rate which is obtained by multiplying the water flux with membrane surface area is the key factor in determining the sustainability of the FO−MD hybrid process,21 comparable water transfer rates from both FO and MD subsystems are required for not only system sustainability but also effective dehydration of acid orange 8 solutions. As illustrated in Figure 3a,c the PAA-Na draw solution is diluted in the individual FO process; thus, water flux also decreases with the progress of time. Since the regeneration of draw solutions starts immediately when running the FO−MD hybrid system, the water transfer rate in the first 30 min experiment calculated from Figure 3a is more meaningful to be 6241



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Figure 8. Effect of time on (a) water transfer rate, (b) acid orange 8 concentration, and (c) PAA-Na concentration. Operation process: FO−MD hybrid process.

instead of 63 °C are employed to dehydrate the acid orange 8 solutions through the FO−MD hybrid processes. The dependence of water transfer rate and the concentration evolution of acid orange 8 and PAA-Na solutions on time is depicted in Figure 8. A steady state of dehydration of the acid orange 8 solution is established through the FO−MD hybrid processes after the first 30 min (Figure 8a). Meanwhile, the concentration of PAANa solution is stabilized around 0.48 g mL−1 during the entire experiment (Figure 8c), indicative of matchable water transfer rates between the FO and MD subsystems. Similar to the individual MD process, no obvious PAA-Na leakage to the cold DI water side is observed in the FO−MD hybrid process. The continuous concentrated process of the acid orange 8 solution shown in Figure 8b demonstrates the practicability of the FO− MD hybrid processes in wastewater treatment. A comparison of Figures 4b, 7b, and 8b reveals that the FO−MD hybrid process is superior to the individual FO process in the dehydration of acid orange 8 solutions, and the most efficient treatment is achieved when the water transfer rate of the FO subsystem matches that of the MD subsystem. The stability and repeatability of the FO−MD processes illustrate the practicability of such a hybrid system in wastewater treatment. This study may open the way for the applications of polyelectrolyte-

promoted FO−MD processes in other membrane-based separation, such as protein or pharmaceutical product enrichment.

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ASSOCIATED CONTENT

S Supporting Information *

Additional details about the relationship between the concentration of acid orange 8 solutions and their absorbance (Figure S1), osmotic pressure of PAA-Na solutions at different concentrations (Figure S2), spinning conditions and characteristics of the PVDF composite hollow fiber membranes (Table S1), and the microstructure of the spun PVDF composite hollow fiber membranes (Figure S3). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: (65) 6516-6645; fax: 65-6779-1936; e-mail: chencts@ nus.edu.sg. Notes

The authors declare no competing financial interest. 6242



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(17) Das, C.; Rungta, M.; Arya, G.; DasGupta, S.; De, S. Removal of dyes and their mixture from aqueous solution using liquid emulsion membrane. J. Hazard. Mater. 2008, 159, 365−371. (18) Sun, S. P.; Hatton, T. A.; Chung, T. S. Hyperbranched polyethyleneimine induced cross-linking of polyamide-imide nanofiltration hollow fiber membranes for effective removal of ciprofloxacin. Environ. Sci. Technol. 2011, 45, 4003−4009. (19) Qin, J. J.; Oo, M. H.; Wai, M. N.; Ang, C. M.; Wong, F. S.; Lee, H. A dual membrane UF/RO process for reclamation of spent rinses from a nickel-plating operationA case study. Water Res. 2003, 37, 3269−3278. (20) Yen, S. K.; Haja N., F. M.; Su, M. L.; Wang, K. Y.; Chung, T. S. Study of draw solutes using 2-methylimidazole-based compounds in forward osmosis. J. Membr. Sci. 2010, 364, 242−252. (21) Wang, K. Y.; Teoh, M. M.; Nugroho, A.; Chung, T. S. Integrated forward osmosis−membrane distillation (FO-MD) hybrid system for the concentration of protein solutions. Chem. Eng. Sci. 2011, 66, 2421−2430. (22) Achilli, A.; Cath, T. Y.; Childress, A. E. Selection of inorganic based draw solutions for forward osmosis applications. J. Membr. Sci. 2010, 364, 233−241. (23) Ge, Q.; Su, J.; Amy, G. L.; Chung, T. S. Exploration of polyelectrolytes as draw solutes in forward osmosis processes. Water Res. 2012, 46, 1318−1326. (24) Ge, Q.; Su, J.; Chung, T. S.; Amy, G. Hydrophilic superparamagnetic nanoparticles: synthesis, characterization, and performance in forward osmosis processes. Ind. Eng. Chem. Res. 2011, 50, 382−388. (25) McNaught, A. D.; Wilkinson, A. Compendium of Chemical Terminology (The “Gold Book”), 2nd ed.; Blackwell Scientific Publications: Oxford, U.K., 1997. (26) Gültekin, I.; Tezcanli-Güyer, G.; Ince, N. H. Sonochemical decay of C.I. Acid Orange 8: Effects of CCl4 and t-butyl alcohol. Ultrason. Sonochem. 2009, 16, 577−581. (27) Su, J.; Chung, T. S. Sublayer structure and reflection coefficient and their effects on concentration polarization and membrane performance in FO processes. J. Membr. Sci. 2011, 376, 214−224. (28) Wang, P.; Teoh, M. M.; Chung, T. S. Morphological architecture of dual-layer hollow fiber for membrane distillation with higher desalination performance. Water Res. 2011, 45, 5489−5500. (29) Schofield, R. W.; Fane, A. G.; Fell, C. J. D. Heat and mass transfer in membrane distillation. J. Membr. Sci. 1987, 33, 299−313. (30) Wang, K. Y.; Chung, T. S.; Gryta, M. Hydrophobic PVDF hollow fiber membranes with narrow pore size distribution and ultrathin skin for the fresh water production through membrane distillation. Chem. Eng. Sci. 2008, 63, 2587−2594. (31) Tomaszewska, M. Membrane distillation. Environ. Prot. Eng. 1999, 25, 37−47. (32) Bonyadi, S.; Chung, T. S.; Rajagopalan, R. A novel approach to fabricate macrovoid-free and highly permeable PVDF hollow fiber membranes for membrane distillation. AIChE J. 2009, 55, 828−833. (33) Wang, K. Y.; Foo, S. W.; Chung, T. S. Mixed matrix PVDF hollow fiber membranes with nanoscale pores for desalination through direct contact membrane distillation. Ind. Eng. Chem. Res. 2009, 48, 4474−4483. (34) Li, B.; Sirkar, K. K. Novel membrane and device for direct contact membrane distillation-based desalination process. Ind. Eng. Chem. Res. 2004, 43, 5300−5309.

ACKNOWLEDGMENTS We acknowledge the financial support from Singapore National Research Foundation under its Competitive Research Program for the project entitled “Advanced FO Membranes and Membrane Systems for Wastewater Treatment, Water Reuse and Seawater Desalination” (Grant R-279-000-336-281). Special thanks are due to Dr. Jincai Su for his valuable help.

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REFERENCES

(1) Han, F.; Kambala, V. S. R.; Srinivasan, M.; Rajarathnam, D.; Naidu, R. Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: A review. Appl. Catal., A 2009, 359, 25−40. (2) Minear, R. A.; Amy, G. L. Water disinfection and natural organic matter: history and overview. In Water Disinfection and Natural Organic Matter; Minear, R. A., Amy, G. L., Eds.; American Chemistry Society: Washington, DC, 1996; pp 1−9. (3) Bhatnagar, A.; Sillanpäa,̈ M. Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatmentA review. Chem. Eng. J. 2010, 157, 277−296. (4) El-Ashtoukhy, E. S. Z.; Amin, N. K. Removal of acid green dye 50 from wastewater by anodic oxidation and electrocoagulationA comparative study. J. Hazard. Mater. 2010, 179, 113−119. (5) Daneshvar, N.; Salari, D.; Aber, S. Chromium adsorption and Cr(VI) reduction to trivalent chromium in aqueous solutions by soya cake. J. Hazard. Mater. 2002, 94, 49−61. (6) Del Río, A. I.; Fernández, J.; Molina, J.; Bonastre, J.; Cases, F. Electrochemical treatment of a synthetic wastewater containing a sulphonatedazo dye. Determination of naphthalenesulphonic compounds produced as main by-products. Desalination 2011, 273, 428− 435. (7) Allen, S. J.; Khader, K. Y. H.; Bino, M. Electrooxidation of dyestuffs in waste waters. J. Chem. Technol. Biotechnol. 1995, 62, 111− 117. (8) Escobar, I. C. A summary of challenges still facing desalination and water reuse. In Sustainable Water for the Future-Water Recycling versus Desalination; Escobar, I. C., Schäfer, A. I., Eds.; Elsevier Science: Amsterdam, The Netherlands, 2010; pp 389−397. (9) Mi, B. X.; Marinas, B. J.; Cahill, D. G. RBS characterization of arsenic(III) partitioning from aqueous phase into the active layers of thin-film composite NF/RO membranes. Environ. Sci. Technol. 2007, 41, 3290−3295. (10) Nanda, D.; Tung, K. L.; Hung, W. S.; Lo, C. H.; Jean, Y. C.; Lee, K. R.; Hu, C. C.; Lai, J. Y. Characterization of fouled nanofiltration membranes using positron annihilation spectroscopy. J. Membr. Sci. 2011, 382, 124−134. (11) Qin, J. J.; Kekre, K. A.; Oo, M. H.; Tao, G.; Lay, C. L.; Lew, C. H.; Cornelissen, E. R.; Ruiken, C. J. Preliminary study of osmotic membrane bioreactor: effects of draw solution on water flux and air scouring on fouling. Water Sci. Technol. 2010, 62, 1353−1360. (12) McCutcheon, J. R.; McGinnis, R. L.; Elimelech, M. A novel ammonia−carbon dioxide forward (direct) osmosis desalination process. Desalination 2005, 174, 1−11. (13) Amini, M.; Arami, M.; Mahmoodi, N. M.; Akbari, A. Dye removal from colored textile wastewater using acrylic grafted nanomembrane. Desalination 2011, 267, 107−113. (14) Bampernga, S.; Suwannacharta, T.; Atchariyawutb, S.; Jiraratananon, R. Ozonation of dye wastewater by membrane contactor using PVDF and PTFE membranes. Sep. Purif. Technol. 2010, 72, 186−193. (15) Othman, N.; Zailani, S. N.; Mili, N. Recovery of synthetic dye from simulated wastewater using emulsion liquid membrane process containing tri-dodecyl amine as a mobile carrier. J. Hazard. Mater. 2011, 198, 103−112. (16) Ahmad, A. L.; Harris, W. A.; Syafie Seng, O. B. Removal of dye from wastewater of textile industry using membrane technology. J. Teknologi. 2002, 36, 31−44. 6243


Polyelectrolyte-Promoted Forward Osmosis–Membrane Distillation

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