Forward Osmosis (FO) for Water Reclamation from Emulsified Oil

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Forward Osmosis (FO) for Water Reclamation from Emulsified Oil/ Water Solutions: Effects of Membrane and Emulsion Characteristics Gang Han, Sun Sun Chan, and Tai-Shung Chung ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01402 • Publication Date (Web): 15 Aug 2016 Downloaded from http://pubs.acs.org on August 20, 2016

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ACS Sustainable Chemistry & Engineering

Forward Osmosis (FO) for Water Reclamation from Emulsified Oil/Water Solutions: Effects of Membrane and Emulsion Characteristics Gang Han 1, Sun Sun Chan 2, Tai-Shung Chung 1,*

1

Department of Chemical and Biomolecular Engineering,

National University of Singapore, 4 Engineering Drive 4, Singapore 117585

2

School of Life Sciences & Chemical Technology,

Ngee Ann Polytechnic, 535 Clementi Road, Singapore 599489

*Corresponding author Tel: +65-65166645; Fax: +65-67791936; Email: [email protected]

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Abstract The effects of membrane and oil/water emulsion characteristics as well as their interactions on the performance and fouling behaviors of forward osmosis (FO) processes for emulsified oily water have not been studied in depth. By constructing thin-film composite (TFC) membranes with tailored surface chemistry and employing petroleum-in-water emulsion solutions with variable physicochemical properties, we have systematically investigated these effects for water reclamation from the emulsified oily water under FO operations. It is found that the surfactant not only plays an important role in determining the emulsion droplet size but also its distribution and surface charge properties, which would significantly affect the fouling propensity and reversibility of the FO membrane. FO shows a relatively high water flux and feed recovery as well as great rejection to oil/water emulsions (>99.9%) under both pressure retarded osmosis (PRO) and FO modes. However, the FO mode is superior to the PRO mode in terms of performance stability, antifouling behaviors and fouling reversibility despite of its lower initial water flux induced by internal concentration polarization. In FO mode, the water fluxes of the fouled TFC membranes could be recovered back up to 92-97% of the original values via water flushing on the fouled surfaces because the fouling primarily occurs on the polyamide skin instead of within the porous substrate. The polyethyleneimine (PEI) modification to reduce membrane surface pore size and/or lower the charge-charge interactions with the emulsion particles could effectively ameliorate fouling and enhance fouling reversibility. The current work would provide insightful guidelines for the development of effective FO membranes and processes for oily wastewater treatment.

Keywords:

forward

osmosis,

oil/water emulsion,

surfactant, dewatering,

antifouling


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Introduction Each year, a huge amount of oil and gas (O&G) wastewater is generated by drilling and hydraulic fracturing of wells.1,2 Although the quality of the produced wastewater varies with geographic locations and O&G operations, the major contaminants generally include oil and grease, suspended solids, dissolved solids, salts, organic matters and chemicals.3,4 Direct discharge of such effluents is inhibited as they may cause severe environmental pollution.3-6 As a result, proper management of the produced oily wastewater is one of the challenges for the O&G industry and government agents to protect environments and public health. Currently, deep-well injections are generally used to manage the produced O&G wastewater because of the relatively low costs.7 However, this method not only consumes a large volume of water but also permanently removes the wastewater from recycling. Other water treatment and discharge processes normally have low water recovery rates; and they cannot effectively remove well-stabilized oil/water emulsions with small particle sizes.8 These residual stabilized oil may increase the biological oxygen demand (BOD) of water sources near the wastewater discharged area and result in sheening.9,10 These problems facilitate the exploration of advanced technologies that can treat and reuse the O&G oily wastewater efficiently. Forward osmosis (FO) is an emerging membrane technology that has received rapid attention in wastewater treatment in recent years.8,10-16 Since water permeation in FO is driven by the osmotic pressure gradient across a semipermeable membrane between the feed and the high salinity draw solution,17-20 FO possesses several unique advantages. In lieu of using hydraulic pressures, FO can use simple and inexpensive low-pressure apparatus and thus reduces the capital cost.21,22 In addition, the fouling in FO is less compacted and more reversible which make the membrane cleaning and regeneration easy and effective.23-25 Furthermore, the low fouling propensity may simplify the pretreatment steps and lower the cleaning frequency. These would 3 ACS Paragon Plus Environment


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lead to a longer membrane life with reduced replacement costs and improved process efficiency.26 Other advantages of FO include high rejections toward inorganic and organic contaminants and high water recovery as well as good system modularity.27-30 As a result, the application of FO for dewatering and separation of the O&G oily wastewater has been explored recently.10-14 Pioneering studies have demonstrated that membrane fouling induced by the emulsified oil droplets is fast and dramatic, which would severely reduce FO performance.10-14 An ideal FO membrane should possess appropriate structure and chemistry in order to sustain its performance in FO processes.12,14,31 Therefore, the aims of this work are to investigate the science and engineering behind the appropriate structure and chemistry in order to design effective FO membranes for oily wastewater treatment. We would study the effects of the membrane and oil/water emulsion characteristics on water flux and oil rejection as well as disclose the influences of their interactions on membrane fouling propensity and reversibility. In specific, three petroleum-in-water emulsion solutions with different particle size, chemistry and surface charge properties would be prepared by using different surfactants and employed as the feed solutions; while three thin-film composite (TFC) membranes with tailored transporting and surface characteristics would be used as the FO membranes. Water flux, salt/oil rejections, fouling propensity and reversibility for different membrane-emulsion pairs would be systematically studied under both PRO and FO modes. This work may provide useful insights for the design of next-generation FO membranes for oily wastewater treatment.

Experimental Methods Materials and chemicals The commercially available polymer Matrimid® 5218 (Vantico Inc., US) was used to fabricate the substrate membrane. N-methyl-2-pyrrolidone (NMP, >99.5%) and polyethylene glycol with a 4 ACS Paragon Plus Environment

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molecular weight of 400 Da (PEG 400, >99.0%) from Merck were utilized as the solvent and additive for dope preparation, respectively. Polyethylene glycol (PEG) and polyethylene oxide (PEO) with various molecular weights from Sigma-Aldrich were employed to determine the pore characteristics and molecular weight cut-off (MWCO) of the membrane substrates. Trimesoyl chloride (TMC, >98%) and m-phenylenediamine (MPD, >99%) were acquired from Sigma– Aldrich as monomers for the formation of the polyamide selective layer via interfacial polymerization. Hexane (>99.9%, Fisher Chemicals) was utilized as the solvent for the TMC monomer. Sodium dodecyl sulfate (SDS, >97%) supplied by Fluka was employed as an additive in the MPD monomer solution. Branched polyethyleneimine with molecular weights of 60 kDa (PEI 60K) and 2 kDa (PEI 2K) from Acros (USA) were used to modify the as-cast Matrimid membrane substrate and the polyamide selective layer of the TFC membrane, respectively. Petroleum (~18% aromatics basis, boiling point of 180-220 °C), hexadecyltrimethylammonium bromide (HTAB, MW=364 Da), Tween 80 (MW=1310 Da), and SDS (MW=288 Da) were ordered from Sigma-Aldrich to prepare the oil-in-water emulsion solutions. HTAB and SDS are ionic surfactants, while Tween 80 is a neutral surfactant. Sodium chloride (NaCl) provided by Merck was employed to prepare the draw solution. Deionized (DI) water was produced by a Milli-Q unit (Millipore) with a resistivity of 15 MΩ cm.

Fabrication of the Matrimid membrane substrate The Matrimid polymer was firstly dried in a vacuum oven at 80 °C for 24 h to remove moisture. Then, the polymer (18 wt%) was dissolved in a mixture of solvent NMP (66 wt%) and the additive PEG 400 (16 wt%) under stirring at 70 °C. The formed homogeneous polymer solution was cooled down to room temperature and degassed overnight before casting. Finally, the flat-



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sheet membrane substrate was fabricated via a lab-scale casting process.32,33 After the nonsolvent induced phase inversion completed, the formed Matrimid substrate membrane was rinsed with deionized water to remove the residual NMP and PEG 400.

Modification of the Matrimid membrane substrate The polyimide structure of the as-cast Matrimid membrane substrate makes it easy to be chemically modified. In order to tailor the membrane surface charges, the substrate was post treated by a PEI 60K aqueous solution (3.0 wt%) at 70 °C for 1 h using a method documented in our previous work.32 After the reaction, the modified substrate was rinsed with deionized water to remove the unreacted PEI. The PEI modified Matrimid substrate was termed as PEI-Matrimid.

Preparation of the TFC-FO membranes The TFC-FO membranes were prepared by depositing a polyamide selective skin on the top surface of membrane substrates via interfacial polymerization reaction between MPD and TMC.20 A membrane substrate was firstly immersed in a 2.0 wt% MPD aqueous solution that contains 0.1 wt% SDS for 2 min. Then, the excess MPD residual droplets on the top surface were removed by filter paper. The MPD saturated membrane substrate was then clamped in between frames and only the top surface was brought into contact with a 0.15 wt% TMC/hexane solution for 2 min. The resultant TFC membranes were then stored in deionized water at 5 °C. The TFCFO membranes made from an as-cast Matrimid substrate and a PEI-Matrimid substrate were denoted as Matrimid-TFC and PEI-Matrimid-TFC, respectively.

Modification of the Matrimid-TFC membrane


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After interfacial polymerization reaction, the formed polyamide selective layer of the MatrimidTFC membrane was further modified by immediately exposing the nascent polyamide surface to a PEI 2K solution (2.0 wt%) for 30 min at ambient temperature.34 After that, the membrane was rinsed with deionized water to remove the un-reacted chemicals. The PEI modified MatrimidTFC membrane was named as Matrimid-TFC-PEI. Figure 1 illustrates the schematic structures of these three membranes.

Membrane characterization Surface characteristics Membrane morphology was observed by using a field-emission scanning electron microscope (FESEM, JEOL JSM-6700LV). The membranes were fractured in liquid nitrogen and then coated by platinum via a JEOL JFC-1300E ion sputtering device for FESEM sample preparation. Water contact angles of the membrane surfaces were measured through a contact angle goniometry (Rame Hart, USA) using deionized water as the probe liquid.34,35 Surface charge characteristics of the membranes were analyzed by a SurPASS electro-kinetic analyzer (Anton Paar GmbH, Austria) via streaming electric potential measurements.14,34 Zetapotential of the membranes was firstly measured with a 0.01 M NaCl solution at neutral pH. After that, a 0.1 M NaOH and a 0.1 M HCl were circulated through the measuring cell to adjust the solution pH by auto-titration. The isoelectric point was determined when the zeta-potential as a function of pH was established. Surface chemistry of the membranes was determined by X-ray photoelectron spectroscopy (XPS, Kratos AXIS UltraDLD spectrometer, Kratos Analytical Ltd.). The base pressure and



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working pressure were 1×10-9 Torr and 5×10-9 Torr, correspondingly. Pass energy for wide and narrow scan was 160 eV and 40 eV, respectively.

Molecular weight cut-off (MWCO), mean pore size and pore size distribution of the substrate membranes The MWCO, mean pore size and pore size distribution of the Matrimid and PEI-Matrimid membrane substrates were obtained via solute rejection experiments using neutral solutes of PEG and PEO with a concentration of 200 ppm at 1.0 bar.36,37 The solute concentrations in the feed (Cf) and permeate (Cp) were measured by a total organic carbon analyzer (TOC ASI-5000A, Shimadzu, Japan). The effective solute rejection R (%) can be calculated as:

R = (1 −

Cp Cf

) × 100%

(1)

The relationship between the solute Stokes diameter (ds, nm) and molecular weight (Mw, g mol−1) of PEG and PEO solutes can be modeled as:36,37 For PEG:

d s = 33 .46 × 10 −2 × M w

For PEO:

d s = 20.88 × 10 −2 × M w

0.557

0.587

(2) (3)

A straight line was obtained by plotting the solute rejection R versus ds on a log-normal probability paper. The mean effective pore size dp in diameter was yielded at R=50%, and the geometric standard deviation σp was calculated as the ratio of ds at R=84.13% and R=50%. Then the pore size distribution of the membrane can be expressed as:

dR(d p ) (ln d p − ln µ p ) 2 1 = exp[− ] dd p 2(lnσ p ) 2 d p lnσ p 2π

(4)


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Determination of pure water permeability A, salt permeability coefficient B, and structural parameter S of the TFC-FO membranes The pure water permeability A and salt rejection Rs of the TFC membranes were measured through a lab-scale nanofiltration setup at 1.0 bar. A (in L m-2 h-1 bar-1) was calculated from the pure water permeation flux as:

A=

Q Am ∆P

(5)

where Q is the volumetric flow rate of water permeation (in L h-1), Am is the effective membrane area (in m2), and ∆P is the trans-membrane pressure difference (in bar). Rs (in %) was determined from measuring the conductivity of the permeate water and the feed of a 1000 ppm NaCl solution as:

Rs = (1 −

Cd p ) × 100% Cd f

(6)

where Cdp and Cdf represent the conductivity of the permeate and feed solutions, respectively. Membrane salt permeability coefficient B (in L m-2 h-1) could be obtained according to the solution-diffusion theory as:13,14

1 − Rs B = Rs A(∆P − ∆π )

(7)

where ∆P and ∆π are the hydraulic pressure difference and osmotic pressure gradient across the membrane, respectively. Membrane structural parameter S (in m) was acquired from the obtained A and B as well as the membrane water flux Jw measured in FO mode using 1M NaCl as the draw solution and deionized water as the feed:13,14



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S=

D Aπ D + B ln J w Aπ F + J w + B

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(8)

where D is the salt diffusivity coefficient, and πD and πF refer to the bulk osmotic pressures of the draw and feed solutions, respectively.

Preparation and characterization of the oil-in-water emulsions The oil-in-water emulsion solutions were prepared by a high-speed blender (HGBTWTS3, Waring, Torrington, USA) following a method described in our previous studies.13,14 Nonionic surfactant Tween 80, anionic surfactant SDS and cationic surfactant HTAB were used as the emulsifiers for the emulsion solutions, respectively. Table 1 summarizes their chemical structures. In a typical preparation, the surfactant was firstly dissolved in a certain amount of deionized water, and then petroleum was mixed with the surfactant aqueous solution with a surfactant/petroleum ratio of 1/9 (wt%). The mixture was blended at a high speed for 5 min to achieve a stable emulsified oil/water solution with a total organic concentration (oil plus surfactant) of 50,000 ppm. After that, the emulsion solution was diluted by deionized water to 2000 ppm for FO tests. The mean particle size, size distribution and surface zeta potential of the prepared 2000 ppm oil/water emulsion solutions were measured via a nanoparticle size analyzer (Nano ZS, ZEN3600).14 The relative viscosity, ηr, of each 2000 ppm emulsion solution was calculated by:13

ηr =

η tρ = η0 t0 ρ 0

(9)

where t (s) is the elution time of the emulsion solution measured by an AVS 360 inherent viscosity meter, ρ (in g cm-3) is the density of the emulsion solution, and t0 and ρ0 are the elution time and density of deionized water, respectively. 10 ACS Paragon Plus Environment

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Forward osmosis (FO) for water reclamation from oil/water emulsions A lab-scale FO system was used to study the membrane performance for dewatering the oil/water emulsion solutions.14,35 The membrane permeation cell was a plate-and-frame design with a spacer-free rectangular channel at each side, and the effective membrane surface area was 10 cm2. The feed and draw solutions were circulated counter-currently by two variable speed peristaltic pumps. The water permeation flux, Jw, was obtained from the weight change of the feed solution over a selected duration. The solution weight was automatically measured through a digital balance (EK-4100i, A&D Company Ltd., Japan) that was connected to a computer. Jw (in L m−2 h−1, abbreviated as LMH) was then calculated as:

J

w

=

∆V Am ∆t

(10)

where ∆V (in L) is the permeate water over a predetermined time ∆t (in h) and Am is the effective membrane surface area (in m2). The reverse salt flux, Js, (in g m-2 h-1, abbreviated as gMH) from the draw solution into the feed was measured by monitoring the feed conductivity change with time, and was calculated as:35 Js =

C f ,tV f ,t − C f ,iV f ,i Am ∆t

(11)

where Cf,t and Vf,t are the salt concentration and feed volume at the end of tests, respectively, and Cf,i and Vf,i refer to the salt concentration and total feed volume at the beginning, respectively. The oil concentration in the solution was measured via a total organic carbon analyzer (TOC, Shimadzu, Japan) and further confirmed by an ultraviolet (UV) spectrometer.12-14 The oil rejection Ro (%) was calculated by: 11 ACS Paragon Plus Environment


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Ro = (1 −

Cp ) ×100% C f ,i

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(12)

where Cf,i is the initial oil concentration in the feed, and Cp is the oil concentration in the permeate water which could be obtained from the oil concentration change in the draw solution as:14

Cp =

C d ,t (Vd ,i + ∆ V ) − C d ,iVd ,i ∆V

(13)

where Cd,i is the oil concentration in the initial draw solution with a volume of Vd,i, and Cd,t is the oil concentration at the end of tests. In terms of Jw, Js and Ro, the FO performances of the TFC-FO membranes for water reclamation from the 2000 ppm oil-in-water emulsions stabilized by Tween 80, SDS, and HTAB were investigated, respectively. Two operation modes were employed: (1) pressure retarded osmosis (PRO) mode where the emulsion feed solutions face the porous substrate; and (2) FO mode where the feed solutions flow against the selective layer. Since the Matrimid-TFC and PEI-Matrimid-TFC membranes possess almost the same TFC layer but different supports, they are tested in PRO mode because they may have the same performance in FO mode. Similarly, the Matrimid-TFC and Matrimid-TFC-PEI membranes have the same substrate but different TFC layers, so they are tested in FO mode. However, in order to compare the performance of one membrane under different modes, the Matrimid-TFC membrane was tested in both FO and PRO modes. The solution cross-flow velocity was kept at 0.2 L min-1 (or 0.017 m s-1) at both sides and there was no hydraulic pressure difference across the membrane. The solution temperature was maintained at 22±0.5 ºC. For the short-term membrane water flux, the averaged Jw over the first 10 min of each test was reported. For long-term performance tests, a 0.5 L emulsion solution was 12 ACS Paragon Plus Environment

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continuously run through the FO membrane until reaching the predetermined duration or recovery rate. During each test, the draw solution concentration was maintained constant by conductivity control to exclude the dilution effects. The feed solution recovery rate, Re (%), was calculated as: Re =

∆V ×100% V f ,i

(14)

where Vf,i (in L) is the initial volume of the feed solution. The fouled membranes were cleaned by flushing with freshwater on the fouled surface for 2 h at a relatively high flow rate of 0.4 L min-1 (or 0.034 m s-1). In order to ensure the experimental reproducibility, three tests were carried out for each condition and the averaged value was reported. During each test, one new membrane coupon was used except for the fouling reversibility evaluation.

Results and Discussion Characterization of the TFC-FO membranes In order to investigate the effects of membrane characteristics and membrane-emulsion interactions on FO performance for dewatering the emulsified oil/water solutions, three TFC-FO membranes with tailored structure and surface properties were molecularly designed. Figure 2 shows the pore size distribution curves of the Matrimid and PEI-Matrimid substrates and their PWP, MWCO, and mean pore sizes. The Matrimid substrate possesses a mean pore diameter of 17.3 nm with a narrow pore size distribution as indicated by the small geometric standard deviation, and a MWCO of 148 kDa. After the PEI modification, the pore size distribution shifts slightly to the smaller value. Therefore, the PEI-Matrimid substrate has a slightly smaller mean pore size of 14.9 nm and MWCO of 133.8 kDa. In addition, its PWP drops significantly from 13 ACS Paragon Plus Environment


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478.0 to 25.6 L m-2 h-1 bar-1, possibly due to the cross-linking reaction induced by PEI as reported in our previous work.32 Figure 3 (a) shows the Zeta-potential of their bottom surfaces as a function of pH value. The Matrimid substrate has an isoelectric point of pH 3.9. It is slightly positively charged below this point but becomes negatively charged above this pH. In contrast, the PEI-Matrimid substrate shows significantly changed surface charge properties and it has an isoelectric point of pH 10.7. Thus, the membrane is extremely positively charged particularly under this pH. The PEI molecules grafted onto the Matrimid substrate have formed amide and amine groups that confer positive charge characteristics.32,38 Figure 4 shows the FESEM morphology of the three TFC-FO membranes. As illustrated in Figure 4 (a), the Matrimid substrate has a fully sponge-like cross-section with a highly porous open-cell microporous structure. Its bottom surface has some tiny pores which can help reduce the transport resistance and internal concentration polarization (ICP). After being modified by PEI (Figure 4 (b)), the PEI-Matrimid substrate shows almost the same cross-section and bottom surface morphology, suggesting that there is no significant change in membrane macro-structure. These are well in agreement with their pore characteristics as displayed in Figure 1. By employing interfacial polymerization, a polyamide selective layer was formed on the top surface of the substrates. The polyamide layer of the Matrimid-TFC membrane shows a typical “ridgeand-valley” morphology with a relatively large “leaf-like” structure.14,39 However, the polyamide layer formed on the PEI-Matrimid substrate is smoother and the “leaf-like” structure becomes much smaller (Figure 4 (b)). This is probably attributed to the effects of PEI modification on surface chemistry and pore size, which may hinder the diffusion of MPD monomer into the reaction zone during interfacial polymerization. The Matrimid-TFC-PEI membrane (Figure 4 (c)) has a polyamide surface morphology between the Matrimid-TFC membrane (Figure 4 (a)) and


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the PEI-Matrimid-TFC membrane (Figure 4 (b)) due to the surface modification of PEI on the polyamide layer.34 The XPS data presented in Table S1 further confirm the successful grafting of PEI on the polyamide selective skin. Table 2 tabulates the transport properties, NaCl rejections, structural parameters and water contact angles of the three TFC-FO membranes. The Matrimid-TFC membrane has a pure water permeability, A, of 1.2 L m-2 h-1 bar-1 with a low salt permeability coefficient, B, of 0.13 L m−2 h−1 and a relatively small structural parameter, S, of 357 µm. The PEI-Matrimid-TFC membrane drops A and B values to 1.0 L m-2 h-1 bar-1 and 0.11 L m−2 h−1, respectively; while its S increases to 524 µm. This is attributed to the fact that its polyamide layer has a reduced surface roughness (i.e., a lower specific surface area) and enhanced transport resistance as shown in Figure 1. The Matrimid-TFC-PEI membrane possesses a higher A of 1.4 L m-2 h-1 bar-1 with a slightly larger B of 0.18 L m−2 h−1 mainly because its PEI modified polyamide skin is more hydrophilic (Table 2). Figure 3 (b) compares the Zeta-potential of the polyamide surfaces of the Matrimid-TFC and Matrimid-TFC-PEI membranes. The Matrimid-TFC is mildly positively charged below its isoelectric point of pH 3.3 but becomes negatively charged above this pH, suggesting the presence of –COOH groups. On the contrary, the PEI modified polyamide skin of the MatrimidTFC-PEI membrane is greatly positively charged within the whole pH range of 2.0-11.0 due to the PEI graft. In summary, the newly prepared TFC-FO membranes possess similar transport properties but quite different surface characteristics.

Characterization of the oil/water emulsion solutions Three 2000 ppm petroleum-in-water emulsion solutions were prepared by using SDS, HTAB and Tween 80 as the surfactants, separately. All oil/water emulsions show good stability but with



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different characteristics. As displayed in Figure 5 and Table 3, the Tween 80-Emulsion has the smallest mean particle size of 344.3 nm in diameter with one major peak diameter of 531.2 nm and one minor peak of 105.7 nm. In contrast, the HTAB-Emulsion and the SDS-Emulsion show much larger mean particle sizes of 849.8 nm and 994.1 nm, respectively. A quite broad size distribution with two peak diameters at 1990.0 nm and 220.2 nm was observed for the HTABEmulsion; while the SDS-Emulsion displays a narrow particle size distribution with only one peak diameter of 825 nm. In addition, the surface charge properties of the emulsion particles vary significantly with the surfactant chemistry. As shown in Table 3, the emulsion particles stabilized by SDS and HTAB possess highly negative and positive surface charges, respectively; while the Tween 80-Emulsion particles have an almost neutral surface. This clearly indicates that the surface charges of the oilin-water emulsions are determined by the surfactants. Furthermore, the emulsion solutions exhibit different pH values ranging from 3.7 to 6.1, but their viscosity is quite low and is close to pure water because of the low oil content. The three emulsion solutions may result in diverse membrane performance and fouling behaviors in FO because they have different particle sizes and surface charge properties.12,14

Forward osmosis (FO) for water reclamation from oil/water emulsions FO performance in PRO mode In order to reduce ICP, the FO membrane is preferred to be operated in PRO mode where the draw solution faces the rejection layer.40 However, the solutes in the feed may trap into the porous substrate layer when the water permeates across the membrane and results in severe fouling, as illustrated in Figure 6. Aiming to investigate the effects of membrane and emulsion


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characteristics on FO performance in PRO mode, the Matrimid-TFC and PEI-Matrimid-TFC membranes were used as the FO membranes because they have almost the same polyamide selective layer yet different substrates, while the three oil/water emulsions were employed as the feed solutions.

Water recovery from oil/water emulsions in PRO mode Table 4 summarizes the initial water flux, Jw0, reverse salt flux, Js, and oil rejection of the Matrimid-TFC and PEI-Matrimid-TFC membranes in PRO mode using 1 M NaCl as the draw solution. It is observed that both membranes show quite low Js values of less than 3.2 g/L and ultrahigh oil rejections of greater than 99.9%, indicating their TFC layers have outstanding selectivity. When deionized water is used as the control feed, an initial flux of 25.6 LMH is achieved by the Matrimid-TFC membrane. However, dramatic declines in Jw0 are immediately observed when the feed is changed to any of 2000 ppm oil/water emulsions. For example, Jw0 drops to 15.0, 17.0 and 12.7 LMH for the Tween 80-Emulsion, HTAB-Emulsion and SDS-Emulsion solutions, respectively (Table 4). These fast and significant flux reductions suggest that the emulsion particles easily enter into the porous substrate when water permeating through the membrane in PRO mode and immediately result in fouling. Figure 7 (a) further shows the flux decreases as a function of operation duration for the Matrimid-TFC membrane using these three emulsion solutions as the feed, separately. The HTAB-Emulsion exhibits the lowest flux reduction of 27% after 180 min, where its Jw slowly drops from the initial value of 17.0 LMH to 12.4 LMH. The fluxes of the Tween 80-Emulsion and SDS-Emulsion solutions rapidly decrease to 60% and 68% of their initial values, respectively, although they have a lower Jw0. Since the



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charge-charge interactions between the emulsion particles and the Matrimid substrate of the Matrimid-TFC membrane is low because of its relatively weak surface charges as depicted in Figure 3 (a), the different flux decline behaviors of the three emulsion solutions are mainly due to the effects of emulsion particle size and distribution (Figure 5). The smaller the particle size is, the greater the final flux declines. Similarly, significant drops in Jw0 are observed by the PEI-Matrimid-TFC membrane in PRO mode when using the emulsion solutions as the feed (Table 4). However, their flux declines as a function of operating duration are different from one another when comparing with those of the Matrimid-TFC membrane. As displayed in Figure 7 (b), the water flux of the HTAB-Emulsion slightly decreases from 17.5 LMH to 15.6 LMH even after a 180-min test. This corresponds to a quite low flux drop of 11% of its initial value. In contrast, the flux of the SDS-Emulsion dramatically decreases to 25% of the initial value within a short duration of less than 40 min, and then rapidly drops to 17% within 180 min. The Tween 80-Emulsion solution shows a flux decline of 41% which is similar to that of the Matrimid-TFC membrane (i.e., 40%). Since the PEI-Matrimid and Matrimid substrates possess almost the same pore size (Figure 1), the different flux reduction behaviors are mainly due to their various surface charge characteristics. As shown in Figure 3 (a), the PEI-Matrimid substrate is greatly positive charged when the pH is less than 10.7; therefore, the highly negative charged SDS-Emulsion particles have strong affinity with the PEI-Matrimid substrate which explains its fast and severe fouling propensity. In contrast, the repulsive force between the positive-charged HTAB-Emulsion particles (Table 3) and the positive-charged PEI-Matrimid substrate (Figure 3 (a)) significantly reduces the membrane fouling. In addition, the HTAB-Emulsion particles have a large particle size (Figure 5), it may help reduce fouling. Since the Tween 80-Emulsion particles possess a near neutral surface, the


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two TFC-FO membranes display similar fouling behaviors when treating the Tween 80Emulsion.

Membrane fouling reversibility in PRO mode After the fouling tests, both Matrimid-TFC and PEI-Matrimid-TFC membranes were immediately cleaned by flushing with freshwater on the fouled bottom surfaces for 2 h. Then, the initial fluxes of the cleaned membranes were re-tested using deionized water as the feed and compared with Jw0 of the fresh membranes. In general, water rinse can only recover part of the water flux in PRO mode, and the cleaning efficiency varies with emulsion solutions and membranes. As displayed in Figure 8 (a), the fouling reversibility of the Matrimid-TFC membrane for the three emulsion solutions shows a similar trend with their fouling propensities (Figure 7 (a)), where a water flux recovery of 54%, 75%, and 73% was obtained by the Tween 80-Emulsion, SDS-Emulsion, and HTAB-Emulsion solutions, respectively. For the PEIMatrimid-TFC membrane, HTAB-Emulsion shows the best fouling reversibility, where its initial water flux can be restored to 89% of the initial value (Figure 8 (b)). This is well aligned with its low fouling propensity. Interestingly, the SDS-Emulsion displays better fouling reversibility than the Tween 80-Emulsion (i.e., 70% vs. 53%), although the former has a greater fouling tendency than the later (Figure 7 (b)). This can be attributed to the smaller emulsion particle size of the Tween 80-Emulsion (Figure 5), as small particles are easily trapped into the porous substrate but very difficult to be rinsed out by water flushing.

FO performance in FO mode



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As illustrated in Figure 6, the fouling induced by oil/water emulsions within the substrate could be minimized by operating the membrane in FO mode where the emulsion solutions face the rejection layer. The Matrimid-TFC and Matrimid-TFC-PEI membranes were employed to study the effects of membrane characteristics on dewatering of these three oil/water emulsions in FO mode because they have the same Matrimid substrate but different polyamide selective skins.

Water recovery from oil/water emulsions in FO mode As shown in Table 5, the Matrimid-TFC and Matrimid-TFC-PEI membranes have a Jw0 of 16.5 LMH and 17.6 LMH with a low Js of 2.1 gMH and 3.0 gMH, respectively, using deionized water as the feed in FO mode. Due to the ICP effects caused by the draw solution, these Jw0 are lower than those in PRO mode. However, when changing the feed to the emulsion solutions, the flux declines of both membranes are very small, where Jw0 slightly drops to 15.5-16.3 LMH and 14.017.0 LMH for the Matrimid-TFC and Matrimid-TFC-PEI membranes, respectively. Figure 9 further shows the water flux reductions of the two membranes as a function of operation duration up to 1400 min. Clearly, the flux declines for all emulsion solutions are much smaller than those in PRO mode (Figure 7). Since the emulsion solutions face the polyamide selective layer in FO mode, the emulsion particles cannot penetrate into the membrane substrate. As a result, fouling mainly happens on the membrane surface instead of within the substrate (Figure 6). Therefore, slower and milder fouling propensity is achieved for the three emulsion solutions. However, fouling still happens on the polyamide surface and causes a certain flux drop particularly after long-term operations. This is possibly because that the polyamide layer is relatively rough and possesses charges, thus the emulsion particles would adsorb and attach onto the surface with water permeation across the membrane. This would reduce effective flow


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channels and hydrophilicity. As presented in Figure 9 (a), fouling propensity on the polyamide surface of the Matrimid-TFC membrane varies with emulsion solutions. During a short test duration of less than 100 min, the Tween 80-Emulsion shows a severer flux decline than the other two solutions. This might be due to its smallest particles size and the hydrogen bonding interaction with the surface.41 In addition, the charge effects are negligible because of its near neutral surface at a pH of 6.1 (Table 3). The HTAB-Emulsion displays a slightly lower flux drop than the SDS-Emulsion even though the former is positively charged while the latter is negatively charged. Since the polyamide layer of the Matrimid-TFC membrane is weakly negative charged between pH 3.7 and 4.5 (Figure 3 (b)), this suggests that there are two competing factor affecting its fouling; namely, charge interaction and emulsion droplet size. When the charge-charge interaction is not significant, the particle size of the emulsion droplets would play a key role in the fouling propensity. As a result, the SDS-Emulsion has greater fouling tendency than the HTAB-Emulsion because the former has a smaller droplet size than the latter. For long-time operations, the Tween 80-Emulsion shows a smaller flux reduction (i.e., 67% of the initial value) than the HTAB-Emulsion (i.e., 58%) and SDS-Emulsion (i.e., 53%) possibly due to its none-ionic characteristics. Figure 9 (b) presents the water flux reductions of the Matrimid-TFC-PEI membrane as a function of operation duration using these three emulsion solutions as the feed, separately. Compared to the Matrimid-TFC, the PEI modified polyamide layer of the Matrimid-TFC-PEI membrane possesses similar transport properties (Table 2), but is greatly positively charged (Figure 3 (b)). Since the HTAB-Emulsion particles have positive surface charges (Table 3), the repulsive force between the emulsion particles and the PEI modified polyamide surface is high. As a result, it shows very mild fouling and the flux slightly drops to 82% of the initial value even



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after a 1400-min test. On the contrary, the flux decline of the SDS-Emulsion is very fast and significant where the flux decreases to 25% of the initial value during the same testing duration, mainly due to the strong charge attraction. The Tween 80-Emulsion has a medium flux decline of 38% because of its near neutral surface and small particle size. As illustrated in Figure 6, when the charge-charge interaction becomes great, surface charge characteristics of the membrane and emulsions would dominate the fouling propensity. In order to simulate the real applications, a 0.5 L of the HTAB-Emulsion solution containing 2000 ppm petroleum and 0.05 M NaCl was continuously run through the Matrimid-TFC and Matrimid-TFC-PEI membranes, respectively, until reaching a high feed recovery of 80%. As shown in Figure 10, membrane fouling happens fast as indicated by the significant flux declines at relatively low recovery rates of less than 20%. Once the emulsions induced fouling is well developed, the decrease of flux becomes mild till to a high recovery rate of 80%. Because of the improved antifouling characteristics of the PEI modified polyamide skin, the flux decline of the Matrimid-TFC-PEI membrane is lower than the Matrimid-TFC. It is also worth noting that the membrane can maintain above 50% of the initial water flux in FO mode even at high recovery rates, suggesting it has good membrane performance and stability.

Membrane fouling reversibility in FO mode Figure 11 shows that water rinse through the fouled polyamide surface can effectively rejuvenate the water fluxes of the Matrimid-TFC and Matrimid-TFC-PEI membranes, which suggests the great fouling reversibility in FO mode. In addition, the fouling reversibility against the three emulsion solutions has the similar trends with their fouling propensities for both membranes. As depicted in Figure 11 (a), the Jw0 of the Tween 80-Emulsion and HTAB-Emulsion fouled


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Matrimid-TFC membranes could be restored to 92-97% of the initial value; while the SDSEmulsion fouled one can only be brought back to 65%. The lower fouling reversibility of the SDS-Emulsion might be due to the formation of hydrogen bonding with the polyamide surface.41 A similar phenomenon is observed by the Matrimid-TFC-PEI membrane as shown in Figure 11 (b). The high fouling reversibility of the Matrimid-TFC-PEI membrane against the HTABEmulsion and the Tween 80-Emulsion is mainly because of its (1) highly positively charged polyamide surface, (2) slightly reduced surface roughness and (3) enhanced hydrophilicity (Figure 4 and Table 2).

Conclusions By molecularly designing TFC membranes with tailored substrates and polyamide selective layers as FO membranes, and using oil-in-water emulsion solutions with different droplet size and charge properties as feed solutions, the effects of membrane and emulsion characteristics as well as their interactions on FO performance and fouling behaviors were systematically investigated in both the PRO and FO modes. The following conclusions can be further drawn from the current study: 1. Surfactant chemistry plays an important role in determining oil droplets’ size, size distribution and surface charge properties. 2. FO shows promising characteristics of relatively high water flux, great salt/oil rejection and high water recovery during the dewatering of the oil/water emulsion solutions. 3. FO membranes have a strong tendency to be fouled in PRO mode, even though the fouling could be partially mitigated by surface modification. The FO operation mode is preferable in terms of low fouling propensity, high fouling reversibility and stable water flux.



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4. The particle size of the emulsion droplets and the charge-charge interactions between the emulsion particles and membrane surface play determinable roles in fouling propensity and reversibility. 5. Flushing with freshwater on the fouled polyamide surfaces of the TFC-FO membranes is effective to remove the fouling layer and recover the membrane water flux in FO mode. The surface modification on the polyamide layer could enhance the fouling reversibility.

Supporting Information Table on the peak ratio analysis from XPS results of the polyamide selective layer of the Matrimid-TFC and Matrimid-TFC-PEI membranes (Table S1).

Acknowledgement This research was funded by the 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: Module designs and integrated systems for sustainable processes” (Grant number: R-278-000-339-281). We thank Mr. Cheng Hui GOH and Mr. Yuan Feng WONG for their experimental assistance.


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References (1)

Kerr, R. A. Natural gas from shale bursts onto the scene. Science 2010, 328, 1624–1626.

(2)

Yang, H. C.; Pi, J. K.; Liao, K. J.; Huang, H.; Wu, Q. Y.; Huang, X. J.; Xu, Z. K. Silicadecorated polypropylene microfiltration membranes with a mussel-inspired intermediate layer for oil-in-water emulsion separation. ACS Appl. Mater. Interfaces 2014, 6, 12566– 12572.

(3)

Fakhru’l-Razi, A.; Pendashteh, A.; Abdulah, L. C.; Biak, D. R.; Madaeni, S. S.; Abidin, Z. Z. Review of technologies for oil and gas produced water treatment. J. Hazard. Mater. 2009, 170, 530–551.

(4)

Chen, M.; Zhu, L.; Dong, Y.; Li, L.; Liu J. Waste-to-resource strategy to fabricate highly porous whisker-structured mullite ceramic membrane for simulated oil-in-water emulsion wastewater treatment. ACS Sustainable Chem. Eng. 2016, 4, 2098–2106.

(5)

Jackson, R. B.; Vengosh, A.; Darrah, T. H.; Warner, N. R.; Down, A.; Poreda, R. J.; Osborn, S. G.; Zhao, K.; Karr, J. D. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 11250−11255.

(6)

Vidic, R. D.; Brantley, S. L.; Vandenbossche, J. M.; Yoxtheimer, D.; Abad, J. D. Impact of shale gas development on regional water quality. Science 2012, 340, 826−835.

(7)

Hansen, B. R.; Davies, S. H. Review of potential technologies for the removal of dissolved components from produced water. Chem. Eng. Res. Des. 1994, 72, 176−188.

(8)

Shaffer, D. L.; Chavez, L. H. A; Ben-Sasson, M.; Castrillón, S. R. V.; Yip, N. Y.; Elimelech, M. Desalination and reuse of high-salinity shale gas produced water: drivers, technologies, and future directions. Environ. Sci. Technol. 2013, 47, 9569−9583.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(9)

Page 26 of 47

McCloskey, B. D.; Ju, H.; Freeman, B. D. Composite membranes based on a selective chitosan-poly(ethylene glycol) hybrid layer: synthesis, characterization, and performance in oil−water purification. Ind. Eng. Chem. Res. 2010, 49, 366−373.

(10) Li, P.; Lim, S. S.; Neo, J. G.; Ong, R. C.; Weber, M.; Staudt, C.; Widjojo, N.; Maletzko, C.; Chung, T. S. Short- and long-term performance of the thin-film composite forward osmosis (TFC-FO) hollow fiber membranes for oily wastewater purification. Ind. Eng. Chem. Res. 2014, 53, 14056−14064. (11) Hickenbottom, K. L.; Hancock, N. T.; Hutchings, N. R.; Appleton, E. W.; Beaudry, E. G.; Xu, P.; Cath, T. Y. Forward osmosis treatment of drilling mud and fracturing wastewater from oil and gas operations. Desalination 2013, 312, 60–66. (12) Duong, P. H. H.; Chung, T. S.; Wei, S.; Irish, L. Highly permeable double-skinned forward osmosis membranes for anti-fouling in the emulsified oil−water separation process. Environ. Sci. Technol. 2014, 48, 4537−4545. (13) Zhang, S.; Wang, P.; Fu, X.; Chung, T. S. Sustainable water recovery from oily wastewater via forward osmosis-membrane distillation (FO−MD). Water. Res. 2014, 52, 112−121. (14) Han, G.; de Wit, J. S.; Chung, T. S. Water reclamation from emulsified oily wastewater via effective forward osmosis hollow fiber membranes under the PRO mode. Water. Res. 2015, 81, 54−63. (15) Zhao, P.; Gao, B.; Yue, Q.; Shon, H. K. The performance of forward osmosis process in treating the surfactant wastewater: The rejection of surfactant, water flux and physical cleaning effectiveness. Chem. Eng. J. 2015, 281, 688−695. (16) Van der Bruggen, B; Luis, P. Forward osmosis: understanding the hype. Rev. Chem. Eng. 2015, 31, 1−12.


Page 27 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17) Zhao, S.; Zou, L.; Tang, C. Y.; Mulcahy, D. Recent developments in forward osmosis: opportunities and challenges. J. Membr. Sci. 2012, 396, 1–21. (18) Han, G.; Zhang, S.; Li, X.; Chung, T. S. Progress in pressure retarded osmosis (PRO) membranes for osmotic power generation. Prog. Polym. Sci. 2015, 51, 1–27. (19) Qi, S.; Qiu, C. Q.; Zhao, Y.; Tang, C. Y. Double-skinned forward osmosis membranes based on layer-by-layer assembly-FO performance and fouling behavior. J. Membr. Sci. 2012, 405–406, 20–29. (20) Han, G.; Zhang, S.; Li, X.; Widjojo, N.; Chung, T. S. Thin film composite forward osmosis membranes based on polydopamine modified polysulfone substrates with enhancements in both water flux and salt rejection. Chem. Eng. Sci. 2012, 80, 219–231. (21) Long, Q.; Qi, G.; Wang, Y. Evaluation of renewable gluconate salts as draw solutes in forward osmosis process. ACS Sustainable Chem. Eng. 2016, 4, 85–93. (22) Liu, Q.; Zhou, Z.; Qiu, G.; Li, J.; Xie, J.; Lee, J. Y. Surface reaction route to increase the loading of antimicrobial Ag nanoparticles in forward osmosis membranes. ACS Sustainable Chem. Eng. 2015, 3, 2959–2966. (23) Liu, Y.; Mi, B. Combined fouling of forward osmosis membranes: synergistic foulant interaction and direct observation of fouling layer formation. J. Membr. Sci. 2012, 407–408, 136–144. (24) Jin, X.; She, Q.; Ang, X.; Tang, C. Y. Removal of boron and arsenic by forward osmosis membrane: Influence of membrane orientation and organic fouling. J. Membr. Sci. 2012, 389, 182–187. (25) Hegab, H. M.; ElMekawy, A.; Barclay, T. G.; Michelmore, A.; Zou, L., Saint, C. P.; GinicMarkovic, M. Fine-tuning the surface of forward osmosis membranes via grafting graphene



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Page 28 of 47

oxide: Performance patterns and biofouling propensity. ACS Appl. Mater. Interfaces 2015, 7, 18004–18016. (26) Cath, T. Y.; Childress, A. E.; Elimelech, M. Forward osmosis: principles, applications, and recent developments. J. Membr. Sci. 2006, 28, 70–87. (27) Wang, R.; Shi, L.; Tang, C. Y.; Chou, S.; Qiu, C. Q.; Fane, A. G. Characterization of novel forward osmosis hollow fiber membranes. J. Membr. Sci. 2010, 355, 158–167. (28) Huang, L.; Bui, N. N.; Meyering, M. T.; Hamlin, T. J.; McCutcheon, J. R. Novel hydrophilic nylon 6,6 microfiltration membrane supported thin film composite membranes for engineered osmosis. J. Membr. Sci. 2013, 437, 141–149. (29) Phuntsho, S.; Shon, H. K.; Majeed, T.; Saliby, I. E.; Vigneswaran, S.; Kandasamy, J.; Hong, S.; Lee, S. Blended fertilizers as draw solutions for fertilizer-drawn forward osmosis desalination. Environ. Sci. Technol. 2012, 46, 4567−4575. (30) Flanagan, M. F.; Escobar, I. C. Novel charged and hydrophilized polybenzimidazole (PBI) membranes for forward osmosis. J. Membr. Sci. 2013, 434, 85–92. (31) Hu, M.; Zheng, S.; Mi, B. Organic fouling of graphene oxide membranes and its implications for membrane fouling control in engineered osmosis. Environ. Sci. Technol. 2016, 50, 685−693. (32) Thong, Z.; Han, G.; Cui, Y.; Gao, J.; Chung, T. S.; Chan, S. Y.; Wei, S. Novel nanofiltration membranes consisting of a sulfonated pentablock copolymer rejection layer for heavy metal removal. Environ. Sci. Technol. 2014, 48, 13880−13887. (33) Ren, J.; O'Grady, B.; deJesus, G.; McCutcheon, J. R. Sulfonated polysulfone supported high performance thin film composite membranes for forward osmosis. Polymer, 2016, doi:10.1016/j.polymer.2016.02.058.


Page 29 of 47

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(34) Zhu, W. P.; Gao, J.; Sun, S. P.; Zhang, S.; Chung, T. S. Poly(amidoamine) dendrimer (PAMAM) grafted on thin film composite (TFC) nanofiltration (NF) hollow fiber membranes for heavy metal removal. J. Membr. Sci. 2015, 487, 117–126. (35) Han, G.; Chung, T. S.; Toriida, M.; Tamai, S. Thin-film composite forward osmosis membranes with novel hydrophilic supports for desalination. J. Membr. Sci. 2012, 423, 543–555. (36) Wang, K. Y.; Chung, T. S.; Amy, G. Developing thin-film-composite forward osmosis membranes based on the PES/SPSf substrate through interfacial polymerization. AIChE J. 2012, 58, 770–781. (37) Van der Bruggen, B.; Vandecasteele, C. Modelling of the retention of uncharged molecules with nanofiltration. Water Res. 2002, 36, 1360−1368. (38) Sun, S. P.; Hatton, T. A.; Chung, T. S. Hyperbranched polyethyleneimine induced crosslinking of polyamide−imide nanofiltration hollow fiber membranes for effective removal of ciprofloxacin. Environ. Sci. Technol. 2011, 45, 4003−4009. (39) Ghosh, A. K.; Jeong, B. H.; Huang, X. F.; Hoek, E. M. V. Impacts of reaction and curing conditions on polyamide composite reverse osmosis membrane properties. J. Membr. Sci. 2008, 311, 34−45. (40) Zhang, S.; Zhang, Y.; Chung, T. S. Facile preparation of antifouling hollow fiber membranes for sustainable osmotic power generation. ACS Sustainable Chem. Eng. 2016, 4, 1154−1160. (41) Duong, P. H. H.; Chung, T. S. Application of thin film composite membranes with forward osmosis technology for the separation of emulsified oil–water. J. Membr. Sci. 2014, 452, 117–126.



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Figure 1. Schematic of the membrane structures of (top) Matrmid-TFC with an as-cast Matrimid substrate and a typical polyamide layer, (middle) PEI-Matrimid-TFC with a PEI modified Matrimid substrate and a typical polyamide layer, and (bottom) Matrimid-TFC-PEI with an ascast Matrimid substrate and a PEI modified polyamide layer.


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Figure 2. Characteristics of the Matrimid and PEI-Matrimid membrane substrates.



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Figure 3. Zeta-potential vs. pH curves of (a) bottom surfaces of the Matrimid and PEI-Matrimid membrane substrates, and (b) top polyamide surfaces of the Matrimid-TFC and Matrimid-TFCPEI membranes.


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Figure 4. FESEM images of the TFC-FO membranes (a) Matrimid-TFC, (b) PEI-Matrimid-TFC, and (c) Matrimid-TFC-PEI.



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Figure 5. Particle size distributions of the 2000 ppm oil-in-water emulsion solutions stabilized by different surfactants.


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Figure 6. Schematic of fouling phenomena of the TFC membranes induced by oil/water emulsions in FO in PRO and FO modes.



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Figure 7. Water flux reductions of (a) the Matrimid-TFC membrane and (b) the PEI-MatrimidTFC membrane as a function of operation time in PRO mode. Draw solution was 1 M NaCl and its salt concentration was maintained constantly through the tests. Deionized water and three 2000 ppm oil/water emulsions stabilized by Tween 80, SDS and HTAB are the feeds.


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Figure 8. Normalized initial water fluxes of the cleaned (a) Matrimid-TFC membrane and (b) PEI-Matrimid-TFC membrane over the initial fluxes of the fresh membranes in PRO mode. Each membrane was fouled by three emulsion solutions, separately. The fouled membranes were cleaned by flushing with freshwater on the membrane bottom surfaces for 2 h. Draw solution: 1 M NaCl; feed: deionized water.



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Figure 9. Water flux reduction of the (a) Matrimid-TFC membrane and (b) Matrimid-TFC-PEI membrane as a function of operation time in FO mode. Draw solution was 1 M NaCl and its salt concentration was maintained constantly through the tests. Deionized water and three 2000 ppm oil/water emulsions stabilized by Tween 80, SDS and HTAB are the feeds.


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Figure 10. Water flux reduction of the Matrimid-TFC and Matrimid-TFC-PEI membranes as a function of feed recovery rate in FO mode. Draw solution was 1 M NaCl and feed was HTABEmulsion containing 2000 ppm petroleum and 0.05 M NaCl.



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Figure 11. Normalized initial water flux of the cleaned (a) Matrimid-TFC and (b) MatrimidTFC-PEI membrane over the initial flux of the fresh membranes in FO mode. Each membrane was fouled by one of the three emulsion solutions. The fouled membranes were cleaned by flushing with freshwater on the membrane top surfaces for 2 h. Draw solution: 1 M NaCl; feed: deionized water.


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Table 1. Chemical structures and molecular weights of the surfactants used in this study Name of surfactant Type of Molecular structure Molecular surfactant weight (g/mol) Sodium dodecyl sulfate (SDS)

Anionic

288

Hexadecyltrimethylamm onium bromide (HTAB)

Cationic

364

Tween 80

Nonionic

1310



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Table 2. Transport properties, rejections, structural parameters and water contact angles of the TFC-FO membranes Membrane Water Salt Salt Structural Water a b permeability, parameter contact angle permeability , A rejection , −2 −1 -2 -1 -1 S (µm) on top (º) Rs (%) B (L m h ) (L m h bar ) Matrimid-TFC

1.2±0.3

0.13

91.3±1.3

395

68±2.5

PEI-Matrimid-

1.0±0.2

0.11

91.5±1.5

524

69±3.0

1.4±0.4

0.18

90.0±1.4

395

65±2.8

TFC Matrimid-TFCPEI a b

A was tested at 2 bar using deionized water as the feed. Rs was tested at 2 bar using a 1000 ppm NaCl solution as the feed.


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Table 3. Characteristics of the 2000 ppm oil-in-water emulsion solutions stabilized by different surfactants Emulsion Surfactant Mean Relative pH Zeta Conductivity solution code

HTAB-

particle size

viscosity

potential

(nm)

(to water)

(mV)

(µS/cm)

HTAB

994.1±9.2

1.0

4.5±0.2

116.8±2.5

46.7±0.5

Tween 80

344.3±5.4

1.0

6.1±0.1

-8.7±1.3

2.2±0.4

SDS

849.8±7.5

1.0

3.7±0.2

-105.3±2.0

45.0±0.6

Emulsion Tween 80Emulsion SDSEmulsion



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Table 4. Short-term FO performance of the Matrimid-TFC and PEI-Matrimid-TFC membranes in PRO mode using different feed solutions Jw0 (LMH) Js (gMH) Oil rejection Operation Membrane code Feed (%) mode Matrimid-TFC

PEI-Matrimid-TFC

Deionized water

25.6±2.3

3.2±1.0

-

PRO

Tween 80-Emulsion

15.0±1.4

1.9±0.8

>99.9

PRO

HTAB-Emulsion

17.0±2.0

2.0±1.3

>99.9

PRO

SDS-Emulsion

12.7±1.2

1.8±0.9

>99.9

PRO

Deionized water

20.0±1.8

2.3±1.1

-

PRO

Tween 80-Emulsion

16.0±0.9

2.0±1.0

>99.9

PRO

HTAB-Emulsion

17.5±1.5

2.1±1.2

>99.9

PRO

SDS-Emulsion

10.7±1.0

1.5±0.4

>99.9

PRO

Draw solution was 1 M NaCl and the oil concentration of the emulsion solutions was 2000 ppm. Test duration for the membrane short-term FO performance was 10 min.


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Table 5. Short-term FO performance of the Matrimid-TFC and the Matrimid-TFC-PEI membranes in FO mode using different feed solutions Jw0 (LMH) Js (gMH) Oil rejection Operation Membrane code Feed (%) mode Matrimid-TFC

Matrimid-TFC-PEI

Deionized water

16.5±1.4

2.1±0.9

-

FO

Tween 80-Emulsion

16.3±1.0

2.1±1.0

>99.9

FO

HTAB-Emulsion

15.5±0.9

1.9±0.7

>99.9

FO

SDS-Emulsion

16.0±1.0

1.4±0.6

>99.9

FO

Deionized water

17.6±1.5

3.0±1.1

-

FO

Tween 80-Emulsion

16.5±0.9

2.7±0.8

>99.9

FO

HTAB-Emulsion

17.0±1.2

3.0±1.3

>99.9

FO

SDS-Emulsion

14.0±1.1

2.4±1.0

>99.9

FO

Draw solution was 1 M NaCl and the oil concentration of the emulsion feed solutions was 2000 ppm. Test duration for the membrane short-term FO performance was 10 min.



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Page 46 of 47

Forward Osmosis (FO) for Water Reclamation from Emulsified Oil/Water Solutions: Effects of Membrane and Emulsion Characteristics Gang Han, Sun Sun Chan, Tai-Shung Chung*

TABLE OF CONTENTS (TOC) GRAPHIC

Synopsis This work provides useful insights for the science and engineering behind the appropriate structure and chemistry of forward osmosis (FO) membranes for oily wastewater treatment.


Page 47 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Forward Osmosis (FO) for Water Reclamation from Emulsified Oil/Water Solutions: Effects of Membrane and Emulsion Characteristics Gang Han, Sun Sun Chan, Tai-Shung Chung*

TABLE OF CONTENTS (TOC) GRAPHIC Synopsis This work provides useful insights for the science and engineering behind the appropriate structure and chemistry of forward osmosis (FO) membranes for oily wastewater treatment.

1

ACS Paragon Plus Environment

Forward Osmosis (FO) for Water Reclamation from Emulsified Oil

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