Forward Osmosis Applications Research Articles

Preparation of modified cellulose acetate membranes using functionalized multi-walled carbon nanotubes for forward osmosis

Novel modified cellulose acetate (CA) membranes using functionalized multi-walled carbon nanotubes (MWCNTs) were synthesized by phase inversion via immersion precipitation technique. Carboxylated functionalized MWCNTs (F-MWCNTs) were used as additives into the casting solution of CA, 1, 4-dioxane, acetone, lactic acid, and methanol to enhance the forward osmosis (FO) membranes performance. Different contents of F-MWCNTs (0.01, 0.05, and 0.1 wt.%) were added into the casting solution. The novel synthesized CA/F-MWCNTs membranes were characterized by various methods in terms of membranes structure and surface properties, as well as FO performance, and then compared with traditional CA membrane and commercial FO membrane. The surface hydrophilicity, porosity, and tensile strength of CA/F-MWCNTs membranes were improved with the increment of the content of F-MWCNTs in the casting solution. The morphological studies showed that the addition of F-MWCNTs significantly changed the surface properties of the modified CA membranes. The FO performance was evaluated using purified water as feed solution and 1M NaCl solution as draw solution. The CA/F-MWCNTs membranes showed higher water permeability and salt rejection in the range of 0.01–0.1 wt.% F-MWCNTs content than CA membrane and the commercial FO membrane. These encouraging results suggested that CA/F-MWCNTs membranes showed superior potential to be further developed for FO applications.

Forward osmosis: an alternative sustainable technology and potential applications in water industry

This paper presents an advancing sustainable membrane-based separation process, which is forward osmosis (FO). The review begins with an introduction of the basic principles of the FO process. Then, a comparison to the most currently well-known desalination technology (RO) is presented. Following section summarizes potential applications of FO in the water desalination field, producing either potable water or irrigation water from brackish/saline feeds. Next, two major FO applications in the domain of water reuse are discussed: wastewater and industrial applications. Wastewater applications are such as OSMBR and landfill leachate treatment; and Industrial applications include oil and gas, pharmaceutical, and food and beverage industries. These different FO applications are briefly reviewed and assessed. Although FO has attracted growing attention in many potential applications, it still experiences several considerable limitations, including concentration polarization, membrane fouling, reverse solute diffusion, and need for membrane and draw solution development.

Effect of operating conditions on osmotic-driven membrane performances of cellulose triacetate forward osmosis hollow fiber membrane

Recent development in forward osmosis (FO) membranes is promising in providing a versatile potential application for further advance in the water treatment and energy production sectors. Using FO hollow fiber membranes to achieve wide application of FO at an industrial level is advantageous because of their large specific membrane area and easy module construction for large-scale applications. In this study, three types of cellulose triacetate (CTA) hollow fiber (HF) forward osmosis membranes with diameters of less than 200μm were evaluated under various operating conditions i.e., draw solution concentration, cross flow velocity, membrane orientation, and temperature. The osmotically driven performance evaluation revealed that the CTA HF membranes featured high water flux-to-reverse salt flux ratios, JwFO/JsFO, exceeding 800L/mol. These values are much higher than those of commercial and reported FO membranes. The performance of the obtained FO membranes was also analyzed theoretically and the theoretical results agreed well with the experimental data.

Synthesis and application of ethylenediamine tetrapropionic salt as a novel draw solute for forward osmosis application

The development of suitable draw solutes for forward osmosis (FO) process is a big obstacle on the way of its real industrialization. In this work, a novel draw solute, ethylenediamine tetrapropionic (EDTP) acid (salt) is developed for FO application. The successful synthesis is confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high resolution mass spectrum. By optimizing the pH of EDTP solution, its composition is varied, and therefore, its water solubility and osmotic pressure are effectively improved. The effects of EDTP concentration on the osmotic pressure and FO performance are also investigated. Its outstanding osmotic pressure and big molecular size result in a high water flux of 22.69 LMH and a low salt flux of 0.32 gMH with 0.8 M EDTP draw solution (water as the feed solution, pressure retarded osmosis mode). The good stability and easy recovery by nanofiltration of EDTP solution also demonstrate its great potential as the draw solute for future FO applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1309–1321, 2015

Synthesis and characterization of novel thin film nanocomposite (TFN) membranes embedded with halloysite nanotubes (HNTs) for water desalination

In this study, a new type of thin film nanocomposite (TFN) forward osmosis (FO) membranes was prepared by incorporating different quantities of halloysite nanotubes (HNTs) into the polyamide layer via interfacial polymerization. The FO performance of all fabricated TFN membranes in terms of water permeability and reverse solute flux was compared and the best performing membrane which showed good balance between permeability and solute flux, among all, was selected for further organic fouling investigation. Using 10mM NaCl concentration in feed solution and draw solution of 2M NaCl, the TFN membrane that was embedded with 0.05% HNTs (i.e. TFN0.05) was identified as the best performing membrane due to its high water permeability and low reverse solute flux. Confirmed by the results of BSA removal in the presence of Ca2+, the TFN0.05 membrane also exhibited significantly higher fouling resistance compared to a typical TFC membrane. As an indication to the TFN0.05 fouling reversibility, it was found that >96% permeate flux could be recovered after a simple water rinse process. Overall, it can be concluded that the addition of an appropriate amount of HNTs into the polyamide layer can remarkably improve the antifouling affinity of conventional TFC membranes for FO applications.

Forward osmosis: understanding the hype

AbstractThe scientific interest in forward osmosis has increased dramatically over the last decade. The hype has resulted in a high scientific production, but research activities seem to go in all directions, and the real benefits of the process are not always well understood. This paper aims to give some directions based on the current state of the art. Without going into details about the process itself, the current research lines and their background are described. While some of these are important, others – notably the search for alternative draw solutions – have become the Holy Grail of forward osmosis. The further analysis of the process is based on suggested applications and uses the observations made on contemporary research topics in the field. At first, direct application of forward osmosis for potable water production is considered. This leads back to the research challenges of the reverse draw solute flux, concentration polarization, and the regeneration of the draw solution. Special attention is given to desalination, as forward osmosis is often incorrectly denoted as a desalination technology. It can be used in the context of desalination; however, the question remains in which applications this is of interest. Combining desalination and wastewater treatment is one such interesting application, which is further described in this paper for some types of wastewater found in the literature. In the last part, the paper emphasizes the need to develop processes in which the challenge of the draw solution is intrinsically solved. The foremost example of such application is the one for which forward osmosis was developed four decades ago: the use of impaired water sources diluted through a forward osmosis membrane by using a concentrated fertilizer solution to provide osmotic pressure. This application was suggested four decades ago but was never applied on any scale. Process economics and an insufficiently developed technology may have been the basis of this failure. However, a renewed focus on such applications would allow forward osmosis to come to its real potential and contribute to solving the global water challenge.

Forward Osmosis in India: Status and Comparison with Other Desalination Technologies.

With an increase in demand of freshwater and depleting water sources, it is imperative to switch to seawater as a regular source of water supply. However, due to the high total dissolved solid content, it has to be desalinated to make it drinkable. While desalination technologies have been used for many years, mass deployment of such technologies poses a number of challenges like high energy requirements as well as high negative environmental impact through side products and CO2 emissions. The purpose of this paper is to present a sustainable technology for desalination. Forward osmosis, an emerging technology, is compared with the other commonly used technologies worldwide, namely, multieffect distillation, multistage flash distillation, and reverse osmosis as well as other emerging technologies like vapour compression, solar humidification dehumidification, nanofiltration, and freezing desalination. As energy consumption and associated greenhouse gas emissions are one of the major concerns of desalination, this paper concludes that forward osmosis is an emerging sustainable technology for seawater desalination. This paper then presents the challenges involved in the application of forward osmosis in India and presents a plant setup. In the end, the cost comparison of a forward osmosis and reverse osmosis plant has been done and it was concluded that forward osmosis is economically better as well.

Enhanced hollow fiber membrane performance via semi-dynamic layer-by-layer polyelectrolyte inner surface deposition for nanofiltration and forward osmosis applications

The layer-by-layer (LBL) polyelectrolyte deposited membranes have drawn increasing attention in various applications due to the ease of selective layer formation and their stability and versatility. In this study, the LBL deposition was performed at the inner surface of the polyethersulfone (PES) hollow fiber substrate to form composite nanofiltration (NF) membrane. The semi-dynamic deposition procedure was adopted with the aid of syringes. The newly developed inner deposited (id-LBL) membranes were then tested in NF and forward osmosis (FO) applications and the performance were compared with outer surface deposition as well as some literature data. The id-LBL membranes could not only withstand higher operating pressure but also possess superior hardness rejection especially in high concentration mixed salt solutions (more than 95% rejection to Mg2+ and Ca2+ in a 5000ppm total dissolved salt (TDS) mixture under 4.8bar). As for the FO process, with only two layer deposition, the id-LBL membranes also demonstrated significant performance improvement with increased water flux (up to 70L/m2h using 0.5M MgCl2 as draw solution in active layer facing draw solution configuration) and reduced salt leakage (around 0.5g/m2h using 1M MgCl2 draw solution in active layer facing feed water configuration). This study suggests that for hollow fiber substrate, the inner surface is more suitable for the formation of the selective layer via LBL deposition than the outer surface.

Opportunities and Challenges in Application of Forward Osmosis in Food Processing

Food processing and preservation technologies must maintain the fresh-like characteristics of food while providing an acceptable and convenient shelf life as well as assuring safety and nutritional value. Besides, the consumers’ demand for the highest quality convenience foods in terms of natural flavor and taste, free from additives and preservatives necessitated the development of a number of membrane-based non-thermal approaches to the concentration of liquid foods, of which forward osmosis has proven to be the most valuable one. A series of recent publications in scientific journals have demonstrated novel and diverse uses of this technology for food processing, desalination, pharmaceuticals as well as for power generation. Its novel features, which include the concentration of liquid foods at ambient temperature and pressure without significant fouling of membrane, made the technology commercially attractive. This review aims to identify the opportunities and challenges associated with this technology. At the same time, it presents a comprehensive account of recent advances in forward osmosis technology as related to the major issues of concern in its rapidly growing applications in food processing such as concentration of fruit and vegetable juices (grape, pineapple, red raspberry, orange, and tomato juice and red radish juice) and natural food colorants (anthocyanin and betalains extracts). Several vibrant and vital issues such as recent developments in the forward osmosis membrane and concentration polarization aspects have been also addressed. The asymmetric membrane used for forward osmosis poses newer challenges to account both external and internal concentration polarization leading to significant reduction in flux. The recent advances and developments in forward osmosis membrane processes, mechanism of water transport, characteristics of draw solution and membranes as well as applications of forward osmosis in food processing have been discussed.

Solution-diffusion with defects model for pressure-assisted forward osmosis

An osmosis transport model is presented that combines the standard internal and external concentration polarization equations in the forward osmosis (FO) field with the selective layer transport equations first proposed by Sherwood in 1967. The Sherwood model describes water flux as the sum of a solute-selective, diffusive component driven by the sum of osmotic pressure and hydraulic pressure differences, and a nonselective, convective component driven by hydraulic pressure difference only. This solution-diffusion with defects (SDWD) model and the solution-diffusion (SD) model were compared against data collected using polyamide thin-film-composite (PA-TFC) and integrally-skinned asymmetric cellulose triacetate (CTA) membranes, evaluated in various configurations. When tested with pure water on the porous support side and 1.5M (π=72.7bar) sodium chloride solution on the selective layer side, applying 1.25bar of hydraulic pressure to the porous support side increased water flux by an order of magnitude for PA-TFC membranes, but had negligible effect on CTA membrane flux. These large flux variations can be explained by the SDWD model, but not the SD model. To confirm the existence of defects, a PA-TFC membrane was coated with a uniform, highly water-permeable, nonselective polymer. After coating to block convection through defects, the influence of hydraulic pressure on water flux through this membrane essentially disappeared. Water flux through these defects is low (<1% of total water flux for PA-TFC membranes) and of little consequence in practical FO or reverse osmosis (RO) applications. But in pressure-assisted forward osmosis (PAFO) or pressure-retarded osmosis (PRO), convective transport through defects affects the solute concentration difference across the membrane selective layer, increasing or decreasing water flux through defect-free regions. The presence of defects may explain why membrane power density in PRO is lower than that predicted based on FO and RO tests.

Fertilizer-drawn forward osmosis for irrigation of tomatoes

Fertilizer-drawn forward osmosis is a low-energy desalination concept particularly developed for the irrigation use of desalinated water. It has an advantage of not requiring regeneration of the draw solution (DS), thus, it can be used directly for the purpose of irrigation without any additional treatment. The current study was aimed to evaluate the real application of forward osmosis (FO) targeting irrigation of tomato crops based from their fertilizer requirements. Fertilizer-DSs were prepared to drive seawater desalination using commercially available fertilizers such as NH4NO3, NH4Cl, KNO3, KCl, NH4H2PO4, and urea. DSs were prepared to represent varying nitrogen:phosphorous:potassium (N:P:K) ratios used in assorted tomato growth stages. The FO performance evaluated in terms of the flux and reverse solute flux (RSF) showed significant variations in outcome. The resultant flux for different DSs was influenced by the particular fertilizer present in DS mixture and its concentration. This flux varied from 2.50 to 12.49 LMH. Comparatively, DS carrying high osmotic pressure components showed high-flux outcome. The fraction Jw/∆π of these fertilizer-DSs varied from 0.062 to 0.19 LMH/bar, which indicates a changing flux outcome against the same osmotic pressure. To select the best performing fertilizer-DS, nitrogen source fertilizers like urea, NH4NO3, and NH4Cl were further evaluated for 10-0-10 NPK value. It was found that NH4Cl-based DS mixtures performed better than urea- and NH4NO3-based DS. The RSF results indicated that all nitrogen- and potassium-based DS exhibited higher N- and K-RSF. However, the DS using NH4H2PO4 delivered extremely low P-RSF of 12.35 g/m2/h. Long-term run tests with seawater quality feed solution resulted in FO producing a final DS enriched in nutrients greater than the tomato plant’s requirement. This implies that the use of dilution or any other technique to reduce excessive nutrients is essential before using the final DS for tomato irrigation.

Forward osmosis dialysate production using spiral-wound reverse-osmosis membrane elements

Presented here is an analysis of a method by which a spiral-wound reverse osmosis (RO) membrane element may be used in forward osmosis (FO) mode to produce dialysate fluid for medical treatment. In this method, dialysate is produced from the draw-side of an FO process by carefully controlling the output concentration, managing the accumulation of salt in the closed, feed-side membrane envelope and using osmotic backwashing to recover the membrane.The analysis shows that a high-quality, spiral-wound, polyamide 4040 RO membrane element may be used to produce un-buffered dialysate when supplied with brackish groundwater and dialysate concentrate. Production is possible for a short period before the membrane needs to be osmotically backwashed to remove accumulated salt. By alternating between production and backwashing cycles, a pair of high-quality 4040 elements may produce dialysate at a rate high enough to enable continuous haemodialysis treatment.The low-cost, compact nature of standard RO elements makes them suitable for water and energy-efficient FO applications. The method proposed here exploits the features of standard RO elements to enable their application in Australian desert regions, where water supplies are slightly brackish and where rates of kidney failure and dialysis treatment are relatively high.

Mesh-reinforced thin film composite membranes for forward osmosis applications: The structure–performance relationship

In this study, thin and durable thin film composite (TFC) polyamide membranes were prepared on mesh-reinforced polysulfone (PSF) supports for forward osmosis (FO) applications. To understand the influence of mesh-incorporation on the formation of support structures and the final FO performance, mesh-embedded PSF supports were prepared via the phase inversion process from various PSF casting solutions in 1-methyl-2-pyrrolidinone (NMP) solvent (9–18wt%) by using a polyester (PE) mesh as a mechanical reinforcing material. A crosslinked aromatic polyamide layer was then fabricated on top of each support to form a TFC membrane. For the mesh-embedded PSF supports prepared with relatively low concentration casting solutions (9 and 12wt%), the PE mesh was oriented towards the bottom of the PSF supports, creating additional macroscopic pores around the mesh lines on the backside surface. However, the PE mesh was moved towards the center of PSF supports when higher viscosity solutions (15 and 18wt%) were used for the support preparation, and consequently the macroscopic pores near the mesh lines were isolated within the support layers without exposing to the bottom surface. The PE-mesh also adversely affected the formation of a finger-like morphology for higher concentration casting solutions (≥12wt%), forming a sponge-like morphology in the lower half of the support layers. A desirable support structure with a well-developed finger-like morphology and macroscopic open-pores on the bottom surface was achieved from the mesh-embedded PSF support prepared with 9wt% casting solution (PSF9). The corresponding TFC membrane (TFC/PSF9) thus exhibited the lowest structural parameter (S=314±29µm) among the tested samples and presented outstanding FO performance, almost 2.5 times higher water flux (49LMH) with lower reverse salt flux (7.0GMH) compared to a commercial CTA membrane in PRO mode evaluation.

Relating thin film composite membrane performance to support membrane morphology fabricated using lignin additive

In this study, three nonwoven fabrics were used as supports to form thin film composite membranes for forward osmosis (FO) applications. Lignin additive was added to the polysulfone layer in two different concentrations to increase the porosity of the substructure. The fabrics were characterized in terms of their Frazier permeability, tortuosity, porosity, thickness, structural parameter and capillary pressure. It was found that the fabric tortuosity and thickness had strong negative correlations with FO water flux, while fabric porosity had a strong positive correlation. The fabric capillary pressure was found to be indicative of how well the polysulfone layer adhered to the fabric layer. The membrane structural parameter of the fabric, unsupported and supported polysulfone layers were measured and compared using a “resistance-in-series” model. Although seepage of the casting solution into the fabric layer was physically observed, the addition of the individual structural parameters of the layers offered a good approximation of the composite membrane structural parameter. Membrane structural parameters calculated for fabric supported composite membranes using reverse osmosis (RO) permeability parameters and FO/RO established transport equations were much larger than structural parameters obtained from physical measurements. The difference may be due to compaction of composite membranes in reverse osmosis experiments, casting solution seepage partially plugging the upper layers of the support fabric and other non-idealities not captured in the established FO/RO transport equations.

The effect of SiO2 nanoparticles on morphology and performance of thin film composite membranes for forward osmosis application

This paper presents polyamide nano-composite membrane containing silica nanoparticles (TFN) synthesized via in situ interfacial polymerization for the forward osmosis (FO) application. Different concentrations of silica nanoparticles (0.01, 0.05 and 0.1% w/v) were added to the aqueous solution as additive to improve the FO membrane performance. The prepared membranes were characterized by ATR-FTIR, SEM, AFM and hydrophilicity measurement. The structure of nanocomposite layer synthesized by interfacial polymerization was characterized by FTIR spectroscopy. The FTIR peaks confirmed the presence of polyamide layer with SiO2 nanoparticles. The morphological studies showed that the SiO2 nanoparticles were effectively attached to the FO membrane surface. The contact angle measurements showed that the hydrophilicity of FO membranes was improved with increasing SiO2 in the aqueous solution. The FO performance was measured using 10mM NaCl solution as feed solution and 2M NaCl solution as draw solution in both orientations. The TFN membranes showed higher water permeability and better salt rejection in the range of 0.01–0.1wt.% silica loading in comparison with the TFC membrane. The water flux of the TFN membrane reached to a maximum of 36±2L/m2h which is nearly 2 times as high as that of the TFC membrane and it was found that the membrane modified with 0.05w/v.% silica nanoparticles showed the highest salt rejection (90±3%).

Membrane scaling and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater

Fertiliser-drawn forward osmosis (FDFO) desalination has been recently studied as one feasible application of forward osmosis (FO) for irrigation. In this study, the potential of membrane scaling in the FDFO process has been investigated during the desalination of brackish groundwater (BGW). While most fertilisers containing monovalent ions did not result in any scaling when used as an FO draw solution (DS), diammonium phosphate (DAP or (NH4)2HPO4) resulted in significant scaling, which contributed to severe flux decline. Membrane autopsy using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) analysis indicated that the reverse diffusion of DAP from the DS to the feed solution was primarily responsible for scale formation during the FDFO process. Physical cleaning of the membrane with deionised water at varying crossflow velocities was employed to evaluate the reversibility of membrane scaling and the extent of flux recovery. For the membrane scaled using DAP as DS, 80–90% of the original flux was recovered when the crossflow velocity for physical cleaning was the same as the crossflow velocity during FDFO desalination. However, when a higher crossflow velocity or Reynolds number was used, the flux was recovered almost completely, irrespective of the DS concentration used. This study underscores the importance of selecting a suitable fertiliser for FDFO desalination of brackish groundwater to avoid membrane scaling and severe flux decline.

Study of Forward Osmosis Membrane Bioreactor

A novel submerged forward osmosis membrane bioreactor (FOMBR) is presented in this study. The selection of optical draw solutions for forward osmosis (FO) applications was developed and the Na2SO4 solution was found to be the most appropriate draw solution among five draw solutions for FO applications. The properties of two hollow fiber composite FO membranes, designated membranes A and B, which consist of an active layer formed atop a support layer, were prepared and utilized. Meanwhile, the water flux and removal efficiencies were evaluated in FO mode. Both of the FO membranes were found to reject greater than 95% of COD and 85% of NH3-N. Water flux changes suggested a better application with membrane A than membrane B for FOMBR.

Three dimensionless parameters influencing the optimal membrane orientation for forward osmosis

In many forward osmosis applications, flux is maximised (and capital costs minimised) when the membrane is oriented such that the feed solution faces the support layer (PRO mode). Here, a framework is developed to understand the factors that determine the membrane orientation that maximises flux. In the absence of fouling, a dimensionless form of the water transport equations reveals the importance of three dimensionless groups: the ratio of draw to feed osmotic pressure, the ratio of draw to feed solute diffusivity, and the resistance to water transport of the support layer relative to the active layer. A parametric study of these parameters and an application of the dimensionless equations to three important FO processes reveal that having the draw solution face the support layer (FO mode) can maximise flux in specific instances. Interestingly, this implies that operation in FO mode can both maximise flux and minimise fouling for fertigation applications and the concentration of flowback waters from hydraulic fracturing.

Low internal concentration polarization in forward osmosis membranes with hydrophilic crosslinked PVA nanofibers as porous support layer

Recent developments on osmotically driven membrane processes (ODMPs), e.g. forward osmosis (FO) and pressure retarded osmosis (PRO), suggest a high viability for clean water and energy production. However, membranes used in these processes encounter high internal concentration polarization (ICP), inherent to osmotically driven membranes, which keeps them from delivering optimum performance in terms of water flux. In this study, a nanofiber thin film composite (NTFC) membrane was synthesized. Crosslinked electrospun polyvinyl alcohol (PVA) nanofiber was uniquely found to be a very effective support layer, specifically for FO applications, due to its very low tortuosity, very high porosity and remarkable hydrophilic property. The successfully fabricated composite exhibited a 7–8 times improved FO water flux as compared to a commercially available FO membrane. Ultimately, our membrane displayed a lower structural parameter (S=66±7.9), a measure of ICP condition, compared to previously synthesized NTFC membranes. Based on the performance of our membrane, this hydrophilic nanofiber supported membrane, with further development, has the high potential to be the next-generation FO membrane.

Preparation of polyethersulfone/carbon nanotube substrate for high-performance forward osmosis membrane

Forward osmosis (FO) process has attracted increasing interest because of its potential applications for low-energy desalination. However, the internal concentration polarization (ICP) has been considered as one of the key issues that can significantly reduce the water flux across the FO membrane. In this paper, we report the preparation of polyethersulfone (PES)/multiwalled carbon nanotube (MWCNT) substrate for the formation of a high-performance FO membrane. Nanocomposite MWCNT/PES substrates were obtained by dispersing carboxylated MWCNTs within PES via solution blending, and subsequent phase inversion process; The FO membranes were then prepared by depositing a polyamide active layer in-situ on the MWCNT/PES substrate with a finger-like macrovoid structure. The influence of addition of MWCNTs on morphology and properties of substrates and final FO membranes was systematically investigated. The results show that the performance of the FO membranes with MWCNT/PES nanocomposite substrates is better than that of the commercial membrane. Furthermore, the tensile strength of the substrate with MWCNTs is also greater than that of the neat PES. This work indicates that the FO membranes prepared from MWCNT–PES substrates are promising for practical FO applications.