Article

Efficient recovery of polyelectrolyte draw solutes in forward osmosis towards sustainable water treatment

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Abstract

Forward osmosis (FO) technology has long been constrained by the slow development of appropriate draw solutes (DS) and the relatively high cost associated with DS recovery. In this study, a series of polyelectrolytes, polyacrylic acid sodium salts (PAA-Na) with different molecular weights, were explored as DS for FO applications with a focus on the recovery using combined pH and microfiltration (MF). The FO system achieved a high water flux of 18.02 ± 0.51 LMH, low reverse salt flux (RSF) of 0.110 ± 0.004 gMH, and the JS/JW of 6.1 ± 0.3 mg L− 1 with 25 wt% PAA-Na (2000 Da) as the DS and DI water as the feed. The DS recovery efficiency by the combined pH + MF approach was 99.68% at pH of 4.35, and the operation cost was estimated at 0.037 $ m− 3. Dynamic light scattering revealed that the hydrodynamic diameter of PAA increased with decreasing pH, resulting in PAA polymers precipitated as aggregates at the pH response point. The 25 wt% 2000 PAA-Na achieved the water flux of 11.56 ± 0.32 LMH from synthetic seawater and 17.19 ± 0.52 LMH from the treated wastewater. These results have demonstrated efficient and cost-effective recovery of PAA DS for FO-based applications.

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... Unlike a pressure-driven RO process that generates fresh water directly, the "energy-efficient" FO process can only yield a diluted draw solution, which requires energy-and cost-intensive downstream separation to regenerate draw solutes (DS) . The third stage of FO development focused on smart selection of easilyrecoverable DS, ranging from economically viable and non-toxic inorganic DS (Achilli et al., 2010), to phase-separation DS (Cai and Hu, 2016), such as magnetic nanoparticles (Alejo et al., 2017), thermolytic ammonium bicarbonate (McCutcheon et al. 2005, and organic polymers (Yang et al., 2017;Zhang et al., 2015). However, these types of DS suffer from high cost due to complicated preparation (Minami et al., 2010), large solute loss , or weakened phase separation after regeneration (Ling et al., 2010). ...
... Besides good water extraction capability (up to 25 LMH water flux) (Ge et al., 2012b), PAA-Na also exhibits extremely low RSF (0.004e0.08 gMH for CTA and 0.002e0.009 gMH for TFC), and very low SRSF (0.002e0.007 g L À1 for PAA-Na with a Mw of 2000e5000 and less than 0.001 g L À1 for PAA-Na with a Mw of 50,000) due to size exclusion (hydrodynamic diameter > 120 nm) (Yang et al., 2017). Nonetheless, little RSF data can be found for most thermal-, magnetic-, electric-, or light-responsive DS (to the best of our knowledge), making it extremely difficult to evaluate RSF decrease for these "smart" DS. ...
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... The water flux difference followed the order NaCl > KCl > KCl + KNO 3 > KNO 3 (see Fig. 4) when using the same concentrations. This finding might be ascribed to the different osmotic pressure calculated by van't Hoff equation, which produced a large osmotic pressure value with a small molecular weight at a constant concentration [34]. At a concentration of 1.0 mol/L, the KCl and mixture KCl + KNO 3 scored the highest water flux of about 14.0 and 13.7 LMH which was slightly reduced to (13.5 and 13.3 LMH). ...
... The specific salt flux defined as the ratio of reverse solute diffusion to the water permeate (J S /J W ) per unit of water permeate [40]. The trend of specific salt flux was in good agreement with the results of reverse solute flux, which is in accordance with Yang's study [34]. Therefore, great osmotic pressure and high concentration of the draw solution will favor the reverse solute diffusion flux. ...
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... At the current stage, the deployment of commercial-scale FO is still largely restricted by the maintenance costs and energy consumption for draw solution recovery. Despite some efforts made in the development of cost-effective process for draw solution recovery, a significant breakthrough is yet to be made in this field [107]. While osmotically driven processes such as FO is less susceptible to fouling, the components of complex oily wastewater can result in highly potential for fouling where chemically assisted membrane cleaning is required to restore the deteriorated membrane performance. ...
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... In terms of chemically responsive draw compounds, many use pH adjustments, which can increase the osmotic pressure of the DS. This is particularly true for tertiary amines or carboxylic groups such as PAA that have negligible osmotic pressure in neutral pH state [84,85] but require membranes that can tolerate acidic/basic conditions. Table 5 shows that a basic pH precipitable sodium salt of PAA result in ~18LMH flux using TFC membranes while other precipitable salts achieved water flux of ~4LMH with CTA membranes in AL-FS orientation with DI water FS reported in Appendix A. DS compounds that can be regenerated through precipitation, which is one of the first recovery methods proposed for FO [86], have preferential characteristics of low MW, low η and high osmotic density but are considered to be not financially feasible because of operational costs [26] and toxicity, if acids are using for recovery, when using them for desalination application. ...
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... These draw solutes are said to have ability to respond to stimuli and are reputed to offer great flexibility that enables them to decrease their propinquity to water and at the same time facilitating increased water flux to suit requirements. Other groups of draw solutes that had been reported in several studies are the inorganic, polymeric and organic compounds, and are said to be non-responsive [47]. More recently, carbonaceous materials have also entered the fray as a group of draw solutes for solar evaporation FO desalination [48]. ...
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A series of tertiary amines have been screened for their function as switchable polarity solvents (SPS). The relative ratios of tertiary amine and carbonate species as well as maximum possible concentration were determined through quantitative 1H and 13C NMR spectroscopy. The viscosities of the polar SPS solutions were measured and ranged from near water in dilute systems through to gel formation at high concentrations. The van't Hoff indices for SPS solutions were measured through freezing point depression studies as a proxy for osmotic pressures. A new form of SPS with an amine:carbonate ratio significantly greater than unity has been identified. Tertiary amines that function as SPS at ambient pressures appear to be limited to molecules with fewer than 12 carbons. The N,N-dimethyl-n-alkylamine structure has been identified as important to the function of an SPS.
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Tertiary amine switchable polarity solvents (SPS) consisting of predominantly water, tertiary amine, and tertiary ammonium and bicarbonate ions were produced at various concentrations for three different amines: N,N-dimethylcyclohexylamine, N,N-dimethyloctylamine, and 1 cyclohexylpiperidine. These amines exhibit either osmotic or non-osmotic character as observed through forward osmosis, which led to this study to better understand speciation and its influence on water transport through a semi-permeable membrane. For all concentrations, several physical properties were measured including viscosity, molecular diffusion coefficients, freezing point depression, and density. Based on these measurements, a variation on the Mark Houwink equation was developed to predict the viscosity of any tertiary amine SPS as a function of concentration using the amine’s molecular mass. The physical properties of osmotic SPS, which are identified as having an amine to carbonic acid salt ratio of 1, have consistent concentration dependence behavior over a wide range of concentrations, which suggests osmotic pressures based on low concentrations freezing point studies can be extrapolated reliably to higher concentrations. The observed physical properties also allowed the identification of solution state speciation of non-osmotic SPS, where the amine to carbonic acid salts ratio is significantly greater than one. These results indicate that, at most concentrations, the stoichiometric excess of amine is involved in solvating a proton with two amines.
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Recently, forward osmosis (FO) has attracted growing attention in many potential applications such as power generation, desalination, wastewater treatment and food processing. However, there are still several critical challenges, including concentration polarization, membrane fouling, reverse solute diffusion and the need for new membrane development and draw solute design in FO. These challenges are also the current research focus on FO. This paper aims to review the recent developments in FO, focusing on the opportunities and challenges. It begins with discussing the advantages of the FO process over pressure-driven membrane processes. These potential advantages lie in FO's low energy consumption, low fouling propensity, reduced or easy cleaning, low costs, high salt rejection and high water flux. Next, the recent applications of FO, as the outcomes of the above advantages, are described. The key part of this review is a detailed discussion of five critical challenges faced by FO and their relationships. Finally, the future of FO is viewed. This review provides a clear outline for FO-concerned researchers on the recent developments in FO.
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Low molecular weight dual responsive polymers, after purging with CO2, become polyelectrolytes with high osmolality, which can be used as draw solutes for seawater desalination. These polymers precipitate above their Lower Critical Solution Temperature (LCST) after removal of CO2via purging with inert gas for ease of recovery and reuse.
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Forward osmosis (FO) is a novel and emerging low energy technology for desalination. It will be particularly more attractive, if the draw solution separation and recovery are not necessary after FO process. The application of this new concept is briefly described here in this paper for the desalination of saline water for irrigation, using fertilizer as a draw agent. Instead of separating the draw solution from desalinated water, the diluted fertilizer draw solution can be directly applied for fertigation. We report the results on the commonly used chemical fertilizers as FO draw solution. Based on the currently available FO technology, about nine different commonly used fertilizers were finally screened from a comprehensive list of fertilizers and, their performances were assessed in terms of pure water flux and reverse draw solute flux. These results indicate that, most soluble fertilizers can generate osmotic potential much higher than the sea water. The draw solutions of KCl, NaNO3 and KNO3 performed best in terms of water flux while NH4H2PO4, (NH4)2HPO4, Ca(NO3)2 and (NH4)2SO4 had the lowest reverse solute flux. Initial estimation indicates that, 1kg of fertilizer can extract water ranging from 11 to 29L from sea water.
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In this work, an extensive analysis on direct contact membrane distillation (DCMD) performance was developed to estimate the mass flux and the heat efficiency, considering transport phenomena, membrane structural properties and most sensitive process parameters, with the aim to provide optimization guidelines for materials and methods. The results showed that an increase of the temperature gradient resulted in the enhancement of both transmembrane flux and thermal efficiency. The investigation of the effects of membrane properties confirmed that better DCMD performance was achieved when using polymeric membranes characterized by low thermal conductivity (flux and thermal efficiency declined by 26% and 50%, respectively, when increasing thermal conductivity from 0.1 to 0.5 W/m K), and high porosity. An optimal thickness value (around 0.7 mm) was identified when operating at low temperature gradient (<5 °C). However, at higher temperature gradient (>10 °C), increasing the membrane thickness from 0.25 to 1.55 mm resulted in a flux decay of about 70% without a significant improvement in thermal efficiency.Exergy analysis, sensitivity study and economical evaluation were carried out to assess the feasibility of DCMD process. For DCMD with heat recovery, the estimated water cost was $1.17 m−3, which was comparable to the cost of water produced by conventional thermal processes: i.e. around $1.00 m−3 for multiple effect distillation (MED) and $1.40 m−3 for multi-stage flash (MSF). However, significant savings are expected when using a low-grade thermal energy source, decreasing the cost of DCMD to values approaching the cost of water produced by reverse osmosis (RO), which is about $0.50 m−3.
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Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
Article
This study demonstrated the feasibility of using regenerable polyelectrolyte membranes to ultimately control the irreversible membrane fouling in a forward osmosis (FO) process. The regenerable membrane was fabricated by assembling multiple polyethyleneimine (PEI) and poly(acrylic acid) (PAA) bilayers on a polydopamine-functionalized polysulfone support. The resulting membrane exhibited higher water flux and lower solute flux in FO mode (with the active layer facing feed solution) than in PRO mode (with the active layer facing draw solution) using trisodium citrate as draw solution, most likely due to the unique swelling behavior of the polyelectrolyte membrane. Membrane regeneration was conducted by first dissembling the existing PEI-PAA bilayers using strong acid and then reassembling fresh PEI-PAA bilayers on the membrane support. It was found that, after the acid treatment, the first covalently bonded PEI layer and some realigned PAA remained on the membrane support, acting as a beneficial barrier that prevented the acid-foulant mixture from penetrating into the porous support during acid treatment. Water and solute flux of the regenerated membrane was very similar to that of the original membrane regardless of alginate fouling, suggesting an ultimate solution to eliminating the irreversible membrane fouling in an FO process. With a procedure similar to the typical membrane cleaning protocol, in-situ membrane regeneration is not expected to noticeably increase the membrane operational burden but can satisfactorily avoid the expensive replacement of the entire membrane module after irreversible fouling, thereby hopefully reducing the overall cost of the membrane-based water treatment system.
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Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min−1 did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m−3. These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.
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Forward osmosis (FO) is one of the evolving membrane technologies in desalination with recent expanded new interest as a low energy process. The most significant parts of FO process are the membrane and draw solution since both play a substantial role in its performance. Hence, the selection of an appropriate membrane and draw solution is crucial for the process efficiency. Improvements in the development of membranes and draw solutes have been recorded recently. However, limitations such as fouling of FO membranes, reverse solute flux, concentration polarization, and low permeate flux in standalone FO systems. This work targets the review of recent progress in FO, aiming on the prospects and challenges. It starts with addressing the advantages of the FO process. The crucial part of this review is a thorough discussion of hybrid FO systems, different FO membranes, and draw solutes available coupled with their effects on FO performance. Finally, the future of FO for sustainable desalination is also discussed.
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Forward osmosis (FO) is a developing technology, which is thought to have a potential of producing potable water in an energy-efficient manner. FO is driven by the natural osmotic pressure difference across a semi-permeable membrane. Despite a number of patents and peer-reviewed papers published for different methods and systems for water desalination by FO, this technology is still in its infancy because of some serious limitations and challenges. Due to many environment and energy related challenges, FO-based desalination has recently gained worldwide attention because it operates at low levels of pressure and temperature. Compared to traditional pressure-driven membrane processes, FO offers recognized advantages including reversible membrane fouling, and potentially less operation energy.
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Copper sulfate is presented as a viable draw solute in forward osmosis (FO) for brackish water desalination. In this study, the osmotic pressure of copper sulfate was calculated as a function of concentration. An investigation into the osmotic pressure revealed that copper sulfate draw solution cannot generate enough osmotic pressure to extract water from seawater feed. A laboratory-scale FO unit utilizing a commercial flat-sheet cellulose acetate membrane was used to desalinate brackish water using 200,000 ppm copper sulfate draw solution. An average water flux of 3.57 L/m2 h was observed. Product water with a salt content of 100 ppm was recovered from the diluted copper draw solution without using any energy. The product water was recovered by metathesis precipitation reaction of copper sulfate with barium hydroxide to remove the soluble chemicals as insoluble copper hydroxide and barium sulfate. At the end, copper sulfate draw solution was recovered by the reaction of copper hydroxide with sulfuric acid.
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Accurate force eld parameters for ions are essential for meaningful simulation studies of proteins and nucleic acids. Currently accepted models of ions, especially for divalent ions, do not necessarily reproduce the right physiological behavior. Saxena and Sept (J. Chem. Theo. Comp. 2013, 9, 3538-3542) described a model, called the multisite-ion model, where instead of treating the ions as an isolated sphere, the charge was split into multiple sites with partial charge. This model provided accurate inner shell coordination of the ion with biomolecules and predicted better free energies for proteins and nucleic acids. Here, we expand and refine the multisite model to describe the behavior of divalent ions in concentrated electrolyte solutions, eliminating the unusual ion-ion pairing and clustering of ions which occurred in the original model. We calibrate and improve the parameters of the multisite model by matching the osmotic pressure of concentrated solutions of MgCl2 to the experimental values and then use the improved parameters to test the behavior of CaCl2 solutions. We find that the concentrated solutions of both divalent ions exhibit experimentally observed behavior with correct osmotic pressure, presence of solvent separated ion pairs instead of direct ions pairs, and no aggregation of ions. The improved multisite model for (Mg (2+) and Ca (2+) ) can be used in classical simulations of biomolecules at physiologically relevant salt concentrations.
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Forward osmosis (FO) membrane technology has attracted rapidly growing research interest because it shows great potential in reducing energy consumption and costs in water desalination and treatment. The lack of a suitable draw agent has been identified as a challenging problem in the commercial implementation of FO technology. Recent years have seen significant advances in the development of smart draw agents with responsive properties, from which water can be recovered under different stimuli. This review highlights the properties and performance of some interesting smart draw agents reported recently, including functionalized magnetic nanoparticles, thermo-responsive polyelectrolytes, and stimuli-responsive polymer hydrogels.
Article
By discovering that poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) in water can react with carbon dioxide (CO2) and have its lower critical solution temperature (LCST) reversibly tuned by passing CO2 and argon (Ar) through the solution, we describe a general strategy for imparting a CO2-switchable LCST or water solubility to polymers of broad interest like poly(N-isopropylacrylamide) (PNIPAM) and poly[2-(2-methoxyethoxy)ethyl methacrylate] (PMEO2MA). We show that by easy copolymerization incorporating DMAEMA as a CO2-responsive trigger into PNIPAM or PMEO2MA, their LCST can effectively be switched by the gases. Two examples of applications were further demonstrated: upon CO2 or Ar bubbling at a constant solution temperature, hydrogels could undergo a reversible volume transition and block copolymer micelles could be dissociated and reassembled. This study opens the door to a wide range of easily accessible CO2-switchable polymers, enabling the use of CO2 as an effective trigger for smart materials and devices.
Article
A major limiting factor of forward osmosis (FO) membrane, particularly in pressure retarded osmosis (PRO) mode, is fouling by natural organic matters. In this work, we investigated the effect of the nanocomposite substrate on the fouling of a thin film nanocomposite (TFN) membrane due to organic foulants in PRO mode. The TFN membrane was synthesized by coating a polyamide film over the surface of substrate made of polysulfone–titanium dioxide. The TFN membrane always showed much higher FO water flux than the typical thin film composite TFC membrane prepared from the pristine polysulfone substrate. Reduced internal concentration polarization following a significant decrease of the structural parameter in the nanocomposite substrate causes the mass transfer coefficient of the substrate to increase. In the PRO mode, BSA removal in the presence of Ca2+ confirmed that the TFN FO membrane could significantly mitigate fouling tendency compared to a typical TFC membrane. Results also showed that fouling in TFN FO is highly reversible, recovering N92% permeate flux after a simple water rinse process. A complete study of the membrane fouling was reported with detailed scientific discussion. To the best of our knowledge, this is the first report on the effect of the nanocomposite membrane on membrane fouling in PRO mode.
Article
Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a "pre-treatment" process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.
Article
In this study, a hybrid forward osmosis–nanofiltration (FO/NF) process was designed for dewatering high nutrient containing sludge and recovering draw solution with minimum energy as well as low fouling. A novel draw solution – EDTA sodium salt – was also systematically studied for dewatering process. Results show that using EDTA sodium salt produced higher water flux and lower reverse salt flux when compared to conventional inorganic salt (NaCl) at pH 8. The final sludge concentration reached 32,000 mg/L after 16 h of operation. Moreover, nutrient compounds in sludge were successfully removed by the FO membrane with a removal efficiency of approximately 97% of NH4+–N, 90% of NO3−–N, 97% of NO2−–N and 99% of PO43−–P, which was attributed to the multi-barrier layers of sludge forming on membrane surface and the steric effect of the FO membrane. The NF recovery of EDTA sodium salt indicated that all NF membranes performed well and TS-80 was the best among the tested membranes.
Article
The feasibility of bilayer polymer hydrogels as draw agent in forward osmosis process has been investigated. The dual-functionality hydrogels consist of a water-absorptive layer (particles of a copolymer of sodium acrylate and N-isopropylacrylamide) to provide osmotic pressure, and a dewatering layer (particles of N-isopropylacrylamide) to allow the ready release of the water absorbed during the FO drawing process at lower solution critical temperature (32 oC). The use of solar concentrated energy as the source of heat resulted in a significant increase in the dewatering rate as the temperature of dewatering layer increased to its LSCT more rapidly. Dewatering flux rose from 10 to 25 LMH when the solar concentrator increased the input energy from 0.5 to 2 kW/m2. Thermodynamic analysis was also performed to find out the minimum energy requirement of such a bilayer hydrogel- driven FO process. This study represents a significant step forward towards the commercial implementation of hydrogel-driven FO system for continuous production of fresh water from saline water or wastewaters.
Article
A series of polyelectrolytes were evaluated as draw solutions for the forward osmosis (FO) process. Such polyelectrolytes were synthesized by copolymerization of N-isopropylacrylamide with different amounts of sodium acrylate. These polyelectrolytes were thermo-sensitive and water soluble. Hot ultrafiltration (HUF) operated at 45 °C and 2 bar was used as a low-energy method to recover the water from the polyelectrolyte draw solutions. The results showed that 4%PNIPAM-SA solution worked best among nine polyelectrolytes in the forward osmosis process and HUF process, and its FO water flux was 0.347 LMH while the feed solution was pure water and its water recovery fraction was 65.2%.
Article
Switchable polarity solvents (SPS), mixtures of carbon dioxide, water, and tertiary amines, are presented as viable forward osmosis (FO) draw solutes allowing a novel SPS FO process. In this study substantial osmotic strengths of SPS are measured with freezing point osmometry and were demonstrated to induce competitive fluxes at high salt concentrations on a laboratory-scale FO unit utilizing a flat sheet cellulose triacetate (CTA) membrane. Under the experimental conditions the SPS degrades the CTA membrane; however experiments with polyamide reverse osmosis (RO) membranes display stability towards SPS. Once the draw is diluted the major fraction of the switchable polarity solvent can be mechanically separated from the purified water after polar to nonpolar phase shift induced by introduction of 1 atm carbon dioxide to 1 atm of air or nitrogen with mild heating. Trace amounts of SPS can be removed from the separated water with RO in a process that avoids solution concentration polarization. The separated nonpolar phase can be regenerated to a full strength draw and recycled with the re-addition of 1 atm of carbon dioxide.
Article
A new class of draw solutes from hydroacid complexes is presented. With hydroacid complexes as draw solutes in FO, superior performance is achieved in terms of high water fluxes and negligible reverse solute fluxes. The characteristics of expanded configurations, abundant hydrophilic groups and ionic species are essential for hydroacid complexes as competent draw solutes.
Article
The use of energy still remains the main component of the costs of desalting water. Forward osmosis (FO) can help to reduce the costs of desalination, and extracting water from impaired sources can be beneficial in this regard. Experiments with FO membranes using a secondary wastewater effluent as a feed water and Red Sea water as a draw solution demonstrated that the technology is promising. FO coupled with low pressure reverse osmosis (LPRO) was implemented for indirect desalination. The system consumes only 50% (~1.5kWh/m³) of the energy used for high pressure seawater RO (SWRO) desalination (2.5–4kWh/m³), and produces a good quality water extracted from the impaired feed water. Fouling of the FO membranes was not a major issue during long-term experiments over 14days. After 10days of continuous FO operation, the initial flux declined by 28%. Cleaning the FO membranes with air scouring and clean water recovered the initial flux by 98.8%. A cost analysis revealed FO per se as viable technology. However, a minimum average FO flux of 10.5L/m²-h is needed to compete with water reuse using UF–LPRO, and 5.5L/m²-h is needed to recover and desalinate water at less cost than SWRO.
Article
For the first time, a potentially sustainable integrated FO–UF (forward osmosis–ultrafiltration) system for water reuse and desalination with the aid of super hydrophilic nanoparticles as draw solutes has been proposed. The system uses an FO membrane as the semi-permeable membrane to reject salts, super hydrophilic nanoparticles as draw solutes to induce water across the FO membrane, and UF membranes to regenerate the draw solutes. For comparison, a magnetic separator was also used to recycle super hydrophilic magnetic nanoparticles but agglomeration was observed. Ultrasonication proved to effectively reduce the size of agglomerated magnetic nanoparticle and the FO performance was partially restored. However, the resultant magnetic properties were weakened under ultrasonic processes and thus jeopardized regeneration efficiency in magnetic fields. The novel FO–UF process was tested for 5 continuous runs for the purpose of desalination without increasing nanoparticle draw solute size or reducing osmotic functionality. UF membranes of small pore diameter and narrow pore size distribution can enhance the recovery efficiency of nanoparticle draw solution. The proposed FO–UF integrated system using super hydrophilic nanoparticles as draw solutes is believed to be a promising technology to desalinate both seawater and brackish water and to reclaim water from wastewater.
Article
In this investigation, a protocol for the selection of optimal draw solutions for forward osmosis (FO) applications was developed and the protocol was used to determine the most appropriate draw solutions for specific FO applications using a currently available FO membrane. The protocol includes a desktop screening process and laboratory and modeling analyses. The desktop screening process resulted in 14 draw solutions suitable for FO applications. The 14 draw solutions were then tested in the laboratory to evaluate water flux and reverse salt diffusion through the FO membrane. Internal concentration polarization was found to lower both water flux and reverse salt diffusion by reducing the draw solution concentration at the interface between the support and dense layers of the membrane. Draw solution reconcentration was evaluated using reverse osmosis (RO) system design software. Analysis of experimental data and model results, combined with consideration of the costs associated with the FO and RO processes showed that a small group of seven draw solutions appeared to be the most suitable. The different characteristics of these draw solutions highlighted the importance of considering the specific FO application and membrane types being used prior to selecting the most appropriate draw solution.
Article
Polysaccharide multinanolayers are becoming a new and general means of modifying and functionalizing surfaces of several materials. This is achieved through changing the interfacial properties of those surfaces followed by sequential adsorption of e.g., polysaccharides. Knowledge of properties of polysaccharide solutions such as zeta potential (Zp) and mean hydrodynamic diameter (Z-average) is crucial to obtain stable, functional nanostructures.In this work sodium alginate, carragennan, chitosan, and two galactomannans were characterized in terms of Zp and Z-average, as a function of polysaccharides and NaCl concentrations and pH. The most relevant effects of these factors on Zp and on Z-average were analysed using a 23 full factorial design.With a few exceptions, the effect of independent variables on Zp and Z-average values is statistically significant. In general (except for k-carragennan solutions) higher polysaccharide concentrations lead to higher Z-average values; and higher pH values lead to higher Z-average values (except for solutions of chitosan and galactomannan of Gleditsia triacanthos). NaCl addition decreases Z-average. For the galactomannans solutions Zp values were found to be neutral (ranging from −13.7 to −2.1 mV) independently of the combinations of variables used.This work establishes a relationship between important polysaccharides properties and the values of pH, polysaccharide and salt concentrations, thus providing insight on how to control the structure and texture of multinanolayered films in view of their potential application e.g., in the food, pharmaceutical, and cosmetic industries.
Article
A novel forward (direct) osmosis (FO) desalination process is presented. The process uses an ammonium bicarbonate draw solution to extract water from a saline feed water across a semi-permeable polymeric membrane. Very large osmotic pressures generated by the highly soluble ammonium bicarbonate draw solution yield high water fluxes and can result in very high feed water recoveries. Upon moderate heating, ammonium bicarbonate decomposes into ammonia and carbon dioxide gases that can be separated and recycled as draw solutes, leaving the fresh product water. Experiments with a laboratory-scale FO unit utilizing a flat sheet cellulose tri-acetate membrane demonstrated high product water flux and relatively high salt rejection. The results further revealed that reverse osmosis (RO) membranes are not suitable for the FO process because of relatively low product water fluxes attributed to severe internal concentration polarization in the porous support and fabric layers of the RO membrane.
Article
The biodegradability (mineralization to carbon dioxide) of acrylic acid oligomers and polymers was studied in activated sludge obtained from continuous-flow activated sludge (CAS) systems exposed to mixtures of low molecular weight (Mw < 8000) poly(acrylic acid)s and other watesoluble polymers [poly(ethylene glycol)s] in influent wastewater. Dilute preparations of activated sludge from the CAS units were tested for their ability to mineralize acrylic acid monomer and dimer, as well as a series of model acrylic acid oligomers and polymers (Mw 500, 700, 1000, 2000, and 4500), as sole carbon and energy sources. Complete mineralization of acrylic acid monomer and dimer was observed in low-biomass sludge preparations previously exposed to the polymer mixture, based on carbon dioxide production and residual dissolved organic carbon analyses. Extensive (though incomplete) degradation was also observed for the low molecular weight acrylic acid oligomers (Mw 500 and 700), but degradation dropped off sharply for the 1000, 2000, and 4500 Mw polymers. Radiochemical (14C) data also confirmed the low degradation potential of the 1000, 2000, and 4500 Mw materials. Degradation of two commercial poly(ethylene glycol)s at 1000 and 3400 Mw was complete and comparable to that of the acrylic acid monomer and dimer. Our results indicate that mixed populations of activated sludge microorganisms can extensively metabolize acrylic acid oligomers of seven units or less. Complete mineralization, however, could be confirmed only for the monomer and dimer material, and carbon mass balance data suggested that the true molecular weight cutoff for complete biodegradation was significantly less than the 500–700 Mw range tested.
Article
pH-Responsive polymers are systems whose solubility, volume, and chain conformation can be manipulated by changes in pH, co-solvent, and electrolytes. This review summarizes recent developments covering synthesis, physicochemical properties, and applications in various disciplines. A variety of synthetic methodologies comprising of emulsion polymerization and living radical polymerization techniques are described, and some of their salient features are highlighted. Several polymeric systems, such as homopolymers, block copolymers, microgels, hydrogels and polymer brushes at interfaces are reviewed, where important characteristics that govern their behavior in solutions are described. Potential applications of these systems in controlled drug delivery, personal and home care, industrial coatings, biological and membrane science, viscosity modifiers, colloid stabilization, and water remediation, are discussed.
Article
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.
Article
Osmosis is a physical phenomenon that has been extensively studied by scientists in various disciplines of science and engineering. Early researchers studied the mechanism of osmosis through natural materials, and from the 1960s, special attention has been given to osmosis through synthetic materials. Following the progress in membrane science in the last few decades, especially for reverse osmosis applications, the interests in engineered applications of osmosis has been spurred. Osmosis, or as it is currently referred to as forward osmosis, has new applications in separation processes for wastewater treatment, food processing, and seawater/brackish water desalination. Other unique areas of forward osmosis research include pressure-retarded osmosis for generation of electricity from saline and fresh water and implantable osmotic pumps for controlled drug release. This paper provides the state-of-the-art of the physical principles and applications of forward osmosis as well as their strengths and limitations.
Article
The development of the forward osmosis (FO) process has been constrained by the slow development of appropriate draw solutions. Two significant concerns related to draw solutions are the draw solute leakage and intensive energy requirement in recycling draw solutes after the FO process. FO would be much attractive if there is no draw solute leakage and the recycle of draw solutes is easy and economic. In this study, polyelectrolytes of a series of polyacrylic acid sodium salts (PAA-Na), were explored as draw solutes in the FO process. The characteristics of high solubility in water and flexibility in structural configuration ensure the suitability of PAA-Na as draw solutes and their relative ease in recycle through pressure-driven membrane processes. The high water flux with insignificant salt leakage in the FO process and the high salt rejection in recycle processes reveal the superiority of PAA-Na to conventional ionic salts, such as NaCl, when comparing their FO performance via the same membranes. The repeatable performance of PAA-Na after recycle indicates the absence of any aggregation problems. The overall performance demonstrates that polyelectrolytes of PAA-Na series are promising as draw solutes, and the new concept of using polyelectrolytes as draw solutes in FO processes is applicable.
Article
It was recently reported that a UK company has developed a naturally non-toxic magnetoferritin to act as a draw solute for drawing water in forward osmosis process. The gist of this technology is the utilization of the magnetic nanoparticle and high-gradient magnetic separation for draw solute separation and reuse. However, any demonstration on this technology has not been reported yet. In this study, a feasibility test of magnetic separation using magnetic nanoparticle was therefore performed to investigate the possibility of magnetic separation in water treatment such as desalination. Basically, a magnetic separation system consisted of a column packed with a bed of magnetically susceptible wools placed between the poles of electromagnet and Fe3O4 magnetic nanoparticle was used as a model nanoparticle. The effect of nanoparticle size to applied magnetic field in separation column was experimentally investigated and the magnetic field distribution in a magnet gap and the magnetic field gradient around stainless steel wool wire were analyzed through numerical simulation. The amount of magnetic nanoparticle captured in the separator column increased as the magnetic field strength and particle size increased. As a result, if magnetic separation is intended to be used for draw solute separation and reuse, both novel nanoparticle and large-scale high performance magnetic separator must be developed.
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