Forward Osmosis-membrane Distillation Research Articles

Osmotically and Thermally Isolated Forward Osmosis-Membrane Distillation (FO-MD) Integrated Module.

In this study, we propose a novel module design to integrate forward osmosis (FO) and membrane distillation (MD). The two processes are sealed in one module and operated simultaneously, making the system compact and suitable for a wide range of applications. To evaluate the system under large-scale module operating conditions, FO and MD experiments were performed separately. The effect of draw solution (DS) temperature on the FO performance was first assessed in terms of flux, reverse salt flux (RSF), and specific RSF (SRSF). While a higher DS temperature resulted in an increased RSF, a higher FO flux was achieved, with a lower SRSF. The influence of DS concentration on the MD performance was then investigated in terms of flux and salt rejection. High DS concentration had a slightly negative impact on MD water vapor flux, but the MD membrane was a complete barrier for DS salts. The FO-MD integrated module was simulated based on mass balance equations. Results indicated that initial DS (MD feed) flow rate and concentration are the most important factors for stable operation of the integrated module. Higher initial DS flow rate and lower initial DS concentration can achieve a higher permeate rate of the FO-MD module.

Use of a Forward Osmosis–Membrane Distillation Integrated Process in the Treatment of High-Salinity Oily Wastewater

In this work, the feasibility of using a hybrid forward osmosis (FO)–membrane distillation (MD) process for treating hypersaline produced water was studied. Four draw solutions [i.e., sodium chlori...

Continuous juice concentration by integrating forward osmosis with membrane distillation using potassium sorbate preservative as a draw solute

A green and sustainable technique is desired for juice concentration to increase its shelf life and save the transportation cost. In this study, we investigated an integrated forward osmosis-membrane distillation (FO-MD) process for juice concentration and developed a food preservative potassium sorbate as a renewable draw solute. The upstream FO process was used to concentrate apple juice in ambient operation conditions for preserving juice nutrition and flavor. Potassium sorbate preservative was developed as draw solute to minimize the accumulation of a draw solute in the concentrated juice without interfering juice flavor, and the slow diffusion of potassium sorbate preservative across the FO membrane to the feed juice concentrate can also prevent the bacterial growth during the concentration process by taking advantage of reverse salt flux. The downstream MD process was used to recover potassium sorbate draw solutes from the FO effluent and maintain the constant draw solute concentration for achieving stable water flux of FO membranes. Thin-film composite (TFC) polyamide membranes and poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun nanofibrous membranes were fabricated and employed in the FO and MD processes, respectively. Results illustrate that the integrated FO–MD process presents a synergistic flux balancing behavior and achieves a constant water flux for both FO and MD membranes. The FO–MD process was able to continuously concentrate apple juice over long-term bench-scale operation. Importantly, the concentrated apple juice has almost no loss in nutrition and also has very low amount of potassium sorbate (0.45 g/L) far below the required maximum level in food industry (1.00 g/L). Our work provides a food preservative potassium sorbate draw solute facilitated FO-MD process for juice concentration, which may have practical application potentials in the food processing.

Domestic wastewater treatment by forward osmosis-membrane distillation (FO-MD) integrated system

In this study, real domestic wastewater treatment by forward osmosis-membrane distillation (FO-MD) integrated system was investigated in laboratory scale. The integrated membrane system presented a good separation performance and the removal efficiency of most contaminants in the domestic wastewater was higher than 90%. High molecular weight contaminants were completely removed, while a few low molecular weight contaminants permeated through the membrane. The FO membrane fouling layer mainly consisted of organic substances like polysaccharides and proteins, and was very loose and could be effectively removed by rinsing the membrane surface with tap water. By comparison, the MD membrane fouling was mainly induced by inorganic salts and was not as severe as that of the FO membrane. During 120 h continuous operation, the FO-MD integrated system exhibited satisfying performance stability and maintained a high water yield and high product water quality. The results indicated the potential of the FO-MD integrated system for municipal wastewater treatment in coastal cities, water purification and desalination.

Exploration of polyelectrolyte incorporated with Triton-X 114 surfactant based osmotic agent for forward osmosis desalination

Selection of a proper osmotic agent is important to make the forward osmosis (FO) feasible. The objective of this study was to enhance FO by lowering reverse solute flux and maintaining high water flux. Poly(propylene glycol) with molecular weight of 725 Da (PPG-725) was found to possess high osmolality, making it a strong candidate for using as a draw agent. In addition, to reduce the partial leakage of draw solute, a non-ionic surfactant (Triton X-114) has been incorporated. Typically, when the hydrophobic tails of Triton X-114 interacted with the membrane surface, a layer on the surface of membrane is produced to constrict the pores and thus minimize the reverse solute flux. In this study, different concentrations of PPG-725 incorporated with different concentrations of Triton X-114 (0.2–0.8 mM) were used to evaluate their osmotic potentials as draw solute. The specific reverse solute flux (Js/Jw) of 40% PPG-725 doped with Triton X-114 was found to be 0.01 g/L, considerably much lesser than the conventional inorganic draw agents. Finally, membrane distillation operation was utilized as the recovery system in which solute rejection of 97% was achieved for 40% PPG-725/Triton X-114. Therefore, the overall performance supported PPG-725/Triton X-114 as being an efficient draw agent for forward osmosis-membrane distillation hybrid process.

Exploration of an innovative draw solution for a forward osmosis-membrane distillation desalination process.

Forward osmosis (FO) has emerged as a viable technology to alleviate the global water crisis. The greatest challenge facing the application of FO technology is the lack of an ideal draw solution with high water flux and low reverse salt flux. Hence, the objective of this study was to enhance FO by lowering reverse salt flux and maintaining high water flux; the method involved adding small concentrations of Al2(SO4)3 to a MgCl2 draw solution. Results showed that 0.5M MgCl2 mixed with 0.05M of Al2(SO4)3 at pH 6.5 achieved a lower reverse salt flux (0.53gMH) than that of pure MgCl2 (1.55gMH) using an FO cellulose triacetate nonwoven (CTA-NW) membrane. This was due possibly to the flocculation of aluminum hydroxide in the mixed draw solution that constricted membrane pores, resulting in reduced salt diffusion. Moreover, average water fluxes of 4.09 and 1.74L/m2-h (LMH) were achieved over 180min, respectively, when brackish water (5g/L) and sea water (35g/L) were used as feed solutions. Furthermore, three types of membrane distillation (MD) membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45μm proved to be the most effective in achieving a high salt rejection (99.90%) and high water flux (5.41LMH) in a diluted draw solution.

Exploring high charge of phosphate as new draw solute in a forward osmosis–membrane distillation hybrid system for concentrating high-nutrient sludge

For the first time, a high charge of phosphate was used as the draw solute in a forward osmosis–membrane distillation (FO–MD) hybrid system for concentrating high-nutrient sludge. A high water flux (12.5L/m2h) and a low reverse salt flux (0.84g/m2) were simultaneously achieved at pH9 by using 0.1M Na3PO4 as the draw solute and deionized water as the feed solution in the FO process. The specific reverse salt flux of 0.1M Na3PO4 (Js/Jw=0.07g/L) was considerably less than that of 0.1M NaCl (Js/Jw=0.37g/L) because the complexion between Na+ and HPO42− at pH9 led to the reduction of free Na+ ions, which subsequently reduced the reverse salt diffusion substantially. Moreover, for a feed solution with an initial sludge concentration of 3500mg/L, the sludge concentration could be concentrated to 19,800 and 22,000mg/L in the pressure-retarded osmosis (PRO) and FO membrane orientations, respectively, after 15h of operation. Four types of MD membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45μm was the most effective in achieving a high water flux (10.28L/m2h) and high salt rejection (approximately 100%) in a diluted Na3PO4 draw solution.

Effective As(III) Removal by A Multi-Charged Hydroacid Complex Draw Solute Facilitated Forward Osmosis-Membrane Distillation (FO-MD) Processes.

Effective removal of As(III) from water by an oxalic acid complex with the formula of Na3[Cr(C2O4)3] (Na-Cr-OA) is demonstrated via an forward osmosis-membrane distillation (FO-MD) hybrid system in this study. Na-Cr-OA first proved its superiority as a draw solute with high water fluxes and negligible reverse fluxes in FO, then a systematic investigation of the Na-Cr-OA promoted FO process was conducted to ascertain the factors in As(III) removal. Relatively high water fluxes of 28 LMH under the FO mode and 74 LMH under the pressure retarded osmosis (PRO) mode were achieved when using a 1000 ppm As(III) solution as the feed and 1.0 M Na-Cr-OA as the draw solution at 60 °C. As(III) removal with a water recovery up to 21.6% (FO mode) and 48.3% (PRO mode) were also achieved in 2 h. An outstanding As(III) rejection with 30-3000 μg/L As(III) in the permeate was accomplished when As(III) feed solutions varied from 5 × 10(4) to 1 × 10(6) μg/L, superior to the best FO performance reported for As(III) removal. Incorporating MD into FO not only makes As(III) removal sustainable by reconcentrating the Na-Cr-OA solution simultaneously, but also reduces the As(III) concentration below 10 μg/L in the product water, meeting the WHO standard.

Integrated forward osmosis-membrane distillation process for human urine treatment

This study demonstrated a forward osmosis-membrane distillation (FO-MD) hybrid system for real human urine treatment. A series of NaCl solutions at different concentrations were adopted for draw solutions in FO process, which were also the feed solutions of MD process. To establish a stable and continuous integrated FO-MD system, individual FO process with different NaCl concentrations and individual direct contact membrane distillation (DCMD) process with different feed temperatures were firstly investigated separately. Four stable equilibrium conditions were obtained from matching the water transfer rates of individual FO and MD processes. It was found that the integrated system is stable and sustainable when the water transfer rate of FO subsystem is equal to that of MD subsystem. The rejections to main contaminants in human urine were also investigated. Although individual FO process had relatively high rejection to Total Organic Carbon (TOC), Total Nitrogen (TN) and Ammonium Nitrogen (NH4+-N) in human urine, these contaminants could also accumulate in draw solution after long term performance. The MD process provided an effective rejection to contaminants in draw solution after FO process and the integrated system revealed nearly complete rejection to TOC, TN and NH4+-N. This work provided a potential treatment process for human urine in some fields such as water regeneration in space station and water or nutrient recovery from source-separated urine.

Integration of forward osmosis and membrane distillation for sustainable wastewater reuse

Abstract This study focuses on the performance of an integrated forward osmosis (FO) and membrane distillation (MD) process for wastewater reuse. FO worked as a pretreatment barrier to remove most contaminants in the feed water and MD was used to recover the draw solutes from FO effluent and simultaneously produce high-quality reusable water. A unique three-channel FO–MD membrane module was designed and built to test water flux and contaminant removal in bench-scale experiments. It was found that the integrated FO–MD system possessed inherent flux balancing mechanism that enabled a stable and equal water flux for both FO and MD membranes for effective recovery of draw solution over long-term experiments. The FO–MD system was able to achieve more than 3 logs (>99.9%) removal of ammonium, COD, arsenic, and combined solutes in both synthetic and real wastewaters. Such a synergistic integration of FO and MD membrane processes offers three major advantages. First, the upstream FO process removes most contaminants and foulants from the feed solution, thus potentially diminishing the fouling and wetting problem for the downstream MD process. Second, the downstream MD process successfully recovers the draw solution for the FO process, enabling a constant water flux for FO. Third, the synergistic removal capability of FO and MD enabled the production of extremely high-quality product water. Additional benefits of the integrated process include ambient pressure operation and potential use of renewable low-grade heat as the energy source.

Evaluation of hydroacid complex in the forward osmosis–membrane distillation (FO–MD) system for desalination

The incorporation of membrane distillation (MD) into forward osmosis (FO) provides process sustainability to regenerate the draw solution and to produce clean water simultaneously. However, the reverse salt flux is the major hurdle in the FO–MD system because it not only reduces the effective osmotic driving force across the membrane but also increases the replenishment cost and scaling issue. For the first time, a hydroacid complex with abundant hydrophilic groups and ionic species is evaluated as the draw solutes in the hybrid FO–MD system consisting of multi-bore PVDF MD membranes for seawater/brackish desalination. In order to evaluate the practicality of the hydroacid complex in the FO–MD system, FO and MD experiments were conducted at elevated temperatures and concentrations. The hydroacid complex has displayed desired properties such as high solubility, low viscosity, excellent thermal stability and minimal reverse salt flux suitable for FO and MD operations. FO–MD desalination process was demonstrated with a highest seawater desalination flux of 6/32 LMH (FO/MD). This study may open up the prospective of employing the hydroacid complex as the draw solute in FO–MD hybrid systems for seawater /brackish desalination.

A Combined Forward Osmosis and Membrane Distillation System for Sidestream Treatment

Separate treatment of high-nutrient sidestream is an efficient and cost effective way to decrease the loading on the main plant, resulting in lower effluent nutrient concentration. This study investigated the use of a combined forward osmosis-membrane distillation (FO-MD) system for the removal of nitrogen present in high concentration in sidestream from anaerobic digestion process. The combined system was able to achieve almost 100% rejection of solids and acetic acid, and more than 98% rejection of NH3-N from the sidestream. The high rejection of NH3-N was mainly achieved by the FO process. The solids in the feed solution contributed to fouling problem in both FO and MD, resulting in significant decline in flux. However, 76% or higher flux recovery was achieved for FO membrane by cleaning with tap water. We observed that flux recovery was due to removal of solids from the membrane surface by the cleaning process. FO membrane also demonstrated excellent performance for continuous operation when cleaned for 15 min in every 24 h interval. Overall, the combined FO-MD system was found to be an effective solution for treatment of nutrient rich sidestream.

Sustainable water recovery from oily wastewater via forward osmosis-membrane distillation (FO-MD)

This study proposed and investigated a hybrid forward osmosis – membrane distillation (FO-MD) system for sustainable water recovery from oily wastewater by employing lab-fabricated FO and MD hollow fiber membranes. Stable oil-in-water emulsions of different concentrations with small droplet sizes (<1 μm) were firstly prepared and applied as the feed solution in the FO process. Fouling was immediately observed in the FO mode and was low on the cellulose triacetate (CTA) – based thin film composite (TFC) membranes. Moreover, slight increment of fouling was observed in the first few hours and the water flux was then stabilized over 24 h. The characterizations of water flux and solute rejection in separate FO and MD processes revealed that a high water flux, good NaCl rejection, impressively high retention of oil droplets and partial permeation of acetic acid could be achieved. Finally, an integrated FO-MD system was developed to treat the oily wastewater containing petroleum, surfactant, NaCl and acetic acid at 60 °C in the batch mode. The water flux in FO undergoes three-stage decline due to fouling and reduction in osmotic driving force, but is quite stable in MD regardless of salt concentration. Oily wastewater with relatively high salinity could be effectively recovered by the FO-MD hybrid system while maintaining large water flux, at least 90% feed water recovery could be readily attained with only trace amounts of oil and salts, and the draw solution was re-generated for the next rounds of FO-MD run. Interestingly, significant amount of acetic acid was also retained in the permeate for further reuse as a chemical additive during the production of crude oil. The work has demonstrated that not only water but also organic additives in the wastewater could be effectively recovered by FO-MD systems for reuse or other utilizations.

Toward Resource Recovery from Wastewater: Extraction of Phosphorus from Digested Sludge Using a Hybrid Forward Osmosis–Membrane Distillation Process

We demonstrate the simultaneous extraction of phosphorus and clean water from digested sludge centrate using a forward osmosis (FO)–membrane distillation (MD) hybrid process. In this FO–MD hybrid process, FO concentrates orthophosphate and ammonium for subsequent phosphorus recovery in the form of struvite (MgNH4PO4·6H2O), while MD is used to recover the draw solution and extract clean water from the digested sludge centrate. A decline in water flux was observed during the FO process, but fouling was largely reversible after a brief, simple membrane flushing using deionized water. The FO process also provides an effective pretreatment capacity to the subsequent MD process, which exhibited stable water flux. The use of MgCl2 as the draw solute for the FO process is another novel aspect of the system. The reverse salt flux of magnesium to the concentrated digested sludge across the FO membrane and the diffusion of protons away from the digested sludge create favorable conditions for the formation of struvit...

A Forward Osmosis–Membrane Distillation Hybrid Process for Direct Sewer Mining: System Performance and Limitations

This study demonstrates the robustness and treatment capacity of a forward osmosis (FO)-membrane distillation (MD) hybrid system for small-scale decentralized sewer mining. A stable water flux was realized using a laboratory-scale FO-MD hybrid system operating continuously with raw sewage as the feed at water recovery up to 80%. The hybrid system also showed an excellent capacity for the removal of trace organic contaminants (TrOCs), with removal rates ranging from 91 to 98%. The results suggest that TrOC transport through the FO membrane is governed by "solute-membrane" interaction, whereas that through the MD membrane is strongly correlated to TrOC volatility. Concentrations of organic matter and TrOCs in the draw solution increased substantially as the water recovery increased. This accumulation of some contaminants in the draw solution is attributed to the difference in their rejection by the FO and MD systems. We demonstrate that granular activated carbon adsorption or ultraviolet oxidation could be used to prevent contaminant accumulation in the draw solution, resulting in near complete rejection (>99.5%) of TrOCs.

Integration of forward osmosis with membrane distillation: effect of operating conditions

Abstract Hybrid desalination systems combining both thermal and membrane desalination processes are currently considered a viable alternative to conventional desalination plants. Recently, an incorporation of forward osmosis (FO) with membrane distillation (MD) has been considered as a new hybrid desalination technology. Nevertheless, few works have been done to design and optimize these types of new hybrid systems. The focus of this study was to investigate FO–MD hybrid process in which MD is being used to recover draw solutes in product water from FO. Laboratory-scale systems for FO and MD were developed to examine the effect of key operating conditions (draw solute concentration, operation time, temperature, etc.) on flux and solute transport. The results indicated that the efficiency of FO–MD hybrid is affected by the selectivity of draw solute transport through the MD membrane. As decreasing the temperature difference between the feed and distillate in MD, the rate of separation decreases but the selectivity increases. Based on these results, a simple model was proposed to analyze the efficiency of this FO–MD hybrid system.

Polyelectrolyte-Promoted Forward Osmosis–Membrane Distillation (FO–MD) Hybrid Process for Dye Wastewater Treatment

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.

Integrated forward osmosis–membrane distillation (FO–MD) hybrid system for the concentration of protein solutions

For the first time, an integrated forward osmosis–membrane distillation (FO–MD) hybrid system has been demonstrated for the concentration of protein solutions, specifically a bovine serum albumin (BSA) solution. A hydrophilic polybenzimidazole (PBI) nanofiltration hollow fiber membrane and a hydrophobic polyvinylidene fluoride-polytetrafluoroethylene (PVDF-PTFE) hollow fiber membrane were fabricated and employed in the FO and MD processes, respectively. A concentrated NaCl solution was employed as the draw solute to dehydrate proteins in FO, while distillate water is a by-product during the re-concentration of diluted NaCl draw solution in MD. To determine suitable operating conditions for the hybrid system, independent characterizations were carried out for both FO and MD processes using different NaCl concentrations as draw solutes in FO and different feed temperatures in MD. It was found that the integrated system is stable in continuous operation when the dehydration rate across the FO membrane is the same as the water vapor rate across the MD membrane. Simple mathematical models consistent with the experimental results were also developed for the FO and the FO–MD hybrid systems. The newly developed FO–MD hybrid system is promising for the concentration of pharmaceuticals/protein solutions in the foreseeable future.