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The imperative to establish environmentally friendly and sustainable food processing techniques has compelled the food industry to explore alternative approaches that uphold food quality, ensure nutritional integrity, and minimize energy consumption. Extensive research conducted in the past decade has substantiated the superiority of membrane-based dewatering technology over conventional methods, owing to its ability to retain nutrients effectively while minimizing energy requirements. Notably, forward osmosis (FO) and membrane distillation (MD) have emerged as viable membrane technologies for food processing in the industry. However, recent reviews have underscored the prominence of FO in the enrichment of liquid food, positioning it as a preferred choice among other membrane-based processes. This review paper aims to elucidate the advancements and contributions of FO and MD in the realm of food processing while evaluating their maturity and technology readiness level for food concentration. Moreover, it endeavors to delineate specific parameters, including pretreatment techniques, membrane cleaning strategies, and membrane configurations/modules tailored to liquid food sources' distinct dewatering requirements. Although most FO and MD studies have focused on lab-scale fruit juice and whey concentration, future investigations should encompass pilot-scale process development alongside comprehensive techno-economic analyses to facilitate the smooth transition of these technologies to an industrial scale. [Display omitted] • FO and MD are the most suitable membrane-based methods for dewatering liquid food at low pressure. • FO advance over the MD since it accounts for a wide range of liquid feed source. • FO studies need to be focused on the regeneration of draw solute for practical implementation in food industry. • Future MD and FO studies need to consider a techno-economic analysis for commercialization. [ABSTRACT FROM AUTHOR]

Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20–30°C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50–70°C) is available. [ABSTRACT FROM PUBLISHER]

Abstract: Forward osmosis (FO) has gained significant research interest due to the wide range of potential applications in desalination and wastewater reuse. However, the FO process being concentration (osmosis) driven has its own intrinsic limitations. Net transfer of water across the membrane occurs until the point of osmotic equilibrium between the draw solution (DS) and the feed solution (FS). Without external intervention, it is impossible to dilute the DS beyond the point of osmotic equilibrium. In this study, the concept of osmotic equilibrium in the FO process is introduced by simulating conditions in a plate-and-frame FO membrane module using established mass transport models. The simulations evaluated the influence of various operating parameters on process performance, assessed in terms of water flux, feed recovery rate and the final concentration of the diluted DS. The counter-current crossflow mode of operation has been observed to be advantageous because it can achieve higher module average water flux, higher feed water recovery rates and higher DS final dilution. Based on the osmotic equilibrium concept and mass balance analysis, a modified equation for the water extraction capacity of a draw solute has been proposed. This study underscores the need for process optimisation for large-scale FO operations. [Copyright &y& Elsevier]

Abstract: The concept of fertiliser drawn forward osmosis (FDFO) desalination lies in the premise that fertilisers that serve as draw solutions (DS) add value to the FDFO product water for fertigation. However, because FDFO desalination is concentration based, the process cannot continue beyond the concentration equilibrium, one of the major limitations of the forward osmosis (FO) process. This results in final FDFO product water that, unless subjected to substantial dilution with fresh water, exceeds the acceptable nutrient concentrations for direct fertigation. In this study, nanofiltration (NF) has been assessed as an integrated process to FDFO desalination, either as a pre-treatment or post-treatment, to reduce the nutrient concentrations in the final product water and thereby allow direct use of the product water for fertigation without further dilution. NF as pre-treatment or post-treatment was found effective in reducing the nutrient concentrations using brackish groundwater (BGW) sources with relatively low total dissolved solid (TDS). However, when using higher TDS BGW sources, the product water still required further dilution or post-treatment before fertigation. NF as post-treatment was found to be more advantageous both in terms of reduced nutrient concentrations in the final product water and energy consumption. [Copyright &y& Elsevier]

The internal concentration polymerization (ICP) phenomenon may hinder the flux of forward osmosis (FO) membranes. The mitigation of ICP can be achieved by employing a porous support layer structure. Nevertheless, conventional interfacial polymerization (IP) methods encounter challenges in establishing a dense selective layer upon a highly porous support layer. In this study, the support-free assembled molecular layer-by-layer (SF-mLbL) was suggested to manufacture the thin-film composite (TFC) membrane by combining the separately fabricated polyamide (PA) selective layer with a tunable thickness and the highly porous support layer. The SF-mLbL (8 wt%) membrane had a higher water flux and selectivity (43.52 ± 0.89 LMH/0.15 ± 0.01 g L−1) than those (10.34 ± 0.48 LMH/0.75 ± 0.02 g L−1 and 7.41 ± 0.18 LMH/0.81 ± 0.01 g L−1) of IP-PA and commercial cellulose triacetate membranes as 0.5 M NaCl draw solution in FO mode. Consequently, the SF-mLbL membranes exhibited significant improvement in the FO process with well-balanced permselectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has great potential for sustainable osmotic dewatering, which can attain several goals including low energy use, high water recovery, and low membrane fouling. However, this technology still involves critical issues that should be explored to achieve successful functioning of osmotic dehydration process, such as feed characteristics, FO membrane performance, and draw solution selection. In this study, the effectiveness of FO for osmotic dehydration was demonstrated by adopting xylose solution as model feed. Aside from current energy intensive evaporation methods, this widely used sweetener needs an advanced and energy-efficient concentration method such as FO. The stable performance showed xylose can be sustainably concentrated with a consistently high dewatering rate, whereas the recovery rate using a pressure-driven membrane system was constrained by the bursting pressure of nanofiltration membrane. Lastly, high-quality of concentrated product can be obtained by selecting a suitable draw solution of which its reversely diffused salts barely affect the xylose solution or are used to enhance the xylose quality. Employing Poly (aspartic acid) sodium salt or sugar-based solutes as draw help to preserve the purity of enriched xylose. These results suggest that FO can provide a feasible solution for food processing which requires product concentration through dewatering while preserving and improving its quality. [ABSTRACT FROM AUTHOR]

This study presents simulation of a closed-loop forward osmosis (FO)-nanofiltration (NF) hybrid system using fertiliser draw solution (DS) based on thermodynamic mass balance in a full-scale system neglecting the non-idealities such as finite membrane area that may exist in a real process. The simulation shows that the DS input parameters such as initial concentrations and its flow rates cannot be arbitrarily selected for a plant with defined volume output. For a fixed FO-NF plant capacity and feed concentration, the required initial DS flow rate varies inversely with the initial DS concentration or vice-versa. The net DS mass flow rate, a parameter constant for a fixed plant capacity but that increases linearly with the plant capacity and feed concentration, is the most important operational parameter of a closed-loop system. Increasing either of them or both increases the mass flow rate to the system directly affecting the final concentration of the diluted DS with direct energy implications to the NF process. Besides, the initial DS concentration and flow rates are also limited by the optimum recovery rates at which NF process can be operated which otherwise also have direct implications to the NF energy. This simulation also presents quantitative analysis of the reverse diffusion of fertiliser nutrients towards feed brine and the gradual accumulation of feed solutes within the closed system. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis (FO) membrane process. The flux distribution model developed in this study showed a good agreement with experimental results, validating the robustness of the model. This model demonstrated, as expected, that the permeate flux decreased along the membrane channel due to decreasing osmotic pressure differential across the FO membrane. A series of fouling experiments were conducted under the draw and feed solutions at various recoveries simulated by the model. The simulated fouling experiments revealed that higher organic (alginate) fouling and thus more flux decline were observed at the last section of a membrane channel, as foulants in feed solution became more concentrated. Furthermore, the water flux in FO process declined more severely as the recovery increased due to more foulants transported to membrane surface with elevated solute concentrations at higher recovery, which created favorable solution environments for organic adsorption. The fouling reversibility also decreased at the last section of the membrane channel, suggesting that fouling distribution on FO membrane along the module should be carefully examined to improve overall cleaning efficiency. Lastly, it was found that such fouling distribution observed with co-current flow operation became less pronounced in counter-current flow operation of FO membrane process. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid system that combines forward osmosis with a reverse osmosis seawater desalination process could reduce both energy requirements and environmental impacts by osmotic dilution of the seawater and concentrated brine with an impaired low salinity stream, such as treated wastewater effluent. In this study, we investigate the membrane fouling behavior in forward osmosis under conditions simulating the osmotic dilution process and the use of hydrodynamic methods without the use of cleaning chemicals, to control membrane fouling. Fouling runs with seawater or SWRO brine draw solution and deionized (DI) water feed solution showed insignificant water flux decline, which implies negligible effect of particulate and organic matter in the seawater/brine on fouling of the FO membrane support layer. Fouling of the membrane active layer was evaluated by using an enriched synthetic wastewater effluent containing a mixture of inorganic and organic foulants, focusing on the impact of permeate drag force on fouling layer formation. Our results demonstrate that higher permeate water flux causes an increase in concentration build-up of foulants at the membrane surface, thereby forming a dense inorganic/organic combined fouling layer during FO fouling runs. We also examined three hydrodynamic methods for minimizing FO membrane fouling in the osmotic dilution process: (1) applying shear force on the membrane surface by increasing the cross-flow velocity, (2) using a feed-channel spacer to induce turbulence, and (3) employing pulsed flow to remove foulants from the membrane surface. Our results show that these hydrodynamic methods substantially reduce fouling and flux decline rate. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Forward osmosis (FO) has attracted growing attention in the field of membrane-based separation technology over the last two decades. Despite recent advancements in various osmosis-assisted processes, few studies have succeeded in commercialization. This paper reviews the state-of-the-art developments of FO membrane, limitation analysis, and commercial proper applications. First, the development of FO technology in terms of FO membranes, FO draw solution (DS), and FO systems is reviewed. Based on a literature database survey spanning 1965-2020, current limitations of FO, particularly in terms of DS regeneration, energy consumption, and scale-up implementation, are identified to overcome the obstacles to commercialization. The key applications of the FO membrane process in commercial sectors are further classified into three configurations (i.e., osmotic dilution, osmotic concentration, and simultaneous osmotic dilution and concentration), and their successful applications are discussed. Since industrial demonstrations of simultaneous osmotic dilution and concentration are in progress, we believe that FO technology with no need for DS regeneration will be commercialized soon in the future. [Display omitted] • Critical review on the current state of osmosis-assisted processes using FO • FO applications limited by DS regeneration, high energy use, and scale-up • Osmotic dilution and concentration by FO without DS reconstitution • Commercial applications of osmosis-assisted dilution/concentration processes [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) membranes generally have a thin-film composite (TFC) structure comprising an ultrafiltration (UF)-grade support layer and a polyamide (PA) active layer. However, the lack of high-performance membranes limits FO. To improve the FO performance, internal concentration polarization (ICP) should be controlled to reduce the water flux within the support layer. In this study, a novel support-free molecular layer-by-layer (SF-mLbL) technique using a microfiltration (MF)-grade support layer for minimum ICP was applied to produce a robust and uniform active layer, even on large pores of the support layer. Based on the location of graphene oxide (GO) nanoparticles, thin-film nanocomposite (TFN) and thin-film nanocomposite-interlayer (TFNi) membranes were fabricated. Among these, the TFNi membrane with the highest performance contained 0.7 wt% GO nanoparticles and was stacked in 15 cycles. The 0.7 wt%-15 cycles TFNi membrane showed high water flux (87.18 ± 0.15 LMH) and low reverse salt flux (5.06 ± 0.11 gMH) when deionized (DI) water and 0.5 M NaCl solution were used as feed and draw solutions, respectively, in FO mode. This study demonstrates that the SF-mLbL technique is suitable for manufacturing high-performance FO membranes. [Display omitted] • The FO membrane was fabricated using novel SF-mLbL technology with GO nanoparticles. • A microfilter was used as a support layer to minimize the ICP phenomenon. • The membranes are divided into two types based on the location of the nanoparticles. • The TFNi membrane exhibited excellent water flux and selectivity. • The SF-mLbL technique provided high tunability of fabricating membranes. [ABSTRACT FROM AUTHOR]

A thin film composite (TFC) forward osmosis (FO) membrane with high performance and superb durability was fabricated on a polydopamine (PDA)-modified polyethylene (DPE) support via an unconventional aromatic solvent-based interfacial polymerization (IP) method. The PDA coating uniformly hydrophilized the hydrophobic pristine polyethylene (PE) support, which enabled the long-term operation stability. The thin (∼8 μm) and highly porous support structure with interconnected pores was preserved after the PDA modification, leading to a remarkably low structural parameter (∼168 μm) of the support. In addition, the use of the toluene-based IP process allowed for the formation of a highly permselective polyamide selective layer on the hydrophilic DPE support, which was challenging with the conventional aliphatic solvent-based IP process. Hence, the prepared DPE-supported TFC (DPE-TFC) membrane exhibited unprecedented high FO performance, i.e., ∼4.5 times higher FO water flux and ∼63% lower specific salt flux (in FO mode) compared to the commercial HTI-CTA membrane. Furthermore, the DPE-TFC membrane possessed superior mechanical robustness, which guarantee durable operability and potential application even in mechanically harsh environments. Hence, the PE-supported FO membrane presents a new paradigm in FO membrane technology. Image 1 • FO membranes were fabricated using polydopamine-modified PE (DPE) supports. • DPE supports were uniformly hydrophilic while preserving their original structures. • The thinness, high porosity and enhanced hydrophilicity of DPE supports reduced ICP. • Toluene-based interfacial polymerization produced a highly permselective layer. • The prepared DPE-TFC membranes showed excellent FO performance and high durability. [ABSTRACT FROM AUTHOR]

Abstract Highly enriched grapefruit juice is expected to be obtained through forward osmosis (FO) without degradation of its nutrients. However, this technology is facing several key issues that must be explored to validate the suitability of FO as a dewatering process, namely, membrane performance testing, fouling control, and product quality assessment. In this work, grapefruit juice was dewatered using a commercial thin-film composite FO membrane that exhibited stable performance. The simulation results also suggested that the dewatering could be further enhanced by improving the S value of the current TFC FO membrane. Severe membrane fouling was observed, and it was predominantly due to suspended particles larger than 0.45 μm, such as pectin. However, sustainable osmotic dewatering operation could be attained by implementing appropriate fouling control strategies, such as separating large-sized particles by sedimentation or centrifugation prior to osmosis and recovering the declined water flux by physical cleaning. The dehydrated feed exhibited no significant loss of nutritional value, suggesting that the FO membrane dewatered the juice effectively while retaining its constituents. In addition, the FO process could be further improved to obtain enhanced-quality grapefruit juice by applying pressure to the feed stream or employing a sugar-based draw solution such as glucose. Graphical abstract Image 1 Highlights • This work probed the challenging issues in osmotic dewatering of grapefruit juice. • Stable flux induced by TFC FO membrane can be improved further by reducing S value. • The severe fouling by particulate substances was alleviated by their separation. • Hydraulic flushing well restored the declined flux caused by dissolved matters. • Applying pressure or adopting glucose further reduced the reversely diffused salts. [ABSTRACT FROM AUTHOR]

The use of forward osmosis (FO) for concentrating radioactive liquid waste from radiation therapy rooms in hospitals was systematically investigated in this study. The removal of natural and radioactive iodine using FO was first investigated with varying pHs and draw solutions (DSs) to identify the optimal conditions for FO concentration. Results showed that FO had a successful rejection rate for both natural and radioactive iodine ( 125 I) of up to 99.3%. This high rejection rate was achieved at a high pH, mainly due to electric repulsion between iodine and membrane. Higher iodine removal by FO was also attained with a DS that exhibits a reverse salt flux (RSF) adequate to hinder iodine transport. Following this, actual radioactive medical liquid waste was collected and concentrated using FO under these optimal conditions. The radionuclides in the medical waste ( 131 I) were removed effectively, but the water recovery rate was limited due to severe membrane fouling. To enhance the recovery rate, hydraulic washing was applied, but this had only limited success due to combined organic-inorganic fouling of the FO membrane. Finally, the effect of FO concentration on the reduction of septic tank volume was simulated as a function of recovery rate. To our knowledge, this study is the first attempt to explore the potential of FO technology for treating radioactive waste, and thus could be expanded to the dewatering of the radioactive liquid wastes from a variety of sources, such as nuclear power plants. [ABSTRACT FROM AUTHOR]

We investigated the possible underlying mechanism of the low fouling potential in the forward osmosis (FO) process during the osmotic dilution of seawater as part of the simultaneous desalination and wastewater reuse by FO and reverse osmosis hybrid system. Long-term experiments revealed an interesting water flux pattern highly dependent on the different operating parameters. The most interesting observation made was the spontaneous increase in the FO permeate flux at regular time interval during the FO operation using synthetic wastewater as feed and seawater. This sinusoidal FO flux pattern related well with the build-up of loose fouling layer and their natural peel-off from the membrane surface upon reaching certain layer thickness due to crossflow velocity shear. This flux pattern was more prominent at higher cross-flow velocity rates, lower feed water pH, for a smoother membrane surface and at lower operating pressure during pressure assisted osmosis (PAO) mode. Based on these results, membrane cleaning strategies were proposed by targeting a higher cross-flow velocity shear at a time when the permeate flux started to just increase. The approach of physical membrane cleaning was observed efficient and was able to almost fully restore the initial flux even under the PAO operation at 4 bar. [ABSTRACT FROM AUTHOR]

Sulphonated polyethersulfone (SPES) has been synthesized for developing high performance thin film composite (TFC) forward osmosis (FO) membranes with enhanced hydrophilic support layer. Sulphonated substrate not only affects the membrane performance but also changes the membrane morphology from finger-like structure to a sponge-like morphology at higher degree of sulphonation thereby affecting the mechanical strength of the FO membrane. Non-sulphonated TFC-FO membrane with 12 wt.% polymer concentration shows a faint finger-like structure while sulphonated samples at a similar polymer concentration show a fully sponge-like structure with a much higher performance. For example, a water flux of 35 Lm − 2 h − 1 and 0.28 g L − 1 specific reverse solute flux was achieved with sulphonated TFC-FO membrane sample (50 wt.% SPES) under the FO mode using 2 M NaCl as the draw solution and deionized water as feed. Substrate sulphonation also considerably decreased the membrane structural parameter from 1096 μm without sulphonation to 245 μm at 50 wt.% sulphonation. This study therefore shows that, besides surface morphology, the water flux of the FO membrane can also be enhanced by improving its substrate hydrophilic property. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has been increasingly studied in the past decade for its potential as an emerging low-energy water and wastewater treatment process. However, the term “low-energy” may only be suitable for those applications in where no further treatment of the draw solution (DS) is required either in the form of pretreatment or post-treatment to the FO process (e.g. where the diluted DS is the targeted final product which can be used directly or simply discarded). In most applications, FO has to be coupled with another separation process in a so-called hybrid FO system to either separate the DS from the final product water or to be used as an advanced pre-treatment process to conventional desalination technologies. The additional process increases the capital cost as well as the energy demand of the overall system which is one of the several challenges that hybrid FO systems need to overcome to compete with other separation technologies. Yet, there are some applications where hybrid FO systems can outperform conventional processes and this study aims to provide a comprehensive review on the current state of hybrid FO systems. The recent development and performance of hybrid FO systems in different applications have been reported. This review also highlights the future research directions for the current hybrid FO systems to achieve successful implementation. [ABSTRACT FROM AUTHOR]

Adequate dilution of fertiliser draw solution (DS) during fertiliser drawn forward osmosis (FDFO) desalination is important to meet nutrient concentration level for direct fertigation. The maximum DS dilution, however, occurs until the point of osmotic equilibrium between DS and feed solution (FS) thereby limiting the extent of DS dilution. Post-treatment such as nanofiltration (NF) process is required to reduce the fertiliser concentration. In this study however, pressure assisted fertiliser drawn osmosis (PAFDO) process was investigated to enhance DS dilution beyond the point of osmotic equilibrium and potentially eliminate NF post-treatment. The hydraulic pressure applied enhanced water flux significantly depending on the pressure. The applied pressure was found more effective at lower DS concentrations than at higher DS concentrations. For example, when a pressure of 10 bar was applied to 10 g/L NaCl FS with 0.1 M (NH 4 ) 2 SO 4 DS, the water flux increased by 1928% against 38% with 3.0 M (NH 4 ) 2 SO 4 DS. This additional water flux could dilute the fertiliser DS beyond the osmotic equilibrium concentrations thereby meeting the fertigation standard. PAFDO could potentially eliminate NF post-treatment significantly helping reduce the footprint and capital cost. However, the effective gain in water flux due to applied pressure at osmotic equilibrium decreased with the increase in the FS concentrations. [ABSTRACT FROM AUTHOR]

Organic fouling mechanisms in forward osmosis (FO) were systematically investigated at varying feed and draw temperatures. The effect of temperature variation on FO performance was first examined without foulants. When draw temperature increased, internal concentration polarization (ICP) decreased, which caused water flux to increase. Water flux was also improved with increasing feed temperature due to water permeability increased by decreased viscosity. Thus it can be deduced that water flux enhancement was induced by combined effects of reduced ICP and enhanced water permeability. A series of fouling experiments was then elaborately designed to fundamentally elucidate organic fouling mechanisms. Results demonstrated that organic fouling was significantly influenced by convective and diffusive organic transports induced by increasing temperature. Faster flux decline was observed with increasing draw temperature, primarily due to increased permeation drag. When increasing feed temperature, FO membrane was less fouled, attributing to enhanced organic back diffusion from membrane surface as well as increased organic solubility. Furthermore, fouling became more severe above certain critical flux at which organic convection by permeation drag dominated fouling mechanism as seen with escalating both temperatures simultaneously. Findings from this study can be utilized beneficially when FO temperature may be varied and needs to be optimized. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we systematically investigated the propensity and reversibility of combined organic–colloidal fouling in forward osmosis (FO) under various solution chemistries (pH and calcium ion concentrations) and applied hydraulic pressure on the feed side. Alginate, silica colloids, and their mixture (i.e., combined organic–colloidal) were used as model foulants. Our findings demonstrate that combined organic–colloidal foulants caused more rapid flux decline than the individual foulants due to the synergistic effect of alginate and silica colloids. As a result, much lower flux recovery was achieved by physical cleaning induced by increasing the cross-flow rate, in contrast to single foulants of which the fouling layer was easily removed under all solution conditions. Interestingly, less flux decline was observed at neutral pH for combined fouling, while acidic conditions were favorable for alginate fouling and basic solutions caused more silica fouling, thereby providing clear evidence for the combined fouling effect. It was also found that calcium ions enhanced water flux decline and induced the formation of less reversible combined organic–colloidal fouling layers. Lastly, the role of applied hydraulic pressure on the feed side in FO was examined to elucidate the mechanism of fouling layer formation, fouling reversibility, and water flux recovery. Higher fouling propensity and lower fouling reversibility of combined organic–colloidal fouling were observed in the presence of applied hydraulic pressure on the feed side. This observation suggests that the lower fouling propensity and greater fouling reversibility in FO compared to reverse osmosis (RO), are attributable to unpressurized operating conditions in FO. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) is an emerging technology for low energy desalination. Amongst the many other factors, temperature of the draw solution (DS) and feed solution (FS) plays an important role in influencing the performance of the FO process. In this study, the influence of the temperature and the temperature difference on the performance of FO process has been studied in terms of water and solute fluxes. Temperature difference was maintained by elevating only one of the solutions (either DS or FS). The results indicate that, water flux on average increases by up to 1.2% for every degree rise in temperature from 25°C to 35°C while this rise is 2.3% from 25°C to 45°C. Providing a temperature difference by elevating only the DS also enhanced the water flux significantly, although it was lower than FO process operated at isothermal conditions. However, elevating only the temperature of FS did not significantly improve the water flux although it was higher than the FO process operated at 25°C. This has significant implications in FO process because the total mass of the DS requiring heat energy is significantly less than the total FS used. The influences of temperature in the FO process such as through changes in the thermodynamic properties of the solutions and the various concentration polarisation effects are also explained in details. [Copyright &y& Elsevier]

Abstract: Colloidal fouling behavior in forward osmosis (FO) was investigated, focusing on the role of reverse salt diffusion. Two suspensions of silica nanoparticles, with average particle diameters of 24 and 139nm, were used as model colloidal foulants. To verify the effect of reverse salt diffusion on the colloidal fouling behavior, NaCl and LaCl3 were employed as draw solutions because they exhibit different reverse diffusion rates. Our results suggest that in colloidal fouling of FO, salts diffuse from the draw to the feed solution and accumulate within the colloidal fouling layer that forms on the membrane surface. The accumulated salts result in a marked acceleration of cake-enhanced osmotic pressure (CEOP), which reduces the net osmotic driving force for permeate water flux. Fouling was not observed with the small, 24-nm particles because of the lack of substantial cake formation, but was notable for the 139-nm particles and for a feed containing a mixture of the 24 and 139nm particles. Our findings further indicate that colloidal fouling is enhanced under solution conditions (ionic strength and pH) within the colloidal cake layer that promote aggregation or destabilization of the silica particles. Colloidal fouling reversibility was also examined by varying the cross-flow velocity during the FO fouling runs. We showed that in the absence of colloidal particle destabilization/aggregation, the permeate flux during colloidal fouling in FO recovered almost completely when the cross-flow velocity was increased from 8.5 to 25.6cm/s. Our results suggest that reverse salt diffusion in FO is a key mechanism that controls colloidal fouling behavior as well as fouling reversibility. Therefore, minimization of reverse salt diffusion through the selection of proper draw solutes and optimization of FO membrane selectivity are important for minimizing colloidal fouling as well as enhancing FO operation efficiency. [Copyright &y& Elsevier]

Abstract: Fouling behaviors during forward osmosis (FO) and reverse osmosis (RO) are compared. Alginate, humic acid, and bovine serum albumin (BSA) are used as model organic foulants, and two suspensions of silica colloids of different sizes are chosen as model particulate foulants. To allow meaningful comparison of fouling behavior, identical hydrodynamic operating conditions (i.e., initial permeate flux and cross-flow velocity) and feed water chemistries (i.e., pH, ionic strength, and calcium concentration) are employed during FO and RO fouling runs. The observed flux-decline behavior in FO changed dramatically with the type of organic foulant, size of colloidal foulant, and the type of the draw solution employed to generate the osmotic driving force. Based on these experimental data and the systematic comparisons of fouling behaviors of FO and RO, we provide new insights into the mechanisms governing FO fouling. In FO, reverse diffusion of salt from the draw solution to the feed side exacerbates the cake-enhanced osmotic pressure within the fouling layer. The elevated osmotic pressure near the membrane surface on the feed side leads to a substantial drop in the net osmotic driving force and, thus, significant decline of permeate flux. Our results further suggest that the structure (i.e., thickness and compactness) of the fouling layers of FO and RO is quite different. By varying the cross-flow velocity during the organic fouling runs, we were able to examine the fouling reversibility in FO and RO. The permeate flux during organic fouling in FO recovered almost completely with increasing cross-flow velocity, while no noticeable change was observed for the RO system. Our results suggest that organic fouling in FO could be controlled effectively by optimizing the hydrodynamics in the feed stream without employing chemical cleaning. [ABSTRACT FROM AUTHOR]

An osmotic dilution process of hybrid forward osmosis (FO) and reverse osmosis (RO) was applied at pilot-scale to integrate wastewater treatment with seawater desalination in a municipal wastewater treatment plant. The aim of this study is to expand the understanding of multiple FO fouling indexes (i.e., MFI-UF and ORI) to not only obtain insight on fouling characteristics of the FO process but also optimize the operation of the osmotic dilution process. The correlation between the fouling indexes and performance of the FO membrane (i.e., transmembrane inlet pressure (TMIP), differential pressure (DP)) was first validated based on the operation data from the seven-month pilot run. MFI-UF was then selected for measuring the fouling potential according to the pretreatment process (or source water), whereas ORI was obtained for optimizing the cleaning protocol of the FO process to support the stable operation of the FO plant. The sensitivity analysis of the seasonal effect verified the correlation between MFI-UF and FO performance. The results of this study are expected to provide practical insight and technical guidelines to FO based plant engineers/operators. Image 1 • Applicability of multiple FO fouling indexes was validated at pilot scale. • Long-term performance was assessed by adopting different pretreatment strategies. • A close relationship between MFI-UF and FO ΔDP was observed. • ORI was able to predict the FO TMIP precisely. • MFI-UF and ORI can be applied as plant–assistance criteria for FO process. [ABSTRACT FROM AUTHOR]

In this study, the FO/crystallization/RO hybrid process was analyzed comprehensively, including experimentation, modeling, and energy and cost estimation, to examine and improve its feasibility to seawater desalination. A new operating strategy by heating the FO process to 45 °C was suggested, and a detailed process design was conducted. A comparative analysis with the conventional seawater reverse osmosis (SWRO) process was performed in terms of specific energy consumption (SEC) and specific water cost (SWC). The hybrid process can produce fresh water with SWC of 0.6964 $/m3, electrical SEC of 2.71 kWh/m3, and thermal SEC of 14.684 kWh/m3. Compared to the conventional SWRO process (SWC of 0.6890 $/m3 and electrical SEC of 2.674 kWh/m3), the hybrid process can produce water with comparable cost and energy consumption. An economic feasibility study that utilized the waste heat and the developed FO technology was also carried out to investigate future developments of the hybrid process. The SWC can be reduced to 0.6435 $/m3 with free waste heat energy. The permeate water quality of the hybrid process was about half that of the conventional SWRO process on molar basis. The results revealed that the FO/crystallization/RO hybrid process can be utilized as a competitive process for seawater desalination with high recovery and high water quality. Image 1 • New operation mode of FO/crystallization/RO hybrid process suggested. • Applicability of FO/crystallization/RO hybrid process experimentally confirmed. • This hybrid process confirmed as cost-competitive for seawater desalination. • Utilizing waste heat, water produced at 7% lower cost than that with SWRO. • Permeate water quality approximately half of the conventional SWRO on molar basis. [ABSTRACT FROM AUTHOR]