Search

Designing a nanofluidic membrane with high selectivity and fast ion transport property is the key towards high‐performance osmotic energy conversion. However, most of reported membranes can produce power density less than commercial benchmark (5 W/m2), due to the imbalance between ion selectivity and permeability. Here, we report a novel nanoarchitectured design of a heterogeneous membrane with an ultrathin and dense zirconium‐based UiO‐66‐NH2 metal–organic framework (MOF) layer and a highly aligned and interconnected branched alumina nanochannel membrane. The design leads to a continuous trilayered pore structure of large geometry gradient in the sequence from angstrom‐scale to nano‐scale to sub‐microscale, which enables the enhanced directional ion transport, and the angstrom‐sized (~6.6–7 Å) UiO‐66‐NH2 windows render the membrane with high ion selectivity. Consequently, the novel heterogeneous membrane can achieve a high‐performance power of ~8 W/m2 by mixing synthetic seawater and river water. The power density can be largely upgraded to an ultrahigh ~17.1 W/m2 along with ~48.5 % conversion efficiency at a 50‐fold KCl gradient. This work not only presents a new membrane design approach but also showcases the great potential of employing the zirconium‐based MOF channels as ion‐channel‐mimetic membranes for highly efficient blue energy harvesting. [ABSTRACT FROM AUTHOR]

Nanofluidic energy harvesting from salinity gradients is studied in 2D nanomaterials‐based membranes with promising performance as high ion selectivity and fast ion transport. In addition, moving forward to scalable, feasible systems requires environmentally friendly materials to make the application sustainable. Clay‐based membranes are attractive for being environmentally friendly, non‐hazardous, and easy to manipulate materials. However, achieving underwater stability for clay‐based membranes remains challenging. In this work, the synthetic clay Laponite is used to prepare clay‐based membranes with high stability and excellent performance for osmotic energy harvesting. The Laponite membranes (Lap‐membranes) are stabilized by low‐temperature annealing treatment to effectively reduce the interlayer space, achieving a continuous operation under salinity gradients. Furthermore, the Lap‐membranes conserve integrity while soaking in water for more than one month. The output power density improves from ≈4.97 W m−2 on the pristine membrane to ≈9.89 W m−2 in the membrane treated 12 h at 300 °C from a 30‐fold concentration gradient. Especially, It is found that the presence of interlayer water to be favorable for ion transport. Different mechanisms are proposed in the Lap‐membranes involved for efficient ion selectivity and the states found with varying annealing temperatures. This work demonstrates the potential application of Laponite based nanomaterials for nanofluidic energy harvesting. [ABSTRACT FROM AUTHOR]

Artificial nanofluidic networks are emerging systems for blue energy conversion that leverages surface charge‐derived permselectivity to induce voltage from diffusive ion transport under salinity difference. Here the pivotal significance of electrostatic inter‐channel couplings in multi‐nanopore membranes, which impose constraints on porosity and subsequently influence the generation of large osmotic power outputs, is illustrated. Constructive interference is observed between two 20 nm nanopores of 30 nm spacing that renders enhanced permselectivity to osmotic power output via the recovered electroneutrality. On contrary, the interference is revealed as destructive in two‐dimensional arrays causing significant deteriorations of the ion selectivity even for the nanopores sparsely distributed at an order of magnitude larger spacing than the Dukhin length. Most importantly, a scaling law is provided for deducing the maximal membrane area and porosity to avoid the selectivity loss via the inter‐pore electrostatic coupling. As the electric crosstalk is inevitable in any fluidic network, the present findings can be a useful guide to design nanoporous membranes for scalable osmotic power generations. [ABSTRACT FROM AUTHOR]

Abstract Nanofluidic energy harvesting from salinity gradients is studied in 2D nanomaterials‐based membranes with promising performance as high ion selectivity and fast ion transport. In addition, moving forward to scalable, feasible systems requires environmentally friendly materials to make the application sustainable. Clay‐based membranes are attractive for being environmentally friendly, non‐hazardous, and easy to manipulate materials. However, achieving underwater stability for clay‐based membranes remains challenging. In this work, the synthetic clay Laponite is used to prepare clay‐based membranes with high stability and excellent performance for osmotic energy harvesting. The Laponite membranes (Lap‐membranes) are stabilized by low‐temperature annealing treatment to effectively reduce the interlayer space, achieving a continuous operation under salinity gradients. Furthermore, the Lap‐membranes conserve integrity while soaking in water for more than one month. The output power density improves from ≈4.97 W m−2 on the pristine membrane to ≈9.89 W m−2 in the membrane treated 12 h at 300 °C from a 30‐fold concentration gradient. Especially, It is found that the presence of interlayer water to be favorable for ion transport. Different mechanisms are proposed in the Lap‐membranes involved for efficient ion selectivity and the states found with varying annealing temperatures. This work demonstrates the potential application of Laponite based nanomaterials for nanofluidic energy harvesting.

The scarcity of energy and water resources is a major challenge for humanity in the twenty-first century. Engineered osmosis (EO) technologies are extensively researched as a means of producing sustainable water and energy. This study focuses on the modification of substrate properties of thin film nanocomposite (TFN) membrane using aluminium oxide (Al2O3) nanoparticles and further evaluates the performance of resultant membranes for EO process. Different Al2O3 loading ranging from zero to 0.10 wt% was incorporated into the substrate and the results showed that the hydrophilicity of substrate was increased with contact angle reduced from 74.81° to 66.17° upon the Al2O3 incorporation. Furthermore, the addition of Al2O3 resulted in the formation of larger porous structure on the bottom part of substrate which reduced water transport resistance. Using the substrate modified by 0.02 wt% Al2O3, we could produce the TFN membrane that exhibited the highest water permeability (1.32 L/m2.h.bar, DI water as a feed solution at 15 bar), decent salt rejection (96.89%), low structural parameter (532.44 μm) and relatively good pressure withstandability (>25 bar). [ABSTRACT FROM AUTHOR]

Abstract Artificial nanofluidic networks are emerging systems for blue energy conversion that leverages surface charge‐derived permselectivity to induce voltage from diffusive ion transport under salinity difference. Here the pivotal significance of electrostatic inter‐channel couplings in multi‐nanopore membranes, which impose constraints on porosity and subsequently influence the generation of large osmotic power outputs, is illustrated. Constructive interference is observed between two 20 nm nanopores of 30 nm spacing that renders enhanced permselectivity to osmotic power output via the recovered electroneutrality. On contrary, the interference is revealed as destructive in two‐dimensional arrays causing significant deteriorations of the ion selectivity even for the nanopores sparsely distributed at an order of magnitude larger spacing than the Dukhin length. Most importantly, a scaling law is provided for deducing the maximal membrane area and porosity to avoid the selectivity loss via the inter‐pore electrostatic coupling. As the electric crosstalk is inevitable in any fluidic network, the present findings can be a useful guide to design nanoporous membranes for scalable osmotic power generations.

Copyright of Iraqi Journal of Chemical & Petroleum Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Clean energy is needed to sustainably power our economies and communities. Salt gradients, which are available in marine ecosystems as well as from the brine of engineered desalination systems, are a renewable source of energy. Membrane-based osmotic power processes have been proposed for converting the free energy of mixing seawater and diluted water to useful mechanical work. It has been shown that during osmosis, the applied mechanical load as well as the circulation rates of diluted feed and concentrated draw through the membrane module have a significant impact of transport dynamics, including polarization and friction. Therefore, to maximize performance of this process, it is necessary to carefully adjust these operating conditions. Using modelling and simulation, our group has previously shown that it is possible to coordinate the control of these key operating variables in order to maximize net power output. In this work, we report on our efforts to experimentally demonstrate the concept of real-time maximum power point tracking for a salt gradient osmotic power system. The transient response of a laboratory scale osmotic system is characterized, showing water permeate flux, pressure losses, and power output in response to step changes in applied pressure and to feed and draw circulation rates. A "perturb and observe" feedback algorithm and control strategy are implemented and as a result, the real-time net power output of the osmotic power system is shown to more than double relative to baseline conditions. Such real-time control strategies have broad applications to a variety of membrane processes and can be customized to track selected performance metrics. [Display omitted] • A maximum power point tracking system is designed for pressure retarded osmosis. • Flow rates and applied pressure are controlled in real-time to maximize net power. • For desalination energy recovery, net power increases >3× over baseline. • For stand alone power applications, net power increases from negative to positive. • This is the first successful experimental demonstration of MPPT for osmotic power. [ABSTRACT FROM AUTHOR]

Nature's various hierarchical structures exhibit exceptional performance in enhancing mass transport. However, how to bionic nano-hierarchical structures to enhance ion dynamics and achieve charge regulation is a significant challenge. Herein, a nano-hierarchical porous hybrid membrane inspired by nature was designed by integrating 1D metal-organic frameworks (MOFs) on the 2D MXene substrate utilizing MOF nanoparticles with tailorable positive and negative surface charges. The synergistic effects of the bioinspired nanohierarchical porous structure and surface charge interactions significantly enhance the performance and stability of the nanoconfined membrane, as corroborated by experimental characterizations and theoretical simulations. As a result, the optimized nanohierarchical porous membrane exhibits high a cation selectivity of 0.95, an outstanding power density of 35.04 W m−2, and excellent stability over one month. Synergizing enhanced mass transport and ion dynamics in nano-hierarchically structured materials with tailored charge improves osmotic power generation efficiency and benefits logic circuits with controlled charge transport. [Display omitted] • The fabrication process of MIL-53-COOH/MXene hybrid membrane is facile. • The MIL-53-COOH/MXene exhibits the exceptional cation selectivity (0.95) and a high power density (35.04 W m−2). • Leveraging the synergistic interplay between the surface negative charges and the nano-hierarchical porous structure. • The MIL-53-COOH/MXene hybrid membrane has universal applicability and notable stability. [ABSTRACT FROM AUTHOR]

• Intercalation of ZnIm provides high water stability to GO membranes. • Surface charge governed ion transport of GO-ZnIm membrane. • High cation K+ selectivity (0.74) of GO-ZnIm membrane. • High output experimental power density of ∼ 11 Wm−2 of GO-ZnIm membrane at 1000 concentration gradient. Generating electricity from seawater by utilizing nanofluidic structures is an appealing strategy for achieving zero-emission energy goals. A nanofluidic channel that is atomically small, tunable, and mechanically stable is the key to solving this problem. In this paper, for the first time, we report the construction of centimeter-sized freestanding zinc-imidazole complex (ZnIm) intercalated graphene oxide (GO) membrane (GO-ZnIm) having uniform 2D nanofluidic channels with interlayer spacing of 9 Å. The pristine GO membrane rapidly disintegrates in an aqueous medium due to membrane swelling; however, treatment with an aqueous zeolitic imidazole framework (ZIF-8) suspension, rendering ZnIm complex, provides long-term stability by restricting the excessive interlayer separation of GO sheets. From ion transport, diffusion, and variable load studies, it is observed that, besides stabilizing the GO membrane, intercalation of ZnIm significantly improves average cation selectivity (from 0.46 for GO to 0.74 for GO-ZnIm , measured up to 1000 concentration gradient) and experimental power density (from 1.7 Wm−2 for GO to 10.8 Wm−2 for GO-ZnIm , at 1000 concentration gradient). Moreover, the practical applicability of the GO-ZnIm membrane has also been investigated under artificial estuary conditions at ambient temperature, rendering an osmotic power density of 4.5 Wm−2, which is very close to the commercial benchmark of 5 Wm−2. A mechanically robust and flexible membrane made up of cost-effective components (GO and ZnIm), able to deliver an osmotic power density close to commercial benchmark at ambient temperature is the main highlight of the present GO-ZnIm membrane, which can be a promising candidate for applications such as separation, desalination, and blue energy harvesting. [ABSTRACT FROM AUTHOR]

In recent years, the utilization of the selective ion transport through porous membranes for osmotic power generation (blue energy) has received a lot of attention. The principal of power generation using the porous membranes is same as that of conventional reverse electrodialysis (RED), but nonporous ion exchange membranes are conventionally used for RED. The ion transport mechanisms through the porous and nonporous membranes are considerably different. Unlike the conventional nonporous membranes, the ion transport through the porous membranes is largely dictated by the principles of nanofluidics. This owes to the fact that the osmotic power generation via selective ion transport through porous membranes is often referred to as nanofluidic reverse electrodialysis (NRED) or nanopore-based power generation (NPG). While RED using nonporous membranes has already been implemented on a pilot-plant scale, the progress of NRED/NPG has so far been limited in the development of small-scale, novel, porous membrane materials. The aim of this review is to provide an overview of the membrane design concepts of nanofluidic porous membranes for NPG/NRED. A brief description of material design concepts of conventional nonporous membranes for RED is provided as well.

Nanofluidic channels in a membrane represent a promising avenue for harnessing blue energy from salinity gradients, relying on permselectivity as a pivotal characteristic crucial for inducing electricity through diffusive ion transport. Surface charge emerges as a central player in the osmotic energy conversion process, emphasizing the critical significance of a judicious selection of membrane materials to achieve optimal ion permeability and selectivity within specific channel dimensions. Alternatively, here we report a field-effect approach for in situ manipulation of the ion selectivity in a nanopore. Application of voltage to a surround-gate electrode allows precise adjustment of the surface charge density at the pore wall. Leveraging the gating control, we demonstrate permselectivity turnover to enhanced cation selective transport in multipore membranes, resulting in a 6-fold increase in the energy conversion efficiency with a power density of 15 W/m 2 under a salinity gradient. These findings not only advance our fundamental understanding of ion transport in nanochannels but also provide a scalable and efficient strategy for nanoporous membrane osmotic power generation.

Atomically thin two-dimensional (2D) materials have emerged as promising candidates for efficient energy harvesting from ionic gradients. However, the exploration of robust 2D atomically thin nanopore membranes, which hold sufficient ionic selectivity and high ion permeability, remains challenging. Here, the single-layer hexagonal boron nitride (hBN) nanopores are demonstrated as various high-performance ion-gradient nanopower harvesters. Benefiting from the ultrathin atomic thickness and large surface charge (also a large Dukhin number), the hBN nanopore can realize fast proton transport while maintaining excellent cation selectivity even in highly acidic environments. Therefore, a single hBN nanopore achieves the pure osmosis-driven proton-gradient power up to ≈3 nW under 1000-fold ionic gradient. In addition, the robustness of hBN membranes in extreme pH conditions allows the ionic gradient power generation from acid-base neutralization. Utilizing 1 m HCl/KOH, the generated power can be promoted to an extraordinarily high level of ≈4.5 nW, over one magnitude higher than all existing ionic gradient power generators. The synergistic effects of ultrathin thickness, large surface charge, and excellent chemical inertness of 2D single-layer hBN render it a promising membrane candidate for harvesting ionic gradient powers, even under extreme pH conditions., (© 2023 Wiley‐VCH GmbH.)

The scarcity of energy and water resources is a major challenge for humanity in the twenty-first century. Engineered osmosis (EO) technologies are extensively researched as a means of producing sustainable water and energy. This study focuses on the modification of substrate properties of thin film nanocomposite (TFN) membrane using aluminium oxide (Al 2 O 3 ) nanoparticles and further evaluates the performance of resultant membranes for EO process. Different Al 2 O 3 loading ranging from zero to 0.10 wt% was incorporated into the substrate and the results showed that the hydrophilicity of substrate was increased with contact angle reduced from 74.81° to 66.17° upon the Al 2 O 3 incorporation. Furthermore, the addition of Al 2 O 3 resulted in the formation of larger porous structure on the bottom part of substrate which reduced water transport resistance. Using the substrate modified by 0.02 wt% Al 2 O 3 , we could produce the TFN membrane that exhibited the highest water permeability (1.32 L/m 2 .h.bar, DI water as a feed solution at 15 bar), decent salt rejection (96.89%), low structural parameter (532.44 μm) and relatively good pressure withstandability (>25 bar).

The osmotic energy generated by the salinity gradient between seawater and river water is a potential blue energy that can be harnessed to alleviate the current energy crisis but without causing environmental pollution. Two dimensional (2D) MXene nano sheets can be horizontally assembled into laminar membranes to create nanochannels enabling the ionic selective transport and thus to capture the osmotic energy. However, the ions have to transport through the maze-like tortuous laminar channels sourced from the interspaces between two neighboring nanosheets, which lead to super-high transport resistance and low power density, hindering their wide applications. Enlightened by the water and mineral ions transport in trees, here, a bioinspired MXene-based membrane with aligned and ordered vertical channels is developed for efficient osmotic power generation from salinity gradient. The peak power density of the electrical devices composed of such maze-breaking membranes could be achieved up to 372 W m−2, which is at least one order of magnitude higher than conventionally horizontal membranes reported in the literature. The high-power generation efficiency was attributed to the shortened ionic transport path (by breaking the maze). Moreover, the membrane possesses a high antifouling performance as well as long-term stability, possibly due to the strong combination of MXene and GO via the hydrogen bonds and cross-linking in preparation. This work reports a new and high-performance MXene-based membrane not only for osmotic energy conversion but also for other practical separations. [Display omitted] • Based on the maze-breaking strategy, the vertical aligned bioinspired membrane is designed. • The ion transport resistance is obviously reduced in vertical MXene-based membrane. • The maximum osmotic power density can achieve about 372 W m−2. • The high anti-pollution performance highlights the advance of practical application. [ABSTRACT FROM AUTHOR]

Salinity gradient energy, as a type of blue energy, is a promising sustainable energy source. Its energy conversion efficiency is significantly determined by the selective membranes. Recently, nanofluidic membrane made by two-dimensional (2D) nanomaterials (e.g., graphene) with densely packed nanochannels has been considered as a high-efficient membrane in the osmotic power generation research field. Herein, the graphene oxide-cellulose acetate (GO–CA) heterogeneous membrane was assembled by combining a porous CA membrane and a layered GO membrane; the combination of 2D nanochannels and 3D porous structures make it show high surface-charge-governed property and excellent ion transport stability, resulting in an efficient osmotic power harvesting. A power density of about 0.13 W/m2 is achieved for the sea–river mimicking system and up to 0.55 W/m2 at a 500-fold salinity gradient. With different functions, the CA and GO membranes served as ion storage layer and ion selection layer, respectively. The GO–CA heterogeneous membrane open a promising avenue for fabrication of porous and layered platform for wide potential applications, such as sustainable power generation, water purification, and seawater desalination.

A membrane-based technique for production of pressure-retarded osmosis (PRO) is salinity gradient energy. This sustainable energy is formed by combining salt and fresh waters. The membrane of the PRO process has a significant effect on controlling the salinity gradient energy or osmotic energy generation. Membrane fouling and operating conditions such as temperature have an extreme influence on the efficiency of the PRO processes because of their roles in salt and water transportation through the PRO membranes. In this study, the temperature impact on the power density and the fouling of two industrial semi-permeable membranes in the PRO system was investigated using river and synthetic sea water. Based on the findings, the power densities were 17.1 and 14.2 W/m2 at 5 °C for flat sheet and hollow fiber membranes, respectively. This is the first time that research indicates that power density at low temperature is feasible for generating electricity using PRO processes. These results can be promising for regions with high PRO potential that experience low temperatures most of the year.

Reverse electrodialysis (RED) using nanofluidic ion-selective membrane may convert the salinity difference between seawater and river water into electricity. However, heterogeneous modification reactions of cellulose commonly leads to the inhomogeneous distribution of surface charges, thereby hampering the improvement of cellulose-based nanofluidic membranes for energy conversion. Herein, RED devices based on cellulose nanofibers (CNF) membranes with opposite charge characteristics were developed for the generation of salinity gradient power. Anion-CNF membrane (A-CNF) with varying negative charge densities was synthesized using 2,2,6,6-Tetramethylpiperidine 1-oxy radical (TEMPO) oxidation modification, whereas cation-CNF membrane (C-CNF) was prepared through etherification. By mixing artificial seawater and river water, the output power density of CNF RED device is up to 2.87 W m -2 . The output voltage of 30 RED units connected in series may reach up to 3.11 V, which can be used to directly power tiny electronic devices viz. LED lamp, calculator, etc. The results of this work provide a feasible possibility for widespread application of ion exchange membranes for salinity gradient energy harvesting., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Pressure retarded osmosis (PRO) is a novel renewable energy technology that generates electricity from two water sources. Due to the osmotic pressure difference, freshwater permeates across a membrane to the other side, where the high-pressure seawater flows and drives a turbine to generate power. Many mathematic models have been proposed to evaluate the performance of a PRO. However, it was found that most performance of the PRO that have been reported were performance by using freshwater with limited supply (batch) in the model. It is not accurate as, in practice, the supply of freshwater occurs in a continuous manner. In this work, the influence of batch and continuous supply of fresh water on the performance of PRO was demonstrated. The effect of flow direction, i.e., concurrent and counter-current flows, was also examined. The model simulation was performed by using MATLLAB program, and the performance of PRO is expressed in terms of average power density. The results revealed that the batch and continuous supplies of freshwater had a strong impact on the performance of the PRO. However, the performance of concurrent and counter-current flow were not significantly different.

• An exergy analysis of a reverse electrodialysis heat engine is presented for the first time. • Irreversibility sources of the system are identified and quantified. • The effect of the main operating variables on the exergy efficiency is assessed. • High-performing membranes in reverse electrodialysis dramatically improve the overall performance. • A maximum exergy efficiency of 24% has been reached. The increasing worldwide energy demand is rising the interest on alternative power production technologies based on renewable and emission-free energy sources. In this regard, the closed-loop reverse electrodialysis heat engine is a promising technology with the potential to convert low-grade heat into electric power. The reverse electrodialysis technology has been under investigation in the last years to explore the real potentials for energy generation from natural and artificial solutions, and recent works have been addressing also the potential of its coupling with regeneration strategies, looking at medium and large energy supply purposes. In this work, for the first time, a comprehensive exergy analysis at component level is applied to a reverse electrodialysis heat engine with multi-effect distillation in order to determine the real capability of the waste heat to power conversion, identifying and quantifying the sources of exergy destruction. In particular, sensitivity analyses have been performed to assess the influence of the main operating conditions (i.e. solutions concentration and velocity) and design features (aspect ratio of the pile), characterizing the most advantageous scenarios and including the effect of new generations of membranes. Results show that the multi-effect distillation unit is the main source of exergy destruction. Also, using high-performing membranes, inlet solutions concentration and velocity of 4.5–0.01 mol/L and 0.2–0.36 cm/s, respectively, a global exergy efficiency of 24% is reached for the system, proving the high potential of this technology to sustainably convert waste heat into power. [ABSTRACT FROM AUTHOR]

Salinity gradients are a non-conventional source of renewable energy based on the recovery of the Gibbs free energy related to the mixing of solutions at different concentrations. Reverse Electrodialysis is a promising and innovative technology able to convert this energy directly into electric current. The worldwide availability of salinity gradients is limited to those locations where water bodies at different salinity levels are present. The present work analyses a number of different scenarios worldwide, in locations where salinity gradients are naturally available or generated by anthropogenic activities. A techno-economic model of the Reverse Electrodialysis process is presented. The model is used to evaluate the energy that can be harvested in each real scenario using a reverse electrodialysis plant and relevant results are reported in terms of power densities and energy yields. Finally, an economic analysis based on the estimation of the Levelized Cost Of Electricity (LCOE) for each scenario is presented, and perspective considerations are reported. Results suggest that competitive values of LCOE may be achieved in some scenarios. Image 1 • A techno-economic assessment of RED process is presented. • Site-specific analysis is carried out, considering different scenarios worldwide. • The effect of different stack sizes and membrane properties on RED performances is assessed. • For each scenario, LCOE values are evaluated considering different conditions. • Future low-cost improved membranes can lead to a competitive LCOE lower than 0.10 €/kWh. [ABSTRACT FROM AUTHOR]

In recent years, pressure retarded osmosis (PRO) has drawn considerable attention due to its feasibility of harvesting clean and sustainable osmotic power through a membrane process. When municipal wastewater is fed into this process, fouling in the porous substrate of the PRO membrane is the major concern since it can hinder the membrane performance tremendously and lower the power generation. In this work, sulfonated hyperbranched polyglycerol (SHPG) polymers with a dendritic architecture have been molecularly designed and then grafted onto the surface of polydopamine (PDA) coated poly(ethersulfone) (PES) hollow fiber membranes. Comparing to the pristine PES membranes, the SHPG modified PRO membranes show significantly improved resistance to protein adhesion and bacterial attachment due to the high wettability of their ionic polymer brushes. In PRO tests under different hydraulic pressures, the SHPG-grafted membranes show a lower flux reduction and a higher flux recovery rate of 94% vs. 87% in comparison with the pristine PES membranes. Therefore, the osmotic power generation can be significantly sustained by modifying the PRO membranes with SHPG polymers. This work may provide a versatile approach and useful insights for the design of membranes with antifouling properties in the molecular level. [ABSTRACT FROM AUTHOR]

Global energy consumption has been highly dependent on fossil fuels which cause severe climate change and, therefore, the exploration of new technologies to produce effective renewable energy plays an important role in the world. Pressure-retarded osmosis (PRO) is one of the promising candidates to reduce the reliance on fossil fuels by harnessing energy from the salinity gradient between seawater and fresh water. In PRO, water is transported though a semi-permeable membrane from a low-concentrated feed solution to a high-concentrated draw solution. The increased volumetric water flow then runs a hydro-turbine to generate power. PRO technology has rapidly improved in recent years; however, the commercial-scale PRO plant is yet to be developed. In this context, recent developments on the PRO process are reviewed in terms of mathematical models, membrane modules, process designs, numerical works, and fouling and cleaning. In addition, the research requirements to accelerate PRO commercialization are discussed. It is expected that this article can help comprehensively understand the PRO process and thereby provide essential information to activate further research and development.

In the pressure-retarded osmosis (PRO) process, the power density was dramatically influenced by the operating conditions including the applied hydraulic pressure difference (ΔP), the ratio of feed to draw flow rate (VF /VD), and the ratio of draw flow rate to membrane area (VD/Sm). A theoretical model considering the non-ideal effects of concentration polarization, reverse salt flux, and pressure losses in draw side through the membrane module was developed to predict the water flux of the PRO, from which the power density and specific energy were predicted. The optimization of operating conditions was conducted by the theoretical model to meet the PRO process’ predefined economic viability of about 5.00 W m–2 for the power density. Experimental verification of the theoretical model was carried out when the applied pressure is <10 bar, which is the maximum pressure resistance of the forward osmosis membrane in the paper. The resulted optimal operating conditions were ΔP of 17 bar, VF /VD of 0.8, and VD/Sm of 47 L min–1 m–2 using seawater–river system, under which the theoretical power density was 5.13 W m–2, higher than the benchmark of 5.00 W m–2. The error between the experimental and theoretical results was <5%, which demonstrated the theoretical model is reliable. [ABSTRACT FROM AUTHOR]

New Mexico oil production generates a significant amount of produced water annually with total dissolved solids (TDS) up to 40%. The intention of this study was to investigate rarely examined power potential of highly saline produced water under pressure-retarded osmosis (PRO). Synthetic brines with TDS up to 10% were used to establish the PRO salinity gradients for model verification. Peak power density was shown to increase with the salinity gradient and data were found to be in good agreement with the model simulations. Internal concentration polarization induced by high membrane structure parameter and salt permeability was the main limiting factor for further power density improvement. Simulations suggested that significant increase of the peak power density from 1.4 to 7.3 W/m2 could be realized for a synthetic produced water pair of 10% and 1.3% TDS if the membrane properties were improved. For oilfield-produced water obtained from a waterflooding operation, an average power density of 3.2 W/m2 was observed for a similar salinity gradient. The deviation was attributed to the additional contribution of osmotic pressure from the organic acids in the oilfield-produced water. Based on observed power density, gross PRO output for the oilfield-produced water was estimated to be ∼630 W for PRO flow rates of 400 m3/day, representing a minor portion of energy consumption at the waterflooding operation. To increase the PRO energy output substantially, significantly higher flow rates of produced water are needed. [ABSTRACT FROM AUTHOR]

One of the main challenges for generating osmotic power by using PRO technology is the membrane fouling which reduces the permeate flux and consequently increases the cost and decreases the osmotic power generation. In this research, different feed waters with various qualities were used to investigate the effect of fouling on a commercial membrane in PRO mode in continuous conditions. Also, the fouling mechanisms were investigated in order to study the cleaning of the membrane in PRO mode in the future research. In addition, four classic fouling models such as complete blocking model (CBM), intermediate blocking model (IBM), standard blocking model (SBM) and cake filtration model (CFM) were used. Cake enhanced osmotic pressure as a new mechanism for osmotically driven membranes was studied as well. According to the results, the fouling rate when the draw solution was synthetic salt water followed the order of: untreated river water > multimedia sand filter > microfiltration > ultrafiltration effluents. The fouling rate in ultrafiltration and microfiltration effluents using sea water occurred faster compared to the results for untreated synthetic salt water. Complete fouling (permeate flux was negligible) occurred after 580 h using feed water from ultrafiltration unit. It was observed that cake filtration and cake enhanced osmotic pressure were the main fouling mechanisms that governed the membrane fouling. These models could describe the membrane fouling in PRO processes. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is a membrane based technology used for generation of osmotic power as a sustainable energy. The main challenge of PRO technology is the membrane fouling which reduces the permeate flux and osmotic power generation which consequently increases the cost. In this research, different quality feed waters were used to identify the main foulants on the surface of a commercial semi permeable membrane in the PRO process. In addition, two cleaning methods were investigated to determine the desirable cleaning methods. According to the results, the main inorganic foulants using synthetic salt water were iron, aluminum, calcium, sodium, and silica and when sea water was used as the draw solution, the same foulants, in addition to magnesium and potassium were detected. The organic foulants were humic substances, polysaccharides and proteins for both synthetic salt and sea water draw solutions. According to the results, the water flux recoveries were 98.4%, 98%, 97.5%, 97.3%, and 97.2% after each sequential chemical cleaning, respectively. Therefore, the most successful cleaning method was with acidic and basic cleaners. This research indicates that chemical cleaning can decrease the membrane fouling in PRO processes and consequently improve the osmotic power generation. [ABSTRACT FROM AUTHOR]

In this study, three pressure retarded osmosis (PRO) power plants are proposed to be built on the Red Sea⁻Dead Sea (RSDS) water conveyance project, to generate power from the salinity gradient between two water streams at different salt concentrations. The first two proposed plants are to be built after sea water reverse osmosis (SWRO) desalination plants, where Red Sea water and the rejected brine from SWRO plants are used as feed and draw solutions, respectively. In the third proposed plant, Red Sea water and Dead Sea water will be used. Results showed that the three proposed plants are technically feasible while the third plant is the only one that is economically feasible with a 134.5 MW capacity and a 0.056 $/KWh levelized cost of electricity (LCE). The power generated from the third PRO power plant accounts for about 24.7% of the power needed for the RSDS project that can be used to power SWRO-2 in order to reduce the electricity consumption by 49.3%. If the generated power from the proposed PRO plant is sold to the Jordanian national electricity grid at the current selling price in accordance with Jordanian prices of electricity, a saving of about 21.2% can be attained. It is found that using the power generated by the current proposed plants for desalination project purposes will significantly reduce the price of desalinated water produced from SWRO desalination plants.

Pressure-retarded osmosis (PRO) is a method for converting salinity gradients to power by allowing water to flow through a semi-permeable membrane against an applied hydraulic pressure. PRO already has a long history, starting from the middle of the last century, and has rapidly improved in recent years. In this paper, we present a historical development of PRO since its inception: the development of this renewable energy process has gone through several stages, depending on technological developments, worldwide energy demands, and environmental concerns. The technological progress of the process is also studied, as well as its cost viability and environmental impact. Finally, some ideas to further develop the PRO process and mitigate its detrimental effects are discussed. [ABSTRACT FROM PUBLISHER]

Internal concentration polarization (ICP) and severe irreversible fouling occurring within the porous and tortuous substrates of the forward osmosis (FO) and pressure retarded osmosis (PRO) membranes have significantly hidden their applications for water purification and osmotic power generation. This study experimentally demonstrates that designing a double-skin structure in FO and PRO membranes can effectively control ICP and their fouling propensity. Thin-film composite (TFC) hollow fiber membranes consist of an inner polyamide selective skin and an outer polyamide sealing layer were successfully fabricated by double interfacial polymerizations on a tailored polyethersulfone (PES) fiber substrate (termed as d TFC-PES). Due to the outstanding rejection of the outer polyamide sealing layer, the penetration of inorganic salts and foulants into the substrate is sufficiently blocked. As a result, not only ICP and fouling inside the membrane are effectively minimized, but also sustainable FO and PRO performances are achieved. By using real wastewater contains multiple inorganic salts and organic foulants as the feed, the d TFC-PES membrane shows a quite low flux decline of 29% in FO operations under the PRO mode at an ultrahigh feed recovery of 80%. Under PRO tests for power generation, the membrane power density slightly drops to 90.8% of the initial value after a 12-h test at Δ P =15 bar. In addition, since foulants are primarily accumulated on the surface of the polyamide sealing layer, physically flushing the fouled membrane surface by either freshwater or commercial cleaner Genesol 704 can efficiently restore the water flux back to its initial level with a recovery rate of 87% or 98%, respectively. This study may offer useful insights and meaningful strategies for the development of effective antifouling FO and PRO membranes. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is a promising technology to harvest the renewable osmotic energy from salinity gradients. There are great progresses in the fabrication of PRO membranes in the last decade. Thin-film composite (TFC) hollow fibers have been widely studied and demonstrated superior performance. However, the lack of effective TFC hollow fiber modules hinders the commercialization of the PRO technology. Knowledge and experiences to fabricate TFC hollow fiber modules remain limited in the open literature. In this study, we aim to reveal the engineering and science on how to fabricate TFC hollow fiber modules including the formation of inner-selective polyamide layers and the repair of leakages. TFC-PES hollow fiber modules with 30% and 50% packing densities have been successfully fabricated, showing peak power densities of 20.0 W/m 2 and 19.4 W/m 2 , respectively, at 20 bar using 1 M NaCl solution and DI water as feeds. The modules may be damaged during handling and high pressure testing. The repaired modules have a power density of 18.2 W/m 2 , 91% of the power densities of the undamaged ones. This study would make up the gap between TFC membrane fabrication and TFC membrane module fabrication in the membrane industry. [ABSTRACT FROM AUTHOR]

Fouling on pressure-retarded osmosis (PRO) membranes leads to severe declines in water flux and power density because their porous substrates are facing the wastewater feed. Thus, inorganics, organics and microorganisms in the wastewater are prone to depositing on the substrate surface and even in its pores. In order to reduce the fouling propensity, coating the substrate surface of PRO membranes with zwitterionic materials proves to be an effective way. In this work, 2-methacryloyloxyethylphosphorylcholine (MPC), is modified and grafted onto the polydopamine (PDA) coated poly (ether sulfone) (PES) hollow fiber substrate. Both the synthesis and surface coating of MPC are easy and facile to be scaled up. Compared with the pristine PES and PES-PDA substrates, the MPC modified substrate (PES-PDA-MPC) exhibits high resistance to protein adsorption as well as bacteria adhesion. By using a state-of-the-art thin-film composite poly (ether sulfone) (TFC-PES) hollow fiber membrane as the control for power generation, the power density of the TFC-PES-PDA-MPC membrane can achieve as high as 7.7 W/m 2 while the unmodified one has only 6.0 W/m 2 after 3 h's PRO tests. In conclusion, the osmotic power generation of PRO membranes can be significantly sustained by modifying the membrane surface with zwitterions. [ABSTRACT FROM AUTHOR]