Pressure Retarded Osmosis Research Articles

Limiting power density in pressure-retarded osmosis: Observation and implications

Pressure-retarded osmosis (PRO) shows promise for mitigating energy and environmental concerns associated with seawater reverse osmosis (RO) desalination. A systematic investigation of PRO membrane fouling and limiting flux was conducted for the RO-PRO scenario, where increasingly complex feed and draw solutions were used to represent treated wastewater and seawater RO brine, respectively. Four membranes were tested for water flux and power density. When there were no foulants in the feed solution, the membranes had distinctly different water flux and power density values. When there were foulants in the feed and draw solution, all membranes converged to similar water flux and power density values regardless of membrane transport parameters. For the first time, this study identified limiting water flux for multiple membranes in PRO and also, a limiting power density. To increase water flux and power density in PRO, it was suggested to first focus efforts on mitigating fouling on the feed side (support layer) of the membrane. If that can be done, then improvement of membrane transport parameters would be important for increasing limiting water flux and power density.

Integration of pressure retarded osmosis in the solar ponds for desalination and photo-assisted chloralkali processes: Energy and exergy analysis

The proposed system uses the thermal energy storage characteristic of the solar pond to power a multi-effect desalination (MED) process with a total fresh water production of approximately 14,000 m3 annually. Pressure retarded osmosis (PRO) alongside photo-assisted chloralkali reactor are employed to utilize the brine rejected from the desalination process. The inclusion of PRO is proposed to take advantage of the salinity difference that occurs as a result of the preparation of the solar pond and desalination process. The quest for zero salt discharge in the proposed energy system configuration is undertaken through the introduction of a photo-assisted chloralkali reactor, which is conducted utilizing the power generated from PRO, and solar pond storage arrangement. This solar pond and desalination coupling system will achieve independence from conventional energy sources, which will lead to a significant contribution to the reduction of greenhouse gas emissions caused by fossil-fuel driven desalination. At solar irradiation of 600 W/m2, the overall energy and exergy efficiencies can reach 16.4% and 1.4%, respectively. The annual average overall energy efficiency of 11.4% is achieved utilizing the integrated system, whereas the average overall exergy efficiency is about 0.9%. Parametric studies are performed to examine the impacts of ambient conditions, irradiance, solar pond geometry, brine salinity, and the total number of MED effects on the performance of the overall integrated system. In addition to the sensitivity analysis, the potential to improve overall energy and exergy efficiencies and fresh water production of the proposed system is demonstrated.

Antifouling Double-Skinned Forward Osmosis Membranes by Constructing Zwitterionic Brush-Decorated MWCNT Ultrathin Films.

Pressure retarded osmosis (PRO) process is hindered by severe fouling occurring within the porous support of the forward osmosis (FO) membranes. We designed a novel double-skinned FO membrane containing a polyamide salt-rejecting layer and a zwitterionic brush-decorated, multiwalled carbon nanotube (MWCNT/PSBMA) foulant-resisting layer on the back side. Our results demonstrated that the coating of the MWCNT/PSBMA layer on the porous polyketone (PK) support imparted enhanced hydrophilicity and smaller membrane pore size, thereby providing excellent resistance toward both protein adhesion and bacterial adsorption. We also further evaluated this resultant double-skinned membrane (i.e., TFC-MWCNT/PSBMA) in dynamic PRO fouling experiments using protein and alginate as model organic foulants. Compared to the pristine TFC-PK and hydrophobic TFC-MWCNT membranes, the TFC-MWCNT/PSBMA membrane exhibited not only the lowest water flux decline but also the highest water flux recovery after simple physical flushing. These results shed light on fabrication of antifouling PRO membranes for water purification purposes.

Thin-film composite hollow fiber membranes incorporated with graphene oxide in polyethersulfone support layers for enhanced osmotic power density

This study focused on the development of pressure retarded osmosis (PRO) thin film composite (TFC) membranes for enhanced osmotic power using hollow fiber polyethersulfone (PES) support structure modified by incorporating hydrophilic graphene oxide (GO) nanosheets. The GO loadings in the hollow fiber substrates were varied to improve water flux performances without compromising the mechanical strength. GO embedded (≤0.2 wt%) PES hollow fiber supports revealed noticeable improvements in pure water permeability, improved structural morphologies, as well as the hydrophilicity within the support layer, without deteriorating the mechanical properties. The GO (0.2 wt%)-incorporated TFC-PRO membrane appeared to have an initial PRO flux (without any applied pressure) of 43.74 L m−2 h−1, lower specific reverse salt flux of 0.04 g L−1 and structural parameter (S) of 522 μm, significantly better than the control membrane. The maximum power density of 14.6 W m−2 was achieved at an operating pressure of 16.5 bar under the condition of DI water and 1 M NaCl as feed and draw solutions, respectively. The results obtained in this study indicate that modification of PRO hollow fiber support layer by incorporating nanoparticles such as GO nanosheet can be a useful tool to improve the PRO performance.

Fabrication and characterization of zeolitic imidazolate framework-embedded cellulose acetate membranes for osmotically driven membrane process

Zeolitic imidazolate framework-302 (ZIF-302)-embedded cellulose acetate (CA) membranes for osmotic driven membrane process (ODMPs) were fabricated using the phase inversion method. We investigated the effects of different fractions of ZIF-302 in the CA membrane to understand their influence on ODMPs performance. Osmotic water transport was evaluated using different draw solution concentrations to investigate the effects of ZIF-302 contents on the performance parameters. CA/ZIF-302 membranes showed fouling resistance to sodium alginate by a decreased water flux decline and increased recovery ratio in the pressure retarded osmosis (PRO) mode. Results show that the hydrothermally stable ZIF-302-embedded CA/ZIF-302 composite membrane is expected to be durable in water and alginate-fouling conditions.

Investigation of the reduced specific energy consumption of the RO-PRO hybrid system based on temperature-enhanced pressure retarded osmosis

Reverse osmosis (RO) has been widely used as a dominant desalination technology to produce fresh water from seawater (SW), but still consumes huge energy. To reduce the energy consumption of RO, pressure retarded osmosis (PRO) has been developed to extract osmotic energy from RO brine. In this study, the PRO process is optimized for efficient energy recovery from RO brine via one system/module-level mathematic model in RO-PRO hybrid system. The system-level model illustrates that the specific energy consumption (SEC) of the hybrid system can be significantly reduced when achieving a high permeate flow under high operating pressure in PRO. However, the specific PRO membrane configuration has to sacrifice a high permeate flow under high operating pressure. The module-level model finds that the increase of PRO operating temperature facilitates to achieve a high permeate flow under a high optimal operating pressure. Furthermore, results present that the SEC at a kiloton-scale SWRO desalination capacity can be reduced by 14.41% (0.6 M NaCl as a draw solution) and 17.93% (1.2 M NaCl as a draw solution) when the PRO operating temperature increases from 25 °C to 50 °C, confirming the great potential of temperature-enhanced PRO to further reduce the SEC of seawater desalination.

Development and performance assessment of a new integrated solar, wind, and osmotic power system for multigeneration, based on thermodynamic principles

This study analyzes a new renewable energy-based multigeneration system, in which the energy sources are efficiently utilized to generate several useful commodities such as hydrogen, oxygen, desalted water, and refrigeration along with electricity. Osmotic power from desalination brine solution is harvested to contribute to the electricity generation and to reduce the environmental impact of brine. The system units are concentrated photovoltaics/thermal (CPVT), wind turbines, thermal energy storage (TES), hydrogen electrolyzer, hydrogen fuel cell, multistage flash (MSF) distillation, vapor compression refrigeration (VCR) cycle, and pressure retarded osmosis (PRO). The energetic and exergetic performance of the overall system, as well as the system units, are calculated based on the first and second law of thermodynamics. Further, a comprehensive parametric study is conducted to investigate the effect of varying environmental and operational conditions, and the input parameters on the production rate, exergy destruction rate and efficiencies. For maintaining the high efficiency of CPV operation, the heat generated on photovoltaic (PV) cells is dissipated by an effective cooling system. This heat is then stored in the TES to be further utilized in desalination. The TES is used for eliminating energy fluctuations in the system and for a continuous operation by storing the energy for the time, when energy from the sun is not available. The electricity from CPV and wind power is used in the VCR cycle and hydrogen electrolysis. The fuel cell can be operated during the time of peak electricity demand. After performing thermodynamic analysis over the system, the overall energy and exergy efficiencies are determined as 73.3% and 30.6%, respectively. The exergy destruction rates of the components are specified. In brief, generation of multiple commodities is assured based on a clean operation by a novel integration of multiple clean energy sources in one system.

Optimization of Pressure-Retarded Osmosis with Hollow-Fiber Membrane Modules by Numerical Simulation

We optimized the operating conditions for maximizing power production by pressure-retarded osmosis using seawater as the draw solution and river (pure) water as the feed solution using a simulation...

Modeling and simulation of the dual stage pressure retarded osmosis systems

Utilization of renewable energy sources, as an approach to reduce Greenhouse Gas (GHG) Emissions, has been globally popular in the last few decades. Among renewable energy sources, pressure retarded Osmosis (PRO) has been scrutinized by scientists since the mid-70’s. However, even today, the existing PRO systems can only marginally meet the generally approved criterion of 5 W/m2 power density, a threshold for an economically feasible river-sea PRO system. As an approach to increase the performance of PRO systems, multi-staging of PRO modules is investigated in this paper.For this purpose, a number of models for scaled up dual stage PRO power plants with different configurations and target functions are presented and compared to a single stage system with the same membrane area. These models consider the pressure and flow drop as well as the salinity change along the membrane. The results indicate that overall performance of the system could be improved by up to 8% with a dual stage PRO in the case of specific energy. Finally, a thermodynamic analysis addresses the sources for irreversible losses, and the contribution from each source.

Nanopore Functionalized by Highly Charged Hydrogels for Osmotic Energy Harvesting.

The salinity gradient between brine and fresh water is an abundant source of power which can be harvested by two major membrane methods: pressure-retarded osmosis and reversed electrodialysis. Nowadays, the latter technology is close to real application, but it still suffers from low power yield. Low membrane selectivity and complex membrane fabrication are the main limiting factors. To improve that, we design a couple of ion-selective membranes based on the track-etched polymer nanopore functionalized by highly charged hydrogels. Two nanopore geometries are compared (cylindrical and conical shape) to generate osmotic energy with gel functions and more importantly can be scaled up. Experiments from the single nanopore and multipore membrane to stacked membranes show complete characterization from ionic transportation to energy generation and a clear relationship from the single pore to stacked membranes. In the actual experiment conditions, a power density of 0.37 W m-2 at pH 7 was achieved. By improving ionic tracks and reducing intermembrane distances, it can be a good candidate for industrial applications.

Tailoring the porous structure of hollow fiber membranes for osmotic power generation applications via thermally assisted nonsolvent induced phase separation

For osmotic power generation using the pressure retarded osmosis (PRO) process, mechanically robust membranes with high osmotic water flux are needed to obtain high power density from a given osmotic pressure difference. Particularly in the case of support-free hollow fiber membranes (HFMs), the pressure tolerance is a critical factor in maximizing power density when operating at high applied pressure with concentrated brine. Here, mechanically robust integrally-skinned asymmetric (ISA) HFMs were developed by combining the nonsolvent induced phase separation (NIPS) with the quenching, into a facile approach called the thermally assisted NIPS (T-NIPS) method, to tailor the membrane structure for PRO applications. The prepared T-NIPS membranes exhibited two distinct layers: a dense ISA outer layer and an isoporous inner layer. Compared to conventional NIPS HFMs, the T-NIPS HFMs showed much higher power density and collapse pressure, up to 5.5 W/m2 and 18 bar, respectively. The effect of pore forming agents on the membrane structure during the T-NIPS process, and on PRO performance, were studied. In addition, the power density and the pressure tolerance were further enhanced by optimizing the membrane dimensions and structure of the T-NIPS HFMs.

Melamine-based covalent organic framework-incorporated thin film nanocomposite membrane for enhanced osmotic power generation

A melamine-based covalent organic framework (COF) nanomaterial, Schiff base network-1 (SNW-1), was incorporated into the polyamide layer of a novel thin film nanocomposite (TFN) pressure retarded osmosis (PRO) membrane. The deposition of SNW-1 was made on an open mesh fabric-reinforced polyamide-imide (PAI) support substrate through interfacial polymerization (IP). SNW-1 loading influence on the water permeability and osmotic power density during PRO operation was investigated. The porous and highly hydrophilic SNW-1 nanomaterial facilitated the flow of water molecules across the membranes, while maintaining satisfactory salt rejection ability of the polyamide selective layer. The membranes exhibited significantly enhanced surface hydrophilicity, water permeability, and power density. The mode of incorporation of SNW-1 during IP was also investigated and it was observed that the secondary amine groups of SNW-1 react with the carbonyl groups of 1,3,5-benzenetricarbonyl trichloride, the acyl halide precursor in polyamide formation; thus, SNW-1 was incorporated through the amine precursor, 1,3-phenylenediamine. Testing with 1.0 M NaCl as the draw solution, the TFN membrane with a loading of 0.02 wt% SNW-1 exhibited the highest water flux of 42.5 Lm−2 h−1 and power density of 12.1 Wm−2, while withstanding hydraulic pressure over 24 bar. This study suggests that COF-incorporation can be a promising method in PRO membrane fabrication to improve both osmotic performance and energy harvesting capability for the PRO process.

Modeling, simulation and optimization of a pressure retarded osmosis power station

Pressure retarded osmosis (PRO) power plants generate power from mixing of saltwater and freshwater by means of membrane systems. In this paper we present a model which describes the complete power station, suitable to optimize the power station both with respect to system parameters and in operating conditions. Special attention is dedicated to the flow model of the “core” membrane unit. It considers the relevant water and salt flows in the system. It also accounts for irreversible losses in the flow across the membrane as well as through the membrane unit, and in the surrounding pump-turbine system. The model represents a compromise between needed complexity (including the most relevant chemo-physics) and simplicity to allow rapid simulations which is an important prerequisit for optimisation. Finally, we optimise numerically, i.e., the net power output (per membrane area) with respect to geometric parameters, membrane parameters as well as operational parameters such as the applied pressure settings during operation.

Pressure retarded osmosis: Operating in a compromise between power density and energy efficiency

Pressure retarded osmosis (PRO) is a promising technology for salinity gradient energy utilization. Here, based on previous literature, we proposed a simplified model to describe the PRO process, which was validated by a great accordance with the experimental data of water flux and power density. A sensitivity analysis of the PRO system indicated that there exist different optimal hydraulic pressure differences leading to the maximum power density and energy efficiency, respectively. The performance of the PRO system under the maximum power density and energy efficiency is systematically investigated based on the GA method. Furthermore, the Pareto front that indicates any arbitrary compromise between the maximum power density and energy efficiency based on NSGA-II was obtained. Factors determining the choice of the final compromise solution in the Pareto frontier remains are systematically discussed, which should be referred to the local energy policies and technical and economic conditions of the PRO systems. For demonstration, the final compromise solution selected by the abstract heuristic TOPSIS method is discussed and a desirable compromise between the power density and energy efficiency is presented.

Novel thin-film composite forward osmosis membrane using polyethylenimine and its impact on membrane performance

ABSTRACTPolyethylenimine (PEI), a cationic, hydrophilic flexible polymer has been incorporated into the polyamide (PA) skin layer through an interfacial polymerization (IP) reaction. The modified thin-film composite (TFC) membranes display improved forward osmosis performance: enhancement in water permeability and antifouling characteristics. The incorporation of PEI into the skin layer has been evidenced by different characterization techniques; FTIR for modification of surface functionalities, zeta potential for surface charge, water contact angle for hydrophilicity of the surface, SEM and AFM for surface morphologies including surface roughness, XPS for surface attachment of heteroatoms and their relative composition. PEI was found to induce a positive zeta potential, high degree of hydrophilicity and high factional free volume into the active skin layer. The increase in the relative composition of PEI in the active skin layer was found to decrease the surface roughness and the skin layer thickness. An optimized PEI composition showed significantly enhanced water permeability, salt rejection and fouling resistance in FO and pressure-retarded osmosis (PRO) mode.

Pre-treatment of wastewater retentate to mitigate fouling on the pressure retarded osmosis (PRO) process

Pressure retarded osmosis (PRO) has been widely investigated to harness the osmotic energy from salinity gradient. Seawater desalination brine (SWBr) and wastewater retentate (WWRe) are employed as the draw and feed solutions respectively due to a large salinity difference between them and reuse of wastewater, but the fouling caused by WWRe on PRO membranes is too severe. In order to mitigate fouling on PRO membranes, several pre-treatment methods, such as ultrafiltration (UF), nanofiltration (NF) and low-pressure reverse osmosis (LP-RO), were adopted and compared in the current study. The filtrate from each pre-treatment method was used as the feed solution in the subsequent PRO tests. Results showed that without pre-treatment, the PRO process at 15 bar produced a power density of 2.92 W/m2 which was only 40% of its initial power density after a 6-h test. The UF pre-treatment was not helpful in fouling mitigation, but NF and LP-RO were effective to remove foulants and scalants. Using NF-filtrates, the PRO process could produce a stable power density of 7.3 W/m2. It was a 10.7% drop from the initial power density. Using LP-RO-filtrates, the PRO process could produce a stable power density of 8.4 W/m2, which was only a 7% drop from the initial power density. NF was recommended to be the optimal pre-treatment method in the future study because it had a higher permeability than LP-RO. The major foulants and scalants were also identified by analysing filtrate samples and fouled membranes. Calcium and phosphate ions formed hydroxyapatite which caused severe scaling inside the PRO membrane. Silica, however, might not cause fouling or scaling in this PRO process.

Modeling and Simulation Studies Analyzing the Pressure-Retarded Osmosis (PRO) and PRO-Hybridized Processes

Pressure-retarded osmosis (PRO) is viewed as a highly promising renewable energy process that generates energy without carbon emissions in the age of the climate change regime. While many experimental studies have contributed to the quest for an efficiency that would make the PRO process commercially viable, computational modeling and simulation studies have played crucial roles in investigating the efficiency of PRO, particularly the concept of hybridizing the PRO process with reverse osmosis (RO). It is crucial for researchers to understand the implications of the simulation and modeling works in order to promote the further development of PRO. To that end, the authors collected many relevant papers and reorganized their important methodologies and results. This review, first of all, presents the mathematical derivation of the fundamental modeling theories regarding PRO including water flux and concentration polarization equations. After that, those theories and thermodynamic theories are then applied to depict the limitations of a stand-alone PRO process and the effectiveness of an RO-PRO hybridized process. Lastly, the review diagnoses the challenges facing PRO-basis processes which are insufficiently resolved by conventional engineering approaches and, in response, presents alternative modeling and simulation approaches as well as novel technologies.

Fabrication of high-performance nanofiber-based FO membranes

Being partially commercialized and has specific application areas, where the reverse osmosis technology cannot serve, forward osmosis (FO) technology is continually receiving extensive research to promote its performance. In this study, high-performance FO nanofiber-based substrate membrane was fabricated for potential application of saline water desalination. Sulfonated polysulfone (sPSU) with definite sulfonation level was used to fabricate support layer. Tubular beadless fiber network owning scaffold-like structure with a fiber diameter of 247 nm was formed. Polysulfone was sulfonated by heterogeneous method using chlorosulfonic acid as a sulfonation agent. The substrate and FO membranes were characterized mainly by means of scanning electron microscopy (SEM), water permeation flux, porometry, contact angle, Fourier transform infrared (FTIR), as well as other tests, while the characterization of thin-film composite separation layer was restricted to SEM and FTIR. The characterization illustrates that the sPSU support layer is highly porous with a narrow pore size distribution. FO performance evaluation of two commercial and newly developed membranes was probed using FO and pressure-retarded osmosis (PRO) modes with cocurrent and counter-current flow scheme. The active layer presents excellent intrinsic properties with A/B of 17.31 and a high salt separation ratio of 99.54%. The newly developed membrane can achieve a high FO and PRO water flux of 65.7 and 313 L m(-2) h(-1), respectively, using a 1 M NaCl draw solution and deionized water feed solution. The corresponding salt flux is only 2.5 and 5.3 g m(-2 )h(-1). The reverse flux selectivity represented by the ratio of water flux to reverse salt flux (J(w)/J(s)) was kept as high as 26.3 and 58.8 L g(-1) for FO and PRO modes. To the best of our knowledge, the performance of the current work-developed membrane is superior to all FO membranes previously reported in the literature.

Hyperbranched poly(ionic liquid) functionalized poly(ether sulfone) membranes as healable antifouling coatings for osmotic power generation

Membrane fouling and membrane deterioration are two major concerns since they greatly worsen membrane performance in pressure retarded osmosis (PRO) and shorten the membrane lifetime.

Effects of feed solution pretreatment on pressure-retarded osmosis: changes in dissolved organic matter according to fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis and liquid chromatography-organic carbon detection

Effects of feed solution pretreatment on pressure-retarded osmosis: changes in dissolved organic matter according to fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis and liquid chromatography-organic carbon detection