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Sub-Saharan Africa, and in particular Mozambique, has considerable potential of salinity gradient energy, which could foster coastal development. However, the lack of scientific based information hinders the development of policies and investments in harnessing this source of energy in Sub-Saharan Africa. The present study, used historical data of temperature and salinity and estimated the potential of salinity gradient power in four main estuaries in Mozambique. The theoretical salinity gradient power ranged, on average, from 843.6 MW, in Incomati River estuary to 2,800.0 MW in Zambezi Delta. The Bons Sinais Estuary and Limpopo Estuary had 1,086.8 MW and 1292.0 MW, on average, respectively. The salinity power estimated in the Mozambique estuaries studied was above the maximum power densities for electrodialysis osmotic energy storage systems, which is set at 5 W m−2, and has potential extractable energy of about 3,000MW, and could benefit about 2 million coastal rural households (about 7% of the total Mozambican population) on irrigation and lighting houses. Further studies may be focused in determining the seasonal and salinity intrusion effects on salinity power gradient in the Mozambican estuaries. [ABSTRACT FROM AUTHOR]

This study explores the utilization of electrospun polysulfone (PSF) as a thin-film support in the pressure-retarded osmosis (PRO) system, leveraging its notable thermal, chemical, and oxidative stability. To enhance the efficiency of the PRO system, the inherently hydrophobic PSF surface is modified through functionalization with benzenesulfonamide groups (BSA-PSF). The modification process involves chloromethylation of PSF, followed by substitution with BSA, and subsequent electrospinning to produce BSA-PSF fibers. A thin-film composite forward osmosis membrane, composed of an electrospun BSA-PSF support layer and a polyamide thin layer synthesized through interfacial polymerization (BSA-PSF/PA), is developed. The incorporation of BSA improves the hydrophilicity of the membrane surface, while also imparting antibacterial features to the electrospun BSA-PSF. Comparative analyses with pristine PSF membranes reveal that the pure water flux of the BSA-PSF membrane achieves a notable 65 LMH, surpassing the pristine PSF membrane’s flux of 45 LMH. Moreover, protein absorption is significantly reduced in the BSA-PSF membrane (40.6 μg cm−2) compared to the unmodified PSF membrane (64.2 μg cm−2). The establishment of a hydration layer near the surface, facilitated by hydrogen interactions between water units and the hydrophilic sulfonamide chains in the polymer, contributes to lower protein adsorption than observed in the pristine PSF membrane. Notably, the prepared BSA-PSF/PA membrane exhibits advanced surface hydrophilicity, commendable antibacterial properties, exceptional fouling resistance, and high water permeability. These attributes position it as a promising candidate for widespread applications in power generation and large-scale water treatment. BSA functionalized the electrospun PSF used as the PRO membrane’s thin-film support. The introduction of BSA to PSF improved the hydrophilicity, water flux, antibacterial properties, and fouling resistance of thin-film composite PRO membraneArticle Highlights: BSA functionalized the electrospun PSF used as the PRO membrane's thin-film support. The introduction of BSA to PSF improved the membrane's hydrophilicity and water flux. BSA-PSF nanofibers exhibit antibacterial properties. BSA-PSF/PA membrane has satisfactory fouling resistance [ABSTRACT FROM AUTHOR]

A process simulator has been developed to model and predict the performance of spiral-wound membrane modules in pressure retarded osmosis processes. This has involved automation of generalized protocols for the numerical integration of the solvent and solute flux equations (in conjunction with a suitable electrolyte equation of state) along the surface area of a spiral-wound membrane leaf. Performance equations are solved for discrete area elements and the spiral-wound character of the module as a whole is realized through the programmed sequence in which discrete elements are evaluated. This arrangement allows for mirroring the parabolic flow pattern of the feed stream in the spiral-wound membrane leaf. The total permeation (and, by extension, power density) is thus calculated in a manner that accounts for the driving force profile consistent with flow patterns specific to spiral-wound membranes. This effective treatment of each discrete element as a flat-sheet membrane enables the transferability of membrane parameters characterized in standard, coupon-scale experiments to the simulation of spiral-wound modules. This transferability is illustrated through comparisons of model predictions with published pilot-scale PRO data. [ABSTRACT FROM AUTHOR]

This work presents a performance assessment of three seawater reverse osmosis—pressure-retarded osmosis (SWRO-PRO) hybrid schemes for energy consumption reduction in seawater desalination applications by using an external low salinity water source. For comparison purposes, another arrangement based on the conventional SWRO process combined with brackish water RO (BWRO) and desalination was analyzed. Reverse osmosis system analysis software environments were used to select the best SWRO configuration and operating conditions. A purposely developed model was used to evaluate the PRO system. Two different cases were assessed depending on the origin of the external low-salinity resource for the PRO process: industrial wastewater and urban treated wastewater. In the case of the industrial wastewater, due to regulations on wastewater reclamation, the best arrangement would be the first SWRO-PRO scheme which was analyzed with a specific energy consumption of 1.54 kWh/m3. If urban treated wastewater is available as an external resource, the results obtained show that this scheme, leading to the minimum specific energy consumption of 1.46 kWh/m3, is the conventional SWRO combined with BWRO. Therefore, hybrid SWRO-PRO systems are recommended to reduce the specific energy consumption of seawater desalination if an industrial wastewater source with low osmotic pressure is available.

Seawater reverse osmosis (SWRO) has played a key role in alleviating water stress worldwide. However, its intensive energy consumption, which is highly dependent on fossil fuels, needs to be reduced to mitigate the CO2 emissions resulting from SWRO. Many technologies, including pressure-retarded osmosis (PRO), have been applied in an attempt to reduce the energy consumption of SWRO. In this study, potential trends in CO2 emissions from SWRO processes in Korea are considered based on SWRO operational data collected from a range of sources and relating to societal scenarios of the future. These societal scenarios are based on current population trends in Korea and the proportion of renewable energy currently utilized in Korea. Next, using a dimensionless performance index for the SWRO-PRO hybrid process, the study presents the potential efficacy of PRO in reducing the magnitude of CO2 emissions from SWRO processes in Korea. The analysis shows that CO2 may be reduced by 10%-40%. The results of the study suggest a promising role for PRO as a suppressor of CO2 emissions. It is anticipated that the study will facilitate further in-depth studies into the use of PRO. [ABSTRACT FROM AUTHOR]

In this study, theoretical models for specific energy consumption (SEC) were established for water recovery in different integrated processes, such as RO-PRO, RO-MD and RO-MD-PRO. Our models can evaluate SEC under different water recovery conditions and for various proportions of supplied waste heat. Simulation results showed that SEC in RO increases with the water recovery rate when the rate is greater than 30%. For the RO-PRO process, the SEC also increases with the water recovery rate when the rate is higher than 38%, but an opposite trend can be observed at lower water recovery rates. If sufficient waste heat is available as the heat source for MD, the integration of MD with the RO or RO-PRO process can significantly reduce SEC. If the total water recovery rate is 50% and MD accounts for 10% of the recovery when sufficient waste heat is available, the SEC values of RO, RO-PRO, RO-MD and RO-MD-PRO are found to be 2.28, 1.47, 1.75 and 0.67 kWh/m3, respectively. These critical analyses provide a road map for the future development of process integration for desalination.

In membrane-based desalination systems, the mass transfer coefficient is a critical determinant when estimating changes within the boundary layers. However, it is pivotal to recognize the substantial role of intrinsic membrane parameters that can significantly influence the formation of boundary layers by modulating the water and salt fluxes. In this context, we investigated the effects of intrinsic membrane parameters on dilutive external concentration polarization (dECP) during forward osmosis (FO) and pressure-retarded osmosis (PRO). In particular, the Péclet number is utilized to evaluate the degree of dECP. The results revealed that the effects of the membrane parameters on dECP differ completely in accordance with the membrane orientations or magnitude of hydraulic pressure. Moreover, this study emphasizes that the reduction of solute permeability, i.e. , improving the selectivity, should be the priority of FO/PRO membrane optimization because solute permeability is the only parameter that simultaneously suppresses both the internal concentration polarization and dECP. Hence, the results of the current study are expected to serve as valuable guidelines for future FO/PRO membrane optimization research. [Display omitted] • New model for dECP in FO/PRO based on film theory and solution-diffusion model • Quantification of dECP with the Péclet number, a ratio of diffusion and advection • Multi-aspect investigation of the effects of intrinsic membrane parameters on dECP • Emphasis on the importance of membrane selectivity over permeability [ABSTRACT FROM AUTHOR]

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.

Osmotic and hydraulic pressures are both indispensable for operating membrane-based desalting processes, such as forward osmosis (FO), pressure-retarded osmosis (PRO), and reverse osmosis (RO). However, a clear relation between these driving pressures has not thus far been identified; hence, the effect of change in driving pressures on systems has not yet been sufficiently analyzed. In this context, this study formulates an actual mathematical relation between the driving pressures of membrane-based desalting processes by taking into consideration the presence of energy loss in each driving pressure. To do so, this study defines the pseudo-driving pressures representing the water transport direction of a system and the similarity coefficients that quantify the energy conservation rule. Consequently, this study finds three other theoretical constraints that are required to operate membrane-based desalting processes. Furthermore, along with the features of the similarity coefficients, this study diagnoses the commercial advantage of RO over FO/PRO and suggests desirable optimization sequences applicable to each process. Since this study provides researchers with guidelines regarding optimization sequences between membrane parameters and operational parameters for membrane-based desalting processes, it is expected that detailed optimization strategies for the processes could be established.

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. • Four FO membranes tested under baseline and fouling conditions in PRO • Limiting water flux and power density observed as independent of membrane properties • Fouling mitigation efforts should focus on feed side (support layer) of membrane in PRO. [ABSTRACT FROM AUTHOR]

Pressure-retarded osmosis (PRO) is the next generation seawater desalination technology, and is considered an eco-friendly and economic renewable energy. As such, there have been studies on methods of efficient cleaning to restore degraded membrane performance due to the reversible membrane fouling that inevitably occurs after prolonged operation. Owing to the fact that fouling occurs differently in each type of pretreatment process involved in PRO, it is important to understand the type of organic matter that causes fouling in each of the PRO pretreatment processes. In this study, the composition of dissolved organic matter (DOM) was characterized and assessed among membrane bioreactor, ultrafiltration, activated carbon/sand filter, and low-pressure reverse osmosis PRO pretreatment processes. The characteristics of DOM that caused fouling in the PRO membrane was identified using fluorescence excitation-emission matrix spectroscopy (F-EEMs) coupled with parallel factor analysis (PARAFAC) and a liquid chromatography-organic carbon detector (LC-OCD) technique. The major components could be summarized as microbial humic-like fluorescence, humic and fulvic substances, terrestrial humic-like fluorescence in high nutrient and wastewater-influenced environments, and tryptophan-like substances. The foulants that affected the PRO membrane were found to be humic and fulvic substances as a result of the PARAFAC analysis and humic substances and building blocks as a result of the LC-OCD analysis. [ABSTRACT FROM AUTHOR]

This study simulates the performance of forward osmosis and pressure-retarded osmosis by the solution diffusion (SD) and the Spiegler–Kedem (SK) models in either complete mixing (CM) or plug flow (PF) configuration. The analysis considers the operating modes of placing the active side of the membrane facing the feed solution or the draw solution. This affects the magnitude of the concentration polarization on solute transport, which may occur inside the membrane support layer or in the bulk of the feed/draw solutions. The simulations illustrate the differences between these models and modes of operation on various important system parameters such as the membrane area, concentration and pressure of draw solution, flow rates of feed and draw solutions, recovery ratio, and power density. The results indicate that the placement of the active membrane layer facing the feed solution should only be considered for feed solutions containing a high concentration of particulate matter or fouling material. This is because operating with the active layer facing the draw solution provides better performance. Deviations in the predictions of the system characteristics by the SD model against the SK model are below 25%. Similarly, simulation of the spiral wound system by the CM model yields results within 15% of those predicted by the PF model. [ABSTRACT FROM AUTHOR]

Abstract The quality of the jet injected from a nozzle is one of the key factors that affects the performance of Pelton turbines. In this study, for the first time, experiments and numerical simulation were conducted to investigate the effect of the spear needle eccentricity on the jet flow in micro Pelton turbines. Results show that the eccentricity of the spear needle causes jet diffusion under low flow conditions and significantly increases the loss of the spear nozzle (injector). Furthermore, the increase in the eccentricity ratio causes extreme jet separation and jet diffusion, and the loss of the spear nozzle increases by 52% (from 453 W to 688 W) when the eccentricity ratio increases by 6%. Analysis of the results confirmed that the pressure deviation and jet velocity imbalance caused by eccentricity are the primary causes of jet diffusion. Furthermore, the results confirm that the eccentricity of the spear needle in the case of a low-capacity Pelton turbine has a significant effect on the jet quality. Thus, further studies on the eccentricity are required to improve the performance of the Pelton turbine. Highlights • Effects of spear needle eccentricity on Pelton turbine are discussed. • The additional loss owing to eccentricity increase sharply if the flow rate decrease. • The spear nozzle loss increases to 52% when the eccentricity ratio is 6%. • Variation in static pressure and jet velocity is the cause of jet quality reduction. [ABSTRACT FROM AUTHOR]

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 (Jw/Js) 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. [ABSTRACT FROM AUTHOR]

Abstract Economic analysis is necessary to ascertain the practical viability of a pressure-retarded osmosis (PRO) system for power production, but high complexity and the lack of large scale data has limited such work. In this study, a simple yet powerful economic framework is developed to relate the lower bound of levelized cost of electricity (LCOE) to net power density. A set of simplifying assumptions are used to develop an inverse linear relationship between net power density and LCOE. While net power density can be inferred based on experimentally measured power density, LCOE can be used to judge the economic viability of the PRO system. The minimum required net power density for PRO system to achieve an LCOE of $0.074/kWh (the capacity-weighted average LCOE of solar PV in the U.S.) is found to be 56.4 W/m2. Using this framework, we revisit the commonly cited power density of 5 W/m2 to conclude that it is not economically viable because net power density would be even lower. Finally, we demonstrate that fundamental difference exists between power density and net power density, and as a result we recommend using net power density as a performance metric for PRO system. Highlights • A novel economic framework was developed for pressure-retarded osmosis. • Net power density was identified as the most important performance metric. • The relationship between net power density and levelized cost of electricity (LCOE) was found. • The existence of an optimal module length was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract This study experimentally and theoretically analyzed the performance of two types of large-scale hollow fiber (HF) forward osmosis (FO) modules for pressure retarded osmosis (PRO). The effects of operating conditions on the module performance of the 5-inch scale HF modules with a cross-wound HF configuration were investigated. A modified analytical model, based on the friction-concentration polarization (FCP) model, which combined the PRO theory with water flux and salt leakage, was proposed for PRO performance estimation. The theoretical results agreed within 9.7% deviation with the experimental results under all conditions. The energy efficiency of the HF PRO module was also theoretically derived. The power generation estimation for the 5-inch membrane module revealed that 10 to 15% of the energy could be recovered from the reverse osmosis seawater desalination process. However, some parts of the membrane could not be used efficiently inside the modules because of the non-optimal dimensions. Therefore, new types of modules, having shorter lengths and larger module diameters, were proposed and provided greater net energy output, as compared with the original module, due to the reduction of both the region where the water was not sufficiently permeated and the pressure drop inside the HF membrane. Graphical abstract Unlabelled Image Highlights • A pilot-scale PRO test was performed using 2 types of 5-inch scale CTA HF modules. • The proposed FCP-based analytical model agreed well with all experimental data. • The positive net energy and energy efficiency of the PRO system were estimated. • A precise analytical model helped propose preferable HF module dimensions for PRO. • Wide and short HF module dimensions were better for positive power generation. [ABSTRACT FROM AUTHOR]

The widely used van ’t Hoff linear relation for predicting the osmotic pressure of NaCl solutions may result in errors in the evaluation of key system parameters, which depend on osmotic pressure, in pressure-retarded osmosis and forward osmosis. In this paper, the linear van ’t Hoff approach is compared to the solutions using OLI Stream Analyzer, which gives the real osmotic pressure values. Various dilutions of NaCl solutions, including the lower solute concentrations typical of river water, are considered. Our results indicate that the disparity in the predicted osmotic pressure of the two considered methods can reach 30%, depending on the solute concentration, while that in the predicted power density can exceed over 50%. New experimental results are obtained for NanoH2O and Porifera membranes, and theoretical equations are also developed. Results show that discrepancies arise when using the van ’t Hoff equation, compared to the OLI method. At higher NaCl concentrations (C > 1.5 M), the deviation between the linear approach and the real values increases gradually, likely indicative of a larger error in van ’t Hoff predictions. The difference in structural parameter values predicted by the two evaluation methods is also significant; it can exceed the typical 50–70% range, depending on the operating conditions. We find that the external mass transfer coefficients should be considered in the evaluation of the structural parameter in order to avoid overestimating its value. Consequently, measured water flux and predicted structural parameter values from our own and literature measurements are recalculated with the OLI software to account for external mass transfer coefficients.

Pressure-retarded osmosis (PRO) has recently received attention because of its ability to generate power via an osmotic pressure gradient between two solutions with different salinities: high- and low-salinity water sources. In this study, PRO performance, using the two pilot-scale PRO membrane modules with different configurations—five-inch cellulose triacetate hollow-fiber membrane module (CTA-HF) and eight-inch polyamide spiral-wound membrane modules (PA-SW)—was evaluated by changing the draw solution (DS) concentration, applied hydrostatic pressure difference, and the flow rates of DS and feed solution (FS), to obtain the optimum operating conditions in PRO configuration. The maximum power density per unit membrane area of PA-SW at 0.6 M NaCl was 1.40 W/m2 and 2.03-fold higher than that of CTA-HF, due to the higher water permeability coefficient of PA-SW. In contrast, the maximum power density per unit volume of CTA-SW at 0.6 M NaCl was 4.67 kW/m3 and 6.87-fold higher than that of PA-SW. The value of CTA-HF increased to 13.61 kW/m3 at 1.2 M NaCl and was 12.0-fold higher than that of PA-SW because of the higher packing density of CTA-HF.

The present study investigates the performance of a hybrid solar thermal membrane-based multigeneration system for generating power, cooling, heating, and water. The integrated arrangement consists of organic Rankine cycle (ORC), Kalina cycle (KC), ammonia-water refrigeration, Pressure retarded osmosis (PRO) and forward osmosis (FO). A comprehensive multicriteria assessment of energy, exergy, economic, environmental, and emergy (5 E) is conducted to ensure a systematic examination. The results indicate that the allocation of R113 in the ORC yielded the highest exergetic efficiency and energy cost of 46.61% and 0.08109 $/kWh, respectively. Additionally, the system achieved the lowest environmental impact of 1694 mPts.h−1 when employing R718. The utilization of rejected water–ammonia in the PRO and FO modules achieves a reasonable power density and water flux of 17.5 W m−2 and 67.94 l m−2h−1, respectively. Finally, emergy-based sustainability analysis revealed that the proposed system obtains a sustainability index of 0.73, which is greater than that of the fossil fuel-based power generation systems. Comparison of three considered scenarios based on emergy and economic analysis demonstrated that fossil fuel driven system is not providing sustainable products even with a 72.3% decrease in initial capital cost. For further improvements, we highlight several areas for additional research and provide recommendations for existing solar- and membrane-driven systems. [Display omitted] • A novel integrated solar-membrane driven multigeneration system in designed. • A comprehensive energy, exergy economic, environment and emergy analysis were performed. • Pressure retarded osmosis can produces power density of 17.5 W m−2 under operational condition. • The highest energy and exergy efficiencies are 49.53% and 46.61%, respectively. • The emergy based sustainability analysis of the system is equal to 0.73. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) and pressure-retarded osmosis (PRO) have gained attention recently as potential processes to solve water and energy scarcity problems with advantages over pressure-driven membrane processes. These processes can be designed to produce bioenergy and clean water at the same time (i.e., wastewater treatment with power generation). Despite having significant technological advancement, these bioenergy processes are yet to be implemented in full scale and commercialized due to its relatively low performance. Hence, massive and extensive research has been carried out to evaluate the variables in FO and PRO processes such as osmotic membrane, feed solutions, draw solutions, and operating conditions in order to maximize the outcomes, which include water flux and power density. However, these research findings have not been summarized and properly reviewed. The key parts of this review are to discuss the factors influencing the performance of FO and PRO with respective resulting effects and to determine the research gaps in their optimization with the aim of further improving these bioenergy processes and commercializing them in various industrial applications.

Cyclic thermal precipitation and dissolution of saturated aqueous solutions and its significance with regard to osmotic heat engines (OHEs) is discussed. Here, the thermal dependence of the solubility is harnessed by alternating thermal solute precipitation and dissolution when heat is either applied (by heating the solution) or extracted (by cooling the solution) depending of the given solution. Utilizing a simplified physical model, it is shown that by the proper choice of the concentration, a closed cycle seems feasible. In contrast with traditional OHEs which working with dilute ideal solutions, the proposed osmotic engine operates at saturation concentration level and therefore the approximation of ideal solution is no longer valid, and then, for a valid approach, an osmotic coefficient was included in the calculations to take account the deviation from the ideal case. The expression for the extractable energy per unit of volume of solution as well as the thermal efficiency of the heat engine were derived considering the spontaneous change in the Gibbs free energy and the enthalpy of precipitation. The specific case for Na 2 SO 4 was analyzed and it was found a percentage of Carnot efficiency as high as 23% which is a little larger than the efficiencies reported by traditional OHEs. The proposed heat engine eliminates the need of evaporation to re-concentrate the draw solution and then the constraint of working with solutions with high vapor pressures. [ABSTRACT FROM AUTHOR]

This study introduces a thin-film composite (TFC) membrane with a dual-layered nanocomposite substrate synthesized using a dual-blade casting approach for application in osmotic power generation by the pressure-retarded osmosis (PRO) process. The approach incorporates halloysite nanotubes (HNTs) into the bottom polymer substrate layer and graphene oxide (GO) on the top layer substrate, on which a thin polyamide active layer is formed. The fabricated membrane substrate showed highly desirable membrane substrate properties such as a high porosity, opened-bottom surface, suitable top-skin surface morphology for subsequent active layer formation and high mechanical strength, which are essential for high-performance PRO processes. At a GO loading of 0.25 wt% and HNT loading of 4 wt%, the power density (PD) of the nanocomposite membrane was 16.7 W/m 2 and the specific reverse solute flux (SRSF) was 2.4 g/L operated at 21 bar applied pressure using 1 M NaCl as draw solution and deionized water as feed, which is significantly higher than the those for a single-layered or commercial PRO membrane. This membrane performance was observed to be stable in the pressure cycle test and under long-term operation. The membrane substrate with HNTs incorporated exhibited high fouling resistance to sodium alginate and colloidal silica foulants, with the PD decreasing by 17% after 3 h of operation, compared to a membrane substrate without HNTs and commercial PRO membranes, which decreased by 26% and 57%, respectively. A fluorescence microscope study of the membranes subjected to feed water containing Escherichia coli confirmed the good antibacterial properties of the dual-layered TFC membrane. The study provides an attractive alternative approach for developing PRO membranes with high PD and fouling resistance. [ABSTRACT FROM AUTHOR]

This study evaluates the pressure retarded osmosis performance of TMA–CO2 for potential use in osmotic heat engines. Power densities up to 18.6 W m−2 were achievable at relatively low pressure (10 bar) using 5 M TMA–CO2 draw solutions. Compared to NaCl control tests, the TMA–CO2 exhibited 20% lower water flux due in large part to its larger molecular size and associated higher solution viscosity and lower diffusion coefficient. Compared to the ammonia‐carbon dioxide draw solution, water flux was comparable but reverse solute flux of TMA–CO2 was nearly one order of magnitude lower. Larger solute size was found to create a performance tradeoff as reduced reverse solute flux improved water flux while higher viscosity and lower diffusion coefficient worsened water flux. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3369–3375, 2018 [ABSTRACT FROM AUTHOR]

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]

This paper reports findings on the role of woven polyester mesh size on burst strength and mass-transfer resistance of thin-film composite membranes used for pressure-retarded osmosis (PRO). Hand-cast and commercial membranes were mounted on standard woven mesh backings with different opening sizes. Characterization of the membranes was done using scanning electron microscopy, tensile tests, and burst pressure measurements. Membrane performance was assessed by water permeance, reverse salt flux, and osmotic water flux measurements; and correlated with estimates of membrane structural characteristics. Results show that woven mesh polyester backings provide sufficient strength to the overall structure for PRO; however, the porous support layer undergoes deformations that depend on the opening size of the backing. An opening size of 125 µm or smaller provided sufficient strength to a commercial porous support layer when operating at transmembrane pressures at or below 2750 kPa. Next, it was found that the nonwoven backing contributes extensively to the value of the overall structural parameter in the case of the commercial SW30HRLE membrane. Using a woven mesh #325 as polyester backing reduced the SW30HRLE structural parameter by 74%, yielding a 48% improvement in power density. These findings support the idea that mass-transfer resistances in osmotic-driven processes like PRO are an additive effect of the multiple layers that compose a membrane (or module), and can be reduced by using more open (yet functional) backing layers such as polyester woven mesh. [ABSTRACT FROM AUTHOR]

Abstract: Although the distillation process was initially applied in seawater desalination plants to solve the current global water shortage, it has been replaced by the energy‐saving type reverse‐osmosis membrane process worldwide since the beginning of this century. Considering the population increase and economic development, the ‘Mega‐ton Water System' research project was conducted to identify the element technologies required for the 21st century in Japan. Enhancing the operational reliability of seawater desalination plants, these development technologies also enable the establishment of earth‐friendly seawater desalination plants anticipating considerable energy savings, lowering of the environmental impact, and reduction of water production costs. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) is a water treatment technique that utilizes a semi-permeable membrane to remove dissolved solutes from water by the use of a salinity gradient. Unlike reverse osmosis (RO), the driving force of FO is not the hydraulic pressure and thus FO does not need high energy to pressurize feed water. However, the efficiency of FO may be deteriorated by the occurrence of fouling induced by the precipitation of inorganic scales if the feed water includes salts such as CaCO3, CaSO4, or silica. The focus of this study was the investigation of FO membrane fouling caused by CaSO4 scale formation. The changes in flux, saturation degree, and the turbidity of the brine were measured as a function of operation time in a laboratory scale FO system. The fouling characteristics of FO were compared with those of RO and pressure-assisted FO (PAFO) under similar filtration conditions. A theoretical model considering different scale formation mechanisms was also applied to quantitatively analyze FO fouling. [ABSTRACT FROM AUTHOR]

Membrane fouling is one of the major problems to be solved to sustain stable pressure-retarded osmosis (PRO) performance. This phenomenon caused diminished water flux productivity. So an effective cleaning method for fouled membrane is necessary. This study was carried out to compare applicable cleaning methods to mitigate organic and inorganic foulants on the PRO membrane. Fouling experiments were divided into two types: organic fouling and inorganic–organic fouling. Humic substance and calcium carbonate were used as model compounds. The fouled PRO membranes were cleaned by seven types of cleaning methods namely: (i) physical flushing, (ii) pressure-assisted physical flushing at feed side, (iii) pressure-assisted physical flushing at draw side, (iv) osmotic backwashing, (v) reverse osmosis flushing, (vi) pressure-assisted osmotic backwashing with low pressure (PAOB-I), (vii) pressure-assisted osmotic backwashing with high pressure. PAOB-I was a more effective method to mitigate foulants on the PRO membrane compared with the other cleaning methods in this study. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) process and its significance for thermosyphon technology is discussed. In previous work the possibility to drive a thermosyphon by difference of densities from induced salinity gradients from evaporation at solar collectors with downward heat transfer was assessed. Nevertheless it was concluded that large evaporative areas or dilution with volatile compounds was mandatory. In this work it is shown that by taking advantage of the energy released during the spontaneous mixing of the low-concentration evaporative fraction and the high-salinity of the no-evaporated fraction which is generally referred as pressure-retarded osmosis (PRO) process, then the thermosyphon can runs with downward heat transfer (hot fluid flows down and cold fluid rises up) and using an evaporative surface area much more smaller and then eliminating the need for dilution with high volatile compounds. [ABSTRACT FROM AUTHOR]

In this paper, we present the hydrodynamic design and performance tests of a Pelton-type energy recovery turbine (ERT) for pressure-retarded osmosis (PRO) systems. We describe the process of selecting the appropriate type of ERT for operating conditions of the PRO system (i.e., 400 ton/day, 30 bar) as well as the design methods for the Pelton-type ERT. Furthermore, we analyse the performance characteristics at design and off-design points and the change in performance with respect to the diameter of the Pelton runner, based on the performance tests of the manufactured Pelton-type ERT. At the design point, the efficiency of the Pelton-type ERT was approximately 85%, and the overall efficiency with the electric generator was approximately 77.2%. The efficiency of the turbine and overall plant was highest when the diameter of the Pelton runner is of the size selected during design. We thus validate the design result through such a performance test. It is expected that this study will be of great assistance to future works involving the selection of ERTs for PRO systems, as well as the design and performance tests of ERTs. [ABSTRACT FROM AUTHOR]

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.