Pressure Retarded Osmosis Research Articles

Techno-Economic Analysis towards Full-Scale Pressure Retarded Osmosis Plants

Pressure retarded osmosis (PRO) is a power generation process that harnesses the salinity gradient between two water bodies of different salinities. Using high salinity water as a draw solution, this work assesses the techno-economic feasibility of the technology to generate electricity using single and multistage systems. This work utilizes a simulator built on the rigorous Q-Electrolattice equation of state and a mass transfer model that accounts for concentration polarization, combined with the Dakota optimization tool to perform sensitivity analysis and optimization studies. The economic indicator of interest is the Levelized Cost of Electricity (LCOE), which serves to compare PRO with other sources of renewable energy. An LCOE value of USD 0.1255/kWh was obtained from the use of commercial membranes at an efficiency of 100% for the mechanical components of the PRO system. This LCOE drops to USD 0.0704/kWh when an ideal membrane is used—thus showing the improvements to economics possible with improved membrane properties. With currently obtainable membrane properties and mechanical equipment, the LCOE of a single-stage process increases to USD 0.352/kWh, which is not cost-competitive with other renewable energy sources. Setting up multistage PRO systems towards minimizing the LCOE was found to be detrimental to the net power production by the plant.

A novel spiral wound module design for harvesting salinity gradient energy using pressure retarded osmosis

Pressure retarded osmosis (PRO) is an evolving form of a renewable energy process which utilizes the salinity gradient energy from two solutions of different concentrations. One of the main problems limiting the application of PRO is the low performance of the commercially available spiral-wound modules which have poor flow distribution and high pressure drop. The present paper proposes a new spiral-wound module design for PRO application. The performance of the new module design was investigated numerically and compared with the available spiral-wound module. Compared to the available module, the power density of the new design was higher by 25% and 15% at draw concentrations of 35 g/kg and 60 g/kg respectively, while there was a 35% decrease in the pressure drop. The new spiral-wound module design presents an enhanced overall performance due to the better flow distribution and lower pressure drop, yielding a higher water flux and power density.

Towards cost-effective osmotic power harnessing: Mass exchanger network synthesis for multi-stream pressure-retarded osmosis systems

Pressure-retarded osmosis (PRO) is a promising technique for osmotic power generation by recovering salinity gradient from high concentration effluents. Prior research has shown that the PRO systems integrating multiple draw/feed streams can achieve a 20+% increase in energy recovery compared with standalone design. However, to date few approaches have been developed to fully utilize this potential. Herein, we propose a novel method for the multi-stream PRO system that optimizes its modules (mass exchangers) layout as a mass exchanger network in three steps. In the first step, the maximum energy conversion is determined and used as an energy target for subsequent mass exchanger network synthesis. In accordance with the energy target, the second step establishes the optimal match of streams by introducing three criteria of “number of streams”, “KP coefficient”, and “maximum mass exchange”. The third step balances the system complexity and energy recovery by relaxing the energy target. An economic model is formulated to evaluate the performance of PRO systems. Several multi-stream PRO system design examples are presented to illustrate the proposed method. Results indicate that the integrated designs generally outperforms the standalone designs by 11.75–21.65 % for energy recovery, and achieves better economic performance and higher power density for large osmotic pressure difference cases with minimum net osmotic pressure difference greater than 0.8 MPa. A minimum levelized cost of energy of 0.1364 $/kWh can be achieved by the proposed design method, constituting a 6.95 % reduction compared with the standalone design.

Fulvic and alginic acid separation during pressure retarded osmosis: Governing effects and fouling mechanisms

In this study, the performance of model foulant (alginate and fulvic acid) separation by pressure retarded osmosis (PRO) was systematically studied. At the various operating conditions tested, fulvic acid had a greater flux decline and power density loss than alginate. The results of membrane resistance test, SEM-EDX images, and the solute diffusion coefficient K demonstrated that fulvic acid was more likely to clog the inside of the porous support layer of the PRO membrane, which would exacerbate the internal concentration polarization (ICP) phenomena. Although model foulants were successfully removed by PRO (with a retention rate of about 95.0%), the presence of either calcium or magnesium ions was detrimental to the fouling process of PRO membranes. According to the XDLVO theory analysis results, the presence of calcium or magnesium ions increased foulant adhesion to the PRO membrane, thereby resulting in membrane fouling. In addition, Pearson correlation coefficient also showed that the hydrodynamic conditions (effective osmotic pressure difference as well as operating hydraulic pressure acting vertically to the membrane and parallel to the membrane cross-flow shear force) had an important effect on the degree of membrane fouling. This is attributed to the influence of the hydrodynamic conditions on the initial influence water flux and thus on the fouling of the PRO membrane.

Opportunities of Reducing the Energy Consumption of Seawater Reverse Osmosis Desalination by Exploiting Salinity Gradients.

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.

Low-Concentration Ozonation as a Feed Pretreatment Strategy to Reduce Organic Fouling in Pressure-Retarded Osmosis

Low-Concentration Ozonation as a Feed Pretreatment Strategy to Reduce Organic Fouling in Pressure-Retarded Osmosis

Challenges Facing Pressure Retarded Osmosis Commercialization: A Short Review

Pressure-retarded osmosis (PRO) is a promising technology that harvests salinity gradient energy. Even though PRO has great power-generating potential, its commercialization is currently facing many challenges. In this regard, this review highlights the discrepancies between the reported power density obtained by lab-scale PRO systems, as well as numerical investigations, and the significantly low power density values obtained by PRO pilot plants. This difference in performance is mainly due to the effect of a pressure drop and the draw pressure effect on the feed channel hydrodynamics, which have significant impacts on large-scale modules; however, it has a minor or no effect on small-scale ones. Therefore, this review outlines the underlying causes of the high power density values obtained by lab-scale PRO systems and numerical studies. Moreover, other challenges impeding PRO commercialization are discussed, including the effect of concentration polarization, the solution temperature, the pressure drop, and the draw pressure effect on the feed channel hydrodynamics. In conclusion, this review sheds valuable insights on the issues facing PRO commercialization and suggests recommendations that can facilitate the successful development of PRO power plants.

Mathematical Modeling of a Hollow Fiber Module Used in Pressure-Retarded Osmosis Process

Pressure retarded osmosis (PRO) can be considered as one of the methods for utilizing osmotic power, which is a membrane-based technology. Mathematical modeling plays an essential part in the development and optimization of PRO energy-generating systems. In this research, a mathematical model was developed for the hollow fiber module to predict the power density and the permeate water flux theoretically. Sodium chloride solution was employed as the feed and draw solution. Different operating parameters, draw solution concentration (1 and 2 M), the flow rate of draw solution (2, 3, and 4 L/min), and applied hydraulic pressure difference (0 - 90 bar) was used to evaluate the performance of PRO process of a hollow fiber module. The effect of these operational parameters was investigated on the theoretical permeate water flux and power density. According to the theoretical results, the permeate water flux and the power density increased with increasing the concentration of draw solution and the flow rate of the draw solution. While decreased with increasing the feed solution concentration. By increasing the applied hydraulic pressure on the draw solution, the water flux decreased and the produced power density increased. The maximum power density and the corresponding permeate water flux of 2 M NaCl draw solution was approximately 16.414 W/m2 and 11.818 LMH respectively, which occurs at an applied hydraulic pressure of 50 bar.

Experimental and theoretical work on reverse osmosis - Dual stage pressure retarded osmosis hybrid system

Two-pass reverse osmosis desalination is a common process to treat high-salinity feed solution and provides a low-salinity permeate solution. This study investigated the significance of the energy generated by the dual-stage pressure retarded osmosis (DSPRO) from the reverse osmosis (RO) brine stream. The main components of the DSPRO-RO hybrid system are RO, pressure retarded osmosis (PRO), and energy recovery device, and their models are determined. Dymola software, using Modelica modelling language, was utilized for solving the hybrid system models. Two different flowsheets were built; the first included a two-pass RO, while the second is a hybrid of a two-pass RO (2RO)-DSPRO system. Seawater salinities of 40 and 45 g/L were the RO feed solution, and 1 g/L tertiary treated wastewater was the feed solution of the DSPRO process. The net specific energy consumption was calculated for the 2RO and 2RO-DSPRO systems for 40 and 45 g/L salinities. At a 47 % recovery rate and 40 g/L seawater salinity, the 2RO-DSPRO system was 14.7 % more energy efficient than the 2RO system. The corresponding energy saving at a 47 % recovery rate and 45 g/L seawater salinity was 17.5 %. The desalination energy for the 2RO system was between 3.25 and 3.49 kWh/m3, and for the 2RO-DSPRO system was between 2.91 and 2.97 kWh/m3. The results demonstrate the great potential of integrating the 2RO with the DSPRO to reduce desalination's energy consumption and environmental impacts.

A novel conductive carbon-based forward osmosis membrane for dye wastewater treatment

Forward osmosis (FO) membrane fouling is one of the main reasons that hinder the further application of FO technology in the treatment of dye wastewater. To alleviate membrane fouling, a conductive coal carbon-based substrate and polydopamine nanoparticles (PDA NPs) interlayer composite FO membrane (CPFO) was prepared by interfacial polymerization (IP). CPFO-10 membrane prepared by depositing 10 mL of PDA NPs solution exhibited an optimum performance with water flux of 7.56 L/(m2h) for FO mode and 10.75 L/(m2h) for pressure retarded osmosis (PRO) mode, respectively. For rhodamine B and chrome black T dye wastewater treatment, the water flux losses were reduced by 21.6%, and 14.5% under the voltages of +1.5 V, and −1.5 V, respectively, compared with no voltage applied after the device was operated for 8 h. The applied voltage had little effect on the fouling mitigation performance of the CPFO membrane for neutral charged cresol red. After the device was operated for 4 cycles, the rejection rates of dyes wastewater treated by the CPFO membranes with applied voltage were close to 100%. The flux decline rate and flux recovery rate of CPFO membrane for rhodamine B and chrome black T wastewater treatment under application of +1.5 V and −1.5 V voltage after 4 cycles were 11.6%, 99.2%, and 16.7%, 98.9%, respectively. Therefore, the voltage-applied CPFO membrane still maintained good rejection and antifouling performance in long-term operation. This study provides a new insight into the preparation of conductive FO membranes for dye wastewater treatment and membrane fouling control.

A systematic methodology for targeting the thermodynamic limit of pressure-retarded osmosis with non-zero driving force

A thermodynamically oriented method is developed to identify the theoretical and practical limits of pressure-retarded osmosis (PRO) on converting salinity gradient power to mechanical energy under constant operating pressure with infinite and finite mass exchange area, respectively. It is proved that pinch analysis can be used to find the mass exchange limit of PRO, and according to which draw and feed streams can be plotted on a graph of net osmotic pressure - water exchange. Based on the graphical method, an expression of optimal pressure change is derived that achieves the maximum work extraction of a PRO process with single draw/feed stream. Moreover, problem table method is presented that serves as an analytical procedure to determine the maximum extractable work of the conceptualized multi-stream PRO process. Examples of both a PRO process with a draw stream (0.6 M NaCl seawater) and a feed stream feed (0.015 M NaCl river water) and a multi-stream PRO are included to illustrate the proposed methods. Results of the former example show that the counter-current design achieves 30.85% and 31.49% increase, respectively, in the maximum theoretical and practical work output, compared with the co-current design. The latter example shows that the problem table method produces a 20.47% increase in the work output, compared with the standalone design.

Sodium docusate as a cleaning agent for forward osmosis membranes fouled by landfill leachate wastewater

Membrane cleaning is critical for economic and scientific reasons in wastewater treatment systems. Sodium docusate is a laxative agent and removes cerumen (ear wax). Docusate penetrates the hard ear wax, making it softer and easier to remove. The same concept could be applied to soften and remove fouling layers on the membrane surface. Once softened, the foulants can be easily flushed with water. This innovative approach can address the challenge of developing superior methods to mitigate membrane fouling and material degradation. In this study, we evaluated the efficiency of sodium docusate for cleaning fouled forward osmosis membranes with real landfill leachate wastewater. Experiments were conducted to examine the impact of dose rate, contact time, flow or static conditions, and process configuration (forward osmosis (FO) or pressure retarded osmosis (PRO) upon fouling created by landfill leachate dewatering. A remarkable (99%) flux recovery was achieved using docusate at a small concentration of only 0.1% for 30 min. Furthermore, docusate can also effectively restore flux with static cleaning without using pumps to circulate the cleaning solution. Furthermore, cleaning efficiency can be achieved at neutral pH compatible with most membrane materials. From an economic and energy-saving perspective, static cleaning can almost achieve the same cleaning efficiency as kinetic cleaning for fouled forward osmosis membranes without the expense of additional pumping energy compared to kinetic cleaning. Since pumping energy is a major contributor to the overall energy of the forward osmosis system, it can be minimized to a certain degree by using a static cleaning approach and can bring good energy savings when using larger membrane areas. Studies of the contact angle on the membrane surface indicated that the contact angle was decreased compared to the fouled membrane after cleaning (e.g. 70.3° to 63.2° or FO mode and static cleaning). Scanning Electron Microscopy revealed that the cleaning strategy was successful. Infrared Spectroscopy showed that a small amount of sodium docusate remained on the membrane surface. Docusate is more environmentally friendly than acid or alkaline solutions from an environmental perspective. Furthermore, the cleaning solution can be reused for several cycles without discarding it due to the surfactant properties of docusate.

Simulation tool for full-scale PRO systems using SWMMs

Pressure retarded osmosis (PRO) is a process that is able to convert a salinity gradient into electrical energy through a turbine. This process has gained attention as a possible renewable energy technology for integration into desalination plants to improve their energy efficiency. Despite recent efforts, PRO is not yet commercially available due to drawbacks related to, among others, PRO membrane and module development. The aim of this study is to provide a simulation tool for full-scale PRO systems that allows accurate estimates of PRO-related energy generation to be made. The proposed tool enables analysis of single-stage systems with PRO modules in series and the setting of boundary conditions per module in terms of maximum flux recovery, and maximum and minimum feed/draw flow. The HTI OsMem™ 2521 spiral wound membrane module (SWMM) was evaluated considering an 8 in. diameter (high active area). Increasing the number of SWMMs in series was found to increase permeate flow and the energy that can be generated, even when considering the pressure drop on both draw and feed side and the effect of the dilution and concentration of the draw and feed solutions. The proposed tool allows to determine the safe operating windows and operating points for maximization of energy generation for fixed and variable operating conditions.

Multilevel optimization framework to support self-sustainability of industrial processes for energy/material recovery using circular integration concept

Climate change, resource scarcity, waste reduction, and the lack of sustainability in process industries are vital concerns that civilization confronts. The process integration methodology may aid such sustainability. In this study, a novel chemical exergy resource recovery network is proposed for optimal energy and waste recovery in high-salinity-gradient chemical industries using a pressure-retarded osmosis membrane while indicating a self-sustainability and allocation in complex industrial networks. The mathematical programming paradigm is expressed as a multilevel optimization model to introduce novel ideas for explicitly modeling the trade-offs between waste and energy flows in circular integration while demonstrating industrial network’s environmental impact assessment. This problem is decomposed into two subproblems (SPs) that must be addressed sequentially. The first SP is designed to decrease the total cost of the network while reducing external resource use. The second SP formulates a mixed-integer nonlinear programming model with the objective of minimizing the environmental effects and exergy consumption rate of the network. A case study of a naphthalene-methaforming plant demonstrates the efficacy of the proposed methodology. The results showed that using a tri-level optimization technique, a considerable improvement in flowrate, total annualized cost, and energy recovery is obtained while limiting the network's environmental impact. The operating phase accounts for approximately 75% of the global warming potential output. The proposed tri-level approach based on Benders’ decomposition approach reduced the overall cost of the network by 19.29%, and 47.42 MW net power is recovered in the case study. In addition, the circular exergy use rate and environmental factor were reduced from 400 to 0.037 MW and from 2.569 to 1.481 kgCO2/year, respectively, using the tri-level decomposition approach.

Novel Thin-Film nanocomposite hollow fiber membranes in modules with reduced reverse solute flux for pressure retarded osmosis

Osmotic energy is released when mixing solutions with different salinities. Pressure retarded osmosis (PRO) is a promising membrane technology to harvest this osmotic energy. However, the current polymeric PRO membranes suffer from the high reverse solute fluxes during PRO processes, which would dramatically diminish the membrane performance, especially in big membrane modules. In order to control the reverse solute flux, two cup-like calix[n]arenes, sulfocalix[4]arene (SCA4) and sulfothiacalix[4]arene (STCAss) were incorporated into the polyamide network to enhance the PRO performance of thin-film nanocomposite (TFN) hollow fiber membranes in 1-inch modules. Due to the unique structures and the enhanced molecular-sieving abilities of both macrocyclic molecules, they were able to effectively improve the selectivity of the resultant TFN hollow fiber membranes. After optimizing the concentration of each nano-filler, it was found that the TFN membrane with 0.20 wt% of STCAss produced a PRO power density of 15.0 W/m2 and a reverse salt flux of 28.3 gMH, while the other containing 0.10 wt% of SCA4 produced a PRO power density of 14.2 W/m2 and a reverse salt flux of 31.6 gMH. In long-term PRO tests at 20 bar, the SCA4-incorporated membrane was more efficient in controlling the concentration polarization (CP) and maintaining the power density comparing to the STCAss membrane because the former has a smaller cavity opening than the latter. This research work may provide useful insights to further design PRO membranes and membrane modules for osmotic power generation.

Preparation and characterization of double-skinned FO membranes: Comparative performance between nanofiber and phase conversion membranes as supporting layers

To address the internal concentration polarization (ICP) effect and membrane fouling problems of forward osmosis technology in pressure retarded osmosis (PRO) mode, another highly selective polyamide (PA) layer was introduced on the other side of the single-skinned forward osmosis (FO) membrane. Recently, a new symmetrical nanofiber support layer has shown excellent performance. For better proof, the nanofiber support layer and the phase inversion support layer were prepared separately in this study, respectively, and two double-skinned FO membranes were obtained via interfacial polymerization. By comparing various surface physicochemical properties of the nanofiber support layer and the phase inversion support layer, it can be seen that the double-skinned PA layer formed on the surface of the nanofiber support layer had better performance. The nanofiber double-skinned FO membrane showed water flux of 19.99 LMH when using 2 M NaCl and DI water as the draw and feed solution, much higher than that of the phase inversion double-skinned FO membrane. Furthermore, the anti-fouling performance of the nanofiber double-skinned FO membrane was also better than that of the phase inversion double-skinned FO membrane. This study pointed out a new direction for a double-skinned FO membrane with high permeability selectivity and provided a promising method for anti-membrane fouling.

An environmental and economic sustainability assessment of a pressure retarded osmosis system

Desalination can meet increasing water demands, but results in high energy consumption and the discharge of highly concentrated brine. Pressure retarded osmosis (PRO) can serve as an efficient energy recovery technology for desalination with the potential to address these challenges. This study provides an environmental and economic sustainability assessment on a hypothetical full-scale PRO system by performing a life cycle assessment (LCA) and a life cycle cost analysis (LCCA). In this hypothetical case study (in Tampa, Florida, USA), the amount of recovered energy impacted most LCA categories, indicating that the overall environmental impact would be lowered when integrated with a desalination plant. The levelized cost of energy (LCOE) ranged from 0.62 $(kWh)−1 to 0.69 $(kWh)−1 depending on the feed water source. Compared to wind power and photovoltaics, the PRO system was highly environmentally competitive due to low GHG emissions, but the baseline design was not found to be economically competitive. Lowering the LCOE would be possible when the feed solution comes from a wastewater treatment plant within 1 km and when high-quality treated wastewater is used to avoid pretreatment; this design achieved an LCOE of 0.14 $(kWh)−1. Future research is recommended on membrane advancements and maintenance improvements for fouling mitigation.

A differential evolution based henry gas solubility optimizer for dynamic performance optimization problems of PRO system

As a promising renewable energy resource, pressure retarded osmosis (PRO) is developing rapidly. Under the fluctuating environmental condition, fewer oscillations and higher convergence speeds are necessary for a stable operation of the PRO system and higher energy extraction. Metaheuristic algorithms are potential techniques for PRO at an accelerating rate, but the balance between the exploitation and exploration process is an inherent challenge in real-time efficiency and accuracy. In this work, a differential evolution (DE) based henry gas solubility optimization (EHO) is proposed for the scaled-up PRO module based on experimental data with respect to varying operational situations. In EHO, the DE mechanism and levy flight technique are applied to enhance the reliability and effectiveness of the classic HGSO strategy. The most advanced intelligent algorithms, including DFOA, GWO and WOA, are conducted for competitive research for verification purposes. Moreover, the superiority of the proposed algorithm has been evaluated and validated in complex operational environments under variations in temperature, draw concentrations and flow rates levels. The modelling results indicate that compared with the classic HGSO method, the proposed method leads to an improvement of the extracted specific energy of the PRO system by an astonishing 84.21%, 111.11% and 175.03%, respectively.

Energetic and exergetic analyses of a closed-loop pressure retarded membrane distillation (PRMD) for low-grade thermal energy utilization and freshwater production

Low-grade thermal energy is abundant but hard to utilize because of the low energy availability. Recently, research on low-grade thermal energy has been conducted to enhance the energy availability. One of these approaches, pressure-retarded membrane distillation (PRMD), has been proposed. It was designed by combining the operating principles of membrane distillation and pressure-retarded osmosis. In this paper, a closed-loop PRMD is proposed to include the structure of thermo-osmotic energy conversion (TOEC) to enable simultaneous desalination and power generation. Mathematical modeling and energetic/exergetic analyses are performed through MATLAB, to evaluate the feasibility of new process. In addition, a sensitivity analysis is conducted to analyze the energy efficiency of the process. The results reveal that the closed-loop PRMD system requires the lowest heat input (1.74 kW/m2) and increases the electrical energy production (1.91 W/m2) to achieve the same water permeation, compared with existing processes. In addition, unlike the TOEC process, water and electrical energy can be produced simultaneously. Moreover, the exergy destruction of the closed-loop PRMD is observed to be the lowest. Thus, the proposed closed-loop PRMD is a promising solution for desalination and energy harvesting systems from low-grade thermal energy.

Optimizing pressure retarded osmosis spacer geometries: An experimental and CFD modeling study

Existing desalination plants face the challenges of high energy costs and environmental impacts from brine disposal. Pressure retarded osmosis (PRO) is a membrane-based technology that could mitigate these issues by capturing the potential energy in the salinity gradient between brine and dilute (e.g., freshwater/wastewater) solutions. Currently, a major challenge facing PRO is concentration polarization (CP), which is the reduction of the salinity gradient caused by the buildup of solutes along both the brine side of the membrane surface (external) and within the membrane support structure (internal). CP can be reduced using membrane spacers, but they have the drawback of increasing the pressure drop along the length of the feed channel. Therefore, it is important to design a membrane spacer that can minimize the effects of both CP and the internal pressure drop. In this study, we simulated the effect that membrane spacer geometries have on CP and the internal pressure drop via computational fluid dynamics (CFD) using the open-source software, OpenFOAM. Simulations were validated using experimental results for five physical spacer geometries on a bench-scale PRO system. The highest performing physical spacer geometry was a 47 mil (1.41 mm) thick parallel oriented spacer (47P), which was then improved upon through integrated CFD-based optimization using the open-source optimization toolkit, DAKOTA. Single-objective genetic algorithms were used to iteratively modify the spacer geometry by increasing the linearity of the thinner cross-strand and decreasing the linearity of the thicker parallel strand, which created a more hexagonally shaped cross-section. This modification was able to increase overall system performance, which was represented by the ratio of the mass flux density of the feed permeate through the membrane to the pressure drop across the length of the feed channel, by 16.3%. This suggests that a membrane spacer with a parallel hexagonal configuration allows the fluid to flow with minimal internal pressure drop while still creating the necessary back-mixing from the membrane surface to the bulk fluid needed to promote mass transfer and reduce the impacts of CP. Implementing these improvements in spacer design would cause the feed pump to consume less energy, which would increase the net energy generation potential and overall sustainability of PRO systems.