Pressure Retarded Osmosis Research Articles

A Novel Hybrid Reactor of Pressure-Retarded Osmosis Coupling with Activated Sludge Process for Simultaneously Treating Concentrated Seawater Brine and Wastewater and Recovering Energy.

As an attractive way to deal with fresh water shortage, membrane-based desalination technologies are receiving increased interest. However, concentrated seawater brine, in needing further treatment, remains a main obstacle for desalination via membrane technology. Here, a hybrid technology integrating pressure-retarded osmosis with activated sludge process (PRO-MBR) was applied for simultaneously treating concentrated seawater brine and municipal wastewater. Performance of the PRO-MBR, including water flux, power density, contaminants removal, and membrane fouling was evaluated and compared at two different membrane orientations (i.e., active layer facing feed solution (AL-FS) mode and active layer facing draw solution (AL-DS) mode). During the PRO-MBR process, the municipal wastewater was completely treated regardless of the membrane orientation, which means that there was no concentrated sewage needing further treatment, owing to the biodegradation of microorganisms in the bioreactor. In the meantime, the concentrated brine of seawater desalination was diluted into the salinity level of seawater, which met the standard of seawater discharge. Owing to the high rejection of forward osmosis (FO) membrane, the removal efficiency of total organic carbon (TOC), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) was higher than 90% at both modes in the PRO-MBR. In addition, the PRO-MBR can simultaneously recover the existing osmotic energy between the municipal wastewater and the seawater brine at both modes. Compared with the AL-DS mode, the AL-FS mode took a shorter time and achieved a bigger power density to reach the same terminal point of the PRO-MBR owing to a better water flux performance. Furthermore, the membrane fouling was much more severe in the AL-DS mode. In conclusion, the current study demonstrated that the PRO-MBR at the AL-FS mode can be a promising and sustainable brine concentrate and municipal wastewater treatment technology for its simultaneous energy and water recovery.

Economic and Reliability Assessment of Hybrid PRO-RO Desalination Systems Using Brine for Salinity Gradient Energy Production

The energy requirements for desalination have made it an expensive process, however, it is still a viable and cost-effective means of water purification amidst freshwater scarcity. The management and disposal of brine is an external and extra desalination cost due to the effect of brine on the environment. The integration of Pressure Retarded Osmosis (PRO) with the Reverse Osmosis (RO) technique as modelled in this paper enhances brine management. The brine is fed back into the PRO unit to create a salinity gradient for water transfer via membrane and generate salinity gradient energy. The hybrid desalination model is designed to be powered by grid-tied offshore wind power. The use of wind power, a clean, renewable energy source devoid of carbon emission, as the main power source to drive the RO unit reduces the cost and effect of carbon emissions from the grid. The proposed model is assessed using Levelized cost of energy (LCOE), Annualized cost of the system (ACS), and cost of water (COW) as economic matrices. In contrast, loss of energy probability is used as a reliability matrix. Obtained results show a LCOE of 1.11 $/kW, ACW of $110,456, COW of 0.13 $/m3, loss of energy probability of 0.341, a low total carbon emissions of 193,323 kgCO2-e, and zero brine production. Results show that the proposed model is economically viable, technically reliable, environmentally friendly, and generally sustainable.

Predicting the performance of spiral-wound membranes in pressure-retarded osmosis processes

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.

Modification of Thin Film Composite Pressure Retarded Osmosis Membrane by Polyethylene Glycol with Different Molecular Weights.

An investigation of the effect of the molecular weight of polyethylene glycol (PEG) on thin-film composite (TFC) flat sheet polysulfone membrane performance was conducted systematically, for application in forward osmosis (FO) and pressure retarded osmosis (PRO). The TFC flat sheet PSf-modified membranes were prepared via a non-solvent phase-separation technique by introducing PEGs of different molecular weights into the dope solution. The TFC flat sheet PSf-PEG membranes were characterized by SEM, FTIR and AFM. The PSf membrane modified with PEG 600 was found to have the optimum composition. Under FO mode, this modified membrane had a water permeability of 12.30 Lm−2h−1 and a power density of 2.22 Wm−2, under a pressure of 8 bar in PRO mode, using 1 M NaCl and deionized water as the draw and feed solutions, respectively. The high water permeability and good mechanical stability of the modified TFC flat sheet PSF-PEG membrane in this study suggests that this membrane has great potential in future osmotically powered generation systems.

Critical Evaluation of Thin Film Composite Membrane on Pesticide Removal

This study focuses on how operating pressure, pesticide characteristics, membrane materials, feed solution and draw solution affect the performance of thin film composite membranes on pesticides removal. The membrane separation discussed in this review involve nanofiltration (NF), reverse osmosis (RO) and forward osmosis processes (FO) (i.e., FO mode and pressure retarded osmosis (PRO) mode). High pressure shows positive effects on NF and RO membranes flux performances, but it could deform PRO membranes. Hydrophobic pesticides that are larger in size, negatively charged with small dipole moments will result in higher retention. Besides, ions in the feed solution increased the rejection efficiency and permeate flux of membrane whereas pesticides concentration has a negative effect on their retention. pH of feed solution determines the zeta potential of membrane. As for the draw solution, NaCl at higher concentration is recommended. This paper is crucial to give an overview on ways to improve the removal of pesticides with various thin film composite membranes.

High-performance thin-film composite forward osmosis membranes with hydrophilic PDA@TiO2 nanocomposite substrate for the treatment of oily wastewater under PRO mode

The applications of thin-film composite (TFC) forward osmosis (FO) membranes are limited by low flux and strong internal concentration polarization (ICP). In this study, a simple, facile, and eco-friendly approach to improve the wettability of the FO membrane substrate using hydroxyl- and amino-functionalized TiO2 nanocomposites by polydopamine (PDA) coating on TiO2 particles is demonstrated. In our research, a composite membrane substrate was fabricated by incorporating PDA@TiO2 into polyethersulfone (PES) through the non-solvent induced phase separation (NIPS) process. Then, a selective active polyamide layer was formed by interfacial polymerization on top of the PES-PDA@TiO2 membrane substrate to obtain the resulting TFC-FO membrane. The composite membrane substrate exhibited higher hydrophilicity (about 25% lower contact angle) and higher porosity than the pristine membrane substrate. The water flux (Jw) of 34.3 L/m2h and 60.1 L/m2h was achieved for the resulting TFC-PDA@TiO2 FO membrane under FO and pressure retarded osmosis (PRO) modes which was ~174% and ~183% higher than that of the pristine TFC-FO membrane under FO and PRO modes respectively. Furthermore, the TFC-PDA@TiO2 membrane exhibited enhanced selectivity, as expressed by the decrease in the specific salt flux (Js/JW) values (from 0.48 g/L and 0.53 g/L of pristine TFC to 0.27 g/L and 0.28 g/L for TFC-PDA@TiO2 under the FO and PRO modes respectively). More importantly, the TFC-PDA@TiO2 membrane exhibited better fouling behavior with the organic foulant solution. These results demonstrate that the fabricated TFC-FO membranes have significant potential for sustainable water reclamation from oily wastewater via FO under the PRO mode.

Desalination Technology in South Korea: A Comprehensive Review of Technology Trends and Future Outlook.

Due to advances in desalination technology, desalination has been considered as a practical method to meet the increasing global fresh water demand. This paper explores the status of the desalination industry and research work in South Korea. Desalination plant designs, statistics, and the roadmap for desalination research were analyzed. To reduce energy consumption in desalination, seawater reverse osmosis (SWRO) has been intensively investigated. Recently, alternative desalination technologies, including forward osmosis, pressure-retarded osmosis, membrane distillation, capacitive deionization, renewable-energy-powered desalination, and desalination batteries have also been actively studied. Related major consortium-based desalination research projects and their pilot plants suggest insights into lowering the energy consumption of desalination and mitigation of the environmental impact of SWRO brine as well. Finally, considerations concerning further development are suggested based on the current status of desalination technology in South Korea.

Simulation of forward osmosis and pressure retarded osmosis membrane performance: Effect of TiO2 nanoparticles loading on the semi-permeable membrane

Forward osmosis (FO) has made significant progress in recent years as an emerging membrane technology for the treatment of water and wastewater. Differential osmotic pressure is used to extract pure water across a semi-permeable membrane in this process. CFD simulations were used to investigate the performance of flux changes in membrane systems in this study. This paper simulates the performance of a thin film composite (TFC) membrane with a titanium dioxide (TiO2) modified substrate in terms of FO and pressure retarded osmosis (PRO). The results showed how the simulation results (CFD) can be used to detect flux changes with additive particles. It was discovered that even a small amount of TiO2 nanoparticles can alter water flux. In the FO and PRO systems, adding 1 wt% TiO2 to the membrane matrix increased water flux by about 15% and 14%, respectively. Nevertheless, the increased solute flux was insignificant in simulation, which indicates the positive effect of adding TiO2 nanoparticles. Finally, a comparison of the results for different membranes indicated the best correlation between the simulation and experimental results, when 0.75 wt% TiO2 was used, and a relative error of 0.3% has been recorded in PRO process. Also, the maximum pure water flux rate (8·974×10−4molm2·s)obtained in the simulation of thin film nanocomposite (TFN) 1 and PRO process.

Flux Increase Occurring When an Ultrafiltration Membrane Is Flipped from a Normal to an Inverted Position—Experiments and Theory

The effects of flipping membranes with hydrophilic/hydrophobic asymmetry are well documented in the literature, but not much is known on the impact of flipping a membrane with dense/porous layer asymmetry. In this work, the pure water flux (PWF) of a commercial polyethersulfone (PES) membrane and a ceramic ultrafiltration (UF) membrane was measured in the normal and inverted positions. Our experimental results showed that the PWF was two orders of magnitude higher when the PES membrane was flipped to the inverted position, while the increase was only two times for the ceramic membrane. The filtration experiments were also carried out using solutions of bovine serum albumin and poly(vinylpyrrolidone). A mathematical model was further developed to explain the PWF increase in the inverted position based on the Bernoulli’s rule, considering a straight cylindrical pore of small radius connected to a pore of larger radius in series. It was found by simulation that a PWF increase was indeed possible when the solid ceramic membrane was flipped, maintaining its pore geometry. The flow from a layer with larger pore size to a layer with smaller pore size occurred in the backwashing of the fouled membrane and in forward and pressure-retarded osmosis when the membrane was used with its active layer facing the draw solution (AL-DS). Therefore, this work is of practical significance for the cases where the direction of the water flow is in the inverted position of the membrane.

Pressure-Retarded Osmosis Using Hollow-fiber Membrane Modules -Pilot Test Using High Salinity Water in Denmark-

Pressure-Retarded Osmosis Using Hollow-fiber Membrane Modules -Pilot Test Using High Salinity Water in Denmark-

Modeling, Simulation and Optimization of a Pressure Retarded Osmosis Power Station: Co vs. Counter Current Setting

Modeling, Simulation and Optimization of a Pressure Retarded Osmosis Power Station: Co vs. Counter Current Setting

Modeling, Simulation and Optimization of a Pressure Retarded Osmosis Power Station: Co vs. Counter Current Setting

Modeling, Simulation and Optimization of a Pressure Retarded Osmosis Power Station: Co vs. Counter Current Setting

Rational design of high power density “Blue Energy Harvester” pressure retarded osmosis (PRO) membranes using artificial intelligence-based modeling and optimization

The challenge in harvesting Salinity Gradient Power (SGP) through pressure retarded osmosis (PRO) requires design of high power density (PD) membranes and optimized process for operation. Recent studies show that for a feasible PRO operation the minimum net PD should be around 50 W/m2. In this study, a data-driven approach has been adopted for designing optimum membranes as well as operating conditions. 200 papers, from last decade, were extensively reviewed and 34 experimental research articles were shortlisted for possible data mining, to predict water flux (WF) and PD. Comprehensive screened/pre-processed data related to both membrane and process (16 inputs) was obtained from 18 articles amounting to 339 data points. Two artificial neural network (ANN) models were explored (i) Levenberg-Marquardt (ANN-LM), and (ii) Bayesian Regularization (ANN-BR) along with a combination of three different activation functions i.e., hyperbolic tangent sigmoid transfer function (Tan-Sigmoid), logarithmic sigmoid transfer function (Log-Sigmoid) in the input and output layers. Out of the six resulting combinations, the best performing combination was found to be Tan-Sigmoid activation function in both layers with ANN-BR model having an R2 value of 0.97 for WF and 0.98 for PD. Membrane properties like the type of membrane, thickness, and water permeability coefficient were found to be the major contributing factors for the prediction of WF while for PD, operating conditions such as applied pressure were found to play the major contributing factor (10–16 %). Optimization results yield a maximum WF of 147 LMH and PD of 87 W/m2. These results were compared with the solution diffusion (S-D) model.

Study of Reverse Solute Flux in Apple Juice Concentration by Forward Osmosis

Reverse solute flux(RSF) is a big challenge of forward osmosis(FO) technology. This experiment was based on the study of the performance of apple juice concentration by FO technology and the solute diffusion law of functional draw solution(sodium acetate, sodium bicarbonate and sodiumcitrate). Firstly, the basic properties of FO system were studied, including water flux, RSF and rejection rate, by varying the concentration of NaCl draw solution, influent flow rate and membrane operation mode. The concentration ability of deionized water and apple juice and solute diffusion law were analyzed. To achieve the purpose of converting the RSF into advantages, the effect of different functional draw solutions on apple juice concentration and RSF were compared. The results showed that the concentration efficiency and RSF were affected by the concentration of draw solution and membrane operation mode. The membrane mode of pressure retarded osmosis(PRO) led to the higher RSF and the concentration degree of apple juice than the FO mode. In the PRO mode, the RSF reach to 87.34±6.32 g·m−2·h−1 with the NaCl draw solution concentration of 5 mol·L−1. The ability of concentrating apple juice by different concentration of functional draw solution was various. The order of water extraction capacity from high to low was sodium bicarbonate, sodium chloride, sodium acetate, sodium citrate and the order of RSF from high to low was sodium citrate, sodium bicarbonate, sodium chloride, sodium citrate. The RSF was 29.61±2.19 g·m−2·h−1 with 2 mol·L−1 NaCl draw solution, which was only half of the same concentration of NaCl draw solution. Compared with traditional NaCl draw solution, sodium citrate draw solution could effectively control RSF.

Modern Use of Water Produced by Purification of Municipal Wastewater: A Case Study

All the urban areas of developed countries have hydric distribution grids and sewage systems for collecting municipal wastewater to treatment plants. In this way, the municipal wastewater is purified from human excreta and other minor contaminants while producing excess sludges and purified water. In arid and semi-arid areas of the world, the purified water can be used, before discharging, to enhance the energy efficiency of seawater desalination and solve the problems of marine pollution created by desalination plants. Over the past half-century, seawater desalination has gradually met demand in urbanized, oil-rich, arid areas. At the same time, technological evolution has made it possible to significantly increase the energy efficiency of the plants and reduce the unit cost of the produced water. However, for some years, these trends have flattened out. The purified water passes through the hybridized desalination plant and produces renewable osmotic energy before the final discharge in the sea to restart the descent behaviour. Current technological development of reverse osmosis (RO), pressure retarded osmosis (PRO) and very efficient energy recovery devices (ERDs) allows this. Furthermore, it is reasonable to predict that, in the short-medium term, a new generation of membranes specifically designed for improving the performance of the pressure retarded osmosis will be available. In such circumstances, the presently estimated 13-20% decrease of the specific energy consumption will improve up to more than 30%. With the hybrid plant, the salinity of the final discharged brine is like that of seawater, while the adverse effect of GHG emission will be significantly mitigated.

Optimal configuration and economic analysis of PRO-retrofitted industrial networks for sustainable energy production and material recovery considering uncertainties: Bioethanol and sugar mill case study

In this study, an optimal scheme is proposed by utilizing waste streams at a plant-wide scale along with pressure retarded osmosis (PRO) membrane allocation in complex industrial networks for energy recovery. Chemical exergy pinch analysis (ChExPA) and process graph (P-graph) are used to address the problem. The ultimate goals of utilizing the tools are (1) determine the optimal external load consumption, (2) minimizing the waste discharge, and (3) sustainable energy production while utilizing high chemical exergy potential waste discharges. A reliability assessment assisted with Monte-Carlo simulation is further performed to evaluate the proposed solutions from P-graph considering uncertainties. The effectiveness of the proposed methodology is explained using three industrial case studies which covered both intra-plant and inter-plant networks. The results indicated that ChExPA and P-graph can effectively identify the optimal location of the PRO membrane in industrial networks. Upon analyzing the complex inter-plant industrial networks 7.795 MW net power output was harnessed, and significantly higher waste of 384.92 kg/s was recovered with a levelized cost of energy of 0.073 $/kWh. The inter-plant network shows the greatest net profit which accounted for approximately $1,191,000 (i.e., 5.84 times higher than stand-alone plants) with a reasonable payback-period of 4.5 years.

Temperature effects on salinity gradient energy harvesting and utilized membrane properties – Experimental and numerical investigation

Salinity gradient energy (SGE) is a source of renewable energy which utilizes the osmotic pressure difference between two water streams of different salinities. The present paper investigates the effect of environmental water temperature variations on the performance of the pressure retarded osmosis (PRO) process employed to harvest SGE. Using experimental and numerical approaches, the effect of water temperature on water and salt permeabilities as well as membrane structure parameter have been measured using a bench scale system and a commercially available FO membrane. The water and salt permeability coefficients have been found to increase with the water temperature while the membrane structure parameter decreases. This variation in the membrane properties has enhanced the maximum power density of the PRO process by about 90% when the water temperature increases from 10 to 35 °C. New correlations to predict the membrane properties at different temperatures have been developed and validated against the tested membrane as well as other membrane properties data available in the literature. This study highlights the importance of understanding the effect of water stream temperature to accurately predict the performance of PRO process that is utilized for harvesting the salinity gradient energy.

Pressure Retarded Osmosis Power Units Modelling for Power Flow Analysis of Electric Distribution Networks

Pressure retarded osmosis (PRO) power units, which produce electrical energy from salinity gradient sources located at coastlines, are a technology still in the process of maturation; however, there is an expectation that this technology will need to be integrated into electrical distribution networks. Such integration will drive changes in the electric response of the distribution systems which may lead to harmful operating conditions. Power flow analysis is a tool used to reveal the steady-state operating condition of distribution systems and which could be extended to study and address the integration of PRO power units. To the best of the authors’ knowledge, such extension of power flow analysis has not yet been addressed in the literature. Accordingly, this paper comprehensively provides a model to evaluate the electric current and complex power produced by PRO power units. This model is directly embedded in the forward-backward sweep (FBS) method, extending the power flow analysis of electric distribution systems in this way so as to consider the integration of PRO power units. The resulting approach permits revealing of the steady-state operating response of distribution systems and the effects that may be driven by the integration of PRO power units, as corroborated through numerical results on a 14-node test distribution system.

Assessing the potential of integrally skinned asymmetric hollow fiber membranes for addressing membrane fouling in pressure retarded osmosis process

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules.

Miniaturized Salinity Gradient Energy Harvesting Devices.

Harvesting salinity gradient energy, also known as “osmotic energy” or “blue energy”, generated from the free energy mixing of seawater and fresh river water provides a renewable and sustainable alternative for circumventing the recent upsurge in global energy consumption. The osmotic pressure resulting from mixing water streams with different salinities can be converted into electrical energy driven by a potential difference or ionic gradients. Reversed-electrodialysis (RED) has become more prominent among the conventional membrane-based separation methodologies due to its higher energy efficiency and lesser susceptibility to membrane fouling than pressure-retarded osmosis (PRO). However, the ion-exchange membranes used for RED systems often encounter limitations while adapting to a real-world system due to their limited pore sizes and internal resistance. The worldwide demand for clean energy production has reinvigorated the interest in salinity gradient energy conversion. In addition to the large energy conversion devices, the miniaturized devices used for powering a portable or wearable micro-device have attracted much attention. This review provides insights into developing miniaturized salinity gradient energy harvesting devices and recent advances in the membranes designed for optimized osmotic power extraction. Furthermore, we present various applications utilizing the salinity gradient energy conversion.