The Experts below are selected from a list of 1530 Experts worldwide ranked by ideXlab platform
Bruce E. Logan - One of the best experts on this subject based on the ideXlab platform.
-
influence of solution concentration and salt types on the performance of Reverse Electrodialysis cells
Journal of Membrane Science, 2015Co-Authors: Weihua He, Bruce E. LoganAbstract:Abstract The influence of salt concentrations on the performance of Reverse Electrodialysis (RED) stacks has rarely been investigated using thermolytic salts such as NH4HCO3, that can be regenerated using waste heat and can be set at any desired concentration below saturation limits. Here, power densities produced by a RED stack were first investigated using different NaCl concentrations, and then tested using NH4HCO3. The power produced by the RED stack increased with NaCl concentrations from 0.6 M to 3.6 M in the HC (high concentration) solution, but it did not increase at higher salt concentrations due to limited ion exchange membrane capacity. NaCl concentrations larger than 0.14 M in the LC (low concentration) solution decreased power primarily as a result of lower salinity ratios (
-
hydrogen production from continuous flow microbial Reverse Electrodialysis electrolysis cells treating fermentation wastewater
Bioresource Technology, 2015Co-Authors: Valerie J Watson, Marta C Hatzell, Bruce E. LoganAbstract:Abstract A microbial Reverse-Electrodialysis electrolysis cell (MREC) was used to produce hydrogen gas from fermentation wastewater without the need for additional electrical energy. Increasing the number of cell pairs in the Reverse Electrodialysis stack from 5 to 10 doubled the maximum current produced from 60 A/m 3 to 120 A/m 3 using acetate. However, more rapid COD removal required a decrease in the anolyte hydraulic retention time (HRT) from 24 to 12 h to stabilize anode potentials. Hydrogen production using a fermentation wastewater (10 cell pairs, HRT = 8 h) reached 0.9 ± 0.1 L H 2 /L reactor /d (1.1 ± 0.1 L H 2 /g-COD), with 58 ± 5% COD removal and a coulombic efficiency of 74 ± 5%. These results demonstrated that consistent rates of hydrogen gas production could be achieved using an MREC if effluent anolyte COD concentrations are sufficient to produce stable anode potentials.
-
patterned ion exchange membranes for improved power production in microbial Reverse Electrodialysis cells
Journal of Power Sources, 2014Co-Authors: Geoffrey M Geise, Fang Zhang, Yujie Feng, Michael A Hickner, Bruce E. LoganAbstract:Abstract Power production in microbial Reverse-Electrodialysis cells (MRCs) can be limited by the internal resistance of the Reverse Electrodialysis stack. Typical MRC stacks use non-conductive spacers that block ion transport by the so-called spacer shadow effect. These spacers can be relatively thick compared to the membrane, and thus they increase internal stack resistance due to high solution (ohmic) resistance associated with a thick spacer. New types of patterned anion and cation exchange membranes were developed by casting membranes to create hemispherical protrusions on the membranes, enabling fluid flow between the membranes without the need for a non-conductive spacer. The use of the patterned membrane decreased the MRC stack resistance by ∼22 Ω, resulting in a 38% increase in power density from 2.50 ± 0.04 W m −2 (non-patterned membrane with a non-conductive spacer) to 3.44 ± 0.02 W m −2 (patterned membrane). The COD removal rate, coulombic efficiency, and energy efficiency of the MRC also increased using the patterned membranes compared to the non-patterned membranes. These results demonstrate that these patterned ion exchange membranes can be used to improve performance of an MRC.
-
methane production in microbial Reverse Electrodialysis methanogenesis cells mrmcs using thermolytic solutions
Environmental Science & Technology, 2014Co-Authors: Fang Zhang, Xiaoyuan Zhang, Xia Huang, Bruce E. LoganAbstract:The utilization of bioelectrochemical systems for methane production has attracted increasing attention, but producing methane in these systems requires additional voltage to overcome large cathode overpotentials. To eliminate the need for electrical grid energy, we constructed a microbial Reverse-Electrodialysis methanogenesis cell (MRMC) by placing a Reverse Electrodialysis (RED) stack between an anode with exoelectrogenic microorganisms and a methanogenic biocathode. In the MRMC, renewable salinity gradient energy was converted to electrical energy, thus providing the added potential needed for methane evolution from the cathode. The feasibility of the MRMC was examined using three different cathode materials (stainless steel mesh coated with platinum, SS/Pt; carbon cloth coated with carbon black, CC/CB; or a plain graphite fiber brush, GFB) and a thermolytic solution (ammonium bicarbonate) in the RED stack. A maximum methane yield of 0.60 ± 0.01 mol-CH4/mol-acetate was obtained using the SS/Pt biocath...
-
salt concentration differences alter membrane resistance in Reverse Electrodialysis stacks
Environmental Science and Technology Letters, 2014Co-Authors: Geoffrey M Geise, Marta C Hatzell, Michael A Hickner, Andrew J Curtis, Bruce E. LoganAbstract:Membrane ionic resistance is usually measured by immersing the membrane in a salt solution at a single, fixed concentration. While salt concentration is known to affect membrane resistance when the same concentration is used on both sides of the membrane, little is known about membrane resistance when the membrane is placed between solutions of different concentrations, such as in a Reverse Electrodialysis (RED) stack. Ionic resistance measurements obtained using Selemion CMV and AMV that separated sodium chloride and ammonium bicarbonate solutions of different concentrations were greater than those measured using only the high-concentration solution. Measured RED stack resistances showed good agreement with resistances calculated using an equivalent series resistance model, where the membranes accounted for 46% of the total stack resistance. The high area resistance of the membranes separating different salt concentration solutions has implications for modeling and optimizing membranes used in RED systems.
Giorgio Micale - One of the best experts on this subject based on the ideXlab platform.
-
The first operating thermolytic Reverse Electrodialysis heat engine
Journal of Membrane Science, 2020Co-Authors: Francesco Giacalone, Alessandro Tamburini, Andrea Cipollina, F. Vassallo, Francesca Scargiali, Giorgio MicaleAbstract:Abstract Thermolytic Reverse Electrodialysis heat engine (t-RED HE) has been recently proposed as a technology for converting low-temperature waste heat into electricity. The construction and operation of the first world lab-scale prototype unit are reported. The system consists of: (i) a Reverse Electrodialysis unit where, the concentration gradient between two solutions of thermolytic salts is converted into electricity and (ii) a thermally-driven regeneration unit where low-temperature heat is used to restore the initial conditions of the two feed streams. Regeneration is based on a degradation process of salts into gaseous ammonia and carbon dioxide, which can be removed almost entirely from the exhausted dilute solution by vapour stripping and, subsequently, reabsorbed into the exhausted concentrate solution, thus restoring the initial salinity gradient of the two streams. For the first time, the feasibility of the process was demonstrated through an experimental campaign to evaluate the system performance via long-run tests.
-
Optimization of net power density in Reverse Electrodialysis
Energy, 2019Co-Authors: Michele Ciofalo, Andrea Cipollina, Luigi Gurreri, Mariagiorgia La Cerva, Massimiliano Di Liberto, Giorgio MicaleAbstract:Abstract Reverse Electrodialysis (RED) extracts electrical energy from the salinity difference between two solutions using selective ion exchange membranes. In RED, conditions yielding a large net power density (NPD) are generally desired, due to the still large cost of the membranes. NPD depends on a large number of physical and geometric parameters. Some of these, for example the inlet concentrations of concentrate and diluate, can be regarded as “scenario” variables, imposed by external constraints (e.g., availability) or chosen by different criteria than NPD maximization. Others, namely the thicknesses HCONC, HDIL and the velocities UCONC, UDIL in the concentrate and diluate channels, can be regarded as free design parameters and can be chosen so as to maximize NPD. In the present study, a simplified model of a RED stack was coupled with an optimization algorithm in order to determine the conditions of maximum NPD in the space of the variables HCONC, HDIL,UCONC, UDIL for different sets of “scenario” variables. The study shows that an optimal choice of the free design parameters for any given scenario, as opposed to the adoption of standard fixed values for the same parameters, may provide significant improvements in NPD.
-
Application of Reverse Electrodialysis to site-specific types of saline solutions: A techno-economic assessment
Energy, 2019Co-Authors: Francesco Giacalone, Giorgio Micale, Alessandro Tamburini, Michael Papapetrou, George Kosmadakis, Andrea CipollinaAbstract:Abstract Salinity gradients are a non-conventional source of renewable energy based on the recovery of the Gibbs free energy related to the mixing of solutions at different concentrations. Reverse Electrodialysis is a promising and innovative technology able to convert this energy directly into electric current. The worldwide availability of salinity gradients is limited to those locations where water bodies at different salinity levels are present. The present work analyses a number of different scenarios worldwide, in locations where salinity gradients are naturally available or generated by anthropogenic activities. A techno-economic model of the Reverse Electrodialysis process is presented. The model is used to evaluate the energy that can be harvested in each real scenario using a Reverse Electrodialysis plant and relevant results are reported in terms of power densities and energy yields. Finally, an economic analysis based on the estimation of the Levelized Cost Of Electricity (LCOE) for each scenario is presented, and perspective considerations are reported. Results suggest that competitive values of LCOE may be achieved in some scenarios.
-
Reverse Electrodialysis heat engine with multi-effect distillation: Exergy analysis and perspectives
Energy Conversion and Management, 2019Co-Authors: Bartolomé Ortega-delgado, Francesco Giacalone, Pietro Catrini, Alessandro Tamburini, Andrea Cipollina, Antonio Piacentino, Giorgio MicaleAbstract:Abstract The increasing worldwide energy demand is rising the interest on alternative power production technologies based on renewable and emission-free energy sources. In this regard, the closed-loop Reverse Electrodialysis heat engine is a promising technology with the potential to convert low-grade heat into electric power. The Reverse Electrodialysis technology has been under investigation in the last years to explore the real potentials for energy generation from natural and artificial solutions, and recent works have been addressing also the potential of its coupling with regeneration strategies, looking at medium and large energy supply purposes. In this work, for the first time, a comprehensive exergy analysis at component level is applied to a Reverse Electrodialysis heat engine with multi-effect distillation in order to determine the real capability of the waste heat to power conversion, identifying and quantifying the sources of exergy destruction. In particular, sensitivity analyses have been performed to assess the influence of the main operating conditions (i.e. solutions concentration and velocity) and design features (aspect ratio of the pile), characterizing the most advantageous scenarios and including the effect of new generations of membranes. Results show that the multi-effect distillation unit is the main source of exergy destruction. Also, using high-performing membranes, inlet solutions concentration and velocity of 4.5–0.01 mol/L and 0.2–0.36 cm/s, respectively, a global exergy efficiency of 24% is reached for the system, proving the high potential of this technology to sustainably convert waste heat into power.
-
thermolytic Reverse Electrodialysis heat engine model development integration and performance analysis
Energy Conversion and Management, 2019Co-Authors: Francesco Giacalone, Giorgio Micale, Alessandro Tamburini, F. Vassallo, Francesca Scargiali, Lyle Griffin, Mariachiara Ferrari, Andrea CipollinaAbstract:Abstract Salinity gradient heat engines represent an innovative and promising way to convert low-grade heat into electricity by employing salinity gradient technology in a closed-loop configuration. Among the aqueous solutions which can be used as working fluid, ammonium bicarbonate-water solutions appear very promising due to their capability to decompose at low temperature. In this work, an experimentally validated model for a Reverse Electrodialysis heat engine fed with ammonium bicarbonate-water solutions was developed. The model consists of two validated sub-models purposely integrated, one for the Reverse Electrodialysis unit and the other for the stripping/absorption regeneration unit. The impact of using current commercial membranes and future enhanced membranes on the efficiency of the system was evaluated, along with the effect of operating and design parameters through sensitivity analyses. Results indicated that exergy efficiency up to 8.5% may be obtained by considering enhanced future membranes and multi-column regeneration units.
Andrea Cipollina - One of the best experts on this subject based on the ideXlab platform.
-
The first operating thermolytic Reverse Electrodialysis heat engine
Journal of Membrane Science, 2020Co-Authors: Francesco Giacalone, Alessandro Tamburini, Andrea Cipollina, F. Vassallo, Francesca Scargiali, Giorgio MicaleAbstract:Abstract Thermolytic Reverse Electrodialysis heat engine (t-RED HE) has been recently proposed as a technology for converting low-temperature waste heat into electricity. The construction and operation of the first world lab-scale prototype unit are reported. The system consists of: (i) a Reverse Electrodialysis unit where, the concentration gradient between two solutions of thermolytic salts is converted into electricity and (ii) a thermally-driven regeneration unit where low-temperature heat is used to restore the initial conditions of the two feed streams. Regeneration is based on a degradation process of salts into gaseous ammonia and carbon dioxide, which can be removed almost entirely from the exhausted dilute solution by vapour stripping and, subsequently, reabsorbed into the exhausted concentrate solution, thus restoring the initial salinity gradient of the two streams. For the first time, the feasibility of the process was demonstrated through an experimental campaign to evaluate the system performance via long-run tests.
-
Optimization of net power density in Reverse Electrodialysis
Energy, 2019Co-Authors: Michele Ciofalo, Andrea Cipollina, Luigi Gurreri, Mariagiorgia La Cerva, Massimiliano Di Liberto, Giorgio MicaleAbstract:Abstract Reverse Electrodialysis (RED) extracts electrical energy from the salinity difference between two solutions using selective ion exchange membranes. In RED, conditions yielding a large net power density (NPD) are generally desired, due to the still large cost of the membranes. NPD depends on a large number of physical and geometric parameters. Some of these, for example the inlet concentrations of concentrate and diluate, can be regarded as “scenario” variables, imposed by external constraints (e.g., availability) or chosen by different criteria than NPD maximization. Others, namely the thicknesses HCONC, HDIL and the velocities UCONC, UDIL in the concentrate and diluate channels, can be regarded as free design parameters and can be chosen so as to maximize NPD. In the present study, a simplified model of a RED stack was coupled with an optimization algorithm in order to determine the conditions of maximum NPD in the space of the variables HCONC, HDIL,UCONC, UDIL for different sets of “scenario” variables. The study shows that an optimal choice of the free design parameters for any given scenario, as opposed to the adoption of standard fixed values for the same parameters, may provide significant improvements in NPD.
-
Application of Reverse Electrodialysis to site-specific types of saline solutions: A techno-economic assessment
Energy, 2019Co-Authors: Francesco Giacalone, Giorgio Micale, Alessandro Tamburini, Michael Papapetrou, George Kosmadakis, Andrea CipollinaAbstract:Abstract Salinity gradients are a non-conventional source of renewable energy based on the recovery of the Gibbs free energy related to the mixing of solutions at different concentrations. Reverse Electrodialysis is a promising and innovative technology able to convert this energy directly into electric current. The worldwide availability of salinity gradients is limited to those locations where water bodies at different salinity levels are present. The present work analyses a number of different scenarios worldwide, in locations where salinity gradients are naturally available or generated by anthropogenic activities. A techno-economic model of the Reverse Electrodialysis process is presented. The model is used to evaluate the energy that can be harvested in each real scenario using a Reverse Electrodialysis plant and relevant results are reported in terms of power densities and energy yields. Finally, an economic analysis based on the estimation of the Levelized Cost Of Electricity (LCOE) for each scenario is presented, and perspective considerations are reported. Results suggest that competitive values of LCOE may be achieved in some scenarios.
-
Reverse Electrodialysis heat engine with multi-effect distillation: Exergy analysis and perspectives
Energy Conversion and Management, 2019Co-Authors: Bartolomé Ortega-delgado, Francesco Giacalone, Pietro Catrini, Alessandro Tamburini, Andrea Cipollina, Antonio Piacentino, Giorgio MicaleAbstract:Abstract The increasing worldwide energy demand is rising the interest on alternative power production technologies based on renewable and emission-free energy sources. In this regard, the closed-loop Reverse Electrodialysis heat engine is a promising technology with the potential to convert low-grade heat into electric power. The Reverse Electrodialysis technology has been under investigation in the last years to explore the real potentials for energy generation from natural and artificial solutions, and recent works have been addressing also the potential of its coupling with regeneration strategies, looking at medium and large energy supply purposes. In this work, for the first time, a comprehensive exergy analysis at component level is applied to a Reverse Electrodialysis heat engine with multi-effect distillation in order to determine the real capability of the waste heat to power conversion, identifying and quantifying the sources of exergy destruction. In particular, sensitivity analyses have been performed to assess the influence of the main operating conditions (i.e. solutions concentration and velocity) and design features (aspect ratio of the pile), characterizing the most advantageous scenarios and including the effect of new generations of membranes. Results show that the multi-effect distillation unit is the main source of exergy destruction. Also, using high-performing membranes, inlet solutions concentration and velocity of 4.5–0.01 mol/L and 0.2–0.36 cm/s, respectively, a global exergy efficiency of 24% is reached for the system, proving the high potential of this technology to sustainably convert waste heat into power.
-
thermolytic Reverse Electrodialysis heat engine model development integration and performance analysis
Energy Conversion and Management, 2019Co-Authors: Francesco Giacalone, Giorgio Micale, Alessandro Tamburini, F. Vassallo, Francesca Scargiali, Lyle Griffin, Mariachiara Ferrari, Andrea CipollinaAbstract:Abstract Salinity gradient heat engines represent an innovative and promising way to convert low-grade heat into electricity by employing salinity gradient technology in a closed-loop configuration. Among the aqueous solutions which can be used as working fluid, ammonium bicarbonate-water solutions appear very promising due to their capability to decompose at low temperature. In this work, an experimentally validated model for a Reverse Electrodialysis heat engine fed with ammonium bicarbonate-water solutions was developed. The model consists of two validated sub-models purposely integrated, one for the Reverse Electrodialysis unit and the other for the stripping/absorption regeneration unit. The impact of using current commercial membranes and future enhanced membranes on the efficiency of the system was evaluated, along with the effect of operating and design parameters through sensitivity analyses. Results indicated that exergy efficiency up to 8.5% may be obtained by considering enhanced future membranes and multi-column regeneration units.
J Veerman - One of the best experts on this subject based on the ideXlab platform.
-
Reverse Electrodialysis: Applications
Sustainable Energy from Salinity Gradients, 2016Co-Authors: Andrea Cipollina, Giorgio Micale, J Veerman, Alessandro Tamburini, Michele Tedesco, Luigi Gurreri, Simon GrasmanAbstract:Abstract Reverse Electrodialysis (RED) technology has grown significantly in the last decade, gaining a fast increase in its technology readiness level and presenting some interesting examples of RED pilot systems operating under very different real environments. In this chapter, an overview of technological developments and piloting examples are reported. In particular, a short introduction is given on the historical trend of RED technology growth, followed by a careful analysis of which feed solutions can be adopted and how these can affect the process performance, potentials, and applications. Most prominent fluid dynamics aspects for the RED process are presented, highlighting how these can influence the design and operation of RED systems, being able to affect the overall performance of a RED plant. For the first time, two practical experiences of RED technology piloting are analysed: the Afsluitdijk pilot plant in The Netherlands ( Blue Energy project), operating with seawater and river water, and the Marsala pilot plant in Italy ( REAPower project), operating with concentrated brines and saline waters. The main achievements, progresses, growth directions and world key actors in the technology development will be underlined. Finally, the envisaged R&D routes and perspectives for the future of RED technology development will be outlined.
-
Reverse Electrodialysis: Fundamentals
Sustainable Energy from Salinity Gradients, 2016Co-Authors: J Veerman, David A VermaasAbstract:Renewable energy can be captured when mixing two water volumes with different salt concentration in Reverse Electrodialysis (RED), using ion exchange membranes (IEMs). This chapter describes the historical development of RED, membrane transport phenomena, practical RED operation, benchmark parameters and R&D perspectives. Amongst others, the effects of feed water composition, membrane and stack design and flow direction on the obtainable power density and efficiency are discussed for practical RED devices. This chapter reviews current research and indicates the remaining challenges and R&D perspectives for producing electricity from salinity gradients with RED.
-
potential of brackish water and brine for energy generation by salinity gradient power Reverse Electrodialysis sgp re
RSC Advances, 2014Co-Authors: Ramato Ashu Tufa, J Veerman, Willem Van Baak, Simon Grasman, Efrem Curcio, Enrica Fontananova, Gianluca Di ProfioAbstract:In the present work, a salinity gradient power-Reverse Electrodialysis (SGP-RE) unit was tested for the production of electrical energy by exploiting the chemical potential of real brackish water and exhaust brine from a solar pond. A cross-flow SGP-RE module (REDstack B.V.), equipped with AEM-80045 and CEM-80050 membranes specifically developed by Fujifilm Manufacturing Europe B.V. within the EU-funded project REAPOWER (“Reverse Electrodialysis Alternative Power Production”), was able to generate a maximum power density (expressed in W m−2 membrane pair – MP) of 3.04 W m−2 MP when operated with pure NaCl aqueous solutions (0.1 M in low concentration compartment – LCC, 5 M in high concentration compartment – HCC) at 20 °C and at a recirculation rate of 20 L h−1. However, a drastic reduction to 1.13 W m−2 (−63%) was observed when feeding the SGP-RE unit with artificial multi-ion solutions mimicking real brackish water and exhaust brine. Further experimental activity allowed to identify Mg2+ ion as responsible for the significant increase in stack resistance and consequent depletion in SGP-RE performance. Therefore, specific softening treatments of the real solutions should be considered in order to maintain the process efficiency at practical level.
-
high efficiency in energy generation from salinity gradients with Reverse Electrodialysis
ACS Sustainable Chemistry & Engineering, 2013Co-Authors: David A Vermaas, J Veerman, Menachem Elimelech, Michel Saakes, Kitty NijmeijerAbstract:Renewable energy can be captured from the mixing of salt and fresh water in Reverse Electrodialysis. This paper investigates the energy efficiency of this process for feed waters that pass a Reverse Electrodialysis cell once and waters that pass multiple cells or electrode segments. So far, the maximum theoretical energy efficiency was considered to be 50% when the feed waters pass a single cell once; significantly higher efficiencies could only be obtained when the waters were recirculated or passed multiple electrodes. In this study, we show that the ion transport corresponding to the obtained energy and the electromotive force mutually influence each other, which enables capture of more than 50% (even up to 95%) of the theoretical energy, even when the feedwater streams pass a Reverse Electrodialysis cell only once.
-
Reverse Electrodialysis a validated process model for design and optimization
Chemical Engineering Journal, 2011Co-Authors: J Veerman, Sybrand J Metz, Michel Saakes, G J HarmsenAbstract:Abstract Reverse Electrodialysis (RED) is a technology to generate electricity using the entropy of the mixing of sea and river water. A model is made of the RED process and validated experimentally. The model is used to design and optimize the RED process. It predicts very small differences between counter- and co-current operation. It was decided to focus on co-current design because co-current operation causes smaller local pressure differences between the river and seawater compartments—hence smaller risk of leakages and the possibility to use very thin membranes with high fluxes and very open spacer structures with low hydrodynamic resistance. Segmentation of the electrodes proved to increase the power density by about 15% under realistic operational conditions. The model shows that with smaller systems – in terms of length of the flow path – higher power densities are possible. This effect is rather dramatical and poses a challenge for designing improved RED stacks on large commercial scale. It is suggested to reduce the flow path length by applying a fractal structure design of the spacers. Such structures can be made by profiling the membrane.
Cees J N Buisman - One of the best experts on this subject based on the ideXlab platform.
-
influence of multivalent ions on power production from mixing salt and fresh water with a Reverse Electrodialysis system
Journal of Membrane Science, 2009Co-Authors: J W Post, Hubertus V M Hamelers, Cees J N BuismanAbstract:Reverse Electrodialysis is a membrane-based technique for production of sustainable electricity from controlled mixing of a diluted electrolyte solution (e.g., river water) and a concentrated electrolyte solution (e.g., sea water). Reverse Electrodialysis has been investigated with pure sodium chloride solutions. In practice, however, in most cases also other ions are present in both feed solutions. In the present paper, the effect of multivalent ions on the performance of a Reverse Electrodialysis stack was investigated. Results show that, besides a higher stack resistance in presence of multivalent ions, especially the presence of multivalent ions in the dilute solution has a lowering effect on the stack voltage. This can be explained by an observed transport of these ions from the diluted electrolyte solution to the concentrated electrolyte solution. In order to prevent or hamper this transport against the activity gradient, monovalent-selective membranes can be used. This shows indeed better results with respect to the stack voltage. Therefore, it would be beneficial to use monovalent-selective membranes in Reverse Electrodialysis, especially in the case of a relatively high content of multivalent ions in the dilute (i.e., in the first stages of the installation where the sodium chloride content in the dilute is still relatively low).
-
salinity gradient power evaluation of pressure retarded osmosis and Reverse Electrodialysis
Journal of Membrane Science, 2007Co-Authors: J W Post, J Veerman, Sybrand J Metz, Hubertus V M Hamelers, Gerrit Jan Willem Euverink, Kitty Nymeijer, Cees J N BuismanAbstract:A huge potential to obtain clean energy exists from mixing water streams with different salt concentrations. Two membrane-based energy conversion techniques are evaluated: pressure-retarded osmosis and Reverse Electrodialysis. From the literature, a comparison is not possible since the reported performances are not comparable. A method was developed which allows for a comparison of both techniques at equal conditions, with respect to power density and energy recovery. Based on the results from the model calculations, each technique has its own field of application. Pressure-retarded osmosis seems to be more attractive for power generation using concentrated saline brines because of the higher power density combined with higher energy recovery. Reverse Electrodialysis seems to be more attractive for power generation using seawater and river water. These conclusions are valid for present and latent performances of both techniques. According to the model, the potential performances of both techniques are much better than the current performances. In order to achieve these potential performances, the development of pressure-retarded osmosis must focus on membrane characteristics, i.e. increasing the water permeability of the membrane skin and optimization of the porous support. The development of Reverse Electrodialysis, however, must focus on system characteristics, i.e. optimization of the internal resistance, which is mainly determined by the width of the spacers.