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A new hierarchical model for the electrodialysis (ED) process is presented. The model has been implemented into gPROMs Modelbuilder (PSE) , allowing the development of a distributed-parameters simulation tool that combines the effectiveness of a semi-empirical modelling approach to the flexibility of a layered arrangement of modelling scales. Thanks to its structure, the tool makes possible the simulation of many different and complex layouts, requiring only membrane properties as input parameters (e.g. membrane resistance or salt and water permeability). The model has been validated against original experimental data obtained from a lab scale ED test rig. Simulation results concerning a 4-stage treatment of seawater and dynamic batch operations of brackish water desalination are presented, showing how the model can be effectively used for predictive purposes and for providing useful insights on design and optimisation. Unlabelled Image • A hierarchical model for electrodialysis based on semi-empirical approach • The model has been validated with original experimental data. • The possibility to simulate different layouts (multistage) has been assessed. • Dynamic simulations have been performed to simulate a batch operation. [ABSTRACT FROM AUTHOR]

In desalination, similarly with other industries, the cost of the final product is one of the most important criteria that define the commercial success of a specific technology. Therefore, when new projects are planned or new technologies are proposed, the analysis of the expected costs attracts a lot of attention and is compared to (perceived) costs of state-of-the-art desalination or costs of alternative fresh water supply options. This comparison only makes sense if the cost assessment methodologies are based on the same principles and use common assumptions. This paper assesses: (i) the methodologies used to calculate the water cost; (ii) the boundary conditions and (iii) the input data and assumptions. It has been found that most papers in the literature use suitable equations and boundary conditions. Also certain elements like land costs are ignored, but in most cases this is duly acknowledged and justified. However, the quality of the input data for the hardware costs, the operating costs, and the financial parameters are not always appropriate. Guidance for the methodology, data and assumptions that should be used is provided depending on the purpose for which the cost of the desalinated water is calculated. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a promising technology to extract energy from salinity gradients, especially in the areas where concentrated brine and saline waters are available as feed streams. A first pilot-scale plant was recently built in Trapani (Italy), and tested with real brackish water and brine from saltworks. The present work focuses on the scale-up of the pilot plant, reaching more than 400 m 2 of total membrane area installed and representing the largest operating RED plant so far reported in the literature. With a nominal power capacity of 1 kW, the pilot plant reached almost 700 W of power capacity using artificial brine and brackish water, while a 50% decrease in power output was observed when using real solutions. This reduction was likely due to the presence of non-NaCl ions in relatively large concentration, which negatively affected both the electromotive force and stack resistance. These results provide relevant and unique information for the RED process scale-up, representing the first step for the feasibility assessment of RED technology on large scale. [ABSTRACT FROM AUTHOR]

Three-phase processes in which particle suspension has to be achieved in conjunction with gas dispersion are traditionally carried out in sparged, baffled stirred tanks. The operation of such tanks can suffer, however, from particles tending to block the sparger holes. A viable alternative might be provided by uncovered unbaffled stirred tanks (UUSTs), where gas self-injection can occur when the free-surface vortex reaches the impeller blades and gas bubbles begin to be ingested by the liquid. In this work, the particle suspension and liquid aeration performances in three-phase UUSTs were experimentally investigated and compared with relevant literature correlations concerning baffled systems. The results show that, at least at the investigated scale, UUSTs are more efficient for suspending particles than relevant baffled systems. Impeller clearance scarcely affects power requirements. Finally, a down-pumping PBT with D/T = 1/3 was found to be the best choice for attaining complete suspension under self-aeration conditions. [ABSTRACT FROM AUTHOR]

This study focuses on computational fluid dynamics model (CFD) for simulation of demisters in multistage flash desalination (MSF). The Eulerian–Lagrangian model (steady-state and two-dimensional) was developed to simulate the demister. The model was used to simulate the flow of water vapor and brine droplets in the demister. The computational domain includes the following three zones: the vapor space above the demister, the vapor space below the demister, and the demister. The demister zone was modeled as tube banks. A sensitivity analysis of the model revealed that vapor velocity is the main parameter that affects demister performance. Additionally, the analysis indicated that vapor temperature had no effect on the pressure drop across the demister. The developed model was validated using data from both the literature and real MSF plants. Analysis indicated that model predictions and experimental data were consistent. This work gives extensive details for CFD modeling of the MSF demister. The work is based on a previous study by Al-Fulaij et al. (2014). This work is part of a group effort to develop a comprehensive CFD simulation for the entire flashing stage of the MSF process, which would provide an extremely efficient and inexpensive design and simulation tool to the desalination community. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (SGP-RE or RED) represents a viable technology for the conversion of the salinity gradient power into electric power. A comprehensive model is proposed for the RED process using sea or brackish water and concentrated brine as feed solutions. The goals were (i) reliably describing the physical phenomena involved in the process and (ii) providing information for optimal equipment design. For such purposes, the model has been developed at two different scales of description: a lower scale for the repeating unit of the system (cell pair), and a higher scale for the entire equipment (stack). The model was implemented in a process simulator, validated against original experimental information and then used to investigate the influence of the main operating factors and on power output. Feed solutions of different salinities were also tested. A good matching was found between predictions and experiments for a wide range of inlet concentrations, flow rates and feed temperatures. Optimal feed conditions, for the adopted system geometry and membranes, have been found employing brackish water (0.08-0.1 M NaCl) as dilute and brine (4.5-5 M NaCl) as concentrate to generate the highest power density at 40 °C temperature. The model can be used to explore the full potential of the RED technology, especially for any investigation regarding the future scale-up of the process. [ABSTRACT FROM AUTHOR]

This paper investigates the integration of solar and geothermal energy in a novel polygeneration system producing simultaneously: electricity, thermal energy, cooling energy and fresh water. The polygeneration system under analysis includes concentrating photovoltaic/thermal solar collectors (CPVT), a Geothermal Well (GW) a multi-effect distillation (MED) system for seawater desalination, a single-stage LiBr–H 2 O absorption chiller and additional components, such as: storage tanks, heat exchangers and balance of plant devices. The CPVT produces simultaneously electrical energy and thermal energy, at a maximum temperature of about 100 °C. The electrical energy is delivered to the grid, whereas the thermal energy can be used for different scopes. First, the thermal energy can be used for heating purposes and/or Domestic Hot Water production. As an alternative, solar thermal energy can be used to drive an absorption chiller, producing chilled water for space cooling. Finally, solar energy, in combination with the thermal energy produced by low-enthalpy (about 80 °C) geothermal wells, may be used by the MED system to convert seawater into desalinated water. Geothermal energy is also used to produce Domestic Hot Water at 45 °C. The system is dynamically simulated by means of a zero-dimensional transient simulation model. The simulation model also includes detailed control strategies, for the management of the different technologies included in such a complex system. The system is assumed to be operated in some of the several small volcanic islands in the Mediterranean Sea, assuming Pantelleria (Trapani, Italy) as main case study. Here, the availability of solar and geothermal energy is high whereas the availability of fresh water is scarce and its cost consequently high. Results show an excellent energetic performance of the system under investigation. From the economic point of view, the profitability of the system dramatically increases when user Domestic Hot Water demand is high. [ABSTRACT FROM AUTHOR]

Abstract: gPROMS software was used to study the dynamics of a multistage flash desalination brine circulation system (MSF-BR) as a function of major operating parameters. Most of the previous studies focused on MSF-BR dynamic model development however; it gave very little information on dynamic response of the system to the most significant process independent parameters. The present model was first validated against available industrial data of different plants. System dynamics were obtained upon increasing/decreasing several of the operating parameters over a range of ±15%. Results show that increase/decrease of the cooling seawater flow rate have limited effect on the system dynamics. Increasing/decreasing the brine recycle flow had more sizeable effects on the system performance. Therefore, it was not possible to operate the system below 7% decrease of the design value. The most sensitive system response was obtained as function of the heating steam temperature. As a result, increase/decrease of this parameter was limited to 2% and 3%, respectively. The system seizes to operate because of the following: increase in the brine level above the design limits (approximately 0.5m below the demister), decrease in brine level below gate height (blow through phenomena), decrease in the production capacity below the minimum design value. [Copyright &y& Elsevier]

Abstract: The possibility of increasing the solubility and activity of rhodium catalysts in the hydroformylation of 1-octene in supercritical carbon dioxide (scCO2) by attachment of tertbutyl (tBu) groups to the triarylphosphine ligand was investigated. The solubility of the parent and monoalkylated ligands in a mixture of gaseous components (CO2/CO/H2) was evaluated by visual observation in a view cell. In the case of triphenylphosphine, introduction of one tertbutyl group does not seem to affect the solubility of the phosphine. When the behaviour of (diphenyl)biphenylphosphine and (para-tertbutyldiphenyl)biphenylphosphine was compared a clear solubilising effect of the tBu group was observed. Ligands where tested in experiments using 0.22±0.01mM Rh concentration with 1-octene/Rh molar ratio close to 800, syngas pressure at 25°C of 2MPa and total pressure of 31–38MPa at 60°C. From the catalytic point of view, attachment of tBu groups on the triphenylphosphine had a detrimental effect on the catalyst activity. In the case of (diphenyl)biphenylphosphine, presence of a branched alkyl group on the diphenyl part of the phosphine allowed the catalyst activity to increase. The results presented in this work suggest that addition of tertbutyl groups to arylphosphines is not always effective to increase the scCO2 solubility and activity of Rh-based catalyst for hydroformylation in scCO2 and that the strategy for molecular design of ligands for hydroformylation in scCO2 must simultaneously take into account solubility, steric and electronic considerations. [Copyright &y& Elsevier]

Abstract: The MSF process has covered in the last years more than 50% of world production of desalinated water from the sea. Although this process has been used for several decades, the large energy requirements force to search for new and feasible ways to improve the overall thermal efficiency. Few studies have bee carried out in lab-scale, pilot and industrial MSF units, underlining the complexity of flashing phenomena and the importance of operating parameters settings for optimal performance. In the present work a study on fundamental phenomena occurring inside MSF chambers has been carried out, focusing on the dependence of flashing efficiency on operating parameters and the effects of flashing promoters. A laboratory-scale MSF unit was built and trends of efficiency parameters were studied with and without different types of efficiency promoters. [Copyright &y& Elsevier]

Abstract: The effluent streams from MSF and MED plants retain substantial thermal and mechanical energy which is usually wasted as the streams are rejected into the environment. Recent environmental studies pose the question of environmental sustainability of desalination due to the large amount of heat and brine dissipated into the sea. Moreover the use of renewable energy so far have been confined to experimental studies or to the use in remote areas and no studies have been carried out on the coupling of a solar still plant with an existing thermal desalination installation in order to take advantage of the heat streams generated by the thermal plants. The combination of a solar desalination system utilizing the heat reject or the brine from MED or MSF as feed water to the solar plant could mitigate the environmental impact and dramatically increase the efficiency and cost effectiveness of solar plant. This paper presents a number of theoretical solutions to couple a thermal plant and a solar distiller. The possibility of further increasing the ‘economical’ efficiency of the process by a batch/continuous crystalliser for producing different sea-salts has also been considered. [Copyright &y& Elsevier]

Abstract: In this paper a brief history of desalination plants in Sicily is presented together with an in-depth description of processes and operating data, relevant to the plants actually operating on the island. 5 multi stage flash (MSF) units and one reverse osmosis (RO)plant are operating in Gela (total nominal production of about 80,000 m3/d), thus providing drinking water for more than 300,000 people living in the southern coast of the island. A thermal vapour compression multiple effect distillation (TVC-MED) plant (36,000 m3/d) is operating in Trapani and a small mechanical vapour compression (MVC) unit (5000 m3/d) is located in Porto Empedocle. In the oldest MSF units in Gela, several revamping actions have been done in order to maintain an outstanding efficient operation of the plant, regardless its long working history, whereas the other plants have shown some difficulties in operation. All these matters, together with an analysis of consumptions and operating costs, are critically and thoroughly discussed in the paper. Finally some proposals of new plants in severely droughty areas are given. [Copyright &y& Elsevier]

A model aimed at predicting the behavior of inclined dense jets in a stagnant environment was proposed. The model takes into account four jet parameters (flow rate, density, inclination and diameter) and results in a set of algebraic and ordinary differential equations, which are easily solved by simple (standard) numerical methods. Model results include information on the trajectory, spreading and dilution of the inclined dense jets. Model predictions were compared with experimental data obtained with different nozzle diameters, jet flow rates, jet densities and nozzle inclinations. Despite the wide range encompassed by the experimental data analyzed, model predictions were always found to agree very well with all other available data. The model may be therefore considered as well validated. Lastly, a sample application to the design of a dense effluent diffuser is presented. [Copyright &y& Elsevier]

• Transient operation of Electrodialysis powered by renewable energy is studied. • Year-time scale simulations show the flexible operability of coupled processes. • Effective control strategies developed to guarantee target water quality. • Short-time scale simulations confirm process stability and control system efficacy. The presence of desalination systems in polygeneration facilities is usually limited by important difficulties in operating under non-stationary regimes typical of renewable energy sources. Reverse osmosis, namely the most common desalination technology, is characterised by slow dynamics that rarely adapts to the power fluctuations of renewables. Therefore, the possibility of using electrodialysis coupled with a hybrid photovoltaic/wind energy source was investigated in this work. In particular, the combination of photovoltaic and wind energy is very attractive in order to achieve a more stable energy production, while electrodialysis is claimed to be a more flexible process compared to reverse osmosis. For this reason, the aim of this work was to analyse the technical advantages of using electrodialysis in the aforementioned scenarios, Suitable transitory simulation models are implemented for modelling electrodialysis units, photovoltaic panels and wind turbines. Dynamic scenarios were analysed, looking at two different time scales. Quasi steady-state simulations were used to study the yearly operation of 4 electrodialysis units operating in parallel, demonstrating process flexibility over a wide range of produced flowrates (from 920 to 230 m3/d) and power inputs (5–45 kW) when producing drinking water at a constant NaCl outlet concentration of 0.25 g/l. Dynamic simulations were adopted to study the daily time scale, where the desalination unit control system, purposely designed and tuned, was able to maintain a relatively stable target value in presence of disturbances in power availability, i.e. with a fluctuation of the outlet concentration lower than ± 10%, in between 0,23 and 0,27 g/l. Simulation results show how the electrodialysis process is particularly suitable for the integration within polygeneration systems as energy-buffer. [ABSTRACT FROM AUTHOR]

Electrodialysis-related technologies keep spreading in multiple fields, among which water desalination still plays a major role. A new technology that has not yet been thoroughly investigated is capacitive electrodialysis (CED), which couples the standard ED with capacitive electrodes. CED has a number of advantages such as removal of toxic products and system simplification. Little mention is made of this technology in the literature and, to the best of our knowledge, no modelling works have ever been presented. In this work, the CED process has been studied through experiments and modelling. A CED model is presented for the first time. With a simple calibration based on macroscopic membrane properties and the characterisation of electrode behaviour, the model is able to simulate the dynamics of simple as well as more complex layouts. An original experimental characterisation of electrodes is presented, showing how the collected data can be implemented into the model. After a successful validation with experimental data, dynamic simulations of a single pass CED unit have been performed with the aim of assessing the effect of different capacitive electrode properties on process performance. Results show how the impact of these properties is different depending on the number of cell pairs. Unlabelled Image • The capacitive electrodialysis (CED) process is studied. • The first process model for CED is presented. • Tests in lab-scale CED unit for electrode characterisation and model validation • Single-pass CED simulations to assess the effect of electrode's properties [ABSTRACT FROM AUTHOR]

In the climate changing context, hydrogen is leading the energy transition path. The present work focuses on the green hydrogen production exploiting salinity gradients via Reverse Electrodialysis (RED), in short-circuit condition (RED SC), and Assisted RED (ARED), studied for the first time in hydrogen production as an improvement of the low current densities generated by RED. An extensive experimental campaign was carried out by feeding a RED stack with different salinity gradients and testing short-circuit-RED and Assisted RED operative conditions. Hydrogen was produced successfully with ∼100 % Faradic Efficiency (FE) and productivity up to 1.7 mol h−1 m−2. Also, the technology was compared with similar technologies and with the most established state-of-the-art electrolysers to identify advantages and disadvantages of the proposed route. Finally, a preliminary economic analysis was carried out and a minimum Levelized Cost of Hydrogen (LCOH) of 3.2 € kg−1 H2 was found, thus leaving room for further studies. [Display omitted] • Green hydrogen production from salinity gradient by Reverse Electrodialysis • Production boosting via Assisted Reverse Electrodialysis (A)RED for the first time • Investigation of hydrogen production under different operating conditions • Comparison of the proposed electrolyser with the state-of-the-art • Preliminary economic assessment with calculation of the Levelized Cost of Hydrogen [ABSTRACT FROM AUTHOR]

The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ranging from ~200 to ~800. A good qualitative agreement between simulations and experiments can be observed for the areal distribution of the normalized heat transfer coefficient. Trends of the average heat transfer coefficient are reported as functions of Re for the geometries investigated, thus providing the basis for CFD-based correlations to be used in higher-scale process models. [ABSTRACT FROM AUTHOR]

The need to reduce energy consumption in seawater Reverse Osmosis (RO) process has pushed research towards the development of new hybrid systems in which, for example, other membrane processes can be used to pre-treat seawater. Electrodialysis (ED) and Reverse Electrodialysis (RED) can act as a pre-desalting step before seawater enters the RO unit, thus leading to an important energy saving in RO. In this work, two coupled models are proposed for the RED-RO and ED-RO systems. Each process model was validated. Then a sensitivity analysis was performed to assess the effect of the integration on the overall process cost saving. The analysis was performed by changing ED or RED voltage and RO pressure and considering eight different cost scenarios. The performance of the hybrid system was compared with the stand-alone seawater RO process. Competitive scenarios were found especially for the RED-RO case, by optimizing the pre-desalting extent, with significant cost saving and promising potentials for future industrial implementation. Unlabelled Image • A validated simulation tool for hybrid membrane desalination systems is presented. • The (A)RED-RO coupling provides energy and cost savings compared to SWRO. • The ED-RO coupling turns out to be non-competitive in the investigated range. • Different costs scenarios highlight the conditions for system competitiveness. • Perspective scenarios using high performing IEMs provide significant cost savings. [ABSTRACT FROM AUTHOR]

This paper describes the experimental campaign carried out with a reverse electrodialysis (RED) demonstration plant (Marsala, Italy) with the main aims of: (i) evaluating the effect of various operating parameters, including the redox processes, on the system performances; (ii) using the plant for the simultaneous generation of electric energy and treatment of wastewater. The prototype (44 × 44 cm 2 , 500 cell pairs) was tested using both real (brackish water and brine) and artificial solutions. Tests with two different electrode rinse solutions (with or without iron redox couples) were performed. In agreement with the data obtained in the laboratory, the presence of iron ions contributes positively to the power production. The effect of flow rates in the electrode and saline compartments, as well as aging of the electrode rinse solution was also investigated. The possibility to remove an organic pollutant (the azoic dye Acid Orange 7) from the electrode solution was tested, obtaining a very fast and total removal of the pollutant. This experimental campaign represents the first demonstration in a real environment of the abilities of a RED plant to treat wastewater, thus giving useful indications for the spreading of RED technology in the near future. [ABSTRACT FROM AUTHOR]

Models of woven-type spacer-filled channels were investigated by Computational Fluid Dynamics (CFD) and parallel experiments in order to characterize the performance of Membrane Distillation (MD) modules. The case of overlapped spacers was analysed in a companion paper. Experiments were based on a non-intrusive technique using Thermochromic Liquid Crystals (TLC) and digital image processing, and provided the distribution of the local convective heat transfer coefficient on a thermally active wall. CFD simulations ranged from steady-state conditions to unsteady and early turbulent flow, covering a Reynolds number interval of great practical interest in real MD applications. A specific spacer aspect ratio (pitch-to-channel height ratio of 2) and two different spacer orientations with respect to the main flow (0° and 45°) were considered. Among the existing studies on spacer-filled channels, this is one of the first dealing with woven spacers, and one of the very few in which local experimental and computational heat transfer results are compared. Results suggest a convenience in adopting the 45° orientation for applications that can be operated at very low Reynolds numbers, since convenience decreases as the Reynolds number increases. [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental and modelling investigation on one method to reduce parasitic currents; • Proposed design to reduce ionic shortcut currents using manifold reducers; • Pressure losses were quantified with and without the presence of manifold reducers; • The model was able to calculate parasitic currents and how they varied in the stack; • The design was found to improve the performance of Acid-Base Flow Battery systems. The Acid-Base Flow Battery is an innovative and sustainable electrochemical storage system storing energy in the form of salinity and pH gradients. However, parasitic currents via manifolds dramatically affect system by reducing its Round-Trip Efficiency (RTE). This work experimentally studies this phenomenon using a purposely designed methodology involving sticks placed in the manifold ducts. Various figures of merit were calculated to evaluate battery performance in the charge and discharge phases. A mathematical model was validated and applied to investigate the ionic parasitic currents. The results highlighted the importance of studying this phenomenon, as achieving a reduction in the parasitic currents caused a 25% increase in the net power and more than tripled the RTE compared to the reference configuration without sticks. Although reducing manifold diameter increases pumping losses, it was found to be anyway really beneficial for the process performance and paves the way for future, more suitable, battery designs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Potential of Bipolar Membrane ElectroDialysis was presented. • A fully integrated multi-scale model was developed. • The model was validated through comparison with original experimental data. • A sensitivity to design and operating variables was presented. • A preliminary techno-economic analysis was carried out. Bipolar membrane electrodialysis (BMED) is a technology combining solute and solvent dissociation to produce chemicals. In the recent decades, it has been typically studied for the production of valuable acid and base solutions from salt streams. Although many works have been devoted to the experimental investigation of BMED, only a few efforts have focused on its mathematical modelling. In the present work, a comprehensive process model based on a multi-scale approach with distributed parameters is presented for the first time. Five models related to four different dimensional scales were fully integrated to form a comprehensive tool. The integrated model was developed by using the process simulator gPROMS Model builder and was based on a semi-empirical approach combining high prediction accuracy and low computational demand. Once validated through a wide range of experimental data, the model capability was shown by carrying out a broad sensitivity analysis assessing the performance of the BMED technology for industrial-scale applications. Results showed how the performance of a BMED unit changes with both varying process conditions and the installed membrane area. Particularly, the non-ideal phenomena that reduce the produced NaOH concentration and increase the energy consumption were thoroughly investigated. Finally, this study demonstrated that a Levelized Cost Of Caustic Soda of about 280 € ton-1 NaOH can be obtained, thus making this technology a possible candidate for the industrial production of caustic soda from brines in the future. [ABSTRACT FROM AUTHOR]

Wastewaters generated by crude oil extraction processes, called "produced waters" (PWs), are complex solutions that contain organic compounds, mainly hydrocarbons, and often exhibit high salinity. The large amounts of PWs represent a global issue because of their environmental impact. An approach widely used in the oil industry is the reinjection of this wastewater into the extraction wells after a suitable treatment. The high salt concentration of such solutions may be used in salinity gradient technologies to produce green electricity. Among these technologies, reverse electrodialysis (RED) is one of the most promising. In this work, the application of RED for energy generation from two different real oil industry brines was investigated. An experimental campaign was performed by testing 10 × 10 cm2 units in long-run continuous operations, monitoring the performance for more than 25 days. Fouling phenomena, occurring during the continuous operation, decrease the unit performance and several anti-fouling strategies were adopted to tackle this issue. As a result, a positive net power density for up to 18 days of continuous operation was obtained. A maximum power density of about 2.5 W/m2 was observed, demonstrating how the RED technology could be an important strategy to harvest energy from an industrial waste. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this study is to focus on simulation of wire mesh demisters in multistage flash desalination (MSF) plants. The simulation is made by the use of computational fluid dynamics (CFD) software. Design/methodology/approach – A steady state and two-dimensional (2D) model was developed to simulate the demister. The model employs an Eulerian-Eulerian approach to simulate the flow of water vapor and brine droplets in the demister. The computational domain included three zones, which are the vapor space above and below the demister and the demister. The demister zone was modeled as a tube bank arrange or as a porous media. Findings – Sensitivity analysis of the model showed the main parameters that affect demister performance are the vapor velocity and the demister permeability. On the other hand, the analysis showed that the vapor temperature has no effect on the pressure drop across the demister. Research limitations/implications – The developed model was validated against previous literature data as well as real plant data. The analysis shows good agreement between model prediction and data. Originality/value – This work is the first in the literature to simulate the MSF demister using CFD modeling. This work is part of a group effort to develop a comprehensive CFD simulation for the entire flashing stage of the MSF process, which would provide an extremely efficient and inexpensive design and simulation tool to the desalination community. [ABSTRACT FROM AUTHOR]

In the present work Electrodialysis with Bipolar Membranes (EDBM) for brine valorisation is for the first time investigated for the simultaneous production of hydrogen and chemicals. EDBM allows current densities one order of magnitude higher than ED and RED electro-membrane processes, making the technology more attractive to the hydrogen market. In this work, an experimental campaign with the Hydrogen-EDBM (H-EDBM) was conducted for the first time, investigating different configurations consisting of different end-membranes for the electrode compartments. The results showed 98 % ±2 % faradic efficiency for hydrogen production, with a productivity of up to 18.4 mol h−1 m−2 at the current density of 1000 A m−2. In addition, the Bipolar Membranes allow the simultaneous production of chemicals such as NaOH, for which a Current Efficiency of 96 % and a Specific Energy Consumptions (SECs) of 1.78 kWh kg NaOH −1 were obtained. Eventually, the research was completed with a preliminary economic analysis combining the different operations and costs of the tested configurations in order to identify the optimum of the process. The Levelized Costs Of Hydrogen (LCOH) and of NaOH (LCONaOH) were used as performance parameters. The minimum LCONaOH of 0.13 € kg NaOH −1 and LCOH of 2.4 € kg H2 −1 were found when bipolar membranes are used as end-membranes and the unit is coupled with onshore wind plant, identifying this configuration as the most promising. Collected results show a great potential for the H-EDBM, thus fully justifying future more in-depth analyses. [Display omitted] • First hydrogen production through electrodialysis with bipolar membranes (H-EDBM) • Experimental campaign with different end-membranes up to 1000 A m−2 current density • Economic assessment to find the best cost-effective configuration • Bipolar end-membranes allow constant concentrations of catholyte and anolyte. • H-EDBM has been demonstrated to be a viable technology for H 2 production. [ABSTRACT FROM AUTHOR]

Water pollution remains a critical issue in the global mining industry. Moreover, the access to a reliable source of raw materials such as Cu, Zn, Mg and Rare Earth Elements has become a challenge for the European Union. In this context, the treatment of Acidic Mine Waters (AMW) with a circular perspective can be a solution to both challenges. This study focused on the integration of crystallization processes and nanofiltration (NF) to selectively recover Mg(OH) 2 (s) and reclaim AMW for irrigation purposes from the Aznalcóllar open-pit (1629 mg/L Mg2+, 360 mg/L Ca2+ and 10,962 mg/L SO 4 2−). The pre-treatment, involving selective precipitation, attained removals higher than 95 % of transitions elements. Different concentrations of NaOH (0.16 M, 0.25 M, 0.5 M) were used for the crystallization of Mg(OH) 2 (s), affecting the morphology and content of the final product. The removal of Ca2+ was performed by the addition of NaHCO 3 at constant pH, achieving Ca removals of 99 %. The remaining salinity removal was achieved using a layer-by-layer hollow-fibre NF membrane, resulting to rejections higher than 80 % for Ca2+, SO 4 2−, and Na+. The obtained results demonstrate that the combined crystallization and NF stages is a feasible approach for the efficient treatment and water reclamation of AMW. [ABSTRACT FROM AUTHOR]

Sodium hydroxide and hydrochloric acid are widely used chemicals in different industrial sectors. To minimize costs and risks associated with transportation, handling and storage, these hazardous chemicals can be produced in situ employing electrodialysis with bipolar membranes (EDBM). This work presents a multi-scale model capable of simulating large scale EDBM units with complex stack configuration (i.e., internal staging) that can be used to design and optimize the process. The model was validated in two different process configurations using experimental results obtained from an EDBM pilot plant. Discrepancies between model and experimental results in the range of 2–11 % were obtained. The validated model was used to conduct a techno-economic evaluation adopting the feed and bleed configuration. Results show that current efficiency increases as the current density rises. At 600 A m−2, values of current efficiency between 72 % and 96 % were found for sodium hydroxide concentration in the range of 0.5–1 mol L−1. The levelized cost of sodium hydroxide (LCoNaOH) was evaluated, in the same range of concentrations, demonstrating that values between 280 and 370 € ton−1 can be obtained, fixing the electricity prince (0.1 kWh kg−1) and the triplet specific cost (600 US$ m−2). Moreover, assuming a reduced cost of electricity and triplet to 0.05 kWh kg−1 and 300 US$ m−2, respectively, an absolute minimum of 140 € ton−1 was found for the target 0.5 mol L−1. A double stage EDBM configuration was simulated to show the scale-up potentials of the multi-scale model. A reduction in the LcoNaOH of 10 % was obtained for a target concentration of 1 mol L−1. These results prove the attractiveness of the EDBM technology for producing in situ chemicals. [ABSTRACT FROM AUTHOR]

Electrodialysis with bipolar membranes (EDBM) can transform concentrated brines into acids and bases through the application of an electric field. Nevertheless, the widespread use of EDBM is limited by its high energy consumption, typically based on fossil fuels. Yet, the integration of EDBM with renewable energy sources, like solar photovoltaic (PV), remains unexplored. This study presents a techno-economic analysis of PV-EDBM to produce NaOH and HCl from seawater reverse osmosis (SWRO) brines. An integrated PV-EDBM model was developed and applied to a hypothetical PV-EDBM plant located in the SWRO facility of Lampedusa (Italy). Results revealed that PV has no negative impact on the performance in terms of product concentration, specific energy consumption and current efficiency. Meanwhile, the levelized cost of NaOH for PV-EDBM was reduced by 20 % in comparison to the electrical grid mix, achieving 210 €·ton−1 NaOH on an annual average for PV-EDBM. Therefore, the investment associated with PV is offset by the benefits of reduced electricity costs from the grid. Consequently, EDBM emerges as a feasible solution to address resource scarcity, representing a significant step towards integrating renewable energies with advanced wastewater treatment technologies, thus paving the path to a greener future. • A novel integrated PV-EDBM model was developed and applied to brine valorization. • NaOH productivity, SEC and CE of grid mix and PV solar powered EDBM compared • Replacing the grid mix by PV solar resulted in similar productivity, SEC and CE. • Using PV solar energy reduces LCoNaOH by about 20 % during the solar year. • PV-EDBM reduces GHG emissions, avoiding costs of carbon tax and EU ETS allowances. [ABSTRACT FROM AUTHOR]

Abstract: A good understanding of the details of hydrodynamic and heat transport conditions and their impact on temperature polarisation and pressure drops is essential for optimum design of membrane distillation (MD) modules. To this end, the present work reports on initial progress in the development of a tool for 3D simulation of spacer-filled MD channels based on the open source CFD code library OpenFOAM. The paper discusses a number of modelling and implementation aspects including model geometry and computational domain, choice of boundary conditions, and discretisation schemes. The results pertaining to the effect of three different spacer types on the fluid dynamics and heat transfer inside the channel are presented and discussed in order to highlight the impact of spacer geometrical features on temperature polarisation and pressure drop. Of the three spacer types considered, the 3-layer spacer with the wall-adjacent filament layers aligned with the flow direction was found to cause the lowest pressure drop while producing a robust symmetrical temperature profile. The 2-layer flow aligned square spacer was found to be the least desirable design, producing asymmetric temperature and velocity profiles and high pressure drops. [Copyright &y& Elsevier]

A novel full-atom multiscale method, combining different computational approaches and aimed to describe diffusion of multiple ions in anion exchange membranes (AEM), is presented. The method is used to evaluate diffusion of chloride and sodium ions in polysulfone tetramethylammonium (PSU-TMA) membranes, with particular attention to the co-ion diffusion. The hydration of the PSU-TMA is computed as a function of the membrane ionic exchange capacity via Density Functional Theory (DFT) and used for carrying out molecular dynamics simulations (MD). An upgraded DFT-based approach is proposed to obtain the atoms' charges used in the force field for the MD simulations. Three approaches have been adopted to evaluate the chloride self-diffusion coefficients, the first based on the Mean Square Displacement, while the others use two analytical models: Mackie-Meares and Yasuda-Lamaze-Ikenberry. For membranes with ideal selectivity, the computed chloride diffusion coefficients result in good agreement with literature values, highlighting the critical role of the water content on the diffusion of ions as the water uptake decreases. The full-atom modelling allows to reproduce the transition from normal to anomalous diffusion when decreasing the water volume fraction as expected experimentally. Moreover, to simulate real conditions, counter-ion and co-ion concentrations inside the AEM have been determined using the Donnan-Manning model. In this case, four approaches have been tested to balance the excess of charge obtained from the DFT calculations, finding, for one of them, a good agreement between theoretical and experimental diffusion coefficients. Finally, the calculation of fundamental quantities, necessary for the modelling of the sodium chloride diffusion, without resorting to adjustable parameters represents the guideline of the proposed methodology. [Display omitted] • Hydration number, λ, of PSU-TMA membrane calculated by DFT based approach. • Chloride diffusion coefficients evaluated by different methods. • Cl- diffusion coefficient for membrane with ideal selectivity at different IEC. • Co-ion and counter-ion diffusion as a function of membrane hydration level. • Na+ and Cl- diffusion coefficients for membrane with nonideal selectivity. [ABSTRACT FROM AUTHOR]

In recent years, the growing interest in the use of Ion-Exchange Membranes, in the treatment of highly concentrated multi-ionic brines for the selective recovery of critical elements, has prompted the research of fundamental models capable of predicting the IEMs selectivity towards like-charged species. Prior studies have proposed ion partitioning models limited to single-salt solutions that were validated only up to moderate salt concentrations. In this work, we developed a novel multi-ionic extension of the Manning counter-ion condensation model, aiming to predict the sorption selectivity of like-charged counter-ions. Furthermore, the peNRTL model was coupled with the extended Manning model to broaden its applicability range, encompassing membrane equilibrated with very highly concentrated solutions. Novel experimental ion sorption tests with single-salt and binary solutions including NaCl, KCl, MgCl 2, and CaCl 2 at high concentrations were performed with the commercial cation-exchange membrane Fumasep FKE-50. To the best of Authors' knowledge, the proposed model for the first time successfully provided quantitative predictions of multi-ionic ion partitioning for all the systems investigated up to extremely high external salt concentrations. The outcomes of this work suggest a strong influence of the local non-electrostatic interactions on the activity coefficients in the membrane phase at high external concentration and highlight the key role of counter-ions hydration state in the condensation phenomenon. [Display omitted] • A multi-ionic version of Manning's counter-ion condensation model is developed. • The extended Manning model is merged with the peNRTL model. • The model was validated against novel ion partitioning tests conducted with highly concentrated brines. • Counter-ions partition selectivity in mixture is related to their Born radii. • Short-range interactions strongly influence partition selectivity at high external concentrations. [ABSTRACT FROM AUTHOR]

A novel technology, the ion exchange membrane crystallizer (CrIEM), that combines reactive and membrane crystallization, was investigated in order to recover high purity magnesium hydroxide from multi-component artificial and natural solutions. In particular, in a CrIEM reactor, the presence of an anion exchange membrane (AEM), which separates two-compartment containing a saline solution and an alkaline solution, allows the passage of hydroxyl ions from the alkaline to the saline solution compartment, where crystallization of magnesium hydroxide occurs, yet avoiding a direct mixing between the solutions feeding the reactor. This enables the use of low-cost reactants (e.g., Ca(OH)2) without the risk of co-precipitation of by-products and contamination of the final crystals. An experimental campaign was carried out treating two types of feed solution, namely: (1) a waste industrial brine from the Bolesław Śmiały coal mine in Łaziska Górne (Poland) and (2) Mediterranean seawater, collected from the North Sicilian coast (Italy). The CrIEM was tested in a feed and bleed modality in order to operate in a continuous mode. The Mg2+ concentration in the feed solutions ranges from 0.7 to 3.2 g/L. Magnesium recovery efficiencies from 89 up to 100% were reached, while magnesium hydroxide purity between 94% and 98.8% was obtained. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and other treatments with significant environmental benefits. ED technologies can be used in operations of concentration, dilution, desalination, regeneration, and valorisation to reclaim wastewater and recover water and/or other products, e.g., heavy metal ions, salts, acids/bases, nutrients, and organics, or electrical energy. Intense research activity has been directed towards developing enhanced or novel systems, showing that zero or minimal liquid discharge approaches can be techno-economically affordable and competitive. Despite few real plants having been installed, recent developments are opening new routes for the large-scale use of ED techniques in a plethora of treatment processes for wastewater. [ABSTRACT FROM AUTHOR]

Anion Exchange Membranes (AEMs) are nowadays used in a very wide range of different applications, from electrodialytic systems for water treatment, to Fuel Cells for energy generation. In many of these cases, the AEM is in contact with water molecules, either in aqueous or gas phase, which can strongly interact with the AEM polymer, thus affecting membrane properties. The role of water in fully swollen AEM and its effect on the diffusion of hydroxide is the focus of this work. Density Functional Theory (DFT) based calculations were merged with Molecular Dynamics (MD) simulations coming to a more accurate description of the ionic exchange capacity effect on the hydroxide ion diffusion in AEM. Hydration of the polysulfone-tetramethylammonium (PSU-TMA), one of the most studied systems in Alkaline anion exchange Membrane Fuel Cells (AMFC), was determined by DFT developing an efficient algorithm. The ab-initio calculations predicted water uptake, at different Ion Exchange Capacity (IEC), resulted in good agreement with the experimental data. The theory-experiment comparison identified a threshold range of 1.2–1.7 meq/g as critical IEC at which over-swelling of functionalized polymer matrix occurs. From this comparison, three IEC values were chosen to perform MD simulations in order to evaluate the hydroxyl diffusion coefficients as a function of the different IEC where the ab-initio water uptake and partial charges, utilized in the force-field, were adopted. Diffusion coefficients in the bulk of the membrane were calculated through the Mean Square Displacement (MSD) over 100 ns MD trajectories, and then compared with the values obtained by the analytical Mackie-Meares's model, finding good agreement between the two computational methodologies. In addition, the computed diffusion coefficients were compared with the experimental conductivity data with a fair agreement. It is worth noting that, thanks to the minimization of adjustable parameters, the present work can be easily adapted to study any type of Ion Exchange Membrane (IEM) and counter-ions diffusion. Image 1 • Hydrated PSU-TMA membranes were studied by DFT and MD methods. • Water Uptake of anion exchange membrane was predicted by DFT at different IEC. • Predicted W U was in good agreement with experimental references for low IEC. • Diffusion coefficients of hydroxide were predicted by MD as a function of IEC. • Hydroxide diffusion was described by analytical model using water volume fraction. [ABSTRACT FROM AUTHOR]

In this paper, a predictive mono-dimensional (1D) model for Mg(OH) 2 precipitation is proposed and its predictive capability is tested. Two different reactor configurations are analyzed and compared, namely a T-mixer and a Y-mixer followed by two consecutive diverging channels and a final coil of constant diameter. Both setups were chosen for their high mixing efficiency. The suspension samples were characterized by Dynamic Light Scattering (DLS), thus obtaining particle size distributions (PSD). The experimental data collected using the T-mixer was used to identify the kinetics parameters set, while the data obtained through the Y-mixer setup was employed to assess the model predictive capability under different fluid dynamics conditions. Computational Fluid Dynamics (CFD) simulations were conducted to characterize the flow fields and the turbulence, which were integrated into the 1D model. Predictions were found to be in good agreement with the experimental data and further improved after introducing a novel correction factor for the aggregation kernel. [Display omitted] • A predictive population balance model for Mg(OH) 2 precipitation is proposed. • The unknown kinetic parameters are inferred and validated in a T-mixer. • The model turns out to have predictive power for the experiments from a Y-mixer. • Predictions improved further using a novel correction factor for the aggregation. [ABSTRACT FROM AUTHOR]

The hydrodynamics of electrodialysis and reverse electrodialysis is commonly studied by neglecting membrane deformation caused by transmembrane pressure (TMP). However, large frictional pressure drops and differences in fluid velocity or physical properties in adjacent channels may lead to significant TMP values. In previous works, we conducted one-way coupled structural-CFD simulations at the scale of one periodic unit of a profiled membrane/channel assembly and computed its deformation and frictional characteristics as functions of TMP. In this work, a novel fluid–structure interaction model is presented, which predicts, at the channel pair scale, the changes in flow distribution associated with membrane deformations. The continuity and Darcy equations are solved in two adjacent channels by treating them as porous media and using the previous CFD results to express their hydraulic permeability as a function of the local TMP. Results are presented for square stacks of 0.6-m sides in cross and counter flow at superficial velocities of 1 to 10 cm/s. At low velocities, the corresponding low TMP does not significantly affect the flow distribution. As the velocity increases, the larger membrane deformation causes significant fluid redistribution. In the cross flow, the departure of the local superficial velocity from a mean value of 10 cm/s ranges between −27% and +39%. [ABSTRACT FROM AUTHOR]

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 H CONC , H DIL and the velocities U CONC , U DIL 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 H CONC , H DIL , U CONC , U DIL 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. • A simplified model of Reverse Electrodialysis is used to predict Net Power Density. • Quantities affecting NPD are classified into optimization and scenario variables. • The model is coupled with a gradient-ascent optimization algorithm. • Conditions of maximum NPD in the space of optimization variables are determined. • Optimum working conditions change significantly with the scenario variables. [ABSTRACT FROM AUTHOR]

Abstract This work proposes a correlation for the specific capital cost of multi-effect distillation (MED) plants, considering their main design options and parameters, such as the number of effects, size/capacity, and heat source temperature. These parameters are varied within a large range to cover as many different cases as possible. The cost correlation decouples the evaporator cost and includes in the expression the ratio of the heat exchanger area to a reference one. This area is calculated using a validated MED numerical model, with the results then processed to produce fitted expressions. Two versions of this correlation with different levels of complexity are proposed, which provide similar results. The results of the improved correlation have been compared with the actual specific cost of a limited number of MED plants for validation purposes. It has been shown that this correlation provides more accurate results in most of the cases, although the sample is small due to limited availability of data from other plants. The specific capital cost of typical MED plants is then examined, presenting the cost when the number of effects and heat source temperature change. These calculations capture the expected trend of the plant cost under different main design options. Highlights • Simulation correlating MED distillate mass flow rate and heat exchanger area • Correlation for MED specific cost based on existing municipal water supply plants • Improved correlation as a function of the number of effects and the heat source T • The improved correlation better captures the cost variations for different designs [ABSTRACT FROM AUTHOR]

Abstract A crucial parameter for the design and operation of electrodialysis (ED) units is the limiting current density (LCD). This is often identified with the diffusion-limited current density, which corresponds to the complete solute depletion in the layer adjacent to the membrane. Current-voltage curves obtained from measurements with electrodes in contact with the solution (i.e. without membranes) are consistent with this interpretation and exhibit a horizontal plateau identifying LCD. However, real ED systems show more complex behaviours, with a reduced-slope tract instead of a plateau and a third region in which the current increases more markedly (overlimiting current). The phenomena involved in the limiting region are not yet totally characterized and the determination of LCD in ED units is still ambiguous. In the present work, we explore the issues related to the identification of LCD, by measurements on ED units, assessing the influence of operating conditions and validating a simplified process simulator. A new method to determine LCD, based on the current efficiency, is proposed and compared with other methods presented in the literature. A second limiting quantity is also identified, i.e. the critical current density, below which diffusion phenomena prevail on migration and a method for its assessment is proposed. Graphical abstract Unlabelled Image Highlights • Methods for the determination of LCD in Electrodialysis are critically discussed. • LCD measurements in real ED stacks for different operating conditions are presented. • A novel method associating LCD with the maximum current efficiency is proposed. • The critical current density, associated with nil current efficiency, is introduced. [ABSTRACT FROM AUTHOR]

The performance of a Reverse ElectroDialysis (RED) system fed by unconventional wastewater solutions for long operational periods is analysed for the first time. The experimental campaign was divided in a series of five independent long-runs which combined real wastewater solutions with artificial solutions for at least 10 days. The time evolution of electrical variables, gross power output and net power output, considering also pumping losses, was monitored: power density values obtained during the long-runs are comparable to those found in literature with artificial feed solutions of similar salinity. The increase in pressure drops and the development of membrane fouling were the main detrimental factors of system performance. Pressure drops increase was related to the physical obstruction of the feed channels defined by the spacers, while membrane fouling was related to the adsorption of foulants over the membrane surfaces. In order to manage channels partial clogging and fouling, different kinds of easily implemented in situ backwashings (i.e. neutral, acid, alkaline) were adopted, without the need for an abrupt interruption of the RED unit operation. The application of periodic ElectroDialysis (ED) pulses is also tested as fouling prevention strategy. The results collected suggest that RED can be used to produce electric power by unworthy wastewaters, but additional studies are still needed to characterize better membrane fouling and further improve system performance with these solutions. [ABSTRACT FROM AUTHOR]

• Multi-ionic solutions in Electrodialysis with bipolar membrane (EDBM) were studied. • A new methodology for evaluating the ion transport in EDBM systems was proposed. • Apparent ion transport numbers and selectivities were calculated and discussed. • Enhanced chloride transport across AEMs and potassium across the CEMs were found. • Results showed SEC of 1.6 kWh kg−1 and current efficiency of 75% with real brines. Electrodialysis with Bipolar Membranes (EDBM) has become a key technology for valorising waste brine streams as a new chemical production route. Even though its application has been widely studied using single electrolyte solutions (e.g., NaCl or Na 2 SO 4), there is still a lack of knowledge about using multi-ionic mixtures. For the first time, this work aims to evaluate the EDBM performance when treating synthetic solutions mimicking the waste brines produced in a integrated process for the valorisation of solar saltworks bitterns. The behaviour of a lab-scale EDBM unit was assessed using SUEZ ion exchange membranes (IEMs), operating at 300 A m−2, and the ion transport through IEMs was investigated, based on the calculation of apparent transport numbers and selectivities. The results highlighted that multi-ionic solutions barely affected the production of hydroxide ions. Chlorides were transported up to 7 times faster than sulphates across the anion-exchange membranes, while the cation-exchange membranes exhibited slightly higher selectivity for potassium than for sodium (∼1.2). The current efficiencies ranged between 70 % and 80 %, while a minimum specific energy consumption of 1.60 kWh kg-1 NaOH was obtained for the most concentrated brine at 1 mol L-1 OH–. These results provide novel and valuable information to support the development and implementation of EDBM as a sustainable technology for supporting a resource-efficient and competitive economy through on-site and delocalized chemicals production routes. [ABSTRACT FROM AUTHOR]

The current maldistribution along the flow path of electrodialysis (ED) units is a well-known phenomenon. However, it has been poorly quantified via experimental tests so far. This work aimed at measuring the current distribution in an ED stack with 40 cm path length, provided with four-segment electrodes. The current-voltage curve (CVC) of each segment was recorded under several operating conditions of inlet concentrations and feed velocity. In the CVC of the first segment, the current increased approaching a saturation, while in that of the remaining segments it passed through a maximum and then settled at near-zero values when high voltage values were applied. The current fraction on the segments decreased from inlet to outlet. In the overall CVC's first region, up to ~50 % of total current flowed through the first quarter of stack. As the voltage increased, the current fraction increased in the first segment, while it decreased in the other ones tending to vanish. At the limiting condition, the relative standard deviation of the current fraction distribution ranged from 40 % to 68 %. This strong non-uniformity in the ED stack, which may represent one stage of an industrial plant, implies that the design of commercial units must be improved. [Display omitted] • An ED stack with 40 cm path length, provided with 4-segment electrodes, was tested. • The CVCs were recorded for brackish water and final stage seawater desalination. • At the limiting voltage, V lim , ~50 % of current (I) flowed through the first segment. • At V lim the relative standard deviation of the I distribution was ~40 % to 70 %. • The nexus between I maldistribution and desalination performance drop was stressed. [ABSTRACT FROM AUTHOR]

This study addresses issues which arise in the computational and experimental modelling of flow and heat/mass transfer in membrane distillation and other processes adopting spacer-filled channels (either planar or spiral wound), but have not been sufficiently clarified in the literature so far. Most of the argumentations presented are based on original computational results obtained by the authors by finite volume simulations; some literature results are also considered. The questions addressed regard the choice of scales for the reduction of data and the definition of dimensionless numbers ( Re , f , Nu , Sh ); the definition of average heat or mass transfer coefficients; the combined effects of the parameters that characterize the process (spacer pitch to channel height ratio l / H , flow attack angle γ and Reynolds number Re ) and the applicability of simple correlations; the influence of the spacer's thermal conductivity. In regard to the influence of the parameters, Re, l / H and γ were found to interact heavily, making a separate-effect analysis impossible and power-law friction or heat/mass transfer correlations of little use. Thermal conduction in the spacer, even for low-conductivity polymeric spacers ( λ ≈ 0.15 Wm − 1 K − 1 ), was found to be responsible for up to 10% of the total heat transfer. [ABSTRACT FROM AUTHOR]

In recent years, the field of process engineering has witnessed an exponential increase in the usage of ion-exchange membranes (IEM) in light of their pivotal function in green technologies such as electrodialysis (ED), reverse electrodialysis (RED) and fuel cells. One of the key parameters in IEMs performance is the equilibrium water uptake (w u) as this has been shown to have a prominent effect on some of their fundamental properties such as ionic diffusivities. In this work, we have elaborated a molecular dynamics (MD) protocol to reliably predict the water uptake of IEMs by considering a polysulfone (PSU) functionalized with tetramethylammonium (TMA) anion-exchange membrane (AEM) compensated with chloride anions as case study. The procedure led to good agreement with reported experimental data in a wide range of ion-exchange capacities (IEC) and improved the results with respect to the DFT-based approach developed in our previous work. The issue of considering too thin membrane models compared to the actual IEM was found to be relevant and was addressed by proposing an ad-hoc simulation setup; this allowed to reconcile results accuracy with reasonable computational costs. Finally, the computed w u were used to evaluate chloride counter-ion diffusivities within three different theoretical frameworks (the Mackie-Meares, Yasuda-Lamaze-Ikenberry and Manning-Meares models) and it was found that a satisfactory agreement with experiments can be achieved. This confirmed the potential of the current strategy to predict the w u and ion diffusivities in IEM without resorting to experimental data, thus paving the way towards a computationally driven design of new membranes. [Display omitted] • Straightforward method combining MD w u and analytic models for Cl− diffusion. • Novel atomistic protocol and setup to predict w u for IEM. • Ion diffusivities prediction via three analytical models as a function of IEC. • PSU-TMA membrane investigated over a wide range of IEC. • Good agreement of w u and ion diffusivities predictions with experimental data. [ABSTRACT FROM AUTHOR]

This work reports experimental data collected for the first time on a full-scale RED pilot plant operated with natural streams in a real environment. The plant – located in the South of Italy – represents the final accomplishment of the REAPower project ( www.reapower.eu ). A RED unit equipped with almost 50 m 2 of IEMs (125 cell pairs, 44x44 cm 2 ) was tested, using both artificial and natural feed solutions, these latter corresponding to brackish water (≈0.03 M NaCl equivalent ) and saturated brine (4–5 M NaCl equivalent ). A power output up to around 40 W (i.e. 1.6 W/m 2 of cell pair) was reached using natural solutions, while an increase of 60% was observed when testing the system with artificial NaCl solutions, reaching up to ≈65 W (2.7 W/m 2 of cell pair). The unit performance was monitored over a period of five months under, and no significant performance losses were observed due to scaling, fouling or ageing phenomena. Such results are of paramount importance to assess the potential of the technology, towards the successful development on the industrial scale. A scale-up of the pilot plant is planned through the installation of two additional RED modules, with an expected power output in the order of 1 kW. [ABSTRACT FROM AUTHOR]

Assisted-Reverse Electrodialysis (A-RED) technology was applied following reverse osmosis (RO) of a surface water resource in order to recover minerals from its brine and directly remineralize the RO unit's permeate. Four different sets of cation/anion exchange membranes were benchmarked using single- and mixed-salts synthetic solutions as well as real brine and permeate streams produced from three-stage reverse osmosis applied to Seine River water. The process, operating under equal permeate and brine channel flows (2 cm/s velocities) and applied voltage varying from 0 to 10 V, showed viable remineralization results. Optimal recovery at 10 V applied allowed increasing permeate mineral content from 20 mg/L CaCO 3 up to values of 553 mg/L CaCO 3 and from 100 μS/cm up to 1284 μS/cm for hardness and conductivity respectively. Tests using spiked micropollutants showed very low levels of micropollutant passage with over 98% rejection for 15 out of 18 compounds tested while natural organic matter (NOM) breakthrough was 2% on average (0.2 mg C/L). [Display omitted] • Application of A-RED for recovery of salts from surface water RO brine to remineralize corresponding permeate was tested. • Recovery of salts from RO brine ranged from 20 to 50% • Permeate hardness was increased from 20 to 553 mg/L CaCO 3 • Passage of 18 organic microcontaminants from brine to permeate was found to be 2% on average [ABSTRACT FROM AUTHOR]