Membrane Desalination Systems Research Articles

A numerical method for simulating variable density flows in membrane desalination systems

We present a novel method for simulating unsteady, variable density, fluid flows in membrane desalination systems. By assuming the density varies only with concentration and temperature, the scheme decouples the solution of the governing equations into two sequential blocks. The first solves the governing equations for the temperature and concentration fields, which are used to compute all thermophysical properties. The second block solves the conservation of mass and momentum equations for the velocity and pressure. We show that this is computationally more efficient than schemes that iterate over the full coupled equations in one block. We verify that the method achieves second-order spatial–temporal accuracy, and we use the method to investigate buoyancy-driven convection in a desalination process called vacuum membrane distillation. Specifically, we show that with gravity properly oriented, variations in temperature and concentration can trigger a double-diffusive instability that enhances mixing and improves water recovery. We also show that the instability can be strengthened by providing external heating.

Estimation of best geometric and operational parameters of a nanophotonics-enabled solar membrane desalination system: A numerical investigation

Nanophotonics-enabled solar membrane desalination (NESMD) system is a sustainable method to address water scarcity by desalinating seawater using solar energy. A layer of nanoparticles absorbs heat, creating localized heating within feed channel, which generates a vapor pressure difference between feed and permeate channels. Distillate water is collected in permeate channel. Numerical modelling of NESMD system, integrating optical and thermal modules in COMSOL Multiphysics, efficiently enumerates distillate flux at specified locations under varying ambient conditions. Reliability of the simulation model is confirmed through validation against in-house experimental results. A set of most effective dimensions and component specifications for NESMD system are computed that maximize distillate flux. Setup width exhibits invariant distillate flux within a range of 2–30 cm, while a feed thickness of 2 mm yields maximum distillate flux, with no change observed for permeate thickness within a range of 2–10 mm. An optimal setup length is determined within 80–200 cm range under varying operating conditions. Membrane porosity of 0.85 is selected to balance both vapor diffusivity and mechanical strength. The optimum membrane thickness lies within 180–225 µm range. An NESMD system with these best suited specifications is demonstrated to produce freshwater at the rate of 4.63 l/m2 per day.

Investigation on the operating capacity expansion through parallel schemes of reciprocating-switcher energy recovery device for desalination: Simulation, verification and parameterization

Parallel operation is a significant and feasible method to compensate the insufficient capacity of single reciprocating-switcher energy recovery device (RS-ERD) in membrane desalination system. To grasp the operating characteristics in capacity expansion, three parallel schemes of RS-ERD, single-operation scheme, two-parallel scheme and three-parallel scheme, are investigated through the numerical simulation, experimental verification and theoretical parameterization. Results indicate that, the two-parallel scheme and three-parallel scheme achieve the flowrate continuity of low-pressure seawater and the flowrate fluctuation amplitudes in parallel RS-ERDs decrease by 50 % and 83 % respectively when compared with single-operation scheme. Parallel operation schemes also broaden the flowrate range with high efficiency for RS-ERD. To ensure the 95 % energy recovery efficiency, two-parallel and three-parallel schemes expand the maximum flowrates to 140 m3/h and 210 m3/h in contrast with the 70 m3/h of single-operation scheme. In addition, the two-parallel and three-parallel schemes of RS-ERD realize the much lower specific energy consumption (SEC) of 2.11 kWh/m3 and 2.09 kWh/m3 than the 2.23 kWh/m3 in single-operation scheme which contributes to the operating costs savings about 63,830 CNY and 75,778 CNY in one year. This research provides a new perspective in capacity expansion through the parallel operation of energy recovery devices.

Scaling up of nanophotonics-enabled solar direct-contact membrane desalination system under ambient condition and sun tracking: Challenges, remedies and performance report

A direct-contact membrane desalination system is fabricated and tested. A hydrophobic PVDF membrane, coated with carbon black nano-particles, is placed between feed and permeate channels. Localized heating through absorption of solar heat by the nano-particle layer produces water vapour, which gets driven through the porous membrane by the vapour pressure gradient maintained by the temperature differential between the channels. Non-requirement of bulk feed heating enhances the photothermal efficiency of nano-particle enabled systems. It is also observed to have advantages such as low scaling and easy cleaning. The major drawback in scaling up conventional membrane desalination system is gradual loss of temperature gradient with length. Here, it is observed that for significantly longer length, temperature gradient is not reduced to a low value to set a practical limit for the system size. 99.5 % salt removal is achieved while the range of flux is 0.14–0.28 kg/m2hr under solar irradiance of 331–839 W/m2 and ambient temperature condition. Two-axis tracking is observed to produce an augmentation of flux by 23.3 %. Numerous challenges, as faced during experiments, are reported in detail along with the corresponding fixes. Thus, the present study provides a technology roadmap for scaling up a nanophotonics-enabled solar membrane desalination system.

Pilot-scale evaluation of the sustainability of membrane desalination systems for the concentrate volume minimization of coal chemical wastewater

5 stars represents the best technical performance/highest cost.

Hybrid vacuum membrane distillation-multi effect distillation (VMD-MED) system for reducing specific energy consumption in desalination

This study focuses on the integration of vacuum membrane distillation into the multi-effect distillation (VMD-MED) system, incorporating heat recovery mechanisms to augment fresh water productivity and minimize the specific thermal energy consumption of the desalination process when compared to stand-alone vacuum membrane desalination systems. The hybrid system was devised by integrating the experimental output of VMD (permeate flux and hot brine) as heat source to MED. Two hybrid systems were investigated in this study: VMD/MED, wherein the heated brine from VMD served as a heat source for MED, facilitating the recovery of sensible heat from VMD; and VMD-HR/MED, where the latent heat of VMD vapor during condensation was utilized to pre-heat the feed water for MED. Based on the performance parameters, it was concluded that the VMD-HR/MED hybrid system outperformed both the stand-alone VMD and VMD/MED hybrid system in terms of efficiency. The latent heat recovery from the condenser of VMD in VMD-HR/MED hybrid system reduces the specific thermal energy consumption (STEC) to 38.42 kWh/m3, however, it enhanced the gain-output-ratio (GOR) and productivity of the system. Additionally, a rise in GOR and a simultaneous decrease in STEC were observed with increasing feed flow rates and vacuum pressure.

Machine learning-aided modeling for predicting freshwater production of a membrane desalination system: A long-short-term memory coupled with election-based optimizer

Membrane desalination (MD) is an efficient process for desalinating saltwater, combining the uniqueness of both thermal and separation distillation configurations. In this context, the optimization strategies and sizing methodologies are developed from the balance of the system’s energy demand. Therefore, robust prediction modeling of the thermodynamic behavior and freshwater production is crucial for the optimal design of MD systems. This study presents a new advanced machine-learning model to obtain the permeate flux of a tubular direct contact membrane distillation unit. The model was established by optimizing a long-short-term memory (LSTM) model by an election-based optimization algorithm (EBOA). The model inputs were the temperatures of permeate and the feed flow, and the rate and salinity of the feed flow. The optimized model was compared with other optimized LSTM models by sine–cosine optimization algorithm (SCA), artificial ecosystem optimizer (AEO), and grey wolf optimization algorithm (GWO). All models were trained, tested, and evaluated using different accuracy measures. LSTM-EBOA outperformed other models in predicting the permeate flux based on different accuracy measures. LSTM-EBOA had the highest coefficient of determination of 0.998 and 0.988 and the lowest root mean square error of 1.272 and 4.180 for training and test, respectively. It can be recommended that this paper provide a useful pathway for sizing parameters selection and predicting the performance of MD systems that makes an optimally designed model for predicting the freshwater production rates without costly experiments.

Seasonal dynamic modeling and simulation of solar thermal membrane desalination system for sustainable freshwater production: a case study of Tanta, Egypt

AbstractMembrane distillation (MD) is an effective process for desalinating seawater, combining the merits of both thermal and membrane distillation. In this context, the sizing methodologies and optimization strategies are developed from the balance of the system’s energy demand. Therefore, accurate numerical modeling of the heat transfer and thermodynamic behavior of the MD systems is crucial for the optimal design of solar-based MD systems. The interest in utilizing solar thermal heating techniques for feed water heating in MD systems is increasing worldwide for sustainable freshwater production and lowering energy consumption. Hence, in this research, a coupled analytical modeling based on heat transfer, mass transport, and thermodynamic analysis is created to dynamically simulate a solar direct contact membrane distillation system (SDCMDS) driven by vacuumed tubes solar collectors (VTSCs) to analyze its performance, under real weather of Tanta, Egypt. The influences of the solar collecting area on the performances of the proposed SDCMDS for augmenting the freshwater production of the SDCMDS are studied. Four cases of the proposed SDCMDS are investigated: two identical VTSCs of 1.80 m2 each unit in summer (Case I), two identical VTSCs in winter (Case II), four identical VTSCs in summer (Case III), and four identical VTSCs in winter (Case IV). The results show that the utilization of four VTSCs connected in series significantly improved the feed seawater temperature range from 30.0 to 70.5 °C compared to a feed temperature range of 30.0–49.5 was achievable by utilizing only two VTSCs. Moreover, the daily averaged permeate flux were 2.21, 1.29, 3.41, and 2.07 L/day per m2 of solar harvesting area with daily cumulative distilled water yield of 7.48, 4.60, 23.04, and 14.78 L/day for Cases I, II, III, and IV, respectively, at a saline flowrate of 0.20 kg/s. The daily average total efficiency of the SDCMDS was obtained to be 14.70%, 12.50%, 24.95%, and 22.50% for Cases I, II, III, and IV, respectively.

Energy and economic performance assessment of a solar-assisted regenerative vacuum membrane desalination system

Vacuum membrane water desalination is a promising technology for freshwater production with the advantages of low conduction heat loss and mass transfer resistance, compared to other membrane technologies. Such systems can be driven by solar thermal collectors for green water production, yet there is a lack of dynamic system simulations in the literature to comprehensively assess the energy and economic system performance and evaluate the impact of brine recirculation as a method of regeneration, especially under hot desert climates where solar resources are abundant, but freshwater resources are scarce (e.g., the northern coast of Egypt, considered as the case study here). In this study, a dynamic system simulation model is developed in TRNSYS, where a new “Type” is introduced for the vacuum membrane module. Initial sizing of the system with ∼20 % solar fraction resulted in annual average gained output ratio and specific thermal energy consumption of 2.51 and 133.5 kWh/m3, respectively, with levelized cost of water and payback period of 14.7 USD/m3 and 1.53 years, respectively. By increasing the solar collectors’ area from 8 to 16 m2, the levelized cost of water increased by 14.54 %. The storage volume was highly influential on the solar fraction, which increased by 101.39 % as the volume increased from 0.3 to 0.7 m3. Increasing the membrane area from 0.3 to 0.5 m2 increased the gained output ratio by 76.75 % while decreasing the levelized cost of water by 14.79 %. Internal heat regeneration through brine recirculation enhanced the system performance at lower recirculation ratios. Without recirculation, the levelized cost of water increased by 117.41 % and the system met the daily distillate water demand for only 90 days of the year.

Comprehensive parametric analysis, sizing, and performance evaluation of a tubular direct contact membrane desalination system driven by heat pipe-based solar collectors

Feed seawater heating is one of the crucial bottlenecks in membrane desalination (MD) systems. The interest of usage solar energy techniques for feed seawater preheating in MD systems is recently regarded as an improvement pathfor sustainable distillate production. This study presents a conceptual design, theoretical modeling, and comprehensive parametric analysis of a tubular direct contact membrane desalination system (TDCMDS) driven by heat pipe-based solar collectors (HPSCs). An improved theoretical model performed in MATLAB software was conducted to simulate the hybrid solar TDCMDS operation in order to analyse its performance in the climate conditions of Tanta, Egypt. The effects of the number of utilized solar collectors, feed seawater flowrate, cooling water flowrate, and utilization of additional electric heaters on the energy performance of the solar TDCMDS are parametrically investigated. The findings show that the number of the utilized solar collectors, feed seawater flowrate, and cooling water flowrate, were the most sensitive to the performance of the solar TDCMDS, which should be desired to be 5.0 ≥n≥ 2.0, 20.0 lpm, and 5.0 lpm, respectively, in the design of the TDCMDS to maximize the freshwater production. Moreover, the maximum permeates flux are 0.45, 0.39, 0.32, and 0.25 kg/h per m2 of solar collecting area with total daily freshwater production of 35.0, 24.60, 15.48, and 7.95 kg/day by integrating five, four, three, and two HPSCs connected in series, respectively, compared to only 0.08 kg/h.m2 and 1.44 kg/day when coupling one solar collector at feed seawater and cooling water flowrates of 20 and 5.0 lpm, respectively. Conclusively, it can be recommended that this investigation provides an emerging strategy for designing solar-based MD systems.

Numerical and Experimental Performance Evaluation of a Photovoltaic Thermal Integrated Membrane Desalination System

Membrane desalination (MD) is preferred over other desalination techniques since it requires a lower temperature gradient. Its performance can be further enhanced by preheating the intake of saline water. In this context, a novel solar-assisted air gap membrane desalination (AGMD) system was hypothesized. The motivation was derived from the fact that the use of solar energy to provide power and a pre-heating source for the intake of saline water can offer a sustainable alternative that can further enhance the acceptance of MD systems. Since solar panels suffer from a loss of efficiency as they heat up during operation, a solar-assisted air gap membrane desalination (AGMD) system can help to improve the overall system performance by (1) providing the necessary pumping power to operate the system and (2) improving solar panel performance by exchanging heat using water that is (3) used to pre-heat the saline water necessary for increased performance of the AGMD system. To verify the hypothesis, a solar-assisted AGMD system for freshwater production was theoretically designed, fabricated locally, and then tested experimentally. The effect of the process operating parameters and the ambient conditions on the overall performance of the proposed solar-assisted AGMD desalination unit is presented in detail, both theoretically and experimentally. The results indicated a direct correlation between the permeate flux, saline hot feed temperature, and hot feed flow rate. In addition, an inverse relationship between the cold feed temperature, cold feed flow rate, and the air gap thickness of the module was also observed and reported, thus, validating the hypothesis that a solar-assisted air gap membrane desalination (AGMD) system can help to boost performance.

Extraction of commercially valuable mineral salt from reverse osmosis brine using a spray dry process

As the need for drinkable water increases, thermal and membrane desalination of seawater have emerged as the two most effective solutions. Both thermal and membrane desalination systems, however, release large quantities of concentrated brine back into the sea. The continuous discharge of enormous amount of brine into the sea will disrupt the aquatic ecosystem and increase the seawater salinity level. In this study, spray dry technology is utilized for isolation of minerals from reverse osmosis brine and there by achieving zero liquid discharge concept. The procedure involves spraying feed into a chamber, followed by the introduction of heated air. The flow rates of the spray dryer and hot air can be adjusted. Consequently, the amount and concentration of feed residue in the chamber can be altered. The residue from the first vaporization chamber was cooled to a specified temperature and centrifuged to separate the minerals in crystal form. The centrifuge reject was fed to a second vaporization chamber for further concentration and separation of pure mineral salts. This cycle was repeated between two and six times to isolate all significant minerals from the brine. The vaporized water from all chambers was condensed to generate pure water as a by-product.

Sustainable Approach of Generating Water and Energy: Techno-Economic Analysis of a Hybrid Solar Photoactive Thermal System Coupled with Direct Contact Membrane Distillation for Water Purification and Electricity Generation

Cogeneration of energy and clean water by incorporating direct contact membrane desalination (DCMD) and photovoltaic hybrid thermal system (PVT) into a residential building is a promising technology for addressing water and energy shortage in distant places. In this study, a microgrid integration between PVT, DCMD, and a residential building is proposed, with an end goal to meet partial electric load in the building and provide a clean water supply. A mathematical model was developed and validated to assess the system’s performance. Artificial Neural Network (ANN) and optimization techniques have been used. The performance of the proposed system was studied under the meteorological conditions of Riyadh, Saudi Arabia, and under several design and operation parameters. The optimal performance of the system is found as functions of the inlet brackish water temperature to the PVT, capital and installation cost, and the desired water productivity. Results reveal that the specific cost of water (SCW) is 23.6 $/m3 achieved with a renewable energy penetration of 25%, depending on the cost of PVT and electricity price. Thus, the proposed system meets 25% of the electric demand for the residential building, while the rest is imported from the grid. In addition, the proposed system reduced the annual greenhouse gas emission by 4300 kg for a single building. This study will contribute to a better understanding of incorporating innovative clean energy and water systems such as PVT and DCMD into a residential house.

Performance investigation and evaluation of a new three-piston pump energy recovery device for small scale desalination system

Energy recovery device is a crucial part for decreasing the energy consumption of membrane desalination system. To meet the energy conservation requirements in small scale desalination system, a new three-piston pump energy recovery device integrating the high pressure pump and booster pump is investigated and evaluated. The flow characteristics in pressure exchanging cylinders are investigated through the numerical method. The operating performance is experimentally evaluated in a membrane desalination system at the seawater pressure and flowrate of 5.00 MPa and 6.10 m3/h. The numerical results indicate that the continuous flow and pressure transition can be realized through the cooperation of three hydraulic pistons in operation. Both the inlet and outlet flowrates demonstrate the half-sine variation trends. The maximum deviation between simulation and experiment is 2.70%. The experimental results prove that the device can achieve the stable pressure exchanging, and the pressure and flowrate fluctuation amplitudes are 0.60 MPa and 0.60 m3/h. The energy recovery efficiency is as high as 82.03% which contributes to a specific energy consumption of 3.62 kW·h/m3 in desalination. This paper provides a new type of multi-functional energy recovery device for the membrane desalination system.

Deep Learning model and Classification Explainability of Renewable energy-driven Membrane Desalination System using Evaporative Cooler

Recently, the scientific community has become more interested in solar-driven steam materials and systems for desalination and disinfection. Solar thermal energy for membrane distillation desalination provides a green and sustainable option for building settings where there is a strong connection between water constraint and high solar irradiation. Artificial intelligence (AI) is rapidly being used to optimize water treatments and saltwater desalination because of its high precision and accuracy. Explainable AI (XAI) enables people to better understand and trust a model's predictions and to detect and rectify inaccurate AI predictions. This study analyses recent advances in solar-driven steam materials engineering and the significant technological constraints that impede its wide-scale deployment. Using local interpretable model-agnostic explanations (LIME), our study provides an interpretable solution (in addition to the binary classification result of the developed black-box deep learning (DL) model) so that experts can understand why the machine thinks this way, providing critical insights for the decision-making process. The proposed XAI-DL model is based on a DL network consisting of three cascaded convolutional blocks for processing tabular data. Therefore, the XAI-DL classification model achieves a cooling quality accuracy of 82.64% during the validation stage, supporting the explaining capability. During the testing, the [inlet-cooling-water-temperature] pushes the model lower, whereas the [ambient-temperature], [feed-water-flow-rate], and the [inlet-feed-water-temperature] pushes the model higher. The LIME explanation result is consistent with the statistical analysis of the data. Consequently, the proposed explainer assists non-experts in comparing and improving the untrustworthy model through and clarifies the importance of each feature and its relationship to other features and its relationship to the class. Finally, the XAI-DL fits and supports the different manufacturers of membrane desalination system(s) to inspect cooling quality in their designed system and consistency of interpretability and trust.

Control design for throughput improvement of fuel cell-integrated solar heated membrane desalination system

The unequal distribution of freshwater resources on Earth has spurred ongoing research to explore alternative sustainable desalination technologies to meet the demand for fresh water. This work features the development of a hierarchical control system incorporating a model predictive controller (MPC) and proportional-integral-derivative (PID) controllers for a fuel cell-integrated solar heated membrane desalination system, which was simulated using Simulink in MATLAB. The process disturbances were identified to be the solar irradiance and ambient temperature, while the manipulated variables were determined to be the seawater flow rate and H2 molar flow rate based on a sensitivity analysis. The hierarchical control system consisted of two levels, i.e., level 1 (base level) with the PID controllers and plant model, and level 2 with the MPC and feedback from the plant output. The system was revealed to be highly dependent on the MPC setpoint, with the optimal setpoint to maintain consistent total produced distillate (TPD) and profit to be around 5 kg h−1 and 6.5 × 10−5 USD s−1, respectively. The insights on the controller design and approach presented in this work are expected to benefit future membrane desalination system development.

Theoretical analysis and parametric investigation of an innovative helical air gap membrane desalination system

A helical air gap membrane desalination (HAGMD) system is designed in the present study. The condenser is designed as a cylindrical shape with helical fins machined on the outer surface of a hollow copper condenser. A detailed theoretical model, studying heat and mass transfer in the HAGMD module, was developed. The theoretical model for a cylindrical system with fins is developed for the first time and is unique in the MD literature. Experimentation was carried out to examine the behavior of the HAGMD module under diverse design and operating conditions. The effect of cold flow rate, feed flow rate, feed temperature, the height of fins, the number of fins, and the length of the module is determined on the performance of the HAGMD system. Permeate flux and gained output ratio (GOR) were considered as the performance indicators of the system. Results showed that permeate flux increases with cold flow rate, feed temperature, feed flow rate, as well as number of fins, while the increase in height of fins negatively affects the flux. Theoretical model and experimental results are found to be in excellent agreement with only 6.7% of error which shows that the present theoretical model is excellent to predict the performance of any HAGMD system. For similar design parameters, the average flux increased by 135% for the finned HAGMD module, with 35 fins over the one with that only for 1 fin. Maximum experimental distillate flux is found to be 20 kg/m2 hr, and GOR is found to be 0.75.

Osmotic water permeability of aquaporin-1 under radial tensile and compressive stimuli

With the rapid development of biological technology and membrane synthesis, water industries have inclined towards biomimetic membranes for water purification and desalination. Aquaporin (AQP) embedded synthetic membranes seem to be promising due to the AQP's high selectivity and permeability, however, the effect of inherent membranous residual stress on protein structure and water permeation has been rarely studied yet and remains unclear. Here, we studied water permeability through the tetrameric human AQP1, embedded in a POPC lipid bilayer, under lateral mechanical stimuli using all-atom molecular dynamics simulations. Four different systems were studied where different stimuli were applied to the simulation cell. By counting the permeation events, we found that radially stretching protein though opens up and widens the pore in the planar direction; it reduced the final permeability compared to control. The hydrostatic pressure stimulus system possesses the highest permeability coefficient followed by the protein compressing system. By screening the water occupancy and pore-lining residues in different systems, we found that stretching the protein increased the dynamics of the pore-lining residues which interrupts the single-file line of water molecules in the pore, hence reducing the likelihood of water molecules to pass the pore. We also observed that the constriction site is located where the two pore-lining residues of ASN76 and ILE 60 meet. Our result provides a benchmark for designing a more efficient membrane desalination system for the treatment of water worldwide.

Guilan combined power plant in Iran: As case study for feasibility investigation of converting the combined power plant into water and power unit

This study aims to find a cost effective solution for converting an existing combined power plant into a CWP system including the membrane and thermal desalination units. Without applying major structural change in power plant, to supply fresh water, the steam lines extracted from heat recovery steam generator are used in the thermal desalination unit and membrane desalination system is connected to the gas turbine. An investigation is performed on the produced water and performance of power plant associated with different conditions of electricity and water demands. Also, the influence of steam corresponding to the low and high enthalpy conditions on the performance of thermal desalination unit and power plant is explored. Furthermore, in view of the production capacity of electricity associated with the gas units and consumption demands of various seasons, the influence of membrane desalination unit on the water production is illustrated. An economic investigation is performed to estimate the selling price of water in each unit. It is concluded that in the thermal unit, using HP line produces about 25,000 m3/day, while the LP line causes up to 7000 m3/day water.

Hybrid renewable energy systems for desalination

Water and energy are two key factors in human life that always control the growth and development of human societies. Climate changes, increasing the population in urban areas and industrialization, have increased the demands for freshwater around the world. Estimates show that a small percentage of all freshwater produced in the world is from renewable sources. By developing the technology, lowering equipment prices and increasing attention to the environmental problems of fossil fuels, utilizing renewable energy is growing. By providing a wide variety of conventional desalination methods driven by various types of renewable energy technologies in the world, water and energy legislators should choose different methods to meet the needs based on the local potentials by paying attention to the desalination processes and power systems. In some cases, concentrated solar power for thermal desalination or electricity generated by the photovoltaic plants for membrane desalination systems can be used in arid areas. Definitely, the most problem of using renewable sources is their unsteady natures, which using storage systems or combining with other renewable sources can solve this problem. This chapter provides extensive information about renewables, desalination and performance analysis of power systems. Reverse osmosis technique is a practical process in desalination which 69% of desalination plants use this system. Solar energy is an important source of energy for hybrid systems. The geothermal has a steady performance at a specified depth. Ultimately, obtained results from energy and exergy analysis would have provided a better insight.