Off-grid Desalination Research Articles

Renewable energy-driven for sustainable off-grid desalination: A comprehensive review on technical highlights and process

Despite the traditional desalination processes have achieved tremendous progress in terms of technology and cost, it is still limited by the high energy consumption and carbon emissions brought about by expensive fossil fuels. Finding alternative energy sources is essential to meet the growing demand for desalination. Over the past few decades, plenty of efforts have focused on driving the desalination process through renewable energy sources in order to achieve the goal of environmentally friendly off-grid desalination and zero liquid discharge. However, limited by technology and economic cost, the desalination processes driven by renewable energy are difficult to carry out large-scale application, and they are more used as an auxiliary unit of the traditional desalination processes. First of all, this article reviews the basic principles of solar interface evaporation technology, and further, summarizes the sustainable desalination technologies driven by solar and geothermal energy completely. In the end, the current global environment and energy troubles are discussed, and the necessity and significance of promoting renewable energy for desalination in the future are emphasized. This review will assist to promote attention to the development and utilization of renewable energy sources, with a focus on large-scale renewable-driven off-grid desalination projects in the future.

Photothermal ZrN composite membranes for solar-driven water distillation

Many regions around the world, including the Arabian Peninsula, face a scarcity of freshwater resources and depend heavily on non-renewable energy sources for energy-intensive desalination processes, emphasizing the need for sustainable water treatment methods. To tackle this challenge, solar energy-driven membrane distillation is a promising and compatible solution for desalinating seawater. In this work, a solar-powered photothermal air gap membrane distillation (AGMD) system has been tested to treat brine by utilizing plasmonic-based composite membranes. Polyvinylidene fluoride (PVDF) membranes were prepared by incorporating low-cost zirconium nitride (ZrN) nanoparticles at varying concentrations to facilitate solar energy harvesting. ZrN-modified PVDF composite membranes significantly boost the solar absorption up to 75 % in the wavelength range of 250–800 nm, when compared to pristine PVDF membranes. The composite membranes with 56 % enhancement in porosity resulted in a permeate flux of 0.36 L m−2 h−1 and a rejection rate of ∼99 %. The developed photothermal water treatment system provides a highly effective and scalable solution for water treatment. Moreover, next-generation materials exhibiting photothermal effects have the potential to exploit solar renewable energy for decentralized off-grid desalination by converting sunlight into heat for a unique and favourable water-energy nexus.

Jellyfish-inspired sustainable and facile porous zwitterionic hydrogel sponge for efficient solar thermal desalination and water purification

Solar thermal desalination (STD), as a type of eco-friendly desalination and water purification technology is instrumental in mitigating the issue of water scarcity globally. Nevertheless, technology challenges persist for accomplishing a multi-purpose, high evaporation rate combine with low-cost and durability. In this research, we glean inspiration from marine jellyfish to propose a novel design for a solar evaporation device that is low-cost, easy to deployment and high efficiency. The evaporator incorporated carbon black for broad spectrum solar absorption, pristine cotton textile capillary action could maintain a sufficient water provision for continuous steam generating. Notably, the zwitterionic hydrogel exhibited excellent salt resistance and water activation properties, promoting water evaporation and enhancing the long-term stability of the evaporator effectively. Under one solar irradiance of 1 kW m−2, the evaporator raised an outstanding evaporation rate of 2.158 kg m-2h−1 and the energy efficiency was 88.71 %. Besides, it demonstrated broad applicability in purifying complex contaminated water sources and could obtain clean water from them. It was anticipated that this evaporator could be an effective solution for alleviating water source shortage especially for economically stressed regions. This research provided novel insights and potential applications for the expansion of STD technology in areas such as renewable energy utilization, off-grid desalination and waste water treatment. Furthermore, it offered guidance and inspiration for future in-depth research of the water-energy-climate nexus.

Computational fluid dynamics modelling and optimization of solar powered direct contact membrane distillation with localized heating for off-grid desalination

Introduction: Membrane distillation (MD) is a promising technique for desalination, capable of utilizing low-grade heat. However, MD faces some challenges such as temperature polarization. To overcome these issues, direct solar MD with localized heating (LHMD) has emerged as a cost-effective and efficient solution by leveraging solar energy.Methods: This study focuses on process optimization of LHMD using computational fluid dynamics (CFD) modeling. CFD simulation was applied to investigate the fluid behavior, heat transfer, and mass transfer within the system. Several key factors, including module geometry, process configuration, solar irradiation, feed flow rate, and feed temperature are investigated.Results: The effects of these parameters on the distillate production rate, thermal behavior, and energy efficiency, are evaluated for optimization. At the optimal conditions, 1 m2 membrane in a module with a length of 50 cm and a channel height of 1.5 mm under a counter-current flow generates 12 L drinking water per day, which meets the basic drinking water demands for 6 people. Over 70% gain output ratio can be achieved when the feed temperature is more than 20°C, the feed velocity is 1–1.5 mm/s, and the feed salinity is less than 1000 mol·m−3. This setup can also produce 6 L of distilled water per day when a water with a salinity six times higher than seawater if the feed velocity is sufficiently low.Discussions: The main feature of the localized heating is the reverse temperature polarization on the feed side, leading to the increase in energy efficiency and the ease of scale-up.

Energy behaviour and economic analysis of a photovoltaic-thermal (PV/T) collector coupled with a reverse osmosis (RO) desalination unit in Tunisian climatic conditions: a feasibility study.

Water scarcity affects about onebillion people in the world. Around two billion people could be living in water-stressed areas by 2050. For this reason, the desalination is always evolving due to the importance of the water resources found in the seas and brackish water. As these systems are generally energy intensive, the use of a renewable energy source is among the most appropriate solution. In this paper, both experimental and numerical investigations have been conducted to evaluate the performances and the economic viability of aphotovoltaic-thermal collector intended to supply a reverse osmosis (RO) unit. Experimental study is based on the input-output and dynamic system testing (DST)according to ISO 9459-5 standard method and computations use the energy and mass balances of the PV/T collector and the RO plant. Results of DST testing showed that the loss coefficient of the PV/T, the tank loss coefficient and the total tank heat capacity are 10.46 W.m-2.K-1, 1.596 W.K-1 and 388MJ.K-1, respectively. The ability to couple the RO technology to PV/T systems has been demonstrated. The complete system has been simulated for a water salinity of 10,000ppm and climatic data of Borj-Cedria (Tunisia) site (longitude 10° 25' 41″ E and latitude 36° 43' 04″ N). Numerical investigations showed that the electricity needs of a small off-grid desalination unit could be met by using a 6.48m2 PV/T panel surface area. In this case, the purified water produced has a salinity of 1500ppm and the flow rate is 24,000l/day. For a grid connected site, the produced and auxiliary powers are found to be equal to 54% and 21%, respectively. Moreover, the economic cost of adding a PV/T system into an existing RO unit has been evaluated and the results showed that the payback period is 6years.

Demand for off-grid desalination technology in small-island communities — Can interfacial solar vapor generation be the answer?

The demand for an off-grid desalination technology and the feasibility of using interfacial solar vapor generation (ISVG) to address the problem were evaluated within the context of Bungin Island. Bungin Island is a small-island community in Indonesia facing water scarcity. By conducting interviews with households there, we found that households located on the exterior portion of the island faced the greatest challenges to water access. For example, only 17 % of exterior households had piped water access, whereas 67 % central households had piped water access. Similar inequities for exterior households were also found with respect to the cost of getting additional water. Thus, we determined that an off-grid desalination technology is best suited for solving the water access problems for the most vulnerable communities in small islands. ISVG technologies that draw on the radiative energy in sunlight to achieve desalination are promising in increasing water access by offering a floating off-grid devices on water near exterior households, passive operation, low capital investment, and simple maintenance. These findings stress the importance of understanding how contextual factors shape barriers to water access and provide a road map on how to begin incorporating these factors into the development of a more sustainable desalination technology.

Upscaling 3D Engineered Trees for Off-Grid Desalination.

More than 70% of the population without access to safe drinking water lives in remote and off-grid areas. Inspired by natural plant transpiration, we designed and tested in this study an array of scalable three-dimensional (3D) engineered trees made of natural wood for continuous water desalination to provide affordable and clean drinking water. The trees took advantage of capillary action in the wood xylems and lifted water more than 1 foot off the ground with or without solar irradiation. This process overcame some major challenges of popular solar-driven water evaporation and water harvesting, such as intermittent operation, low water production rate, and system scaling. The trade-off between energy transfer and system footprint was tackled by optimizing the interspacing between the trees. The scaled system has a ratio of surface area (vapor generation) to project area (water transport) up to 118, significantly higher than the prevailing flat-sheet design. The extensive surface area evaporated water at a temperature cooler than the surrounding air, drawing on multiple environmental energy sources including solar, wind, or ambient heat in the air and realized continuous operation. The total energy for evaporation reached over 300% of the one-sun irradiance, enabling a freshwater production rate of 4.8 L m-2 h-1 from an array of 16 trees in an enclosed room and 14 L m-2 h-1 under a 3 m/s airflow. Furthermore, we found that the ambient heat in the air contributed 60%-70% of the total latent heat of vaporization when energy sources were decoupled. During long-term desalination tests, the engineered trees demonstrated a self-cleaning mechanism with daily cycles of salt accumulation and dissolution. Combining the quantification from an evaporation model and meteorology data covering the globe, we also demonstrated that the 3D engineered trees can be of particular interest for sustainable desalination in the Middle East and North Africa (MENA) regions.

Exergoeconomic and exergoenvironmental analyses of an off-grid reverse osmosis system with internal combustion engine and waste heat recovery

Recognizing the intensive energy consumption of desalination and the importance of the water-energy nexus, integrated energy schemes can reduce energy costs and carbon emissions while simultaneously increasing energy efficiency. This study presents exergoeconomic and exergoenvironmental assessments for a stand-alone, off-grid desalination plant, constituted by an internal combustion engine, a Rankine-based heat recovery unit, and a seawater reverse osmosis system. The use of fossil diesel is compared to soybean biodiesel. The exergoeconomic analysis follows the SPECO method, and the exergoenvironmental analysis employs environmental data obtained from a Life Cycle Assessment using the Eco-indicator 99 impact assessment method. The exergy efficiency of the plant is 6.9% and 6.7% for the fossil diesel and biodiesel scenarios, respectively. The highest destructions of exergy occurred in the engine, followed by the reverse osmosis system, for both fuel scenarios. Results of the exergoeconomic and exergoenvironmental assessments suggest that the reverse osmosis system and the engine should be the first focuses of actions aimed at reducing overall costs and environmental impacts. The levelized cost of freshwater is 1.312 $/m³ and 2.164 $/m³ (within literature values), and the environmental impact of freshwater is 207.5 mPt/m³ and 70.4 mPt/m³ for the fossil diesel and biodiesel scenarios, respectively. The environmental impacts associated with freshwater are 75% lower for biodiesel because the impacts associated with its production are significantly lower. The system proposed herein is technically viable and an alternative for off-grid seawater desalination.

Achieving maximum recovery of latent heat in photothermally driven multi-layer stacked membrane distillation

Photothermal membrane distillation (PMD) has received increased attention for water desalination because it uses abundant sunlight as its main energy source. It can also be implemented in a modular configuration and work well for decentralized communities. Here we present a multi-layer stacked membrane module with airgaps that can reduce conductive heat loss and recover latent heat. The membrane is synthesized by a simple and scalable spray-coating method that prepared by graphene nanosheets deposition onto a hydrophobic polytetrafluoroethylene (PTFE) membrane with polymerized dopamine (PDA) and trichloro(1H,1H,2H,2H-perfluorooctyl) silane (FTCS). Graphene nanosheets are employed as a photothermal material because of its broad light absorption in the solar spectrum and efficient photothermal conversion. To maximize the water flux, the airgap thickness was optimized, and multiple heat recovery layers were stacked. Using the optimized airgap and four stacked layers, we achieved a high water flux of 1.17 kg/m 2 /h under 0.75 kW/m 2 , equivalent to 105% solar conversion efficiency, which is the highest efficiency reported among all PMD studies (20–70%). To predict the water flux, we further constructed a theoretical model to estimate the membrane surface temperatures that are photothermally heated, which will be helpful in understanding and optimizing future PMD systems. The high efficiency of the multi-layer stacked PMD module in this study bespeaks its great promise as a sustainable and off-grid desalination technique. With an efficient graphene nanosheet-based photothermal membrane, we demonstrate that the performance of the photothermal membrane distillation was largely improved by effectively recovering latent heat generated during condensation of vapor. Using the optimized airgap and four stacked layers, we achieved a high water flux of 1.17 kg/m 2 /h under 0.75 kW/m 2 , equivalent to 105% solar conversion efficiency. • Graphene-based photothermal membranes were fabricated with a simple spray coating. • In our novel multi-layer stacked module, latent heat was efficiently recovered. • With an optimal setting, we achieved the high solar-to-water efficiency (~ 105%). • Synthesized membranes were mechanically and chemically robust for long-term use.

Development of an off-grid solar energy powered reverse osmosis desalination system for continuous production of freshwater with integrated photovoltaic thermal (PVT) cooling

Increasing urbanisation and population growth have caused depletion of freshwater resources leading to exacerbation of water scarcity in remote communities. Whilst much attention has been paid to improving industrial-scale desalination plants over the past decade, the development of small-scale off-grid desalination units to facilitate freshwater supply for remote communities has been overlooked. This study presents a novel method for coupling solar photovoltaic thermal (PVT) cells to reverse osmosis (RO) desalination introducing seawater as the cooling medium to increase the thermal efficiency of solar energy generation and subsequently maximising the rate of freshwater production. The inclusion of a battery unit will enable a constant rate of freshwater supply leading to minimisation of membrane fouling which often occurs in renewable energy powered membrane desalination units. The integrative system has been simulated for the seawater properties and climatic conditions in Alexandria, Egypt. Furthermore, the modelling results indicate that using the proposed method will lead to a reduction of 0.12 kWh/m3 in the specific electricity consumption rate of RO desalination, as well as increasing the electricity generation capacity of the PVT cells leading to a 6% reduction in the required solar panel surface area.

High-efficiency solar-driven water desalination using a thermally isolated plasmonic membrane

This study presents an experimental demonstration of a highly efficient solar-driven interfacial evaporation system for potable water production. The engineered evaporation system consist of a photothermal structure (plasmonic titanium nitride nanoparticles (TiN NPs) coated on a hydrophilic porous membrane), and a thermally insulating nano silica aerogel. During the solar-driven vapor generation test, a hydrophilic membrane functioned as a porous support and drew underlying water to the surface through its microporous channels; the TiN NPs coated on a membrane surface functioned as a photothermal layer and generated localized heat at the water–vapor interface upon light irradiation; and an aerogel mat positioned between the photothermal membrane and the underlying bulk water served as a thermally insulating barrier, to suppress parasitic heat dissipation. The results reveal that the optimized TiN photothermal membrane when tested in a thermally-insulated system, efficiently produced clean water at a rate of 1.34 kgm−2h−1 that corresponds to a solar-thermal conversion efficiency of 84.5% under 1 sun. A superior efficiency of the system was primarily attributed to the broadband light absorption and superior light to heat conversion properties of plasmonic TiN NPs, as well as to the suppressed heat loss from the heated surface to the underlying water. It is believed that the application of TiN-membranes fabricated via a simple and scalable method presents a concrete step for solar-assisted off-grid desalination, particularly at remote locations with limited or no access to electricity.

Scaling Resistance in Nanophotonics-Enabled Solar Membrane Distillation.

This study compares the scaling behavior of membrane distillation (MD) with that of nanophotonics-enabled solar membrane distillation (NESMD). Previous research has shown that NESMD, due to its localized surface heating driven by photothermal membrane coatings, is an energy-efficient system for off-grid desalination; however, concerns remained regarding the scaling behavior of self-heating surfaces. In this work, bench-scale experiments were performed, using model brackish water, to compare the scaling propensity of NESMD with MD. The results showed NESMD to be highly resistant to scaling; a three times higher salt concentration factor (c/c0) was achieved in NESMD compared to MD without any decline in flux. Analyses of the scaling layer on NESMD membranes revealed that salt deposition was 1/4 of that observed for MD. Scaling resistance in NESMD is attributed to its lower operating temperature, which increases the solubility of common scalants and decreases salt precipitation rates. Precipitation kinetics measurements revealed an order of magnitude faster precipitation under heated conditions (62 °C, k = 8.7 × 10-2 s-1) compared to ambient temperature (22 °C, k = 7.1 × 10-3 s-1). These results demonstrate a distinct advantage of NESMD over MD for the treatment of high scaling potential water, where scaling is a barrier to high water recovery.

Preliminary assessment of innovative seawater reverse osmosis (SWRO) desalination powered by a hybrid solar photovoltaic (PV) - Tidal range energy system

This paper proposes an innovative desalination technology for sustainable off-grid systems taking advantage of complementary features of tidal range and solar PhotoVoltaic (PV) energies. According to the literature survey, this proposal has not been considered before. Since fresh water production can be easily stored, the key issue in designing SeaWater Reverse Osmosis (SWRO) desalination plants is to minimise the capital cost required per m3 of fresh water produced throughout the plant lifetime. In addition, water cost of renewable energy - driven desalination strongly depends on decisions concerning battery capacity and nominal power installed, thus hybrid systems play and important role in this regard. The energy analysis performed quantifies the temporal complementarity of tidal and solar resources in an exemplary case study of a semiarid plant location at Broome, Australia. An estimation of the yearly energy production profile of the tidal range power plant is calculated with a zero-dimensional numerical model whereas the System Advisor Model (SAM) is used for the solar PV plant. The main result obtained is the great temporary complementarity of tidal and solar photovoltaic resources for SWRO application. For a given size of the PV generator the inclusion of the tidal range power plant implies an increase of the operating time of the desalination plant at nominal capacity between 1.8 and 2.8 times compared to the only solar PV driven case. This result depends on the SWRO nominal capacity. The recommended design for the case study consists in off-grid desalination plants, with minimum battery capacity if any, powered by a hybrid energy system with a ratio of installed desalination capacities of 55·103 m3/d per each hydraulic turbine of 10 MW. This system can be operated at full load a 42% of the year maximizing the yearly fresh water production.

Off-grid desalination for irrigation in the Jordan Valley

Groundwater resources in many regions of the world are becoming increasingly depleted and salinized. With many aquifers straddling political boundaries, on-going depletion presents both a flash-point for conflict and an opportunity for cooperation. A salient example is that of transboundary groundwater resources in the Jordan Valley. These are shared among Israeli, Jordanian and Palestinian residents. Here we describe a collaborative project aiming to develop a desalination system for use by Palestinian farmers in the West Bank. Students have collaborated across borders in a programme of training and research, in which they have constructed desalination prototypes. These are based on a simple but efficient batch-reverse osmosis (RO) technology that incorporates energy recovery and brine recirculation to achieve 70%–76% recovery and specific energy consumption <1.3 kWh/m 3. The technology can be solar powered with minimal PV footprint. Being built almost entirely from off-the-shelf parts, the system is readily implemented with levels of engineering expertise available in many areas of the world. To test and upscale the technology, and to propagate the knowledge about it, it is being trialled at centres in the UK, Israel and soon in Palestine. It is concluded that the project demonstrates a valuable approach in regions facing transboundary groundwater challenges, and that further learning resources should be developed for free access to foster collaboration across borders.

Optimization and design of a low-cost, village-scale, photovoltaic-powered, electrodialysis reversal desalination system for rural India

This paper presents the cost optimization of a photovoltaic-powered electrodialysis reversal (PV-EDR) system for village-scale applications in rural India based on current component costs and performance. A PV-EDR alternative was explored because it requires half the specific energy (and thus half the power system cost), and reduces water wastage from 60% to less than 10%, compared to small-scale reverse osmosis (RO) systems for groundwater salinity levels commonly found in India. Through co-optimization of the PV and EDR subsystems, the optimal system was predicted to cost $23,420 (42% less than a system designed using conventional engineering practice). A key to the cost reduction was flexible water production that accommodates daily changes in solar irradiance with overproduction on sunny days and water buffer storage tanks. A sensitivity analysis revealed that the capital cost of the total system is most sensitive to membrane area; reducing membrane cost by 87% would half the system capital cost. The optimization method presented here, as well as the cost saving strategies of time-variant operation and load matching with solar irradiance availability, provide design strategies that are relevant to other PV-EDR architectures and general off-grid desalination applications.

Decentralized desalination of brackish water using an electrodialysis system directly powered by wind energy

A novel directly coupled wind–electrodialysis system (wind–ED) with no energy storage was developed. The aim was to perform laboratory experiments, investigating the impact of wind speed (2–10m/s), turbulence intensities (0–0.6 TI), and periods of oscillation (0–180s) on desalination performance and energy consumption. The system produced good quality drinking water (<600mg/L NaCl) over the range of parameters tested. Water production and energy consumption increased with wind speed, until both parameters levelled off at wind speeds above the rated value of the wind turbine (vrated: 7.9–8.4m/s). The impact of wind speed fluctuations on system performance was insignificant up to a TI of 0.4 (i.e., moderate fluctuations). The water production declined under high turbulence intensity fluctuations (TIs≥0.5) and long periods of oscillation (>40s). The main challenge in direct coupling of ED to wind energy was not the magnitude of fluctuations but the impact of power cycling off during long periods of oscillation and lengthy periods of no wind. Interestingly, the specific energy consumption of the process remained relatively unaffected by the fluctuations, suggesting the system to be an electrically robust and reliable off-grid desalination technique for remote water stressed locations.

Ruled-based control of off-grid desalination powered by renewable energies

A rule-based control is presented for desalination plants operating under variable, renewable power availability. This control algorithm is based on two sets of rules: first, a list that prioritizes the reverse osmosis (RO) units of the plant is created, based on the current state and the expected water demand; secondly, the available energy is then dispatched to these units following this prioritized list. The selected strategy is tested on a specific case study: a reverse osmosis plant designed for the production of desalinated water powered by wind and wave energy. Simulation results illustrate the correct performance of the plant under this control.

Use of multiple extractions and injections to thermodynamically balance the humidification dehumidification desalination system

Humidification dehumidification (HDH) desalination systems are well suited for small scale, off-grid desalination. These systems are very robust and can tolerate a wide range of feed salinities, making them a good candidate for treating produced water from hydraulically fractured natural gas wells. A primary engineering challenge for these systems is their high thermal energy consumption. In this study, we examine the use of multiple air extractions and injections to thermodynamically balance the HDH system, so as to make it more energy efficient. The effect of the number of extractions on several performance parameters is studied. In addition, we study the effect of the enthalpy pinch, which is a measure of performance for a heat and mass exchanger, on these performance parameters. Finally, we present results that can be used as guidelines in designing HDH systems. These results include the identification of appropriate temperatures for the extracted/injected air streams, the division of the heat duty between stages, and the value of the mass flow rate ratio in each stage at various values of enthalpy pinch.

A wave energy driven RO stand-alone desalination system: initial design and testing

Traditional desalination systems have high energy requirements which can be considered as the limiting factor for their application. Using renewable energy sources for desalination of seawater and brackish water can help to alleviate water scarcity in those areas with no electricity grid connection or supply shortages. This paper describes the development of a stand-alone, off-grid desalination system powered by wave energy. The device is designed to drive a reverse osmosis (RO) membrane. No electricity is required. The system consists of two main parts; a high pressure pump (WaveCatcher) that allows generation of a high pressure head from low head differences, and a wave driven pump to supply the necessary head to the WaveCatcher. The high pressure pump is designed to produce 6 MPa of pressure which is necessary to drive a RO membrane for desalination of water. A 1:6 scale physical model was built and tested; pressures of 42 m were achieved from an initial pressure head of 0.2 m. Delivery of water to the...

04/02563 Thermal environment in a confined space of high-risebuilding with split air conditioning system: Xue, H. et al. Building and Environment, 2004, 39, (7), 817–823

Humidification dehumidification (HDH) desalination systems are well suited for small scale, off-grid desalination. These systems are very robust and can tolerate a wide range of feed salinities, making them a good candidate for treating produced water from hydraulically fractured natural gas wells. A primary engineering challenge for these systems is their high thermal energy consumption. In this study, we examine the use of multiple air extractions and injections to thermodynamically balance the HDH system, so as to make it more energy efficient. The effect of the number of extractions on several performance parameters is studied. In addition, we study the effect of the enthalpy pinch, which is a measure of performance for a heat and mass exchanger, on these performance parameters. Finally, we present results that can be used as guidelines in designing HDH systems. These results include the identification of appropriate temperatures for the extracted/injected air streams, the division of the heat duty between stages, and the value of the mass flow rate ratio in each stage at various values of enthalpy pinch.