Osmotic Desalination Research Articles

Optimising the effectiveness of osmotic desalination process by using graphene-based nanomaterials

This work examines how graphene-based nanoparticles can be integrated into membranes to improve the effectiveness of water treatment in osmotic desalination processes. This is important since sustainable practices can help address the world's water scarcity. Water treatment, desalination, and resource recovery are areas where osmotic desalination shows great potential. However, membrane performance constraints frequently impede its efficacy. High mechanical strength, superior hydrophilicity, and the ability to lessen internal concentration polarisation are just a few of the remarkable qualities that make graphene-based nanoparticles stand out. In order to increase the membranes' overall functionality, these nanoparticles were created and added to them. Comparing the study to conventional membranes, the main goals were to increase water flux rates and salt ion rejection capacities. It was shown by experimental results that the membranes strengthened with graphene-based nanoparticles performed better. They outperformed conventional membranes in terms of water flow growth and salt ion rejection rates improvement. In order to advance osmotic desalination technologies towards more effective and sustainable water treatment options, this study highlights the revolutionary potential of graphene-based nanoparticles. Graphene-based nanoparticles provide an attractive option for tackling major water issues worldwide by improving membrane characteristics that are essential for osmotic desalination, such as permeability and selectivity. Water management techniques that are environmentally sustainable are supported by their integration into membranes, which also enhances performance metrics. This study opens the door for creative approaches to resource recovery and water treatment by providing important insights into the creation of cutting-edge materials specifically designed for osmotic desalination applications.

Industrial Scale Manufacturing Sub‐10 nm Reverse Osmotic Desalination Membrane on Metallic Single‐Walled Carbon Nanotubes Network

AbstractDifferent from extensively reported carbon nanotubes‐polyamide (PA) composite membranes, this work reports the scalable, low‐cost manufacturing of metallic single‐walled carbon nanotubes network supported PA reverse osmotic desalination membranes. Metallic single‐walled carbon nanotubes (SWCNTs) separated from high‐pressure carbon monoxide conversion (HiPCO) SWCNTs with a diameter ranging from 0.6 to 1.2 nm are deposited on polyethersulfone (PES) films by replacing surfactants around SWCNTs dispersed in aqueous solution, for supporting uniform and smooth sub‐10 nm PA nanofilm formed through aqueous‐organic bilayer interfacial polymerization. The industrial scale manufactured PA/SWCNTs/PES desalination membranes (508 mm × 915 mm) are rolled into spiral wound elements without damage through cutting, gluing, and rolling. The desalination tests on flat PA/SWCNTs/PES membranes exhibits 30 l m−2 h−1 (LMH) under 17.2 bar with 98.45% salt injection when fed with 2000 ppm NaCl at pH = 9. The normalized permeate flux of PA/SWCNTs/PES spiral wound elements is ≈17 LMH under 13.8 bar with 90% salt injection underfed with 2000 ppm MgSO4 at pH = 9–11 condition. The high‐performance sub‐10 nm smooth PA/SWCNTs/PES desalination membranes are fabricated with materials savings and can promote low operation costs compared to conventional 50–100 nm crumpled PA films on any supporting substrates.

Solar driven thermal responsive polyionic liquid/PDDA semi-IPN hydrogel for near-room temperature membrane-free osmotic desalination

The designed thermally responsive polyionic liquid (TPIL)/ poly (diallyl dimethylammonium chloride) (PDDA) hydrogel with a semi-interpenetrating (semi-IPN) structure, containing highly charged chloride anions, was fabricated to explore the comprehensive capabilities of solar driven membrane-free osmotic desalination. Introducing linear PDDA polyelectrolyte with higher charge density has effectively excluded salt ions from entering the TPIL hydrogel matrix due to the strong charge concentration gradient established between the hydrogel and the saline reservoir. Meanwhile, the thermo-sensitivity of the polyionic liquid/PDDA semi-IPN (PNCl) hydrogel enabled the release of absorbed salt-depleted water at a temperature above the Lower Critical Solution Temperature (LCST). The multiple purification process established by partial submersion of PNCl hydrogel in saline enabled continual reduction of the salt ion concentration during the upwards transportation of water along the polyelectrolyte network. Moreover, a mushroom-shaped hydrogel demonstrated enhanced the effectiveness in long-term cyclic desalination. The “mushroom cap” was loaded with photo-thermal conversion fillers (Ti3C2Tx MXene) to achieve higher photo-thermal conversion efficiency for water recovery. A record high salt rejection rate of more than 93% was obtained for membrane-free osmotic desalination. More importantly the whole desalination/water absorption/release process was solely supported by gently heating the PNCl hydrogel under the illumination of renewable solar energy.

4E investigation of solar-driven RO and RRO osmotic desalination systems from water, energy, and environment relevance perspective: a comparative approach

In this paper, two osmotic desalination systems, namely, plug reverse osmosis (RO) and recirculation reverse osmosis (RRO) systems integrated with solar and organic Rankine cycle (ORC), have been presented. These systems are modeled and optimized from energy, exergy, economic, and environmental perspectives. The objective functions are the concentration disposal index (CDI) and unit cost of the product (fresh water) (UPC). The results show that the RO cycle has an optimal configuration grounded on max (CDI) and min (UPC). At identical UPC, the environmental effects of the RO system were less than those of the RRO. This is attributed to higher recovery with increasing temperature of discharged water into the sea in a smaller area and at a higher rate. For the RO system, the values for CDI, exergy efficiency, and fresh water production are 0.193, 45.6%, and 13.1 m3/h for R245ca fluid. Also, the share of RO and RRO in the total TAC costs is 19.44% and 17.33%, respectively. The R245ca working fluid is selected for both cycles, which is more productive than the other fluids. The results show that more than 50% recovery is achieved for the SW30HR-320 membrane at the optimum for the RO system.

Graphene Oxide-alginate Hydrogel for Drawing Water through an Osmotic Membrane.

We report the preparation and evaluation of graphene oxide (GO)-enhanced alginate hydrogels for drawing water across an osmotic desalination membrane. GO-incorporated calcium alginate hydrogels (GO-HG) and pure calcium alginate hydrogels (P-HG) were synthesized for this study. Environmental scanning electron microscopy, water contact angle, and water uptake tests showed both samples to be strongly hydrophilic. The synthesized hydrogels demonstrated the ability to successfully and continuously draw water through a selective osmotic membrane in experiments. This was driven by the surface energy gradient-induced negative pressure between the more hydrophilic hydrogel and less hydrophilic membrane surface. The GO-HG was found to draw 21.2% more water than the P-HG, owing to the flexible GO nanosheets, which can be easily incorporated into the hydrogel framework. The GO nanosheets not only offer more hydrophilic functional sites but also enhance the connectivity within the alginate hydrogel framework so as to enhance the water production performance. The average amount of water drawn through the membrane by the GO-HG and the P-HG is 23.4 ± 0.9 g and 19.3 ± 1.8 g, respectively. It was found that no external stimuli were needed as water flows through the hydrogel due to gravitational force. The GO-enhanced alginate hydrogel, combined with the osmotic membrane, is a promising surface energy gradient-driven functional material for water purification and desalination without applying external pressure.

Membrane-free osmotic desalination at near-room temperatures enabled by thermally responsive polyionic liquid hydrogels

A chloride-anion-rich TPIL hydrogel, acting as a separation and a drawing agent, is used for membrane-free osmotic desalination. Salt-depleted water can be retrieved easily by mild heating originating from human body or solar energy assisted by photothermal fillers.

Interfacial polymerization of thin film selective membrane layers: Effect of polyketone substrates

Thin film composite (TFC) membranes are the most widely used technology in reverse osmosis (RO)-based desalination processes, due to their desirable separation performance derived from the combined structure of the porous support and thin film active layer. Typically, TFC membranes are fabricated via an interfacial polymerization (IP) technique, where the porous substrate plays an indispensable role in forming the thin film layer. In this study, a porous polyketone membrane with a fibrous structure and intrinsically moderate hydrophilicity prepared using non-solvent induced phase separation (NIPS) was employed as the substrate to explore its suitability for fabricating high-performance TFC membranes. Investigations on structure control and chemistry regulation via the NIPS process and in-situ post-treatment revealed that porous polyketone substrates display different morphologies and chemistries, significantly altering the thin layer formation during IP. The resulting TFC membranes exhibited up to 14-fold permeance difference, which was attributed to the variance of “ridge-and-valley” structures in different thin film layers formed on different polyketone substrates. It was found that a polyketone membrane with an appropriate surface roughness could generate favorable “ridge-and-valley” structures in the thin film layer to enhance the surface area, realizing high water permeance as well as high salt rejection in reverse osmotic desalination of NaCl solution.

Direct Osmotic Desalination Technique by Solar Energy

Over the last decade direct (forward) osmosis has attracted much attention in practical applications including artesian water desalination, green power generation, industrial water purification etc. In comparison with the traditional reverse osmosis process the separation is due to natural osmosis, providing lower energy cost for external pressure that is needed for reverse osmosis and lower membrane fouling potential. The main problem for the direct osmosis application efficiency is a selection of appropriate draw solute (otherwise known as a working substance). In the present paper diethyl ether (C₂H₅)₂O has been considered as a working substance having a relatively high osmotic pressure. Heating regeneration has been explored to obtain fresh water and recover the proposed draw solution. The advantage of the diethyl ether over known draw solutes has been discussed. It was noted that for further commercial applications of the diethyl ether as a working substance the membrane should have better characteristics of water permeability, stability, selectivity, and mechanical strength. The pilot device based on the described direct (forward) osmosis technique with the productivity of 1 m³/hr has been manufactured. In the beginning of 2020 the pilot device was successfully installed in a village of Navoiy Region, Uzbekistan to provide its inhabitants with the clean water.

Optimization of Osmotic Desalination Plants for Water Supply Networks

Water scarcity and the poor quality of water resources are leading to a wider diffusion of desalination plants using the Reverse Osmosis (RO) process. Unfortunately, the cost of a cubic meter of fresh water produced by an RO plants is still high and many efforts are in progress to increase the efficiency of the membranes used in osmotic plants and to limit the energy required by the process. A further reduction of the energy cost could be obtained by an optimal operation of the desalination plant so reducing the hourly energy cost, or by coupling the RO plant with an energy production plant based on direct osmosis (Pressure Retarded Osmosis PRO). The economic viability of the desalination process has been analyzed until now without accounting for the integration of the RO plant with the existing water network. This analysis is developed in the present paper with reference to a hypothetical change of water supply in a real network, where a desalination plant is used to satisfy the fresh water demand. Several scenarios will be analyzed to assess the minimum cost of fresh water production and water supply to the network, including the use of energy recovery systems, such as an integrated use of RO and PRO processes, or the regulation of pressure at the network intake by a micro hydro power plant.

Impact of intrinsic properties of foulants on membrane performance in osmotic desalination applications

This study investigates the effect of intrinsic physico-chemical properties of polysaccharides and proteins on the performance of flat sheet and hollow fiber forward osmosis (FO) membranes in different modes. Results showed that the foulant hydrodynamic diameter, zeta potential and rheological behavior were essential characteristics that govern the osmotic desalination processes. Diffusivity was the dominant mechanism governing the performance of hollow fiber membranes in FO mode, while the performance of flat sheet membrane in pressure retarded osmosis (PRO) mode was controlled by a combination of three mechanisms: diffusivity, size exclusion and electrostatic forces.

An explicit solution of the mathematical model for osmotic desalination process

Membrane processes such as reverse osmosis and forward osmosis for seawater desalination have gained attention in recent years. Mathematical models have been used to interpret the mechanism of membrane processes. The membrane process model, consisting of flux and concentration polarization (CP) models, is coupled with balance equations and solved simultaneously. This set of model equations is, however, implicit and nonlinear; consequently, the model must be solved iteratively and numerically, which is time- and cost-intensive. We suggest a method to transform implicit equations to their explicit form, in order to avoid an iterative procedure. In addition, the performance of five solving methods, including the method that we suggest, is tested and compared for accuracy, computation time, and robustness based on input conditions. Our proposed method shows the best performance based on the robustness of various simulation conditions, accuracy, and a cost-effective computation time.

Circulatory osmotic desalination driven by a mild temperature gradient based on lower critical solution temperature (LCST) phase transition materials

Abrupt changes in effective concentration and osmotic pressure of lower critical solution temperature (LCST) mixtures facilitate the design of a continuous desalination method driven by a mild temperature gradient. We propose a prototype desalination system by circulating LCST mixtures between low and high temperature (low T and high T) units. Water molecules could be drawn from a high-salt solution to the LCST mixture through a semipermeable membrane at a temperature lower than the phase transition temperature, at which the effective osmotic pressure of the LCST mixture is higher than the high-salt solution. After transfer of water to the high T unit where the LCST mixture is phase-separated, the water-rich phase could release the drawn water into a well-diluted solution through the second membrane due to the significant decrease in effective concentration. The solute-rich phase could be recovered in the low T unit via a circulation process. The molar mass, phase transition temperature, and aqueous solubility of the LCST solute could be tuneable for the circulatory osmotic desalination system in which drawing, transfer, release of water, and the separation and recovery of the solutes could proceed simultaneously. Development of a practical desalination system that draws water molecules directly from seawater and produces low-salt water with high purity by mild temperature gradients, possibly induced by sunlight or waste heat, could be attainable by a careful design of the molecular structure and combination of the circulatory desalination systems based on low- and high-molar-mass LCST draw solutes.