Desalination Process Research Articles

Sodium functionalised carbon nanofibers draw solution for a solar-thermal forward osmosis water desalination system

Desalination offers the potential to bridge the demand-supply gap in the increasing global freshwater scarcity, with the forward osmosis (FO) technique appearing as an attractive solution amongst the various desalination technologies. However, the significant energy demand encountered during the draw-solute recovery process in FO desalination is considered the major anathema amongst other contending factors for which the allure of FO as a desalination technology becomes questioned. Consequently, a potentially innovative draw solution (DS) regeneration strategy, enabling the circumvention of the energy requirements associated with the recovery stage in FO desalination, is evaluated. The direct solar thermal FO (DSTFO) desalination concept is predicated on engineering and applying solar absorptive DS to directly leverage solar energy for solute recovery without recourse to electric power. In advancing the DSTFO concept, this study fabricated and evaluated a novel and highly osmotic sodium functionalised carbon nanofibres (Na/CNF) DS having a high osmotic pressure (93.9 bar), a low reverse solute flux (RSF) of 0.24 gMH, and a photothermal conversion efficiency of 63.49%, resulting in an evaporation rate of 1.85 kg/m2/hr under 2 suns of solar radiation. The DSTFO strategy offers a low-cost solution for enhancing water recovery and decreasing energy use in FO desalination systems.

Solvent-free polyamide TFC membrane fabrication based on TMC vaporization for saline water recovery

While thin film composite (TFC) membranes have dominated the global desalination process, using large amounts of organic solvent during membrane manufacturing remains a major concern. Thus, a greener approach to prepare TFC membranes based on solvent-free trimesoyl chloride monomer vaporization is presented in this work. This study fabricated the solvent-free membranes by varying relevant parameters during the vapor interfacial polymerization (VIP) process and studied their impacts on the membrane properties. Evidently, the VIP membranes exhibited thinner polyamide layers than conventionally prepared membrane following the slow polymerization rate. This resulted in higher pure water permeability (2.93 L/m2.h.bar) than the conventional membrane (2.53 L/m2.h.bar) when both membranes were tested at 8 bar. Despite demonstrating slight decrease in salt rejection, the saline water recovery performance of VIP membrane was unaffected, as high salt rejection was unnecessary. Under the best synthesis conditions, a VIP membrane with lower salt rejection could rival the conventional membrane with a >98 % dye rejection while attaining substantially higher NaCl/dye selectivity (up to 330) than the conventional ones (68.75). Pertinently, the study findings demonstrated the potential of the solvent-free IP-fabricated TFC membrane for saline water recovery.

Fabrication of nanoporous multilayer graphene nanoplatelets membrane for water desalination

In recent years, graphene-based membranes are extensively explored for desalination process to fulfil the pure water scarcity. Still, there is a noticeable gap in the research on a technique that simultaneously deposits a membrane and also generates pores in the flake of membrane. In this work, we demonstrated a one-step and scalable protocol i.e. a conventional atmospheric plasma spraying (APS) to fabricate a graphene nanoplatelets (GNP) membrane for water desalination application. Various characterization tools: FE-SEM, Raman, and TEM etc. utilized to evaluate the deposition of GNPs flakes and induced sub-nanometer pores in the large area GNP membrane. Plasma-sprayed GNP membrane showed impressive desalination performance in terms of water flux, salt rejection, and permeability around ~67 Lm−2 h−1, ~99 %, and ~ 115 Lm−2h−1bar−1 respectively at 0.6 bar of transmembrane pressure (TMP). This performance of the GNP membrane was attributed to the critical role of graphene in terms of its structures, including induced pores within graphene sheets and its functions. Our deposited GNP membrane is cost-effective and showed the applicability of conventional plasma spraying in the design of nanomaterials-based membranes for various water purification protocols.

Nutrient recovery from wastewater for hydroponic systems: A comparative analysis of fertilizer demand, recovery products, and supply potential of WWTPs

Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

“Ion-cage” structure of graphene oxide membranes with stable interlayer spacings towards efficient desalination

Multilayered graphene oxide (GO) membrane with sub-nanometer channels is an ideal candidate for desalination. However, excluding small ions using GO-based membranes in the pressured filtration processes remains a great challenge due to the tortuous transport paths of laminates and their water-swelling characteristic. In our previous work, we developed the cation-controlled theory to precisely regulate the interlayer spacing of GO membranes in aqueous solutions. In this work, we proposed an “ion-cage” strategy to enhance the stability (anti-swelling) of the K-controlled GO (icGO-K) membrane for achieving efficient desalination. The icGO-K membrane, coated with positively charged polyethyleneimine (PEI) on its upper and lower surfaces, immobilized intercalated cation K+ between the laminates by electrostatic repulsion to maintain the stability of the confined interlayer spacing. The icGO-K membrane demonstrated superior rejection of 95.3 %, 83.2 %, 81.8 %, and 70.7 % for MgCl2, MgSO4, NaCl, and Na2SO4 while maintaining competitive permeance of ∼ 3.5 L m-2h−1 bar−1 in the desalination process. More importantly, the icGO-K membrane exhibited ultra-long desalination stability up to 720 h. The enhanced performance can be attributed to the synergistic effect of the confined interlayer spacing and surface electrostatic repulsion. Overall, this work provides attractive strategy to fabricate fine-tuning 2D laminate nanochannels for high efficiency of desalination application.

Borate Anion‐Intercalated NiV‐LDH Nanoflakes/NiCoP Nanowires Heterostructures for Enhanced Oxygen Evolution Selectivity in Seawater Splitting

AbstractResourceful and inexpensive seawater direct splitting omits the desalination process and effectively increases the efficiency of hydrogen energy generation. However, the development of seawater splitting is hampered by the competing selectivity challenges from anodic oxygen evolution reaction (OER) and chlorine evolution reaction and the issues of electrode corrosion. Herein, the borate anion‐intercalated NiV‐LDH nanoflakes/NiCoP nanowires heterostructures supported on Ni foam (2D/1D NiV‐BLDH/NiCoP/NF) is synthesized. Theoretical calculations show that a small amount of V atom doping in Ni(OH)2 is favorable for changing the electronic environment around Ni atoms via bridging Ni─O, which can construct Ni─O─V to accelerate electron transfer and promote catalytic activity. The borate anions (B(OH)4−) intercalation not only results in the good hydrophilicity and high OH− selectivity but also weakens the adsorption of chlorine (Cl−), which effectively restrains the chlorine evolution reaction. Thus, the component optimized NiV0.1‐BLDH/NiCoP/NF electrocatalyst only requires 268 mV overpotential to reach 100 mA cm−2 for OER in an alkaline environment. Particularly, the NiCoP/NF||NiV0.1‐BLDH/NiCoP/NF cell exhibits attractive overall water splitting performance with a low voltage of 1.46 and 1.53 V at 10 mA cm−2 in alkaline freshwater and alkaline seawater, respectively. The design strategy of this electrocatalyst provides a new avenue for seawater splitting.

Improving water flux of UiO-66 immobilized on ceramic hollow fiber

The study focused on the development of a modified membrane using a zirconium-based metal–organic framework (UiO-66) to enhance the desalination process in the membrane distillation system. UiO-66 was successfully synthesized on an alumina hollow fiber before fluoroalkylsilane grafting. The effect of UiO-66 concentration loading during membrane fabrication was examined concerning membrane porosity, performance, wettability and surface roughness. Hydrophobic UiO-66 membranes with a contact angle ranging from 130.9° to 139.1° were obtained. The modified membranes were tested in direct contact membrane distillation. With increasing UiO-66 concentration, water fluxes increased from 1.30 to 12.01 kg/m2∙h, and the membrane with 0.4 M of UiO-66 achieved the highest water flux. The optimum membrane was further evaluated under direct contact membrane distillation for seawater desalination to investigate performance stability. The membrane demonstrated a water flux of 9.26 kg/m2∙h with 100 % salt rejection. Moreover, the membrane powder maintained its crystallinity in seawater, demonstrating its long-term stability and substantial capabilities in terms of desalination.

Influence of Concentration Gradients on Electroconvection at a Cation-Exchange Membrane Surface.

Membrane-based systems, such as electrodialysis, play an important role in desalination and industrial separation processes. Electrodialysis uses alternating anion- and cation-exchange membranes with a perpendicular electric field to generate concentrated and diluate streams from a feed solution. It is known that under overlimiting current conditions, reduced charge and mass transfer at the membrane interface leads to regions of high ion depletion generating instability and vortices termed electroconvection. While electroconvective mixing is known to directly impact the separation efficiency of electrodialysis, the influence of ion concentration gradients across the membrane experienced in a functional electrodialysis system is not known. Here, we report the influence of ion concentration gradients across a cation exchange membrane (Nafion) that is both aligned with and opposed to the applied electric field. Experiments were conducted by coflowing NaCl solutions of different concentrations (0.1-100 mM) on each side of the membrane, and electroconvection was visualized with a fluorescence dye (Rhodamine 6G). We obtained concentration profiles from fluorescence image data and systematically measured the thickness of the depletion boundary layer dBL under different conditions. We found smaller dBL values at a higher flow rate both with and without concentration gradients. Our results show that electroconvection is enhanced when the electric field is opposite to the direction of the concentration gradient.

Response to discussion of “Comprehensive simulation to uncover the ideal properties of a hollow fiber forward osmosis membrane module for the seawater desalination process”

Response to discussion of “Comprehensive simulation to uncover the ideal properties of a hollow fiber forward osmosis membrane module for the seawater desalination process”

Reinforced PS-PVDF-WO3 superhydrophobic antiwetting membrane for membrane distillation

Membrane distillation (MD) is an energy-efficient desalination process with abilities to achieve nearly zero liquid discharge and recovery of resources. Nevertheless, MD's transition from laboratory to industrial scale has been largely challenged by expensive and complex fabrication methods for hydrophobic membranes, as well as lack of resistance against wetting and scaling. Present study demonstrates about the development of a hydrophobic electrospun membrane using a low-cost polystyrene (~1.057 $ per kg) polymer blended with PVDF (~80 $ per kg), followed by the surface modification via electrospraying of silane functionalized tungsten trioxide (WO3) nanoparticles. The characteristics of the fabricated membrane in terms of deionized water contact angle revealed ultra-high surface contact angle (~172°) and low sliding angle (<5°). The low thermal conductivity (~0.166 W/mK) of electrospun membrane accredited decreases in temperature polarization during MD operation, resulting in enhanced transportation of water vapors from feed to permeate side. Furthermore, the electrospun membrane attained resilience against wetting, along with stable permeate flux (~25 LMH) and high salt rejection (>99.9 %) with low surface tension (~28 mN/m) saline feed. Tensile tests (firm up to 45 N) and harsh chemical exposure (durable at pH 2 and pH 12) confirmed the structural robustness of the fabricated membrane.

Inhibition of phenol entering condensed freshwater by activated peroxides during photothermal distillation desalination process

The formation of “high-temperature, high-salt and intense-light” environment during the new process of photothermal distillation desalination causes volatile pollutants such as phenol in seawater to volatilize into condensed freshwater, resulting the quality safety risk of the freshwater. In this work, activated peroxides processes including hydrogen peroxide (H2O2), peroxyacetic acid (PAA), peroxodisulfate (PDS) and peroxymonosulfate (PMS) were applied for the inhibition of phenol entering condensed freshwater by making full use of the “high-temperature, high-salt, intense-light” media. Under the same conditions, the phenol removal efficiency by the activated peroxides were in the order of H2O2 < PDS < PAA < PMS. The effects of the salinity, peroxide dosage, initial phenol concentration, humic acid and sunlight intensity on the distillation rates (RD) of phenol were investigated. It was revealed that the main factor for activation of H2O2, PAA, PDS and PMS were heat, Cl−/heat, heat/light and Cl−, respectively. Though both PMS and PAA could completely degrade phenol and reduced its entry into condensed freshwater, PMS formed fewer halogenated distillation by-products and was more promising for future applications.

Exploring time-dependent seawater desalination capacity of terracotta clay soil and coconut shell charcoal

A study assessed the effectiveness of two locally available materials, terracotta clay soil, and coconut shell charcoal, as desalination membranes. The research also explored the impact of exposure time on the desalination process. The study employed a 3 × 3 factorial experiment using a Randomized Complete Block Design (RCBD) with three replications. It compared three different desalination membranes: pure clay, pure charcoal, and a combination of clay and charcoal in a 2:3 ratio. Additionally, three exposure times of seawater to the membranes were examined: 4 h, 8 h, and 12 h. The findings revealed that the different desalination membranes significantly affected (p < 0.05) the salinity level and the treated seawater's sodium and chloride ions content. Notably, clay soil demonstrated higher effectiveness in desalinating water than charcoal and the combination of clay and charcoal. However, the exposure time to the membranes did not significantly affect any of the parameters studied. Based on these results, it is evident that clay soil possesses the potential to serve as a desalination membrane, attributed to its higher Cation Exchange Capacity (CEC) and efficiency in reducing salinity. Future research could investigate ways to improve the efficiency of this material, study the effects of various parameters on the desalination process, and explore scaling up the desalination process for large-scale water production. Overall, this study contributes to developing cost-effective and sustainable methods for providing clean water to areas facing limited access to fresh water.

Selection of the best process for desalination under a Treesoft set environment using the multi-criteria decision-making method

Multi-criteria decision-making (MCDM), which has been called a revolution in the field, is one of the most exact methods for making decisions. Multicriteria decision-making (MCDM) is the process of selecting options by considering multiple criteria to determine which is best. A multitude of applications in engineering, design, and finance are possible with the tools and methods derived from MCDM. Application-oriented problems with multiple criteria involve ambiguous and more inaccurate options, to deal with this ambiguity Smarandache introduced Treesoft sets, which are an extension of hypersoft sets. So, in this paper, we will consider a real-life application-oriented problem “Desalination process” under the treesoft sets environment and find the best method for desalination using one of the MCDM methods.

Innovative thermo-compressor nozzle design for enhanced mixing in TVC desalination plants

This paper introduces an innovative nozzle design for steam jet thermo-compressors used in Thermal Vapor Compression (TVC) desalination plants. Using advanced computational techniques, we compare the performance of the novel nozzle design with a traditional conical nozzle under identical conditions. Resultsunequivocally show that the novel thermo-compressor nozzle design enhances mixing and increases entrainment ratios compared to the conventional nozzle across different conditions. Additionally, we explore a variant of the new design featuring a carefully tuned divergent shape, showing potential for further improving entrainment ratios.This research opens new avenues for optimizing thermo-compressor technology in TVC desalination plants, improving mixing efficiency, and potentially enhancing the overall desalination process.

Optimizing humidifier performance by modifying packing material location and thickness

Humidifiers play a substantial role in evaporative cooling, air conditioning, and desalination process. As of yet, the impact of packing material thickness and position has not been studied, and this study seeks to fill this gap. A counter-flow humidification test rig is developed using cellulose pads varying in thickness (25 mm, 75 mm, 100 mm, and 150 mm) and position (at 425 mm, 310 mm, and 180 mm from the inlet of the air). Air and water flow rates are operational parameters. There is a range of 1.59 to 5.22 kg/min for air and 8.7 to 23.14 kg/min for water. The humidification efficiency is maximised when the air flow rate is kept at its lowest value (1.59 kg/min) and the water flow is at its highest value (23.14 kg/min). The 25 mm of packing material placed at 425 mm from the air inlet yields a high humidification efficiency (99.79%), an outlet velocity of 10.6 m/s, a cooling capacity of 0.04 kW, a specific cooling capacity of 0.20 kWh/kg, a Coefficient of Performance of 0.19, and a minimum pressure drop of 6.85 Pa for the cooling system. An 80-day payback period has been determined.

Numerical Study of the Efficiency of Multi-Layer Membrane Filtration in Desalination Processes

Numerical Study of the Efficiency of Multi-Layer Membrane Filtration in Desalination Processes

Finely tuned water structure and transport in functionalized carbon nanotube membranes during desalination.

Molecular dynamics simulations were performed to tune the transport of water molecules in nanostructured membrane in a desalination process. Four armchair-type (7,7), (8,8), (9,9) and (10,10) carbon nanotubes (CNTs) with pore diameters around 1 nm were chosen, their interior surfaces were modified with -OH, -CH3 and -F groups. Simulation results show that water transport in nanochannel depends on confined water structures which could be regulated by precisely controlled channel diameter and chemical functionalization. Increasing CNT diameter changes water structures from single-file-like to be square and hexagonal-like, then into a disordered pattern, resulting in a concave-shaped trend of water permeance. The -OH functional groups promote structural ordering of water molecules in (7,7) CNT, but disrupt water structures in (8,8) and (9,9) CNTs, and reduce the order degree of water molecules in (10,10) CNT, moreover, exert an attraction to enhance surface friction inside channel. The -CH3 groups induce more strictly single-file movement of water molecules in (7,7) CNT, turning water structures in (8,8) and (9,9) CNTs into two and triangular column arrangements, improving water transport, however, causing again square-like water structure in (10,10) CNT. Fluorinations of CNT make water structure more disordered in (7,7), (9,9) and (10,10) CNTs, while enhance the square water structure in (8,8) CNT with a lower water permeance. Through changing channel diameter and functionalization, the low tetrahedral order corresponds to a more single-file-like water structure, associated with rapid water diffusion and high permeability; an increase in tetrahedrality results in more ice-like water structures, lower water diffusion coefficients, and permeability. The results of this study demonstrate that water transport could be finely regulated via a functionalized CNT membrane.

Photovoltaic panel and wind turbine as an electric energy source for water evaporation and desalination

The purpose of the article is to study the process of heating and desalination of seawater due to electricity from wind turbines and solar panels. This electric current is collected and transmitted through wires to be used to power electrical devices. The advantages of using solar panels as an alternative energy source include environmental cleanliness, long service life, no noise, low cost of operation and no emissions of harmful substances. Boiling water using wind turbine energy is a great way to use renewable wind energy to support daily activities. By placing a wind turbine in an area with a steady wind, the turbine can collect kinetic energy from the air and convert it into mechanical energy that can be used to rotate the generator. This generator can then convert mechanical energy into electrical energy, which can be used to power an electric boiler. The boiler can then use electrical energy to heat the water, producing steam to boil the water.

INTEGRATION OF REAL-TIME DATA MONITORING IN VAPOR COMPRESSION DISTILLATION: A SCADA-BASED APPROACH

This study delves into the enhanced integration of Supervisory Control and Data Acquisition (SCA-DA) systems into Vapor Compression Distillation (VCD) processes for water treatment and desalination. Recognizing the limitations of current VCD systems—such as inefficient real-time data utilization, a pre-dominant focus on theoretical models, and insufficient attention to maintenance and reliability in chal-lenging environments—this research presents a comprehensive SCADA-based VCD system designed to overcome these challenges. Our system significantly improves real-time monitoring and dynamic opera-tional adjustment capabilities, thereby optimizing system responsiveness and operational efficiency. By incorporating advanced sensor technologies and predictive maintenance algorithms, the study ensures heightened reliability and reduced downtime, marking a substantial improvement over traditional VCD systems. The practical implementation of these enhancements is validated in a live operational setting, demonstrating their effectiveness in real-world applications. The findings underscore the potential of integrating SCADA systems to revolutionize VCD processes, making significant strides towards more sustainable and efficient water treatment solutions.

Effects of Desalination Processes on the Water Circulation and Earth System

Effects of Desalination Processes on the Water Circulation and Earth System