Seawater Utilization Research Articles

Investigating Water and Ion Transport in a Novel Cell Design for Seawater Electrolysis

With increasing concerns about the climate change associated with the carbon dioxide emission from utilizing traditional fuels, hydrogen has become a preferred low-carbon energy carrier. For hydrogen to truly be a clean source of energy, it must be produced from a renewable source of energy through water electrolysis. Theoretically, for each kilogram of hydrogen to be produced 9 kg of high-purity water need to be consumed, thus the enormous use of clean water for H2 production may worsen the shortage of fresh water in many parts of the world.Owing to its abundance, seawater has received great attention in the field of hydrogen production; however, there are many challenges associated with the direct use of seawater for electrolysis. In traditional systems, the seawater is first deionized by reverse osmosis (RO) before being fed to the electrolyzer. The RO system adds complexity to the system and requires energy to be expended for the deionization. Therefore, modern systems have aimed to directly electrolyze seawater, but this comes with it own issues including electrode corrosion, scaling from the ions present in saline water, environmental concerns associated with competitive chlorine evolution reaction, and increased membrane resistance limiting the overall performance of saline water electrolysis. Several strategies have been proposed to overcome these challenges including developing selective electrocatalysts, blocking strategy, pH buffer strategy, etc.This project sought to overcome the issues with direct seawater utilization by designing a cell that is driven by osmotic separation, but does not require an external power source. In this device, high concentration acid/base concentrations are maintained in contact with another compartment containing seawater. The acid/base reservoirs act as draw solutions, taking water passively from seawater due to their differences in osmotic pressure. This talk will focus on the cell design and operation, and include both experimental and modeling results. The rate of water transport with various cell operating configurations was quantified alongside the rate of chloride ion crossover through the anion exchange membrane. New methods for chloride mitigation were explored – including cell operating conditions, membrane design and absorption. Multiple cell configurations will be shown and strategies for reducing the cell operating voltage will be discussed.

Electricity-driven synergistic sulfur recovery and sulfate elimination in seawater

High sulfate (SO42-) concentration inhibits seawater utilization but provides a potential source for elemental sulfur (S0) production. The aim of this study was to investigate the feasibility of SO42- removal with the enhancement of S0 recovery simultaneously using a biotic-abiotic hybrid electrochemical (BAHE) process. Long-term operation (i.e., ∼ 240 d) of the biotic electrochemical unit (i.e., single-chamber bioelectrochemical system) obtained a low S0 recovery of 0.78 ± 0.08 % with high SO42- removal exceeding 95 %. The non-conductive S0 precipitated on the anodic surface inhibited continuous electrochemical oxidation of S2-, resulting in the S2- accumulation in the effluent of the bioelectrochemical process and low S0 recovery. In contrast, efficient S2- oxidation took place on the anode surface of the abiotic electrochemical process with electricity generation. The final S2- concentration in the BAHE process was much lower than that in the individual bioelectrochemical process (3 ± 1 vs. 539 ± 60 mg/L). Efficient S0 recovery (i.e., 71.73 ± 7.17 %) and SO42- reduction (92 ± 5 %) were realized in the BAHE process, mainly attributed to the synergistic effect between the single-chamber bioelectrochemical and abiotic electrochemical cells. Our results may provide a promising way for both seawater utilization and elemental sulfur production.

Anions regulation strategy in simulated seawater: A sustainable and efficient approach for on-site hydrolysis hydrogen generation from Mg alloy waste

This innovative study addresses a critical gap in ‘Green hydrogen’ technology by examining the impact of anions on the hydrolysis of residuary waste AZ91D alloy (Rw-AZ91D) in simulated seawater. Despite seawater's potential as an abundant resource for hydrogen production, its complex anionic composition presents efficiency challenges. Through meticulous regulation of anion types and concentrations, the results demonstrate that under ideal conditions (0.5 M NaCl at 298 K), Rw-AZ91D yields a remarkable hydrolysis capacity of 727.0 mL g−1, with a rapid onset (0.42 min) and low activation energy (27.8 kJ mol−1). Intriguingly, oxygenated acid anions notably impede both kinetics and yield. In 0.5 M NaCl solution respectively mixed with 0.1 M Na2SO4, Na2CO3 and NaNO3 solution, the hydrolysis capacities of Rw-AZ91D increase to 409.5, 514.4 and 118.6 mL g−1. When the concentration of employed anions decreases to 0.02 M, 516.5, 621.0 and 480.5 mL g−1 H2 can be obtained. Microstructural and thermodynamic assessments indicate that anions affect hydrolysis via their ionic size, chemistry, induced acidity, and solubility of Mg2+-complexed metallic compounds. This work introduces a cost-effective and eco-friendly method to manage anions during hydrogen production, thereby bolstering the feasibility of portable hydrogen generators and advancing sustainable seawater utilization in Mg alloy waste-based hydrogen generation systems.

Concept and investigation of Selective Forward Osmosis (SFO) for Salt-Salt Separation as a Pretreatment of Seawater for Resource Utilization

Seawater utilization is crucial for the sustainable human development. Despite growing interest in forward osmosis (FO) due to its unique properties, conventional FO membranes with salt-water selectivity have limitations in applying to specific salt-salt separation processes, which hinders their application in resource utilization. In this work, a new concept, “selective forward osmosis (SFO)”, was proposed, which ingeniously employed an SFO membrane consisting of an ion-selective layer on a denser substrate. The denser substrate is designed to control water flux so as to alleviate the solution dilution and improve the salt-salt separation. Moreover, the sucrose and pure water were used separately as feed solution to provide different water flux to influence the various salt fluxes, showing that pure water feed could enhance the salt-salt separation efficiency, although it could dilute the draw solution to some extent. Therefore, pure water was selected as feed in the subsequent experiments. The optimized SFO membrane achieved high Na2SO4/NaCl selectivity (∼54.8) and MgCl2/NaCl selectivity (∼9.2) in single-salt draw solutions. With mixed-salt and heavy-metal-mixed-salt draw solutions, the Mg2+/Na+ selectivity was enhanced to ∼14.5, and further to 29.3. In real seawater tests, the SFO system effectively permeated monovalent elements (such as Na flux of ∼68.6 g m−2 h−1) while maintaining a higher rejection for bivalent elements (such as Mg flux of ∼0.08 g m−2 h−1), showing high selectivities for Mg/Na, U/Na, Sr/Na, Ni/Na, and Ca/Na. These results demonstrate the potential of SFO for resource utilization, especially in complex saline environments. This work contributes a new route for salt-salt separation in the pretreatment of seawater resources.

A system dynamics simulation-based strategic analysis of integrated water resources utilization and management in Shenzhen city.

As one of the most rapidly developing cities in China, Shenzhen grapples with an increasing challenge in managing water resources due to escalating conflicts with its soaring water demand. This study established a system dynamics (SD) model based on a causal loop diagram to explore the intricate interconnections within the urban water resources system. Through simulating water supply and demand in Shenzhen from 2021 to 2035, the model identified key sensitive factors and examined various utilization scenarios for multiple water resources. Results indicated that water scarcity posed a significant obstacle to Shenzhen's development. To tackle this challenge, several effective measures should be implemented, including enhancing water conservation capabilities, developing seawater resources, promoting water reuse, optimizing the economic structure, and managing population growth. Prioritizing water conservation efforts and maximizing the utilization of seawater resources were regarded as the most impactful strategies in alleviating the water crisis. Furthermore, the relationship between water conservation capabilities and seawater utilization scale was analyzed using the SD model, contributing to the development of a comprehensive water resources management strategy. The findings from this study would provide insights into robust methods for allocating water resources, thereby enhancing sustainable water management strategies applicable to regions facing similar challenges.

Engineering high-valence metal-enriched cobalt oxyhydroxide catalysts for an enhanced OER under near-neutral pH conditions.

Understanding water splitting in pH-neutral media has important implications for hydrogen production from seawater. Despite their significance, electrochemical water oxidation and reduction in neutral electrolytes still face great challenges. This study focuses on designing efficient electrocatalysts capable of promoting the oxygen evolution reaction (OER) in neutral media by incorporating high-valence elements into transition-metal hydroxides. The as-prepared and optimized two-dimensional Mo-Co(OH)2 nanosheets, which undergo operando transformation into oxyhydroxide active species, demonstrated an overpotential of 550 mV at 10 mA cm-2 with a Tafel slope of 110.1 mV dec-1 in 0.5 M KHCO3. In situ X-ray absorption spectroscopy revealed that the incorporation of high-valence elements facilitates the generation of CoOOH active sites at low potential and enhances electron transfer kinetics by altering the electronic environment of the Co center. This study offers new insights for developing more efficient OER electrocatalysts and provides fresh ideas for seawater utilization through the study of the reaction mechanism of the near-neutral-pH OER.

Construction of integrated model of bipolar membrane electrodialysis membrane process and gas absorption-ion reaction process

The bipolar membrane electrodialysis (BMED) possesses the capability of green and efficient recovery of salt resources and alkali production, making it suitable for coupling with seawater utilization and CO2 absorption-mineralization processes. In order to reveal the process control mechanism and dynamic equilibrium, the imperative arises to construct a transport-reaction differential model. The overall process is subdivided into distinct modules: mass transport, reaction, electrical, and tank, with the aim of streamlining this intricate coupling procedure. Based on the Nernst-Planck model and combined with semi-empirical models, the models for each module were constructed, and differential equations were used for model integration. This approach addresses the complexity of multiphase reactions and mass transport processes that are challenging to describe through mathematical models. This model can predict indicators such as decalcification rate, carbon fixation rate, and energy consumption, and the accuracy of these results under various conditions was thoroughly verified through experimental data. This study is expected to provide guidance for the modeling of membrane process coupling.

Pengembangan Alat Desalinasi Air Laut dengan Teknologi Thermal Energy Storage

The need for clean water in household life is very important because humans cannot live without it. The composition of seawater consists of 96.5% pure water and 3.5% other materials, namely salts, dissolved gases, and others. Indonesia is one of the countries that has the second-longest coastline in the world, so the potential for utilizing sea water is very large, one of which can be through the desalination process. Distillation itself is distillation, and its by-product is salt when seawater is heated using a heat energy source with a concentrated solar power (CSP) system. Based on research that has been done previously, the tool is a lab-scale seawater desalination device, but the process of making a lab-scale seawater desalination tool is not optimal. Then design the construction of a lab-scale seawater desalination device with the Multi Stage Flash (MSF) type, and the aim is to determine the performance and functionality of the MSF-type lab-scale seawater desalination device. The results show that the results of the coil heat exchanger development obtained an inlet temperature of 85.9°C and an outlet temperature of 67.8°C, and the room temperature in the chamber can be maintained at a temperature of 68.9°C. As for the components being developed, such as sea water pumps, hoses, tees, and sprayers, a sea water debit of 53.78 liters per hour has been obtained.

Construction of desert rose flower-shaped NiFe LDH-Ni3S2 heterostructures via seawater corrosion engineering for efficient water-urea splitting and seawater utilization

A desert rose flower-shaped NiFe LDH-Ni3S2 heterostructure was prepared by seawater corrosion engineering technique and applied for efficient water-urea splitting and seawater utilization.

Sulfate removal from the seawater using single-chamber bioelectrochemical system

The aim of this study was to investigate the feasibility of sulfate removal from seawater using the bioelectrochemical system (BES). A single-chamber BES was constructed with graphite felt as the anode and carbon brush as the cathode. The BES was inoculated with sea mud and tested with seawater containing 2200 ± 200 mg/L SO42− and 2 g/L sodium acetate as the substrate under an applied voltage of 0.8 V. Results showed that 98.5 ± 5.0 % of SO42− in the seawater was efficiently removed in the BES within 132 h. The maximum current density in the BES reached 3.4 ± 0.1 A/m3 with ~100 % acetate utilization. Most of SO42− was reduced to S2− and the final S2− concentration reached 498 ± 25 mg/L in the BES. Organic sulfur compounds were detected in the SO42− reduction. According to bacterial community and reconstruction of unobserved state analyses, the SO42− removal was mainly attributed to the reaction in the cathodic biofilm. The electricity consumption for the SO42− removal was much lower in the BES than in the membrane technology. Our results can provide a promising method to enhance the seawater utilization in the industry.

A Na+ ion-selective desalination system utilizing a NASICON ceramic membrane

Seawater is a virtually unlimited source of minerals and water. Hence, electrodialysis (ED) is an attractive route for selective seawater desalination due to the selectivity of its ion exchange membrane (IEM) toward the target ion. However, a solution-like IEM, which is permeable to water and ions other than the target ion, results in the leakage of water as well as extraction of unwanted ions. This degrades the productivity and purity of the system. In this study, A novel desalination system was developed by replacing the cation exchange membrane (CEM) with a Na super ionic conductor (NASICON) in ED. NASICON exceptionally permits Na+ ion migration, and this enhanced the productivity of desalted water by removing 98% of Na+ while retaining water and other cationic minerals. Therefore, the final volume of desalted water in N-ED was 1.36 times larger compared to that of ED. In addition, the specific energy consumption for salt (NaCl) extraction was reduced by ∼13%. Furthermore, the NASICON in N-ED was replaced into a two-sided NASICON-structured rechargeable seawater battery, thereby further conserving ∼20% energy by simultaneously coupling selective desalination with energy storage. Our findings have positive implications and further optimizations of the NASICON will enable practical and energy-effective applications for seawater utilization.

Hydrogen synthesis from seawater by means of solar energy

In the electrolysis of seawater as a source of hydrogen, two options exist for the performance of the electrolysis process. The first option is the total desalination of the sea water and then add alkalis for the process of electrolysis to produce hydrogen in the cathode and oxygen in the anode. The disadvantages of this approach are the high cost of desalination and the water treatment to make it alkaline. The main advantage is the ability to use developed technology for the direct electrolysis of fresh water. The second option is to design an electrolyze system capable of utilizing sea water for direct electrolysis at a low power density and electrolyze only a small portion of the water in contact with the electrodes. The advantage of this method is the lower capital required for the system and natural elimination of the waste brine which is only slightly enriched with salts. Also using this technic is possible to produce important amounts of chlorine as a sub-product and also magnesium and sodium as hydroxides that have many uses in the chemical industry. In this research we produced hydrogen via electrolysis from simply natural resources, seawater and solar energy. In order to carry out this experiment we used water from Bahia of Kino Sonora, a place no too far from the University of Sonora, only 100 kilometers away, and a 100-W solar panel that generate DC electricity using directly sunlight that is an abundant resource in the coasts of Sonora. In this work we have been able to produce about 2 liters of hydrogen per hour and nearly 1.2 liters of chlorine per hour with a normal direct radiation of 900 W/m2. This technique could be the solution to the fuels problematic of the ethnicities that inhabit the shores of Sonora and other states of México.

Application of Seawater Plant Technology for supporting the Achievement of SDGs in Tarawa, Kiribati

Pacific island countries, including Kiribati, are suffering from a shortage of essential resources as well as a reduction in their living space due to sea level rise and coastal erosion from climate change, groundwater pollution and vegetation changes. Global activities to solve these problems are being progressed by the UN's efforts to implement SDGs. Pacific island countries can adapt to climate change by using abundant marine resources. In other words, seawater plants can assist in achieving SDGs #2, #6 and #7 based on SDGs #14 in these Pacific island countries. Under the auspice of Korea International Cooperation Agency (KOICA), Korea Research Institute of Ships and Ocean Engineering (KRISO) established the Sustainable Seawater Utilization Academy (SSUA) in 2016, and its 30 graduates formed the SSUA Kiribati Association in 2017. The Ministry of Oceans and Fisheries (MOF) of the Republic of Korea awarded ODA fund to the Association. By taking advantage of seawater resource and related plants, it was able to provide drinking water and vegetables to the local community from 2018 to 2020. Among the various fields of education and practice provided by SSUA, the Association hope to realize hydroponic cultivation and seawater desalination as a self-support project through a pilot project. To this end, more than 140 households are benefiting from 3-stage hydroponics, and a seawater desalination system in connection with solar power generation was installed for operation. The Association grows and supplies vegetable seedlings from the provided seedling cultivation equipment, and is preparing to convert to self-support business from next year. The satisfaction survey shows that Tarawa residents have a high degree of satisfaction with the technical support and its benefits. In the future, it is hoped that SSUA and regional associations will be distributed to neighboring island countries to support their SDGs implementations.

A Dually Charged Membrane for Seawater Utilization: Combining Marine Pollution Remediation and Desalination by Simultaneous Removal of Polluted Dispersed Oil, Surfactants, and Ions.

Shortage of freshwater and deterioration of the marine environment have a serious effect on the human body and ecological environment. Here, we demonstrated a facile way to prepare a multiple-target superwetting porous material to obtain available water without cumbersome steps. Through the facile immersion and hydrothermal method, a charge-enhanced membrane material combining superwettability, electrostatic interaction, and the steric effect is prepared. Such a material breaks through the limitations of single size sieving and has a universal effect on different kinds of contaminants with accurate wettability manipulation and fluid separation control. The protonation and deprotonation of active carboxyl groups at the novel created solid/liquid interface facilitate the surface wettability and flux transition, which will bring out superior continuous separation and surface lubrication control.

Strategy of seawater utilization for tackling water shortage in Qingdao

Strategy of seawater utilization for tackling water shortage in Qingdao

Membrane Technology in Deep Seawater Exploration: A Mini Review

Deep seawater is a valuable renewable resource. Due to its outstanding characteristics (i.e., clean, nutrient-rich and cold), deep seawater has been utilized in various subjects, such as mariculture, agriculture, food and beverage, pharmaceutical, medical, and renewable energy. As a result, deep seawater utilization cannot be separated from membrane technologies. Reverse osmosis has become the most common desalination process to prepare deep-sea drinking water with microfiltration and ultrafiltration membranes as the essential pretreatments to remove organisms, biomass and other pollutants. Besides, nanofiltration and electrodialysis have been very useful to reduce fouling, increase water recovery, and extract valuable minerals and metals, such as lithium, uranium, precious metals, and rare earth elements from deep seawater. This review paper discusses these aspects, comprehensively.

Improved Salt Tolerance and Metabolomics Analysis of Synechococcus elongatus UTEX 2973 by Overexpressing Mrp Antiporters.

The fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 (Syn2973) is a promising candidate for photosynthetic microbial factory. Seawater utilization is necessary for large-scale cultivation of Syn2973 in the future. However, Syn2973 is sensitive to salt stress, making it necessary to improve its salt tolerance. In this study, 21 exogenous putative transporters were individually overexpressed in Syn2973 to evaluate their effects on salt tolerance. The results showed the overexpression of three Mrp antiporters significantly improved the salt tolerance of Syn2973. Notably, overexpressing the Mrp antiporter from Synechococcus sp. PCC 7002 improved cell growth by 57.7% under 0.4 M NaCl condition. In addition, the metabolomics and biomass composition analyses revealed the possible mechanisms against salt stress in both Syn2973 and the genetically engineered strain. The study provides important engineering strategies to improve salt tolerance of Syn2973 and is valuable for understanding mechanisms of salt tolerance in cyanobacteria.

Solar-assisted fabrication of dimpled 2H-MoS2 membrane for highly efficient water desalination

Solar-driven evaporation has been proposed as an efficient way to harvest solar energy for water treatment and desalination. However, the complex preparation process and the degradation of photothermal absorbers restrict their practical applications in solar thermal technology. Herein, a solar-assisted fabrication of three-dimensional dimpled MoS2 membrane (DMM-SA) with an open macroporous (1–2 μm) network is fabricated by folding and overlapping nanosheets under solar illumination. DMM-SA exhibits superior water permeability (334–461 LMH/bar) and extraordinary chemical and structural stability. Compared to the 1T and mixed-phase DMM-SA samples, 2H-DMM-SA floating on the water surface generates high heat localization and achieves high evaporation efficiencies of 83.8 ± 0.8% and 91.5 ± 1.1% at 1 and 3 sun illumination, respectively. After multiple illumination and regeneration cycles, 2H-DMM-SA presents high water evaporation and salt rejection performance. After desalination, the salinity level of permeate water is far below the World Health Organization (WHO) standard. Numerical simulations verify that the inner spaces between two nanosheets and the nanochannels contribute to the high bulk water and vapor fluxes during desalination. The facile and efficient design of 3D 2H-DMM-SA provides a novel avenue for seawater utilization by harvesting solar energy.

Anticorrosion performance of acriflavine–Zn2+ system for mild steel in seawater utilization

An organic/inorganic hybrid corrosion inhibitor based on acriflavine/zinc acetate in controlling corrosion of mild steel in natural seawater was studied through electrochemical techniques, scanning electron microscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and quantum chemical calculations. The experimental results demonstrated the incorporation of acriflavine and Zn2+ significantly improve the uniformity and corrosion resistance of the protective film, and showed a synergistic inhibition effect. Electrochemical measurements indicated the acriflavine acts as a mixed-type inhibitor, and the acriflavine-Zn2+ complex acts as an anodic inhibitor. The optimal mass ratio of acriflavine to Zn2+ was found to be 1:1 in view of the inhibition efficiency of polarization curves. Surface analysis verified the formation and characteristic of acriflavine-Zn2+ film on steel surface. The complex film was mainly composed of Zn(OH)2, [Fe(III), Zn(II)–AF] and oxides/hydroxides of iron(III) based on XPS analysis.

Effect of aquaculture salinity on nitrification and microbial community in moving bed bioreactors with immobilized microbial granules

The novel immobilized microbial granules (IMG) shows a significant effect of nitrification for freshwater aquaculture. However, there is lack of evaluation study on the performance of nitrification at high salinity due to the concentration of recycled water or seawater utilization. A laboratory scale moving bed bioreactor (MBBR) with IMG was tested on recycled synthetic aquaculture wastewater for the nitrification at 2.5 mg/L NH3-N daily. The results indicated that IMG showed a high salinity tolerance and effectively converted ammonia to nitrate up to 92% at high salinity of 35.0 g/L NaCl. As salinity increased from near zero to 35.0 g/L, the microbial activity of nitrite oxidation bacteria (NOB) in the IMG decreased by 86.32%. The microbial community analysis indicated that salinity significantly influenced the community structure. It was found that Nitrosomonas sp. and Nitrospira sp. were the dominant genera for ammonia oxidation bacteria (AOB) and NOB respectively at different salinity levels.