Seawater Desalination Process Research Articles

A new suggestion to marine gold extraction: Utilizing reduced graphene oxide membranes within seawater desalination processes

Traditional mining practices not only cause severe environmental issues, but also face the problem of insufficient production capacity of gold to meet its growing demand. The proposed alternative strategies for gold production, such as the extraction of gold from seawater, still keep a formidable challenge due to their strong dependence on adsorbent materials with high capacity, selectivity, and sensitivity, while also needing to meet the demands of being environmentally friendly and cost-effective. In practice, the direct extraction of gold from seawater is limited by its extremely low yield and high energy expenditure. However, if the combination of gold extraction techniques with seawater desalination can substantially reduce the energy consumption, the extraction of gold from seawater will become economical and feasible. In this paper, we evaluate the feasibility of marine gold extraction using reduced graphene oxide membranes (rGOM) during the seawater desalination process. The rGOM can adsorb almost all Au3+ from the solutions with trace concentrations of Au3+ ranging from 10 ppb to 200 ppb. The adsorption quantity is linearly related to the concentration, indicating that the adsorption capacity of rGOM is much higher than the total amount of Au3+ in the solution. Additionally, the rGOM can selectively adsorb 99 % of Au3+ in the mixed solution while hardly adsorbing other common elements in seawater. More importantly, the rGOM exhibits the long-term stability over 30 days when being immersed in the solution, making it directly compatible with the existing seawater desalination processes. These specific properties allow the rGOM to be an ideal candidate for combining the extraction of gold from seawater with seawater desalination processes. Our findings provide a methodology for enhancing the economic efficiency of the extraction of gold from seawater and hold promise for addressing the problem of gold scarcity.

Constructing spherical-beads-on-string structure of electrospun membrane to achieve high vapor flux in membrane distillation

Hydrophobic membranes with a reentrant-like structure have shown high hydrophobicity and high anti-wetting properties in membrane distillation (MD). Here, PVDF spherical-beads-on-string (SBS) fibers were electrospun on nonwoven fabric and used in the MD process. Such a reentrant-like structure was featured with fine fibers, a low ratio of bead length to bead diameter, and high bead frequency. It was revealed that the SBS-structured membranes exhibited an exceptional capability for vapor flux, due to the formation of a network of more interconnected macropores than that of fibers and fusiform-beads-on-string structures, ensuring unimpeded vapor diffusion. In the desalination of formulated seawater (3.5 wt.% NaCl solution), a vapor flux of 61 ± 3 kg m−2 h−1 with a salt rejection of >99.98 % was achieved at a feed temperature of 60 °C. Furthermore, this SBS structured membrane showed satisfactory seawater desalination performance with a stable flux of 40 kg m−2 h−1 over a 27 h MD process. These findings suggest a viable approach for fabricating SBS-structured membranes that significantly enhance vapor flux in MD for desalination applications. Besides, the hydrophobic membranes with SBS structure can be prepared by single-step electrospinning, and it is facile to scale-up manufacture. This strategy holds promise for advancing the development of high-performance MD membranes tailored for efficient seawater desalination processes.

Optimization of seawater desalination processes with the ideal reverse osmosis equation

The optimization of a membrane seawater desalination system is used to be a very complicated and time consuming process because tedious calculations are required to determine permeate recovery of the membrane system. This process can be greatly streamlined when the ideal reverse osmosis model is used to calculate the recovery of the membrane system. With this model, the pressure for a designated recovery can be determined conveniently and accurately from the basic parameters of a membrane system. Then the specific cost under various conditions can be calculated for the recovery. Finally, the recovery that minimized the specific cost for the permeate production can be easily determined graphically. The impacts of energy, membrane, feed water pretreatment, and concentrate handling on the optimal recovery of a membrane desalination process are demonstrated. The avoidance of a large number of equations and numerical integration in the determination of permeate recovery can greatly facilitate the optimization of design and operation of seawater desalination processes.

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”

Evaluating the photochemical reactivity of disinfection byproducts formed during seawater desalination processes

Reverse osmosis (RO) is widely used for seawater desalination but pre-chlorination of intake water produces halogenated disinfection byproducts (DBPs). The fate and environmental impacts associated with the discharge of DBP-containing RO brine wastewater are unknown. Therefore, to evaluate if photochemistry plays a role in DBP degradation in seawater, we collected samples at a desalination plant, which were desalted and concentrated using two-inline solid phase extraction (SPE) techniques combining reverse-phase polymeric (PPL) and weak anion exchange (WAX) resins. Both filtered water samples and SPE samples (extracts reconstituted in open ocean seawater) were exposed to simulated sunlight in a custom-built flow-through system. Optical property analysis during irradiation experiments did not provide distinguishing features between intake water and RO reject water (brine). Extractable organic bromine (organoBr) concentrations were low in intake water samples (7.8 μg Br L−1) and did not change significantly due to irradiation. OrganoBr concentrations in laboratory-chlorinated raw water were much higher (135 μg Br L−1) and on average decreased by 42 % after 24 h irradiation. However, while organoBr concentrations were highest in RO reject water (473 μg Br L−1), changes in organoBr concentrations in PPL SPE samples after 24 h irradiation were variable, ranging from a 1–46 % loss. Furthermore, most bromine-containing molecular ions identified by high resolution mass spectrometry that were present in RO reject water before irradiation were also found after both 24 h and 50 h exposures. Although only one RO reject water sample was tested in this study, results highlight that hundreds of yet to be identified brominated DBPs in RO reject water could be resistant to photodegradation or phototransform into existing DBPs in the environment. Future work examining the biolability of DBPs in RO reject water, as well as the interplay between photochemical and biological DBP cycling, is warranted.

Scalable Carbon Black‐Enabled Membranes for Sustainable Solar Membrane Desalination

AbstractSolar energy is used worldwide for generating electricity or desalting seawater. Photothermal membrane distillation (PMD), an emerging thermal‐driven process for seawater desalination, combines interfacial heating with membrane distillation (MD) technology to address the energy consumption issues of conventional MD. However, it is still a great challenge to develop a cost‐effective and scalable membrane, which hampers the practical use of PMD. Herein, a dual‐layer carbon black (CB)/PVDF membrane is prepared via direct electrospraying on a commercial PVDF membrane. With the introduction of a functional layer, a photothermal effect is imparted to the bare membrane, thus significantly increasing the water production rate and solar utilization efficiency (SUE) during exposure to artificial sunlight (≈57% enhancement and 72% SUE under 1 sun). In addition to the outstanding photothermal properties, this functional layer also served as a passivation coating to synergistically reduce the crystallization rate and physical binding of inorganic salts on the modified membrane without adding hazardous chemicals or using laborious steps. This multifunctional coated membrane and fast‐growing solar desalination technology provides a promising solution to the water crisis, especially in off‐grid areas where energy and resources are both relatively insufficient.

RETRACTED: A Study on Life Cycle Impact Assessment of Seawater Desalination Systems: Seawater Reverse Osmosis Integrated with Bipolar-Membrane-Enhanced Electro-Dialysis Process

A lot of research has been carried out to improve the sustainability of seawater desalination. Despite progress, relatively few studies have analyzed the sustainability of seawater desalination processes integrated on two fronts, i.e., (i) process integration and (ii) energy integration. In addition, life cycle assessment studies on multi-stage flash (MSF) desalination often neglect the impact of the disposed brine by assuming that dilution of the discharged brine impacts on ecological systems less. The present study contributes to these omissions by exploring the environmental sustainability of seawater desalination systems using life cycle impact assessment (LCIA). More specifically, the LCIA of Seawater Reverse Osmosis (SWRO) integrated with (i) an Electro-Dialysis (EDBMED) process and (ii) solar photovoltaics (PV) is investigated. Life cycle analysis was used to identify pertinent indicators of the LCIA and their implications in SWRO. The comparative analysis reveals that the advantage of SWRO as compared to other technologies such as MSF is energy efficiency, at estimated levels of 75.0%. The study concludes that despite the technological challenges associated with sustainable desalination and sustainable brine management, integrating renewable energy into seawater desalination can contribute to the sustainability improvements of seawater desalination systems. The findings of this paper provide an initial assessment of the ecological footprints of seawater desalination systems.

A Lotus Seedpods-Inspired Interfacial Solar Steam Generator with Outstanding Salt Tolerance and Mechanical Properties for Efficient and Stable Seawater Desalination.

Interfacial solar steam generators (ISSGs) can capture solar energy and concentrate the heat at the gas-liquid interface, resulting in efficient water evaporation. However, traditional ISSGs have limitations in long-term seawater desalination processes, such as limited light absorption area, slow water transport speed, severe surface salt accumulation, and weak mechanical performance. Inspired by lotus seedpods, a novel ISSG (rGO-SA-PSF) is developed by treating a 3D warp-knitted spacer fabric with plasma (PSF)and combining it with sodium alginate (SA) and reduces graphene oxide (rGO). The rGO-SA-PSF utilizes a core-suction effect to achieve rapid water pumping and employs aerogel to encapsulate the plasma-treated spacer yarns to create the lotus seedpod-inspired hydrophilic stems, innovatively constructing multiple directional water transport channels. Simultaneously, the large holes of rGO-SA-PSF on the upper layer form lotus seedpod-inspired head concave holes, enabling efficient light capture. Under 1kWm-2 illumination, rGO-SA-PSF exhibits a rapid evaporation rate of 1.85kgm-2 h-1 , with an efficiency of 96.4%. Additionally, it shows superior salt tolerance (with no salt accumulation during continuous evaporation for 10 h in 10% brine) and self-desalination performance during long-term seawater desalination processes. This biomimetic ISSG offers a promising solution for efficient and stable seawater desalination and wastewater purification.

An efficient data-driven desalination approach for the element-scale forward osmosis (FO)-reverse osmosis (RO) hybrid systems

Freshwater shortages are a consequence of the rapid increase in population, and desalination of saltwater has gained popularity as an alternative water treatment method in recent years. To date, the forward osmosis-reverse osmosis (FO-RO) hybrid technology has been proposed as a low-energy and environmentally friendly next-generation seawater desalination process. Scaling up the FO-RO hybrid system significantly affects the success of a commercial-scale process. However, neither the ideal structure nor the membrane components for plate-and-frame FO (PFFO) and spiral-wound FO (SWFO) are known. This study aims to explore and optimize the performance of SWFO-RO and PFFO-RO hybrid element-scale systems in the desalination of seawater. The results showed that both hybrid systems could yield high water recovery under optimal operating conditions. The prediction of the system performance (water flux and reverse salt flux) by artificial intelligence was considerably better (R > 0.99, root mean square error <5%) than that of conventional mass balance models. A Markov-based decision tree successfully classified the water flux level in hybrid systems. An optimal set of operational conditions for each membrane system was proposed. For example, in RO, a combination of the feed solution (FS) flow rate (≥17.5 L/min), FS concentration (<17,500 ppm), and operation pressure (<35 bar) would result in high water permeability (>40 LMH). In addition, five SWFO elements and four PFFO elements should be the optimal numbers of FO membranes in the hybrid FO-RO system for effective seawater desalination, especially for long-term operation.

Double-photoelectrode redox desalination of seawater

High energy consumption and low salt removal rate are key barriers to realizing practical electrochemical seawater desalination processes. Here, we demonstrate a novel solar-driven redox flow desalination device with double photoelectrodes to achieve efficient desalination without electrical energy consumption. The device consists of three parts: one photoanode unit, one photocathode unit, and one redox flow desalination unit sandwiched between the two photoelectrode units. The photoelectrode units include a TiO2 photoanode and a NiO photocathode sensitized with N719 dye, triiodide/iodide redox electrolyte, and graphite paper integrated electrodes decorated with 3,4-ethylene-dioxythiophene. Two salt feeds are located between two ferro/ferricyanide redox flow chambers. Under light illumination, high-quality freshwater is obtained from brackish water containing different concentrations of NaCl from 1000 to 12,000 ppm with a high NaCl removal rate. The device can work in multiple desalination cycles without significant performance declines. Furthermore, natural seawater with an ionic conductivity of 53.45 mS cm−1 is desalinated to freshwater. This new design opens opportunities to realize efficient and practical solar-driven desalination processes.

Materials and Corrosion in Seawater Reverse Osmosis Plants: A Review

Desalination is emerging as one of the most promising solutions to extraction and increasing global demand for drinking water. A water purification process called reverse osmosis (RO), in which dissolved solids are separated from solutions by partially permeable membranes. Advances in membrane technology have resulted in the removal of up to 99% of salts in seawater. However, the process and system of seawater treatment RO are associated with many problems, such as scaling and fouling of the membranes, corrosion of the pumps, valves and piping system due to the highly concentrated salt solution and high chemical consumption. Nowadays, these problems have become very critical as they severely affect the desalination process and also massively deteriorate the performance and lifetime of the system components and materials. To ensure that the desalination process is always the best option for a low-maintenance, highly efficient and cost-effective system and process, a comprehensive study of these problems is essential. Therefore, this article addresses the characteristics of metallic materials and corrosion problems in the reverse osmosis process of seawater desalination, as well as the best solutions to focus on and evaluate for an optimal seawater desalination process, and the selection of the category of duplex stainless steels suitable for seawater desalination plants to reduce maintenance, avoid plant shutdown and ensure plant safety.

Process design and technoeconomic analysis for zero liquid discharge desalination via LiBr absorption chiller integrated HDH-MEE-MVR system

A novel multipurpose seawater desalination process is presented that integrates a Lithium Bromide (LiBr) absorption chiller, humidification-dehumidification (HDH), multi-effect evaporator, and mechanical vapor recompression (MVR) to improve the energy effectiveness of conventional desalination processes. The proposed process uses the LiBr absorption chiller cycle to preheat the seawater prior to the steam generation in the multi-effect evaporators while the MVR system activates the LiBr cycle. The integration of HDH further allows to recover the excess water in the process stream and concentrates the brine effluent for zero liquid discharge processing. A stand-alone HDH desalination is comparatively studied with the integrated system to quantify their respective performances over several metrics. Technoeconomic analysis is also performed to assess the economic feasibility and a sensitivity analysis is carried out to observe the effects of changing process variables on the overall performance of these systems. The results show that the proposed process design achieves several times higher gain-output ratio compared to a conventional HDH system of equal capacity, with a levelized water production cost of $8.4/m3 and 6 kW of cooling capacity that can be used for air conditioning.

Electrosorption Integrated with Bipolar Membrane Water Dissociation: A Coupled Approach to Chemical-free Boron Removal.

Boron removal from aqueous solutions has long persisted as a technological challenge, accounting for a disproportionately large fraction of the chemical and energy usage in seawater desalination and other industrial processes like lithium recovery. Here, we introduce a novel electrosorption-based boron removal technology with the capability to overcome the limitations of current state-of-the-art methods. Specifically, we incorporate a bipolar membrane (BPM) between a pair of porous carbon electrodes, demonstrating a synergized BPM-electrosorption process for the first time. The ion transport and charge transfer mechanisms of the BPM-electrosorption system are thoroughly investigated, confirming that water dissociation in the BPM is highly coupled with electrosorption of anions at the anode. We then demonstrate effective boron removal by the BPM-electrosorption system and verify that the mechanism for boron removal is electrosorption, as opposed to adsorption on the carbon electrodes or in the BPM. The effect of applied voltage on the boron removal performance is then evaluated, revealing that applied potentials above ∼1.0 V result in a decline in process efficiency due to the increased prevalence of detrimental Faradaic reactions at the anode. The BPM-electrosorption system is then directly compared with flow-through electrosorption, highlighting key advantages of the process with regard to boron sorption capacity and energy consumption. Overall, the BPM-electrosorption shows promising boron removal capability, with a sorption capacity >4.5 μmol g-C-1 and a corresponding specific energy consumption of <2.5 kWh g-B-1.

CuO/water and Al2O3/water nanofluids as working fluid in an abandoned oil well to improve thermal performance in the seawater desalination process

BackgroundAbandoned Oil/gas wells could be employed as heat sources for various technical processes such as seawater desalination. MethodsIn this study, the thermal performance of an abandoned oil well is enhanced by the addition of nano Cu and Al2O3 particles into the working fluid (water) and by using two distinct thermal insulations in the coaxial double-pipe borehole heat exchanger to decrease heat losses of the heated working fluid. Diligent simulation of the process was carried out using the k-ω SST turbulence model and sweep meshing method. The effect of Cu/water and Al2O3/water nanofluid concentrations on extracted fluid temperature was investigated. Significant FindingThe results revealed that 0.5 wt.% of Cu/water and Al2O3/water as working fluid at a flow rate of 2 kg/s raised the extracted fluid temperature by 14% and 12.9% compared to pure water, respectively. Also, SiO2/GO composite thermal nano-insulation could improve heat loss by 7.4% compared to polystyrene thermal insulation. Furthermore, 806 m3/day of potable water was produced by a multi-effect distillation modified with flash-boxes desalination, where brines were reused as a secondary feed for potable water production. Noticeable increase achieved compared to conventional multi-effect distillation systems.

Development of softening and ballasted flocculation as a pretreatment process for seawater desalination through a reverse osmosis membrane

Efficient desalination through a reverse osmosis (RO) membrane requires the prior removal of blockade-causing substances from raw seawater. To achieve ultrahigh-speed processing of a pretreatment process for seawater RO desalination, we combine traditional softening with ballasted flocculation (SBF) for Ca2+ and Mg2+ removal. An alkaline mixture of Ca(OH)2 and Na2CO3 was the most suitable softening agent for Ca2+ and Mg2+ removal with a reduced amount of generated sludge. This softening treatment simultaneously removed the suspended solids and bacteria from actual seawater. The settling velocity of the suspended solids generated via seawater softening was extremely low. Under the optimum conditions for desalinating actual seawater using an anionic polymer flocculant and microsand, the settling velocity exceeded 3.5 cm/s, 833 times higher than that of softening without ballasted flocculation. The amount of sludge after standing for 3 min was 76.5% lower in SBF than in conventional softening. The silt density index of the treated seawater met the water-supply standard of RO membranes (i.e., <3.0). Furthermore, the SBF-generated sludge exhibited considerably improved dewatering property than the sludge obtained via conventional softening. SBF can efficiently and quickly remove the causative substances of RO membrane fouling from seawater, thereby improving the treatability of generated sludge. SBF provides a new pretreatment process for seawater desalination using RO membranes.

Stable, Cost‐Effective TiN‐Based Plasmonic Nanocomposites with over 99% Solar Steam Generation Efficiency

AbstractPlasmonic nanoparticles (NPs), such as Au, Ag, and Cu, are considered as promising photothermal materials and attract extensive attention for freshwater production by solar steam generation. However, high cost, narrow absorption range and/or poor stability greatly limit their practical applications. Herein, a high‐efficiency solar energy conversion material consisting of low‐cost non‐metal, extremely thermally‐stable plasmonic TiN NPs and hydrophilic semi‐reduced graphene oxide (semi‐rGO), with broadband solar absorption capability, by a fast in situ microwave reduction method is prepared. The 2D semi‐rGO serves as a support for the loading of plasmonic NPs, and meanwhile accelerates the transport and evaporation of water due to its hydrophilicity. Then, decoration of plasmonic TiN NPs further enhances the solar photon absorption and hydrophilicity while suppressing the heat loss, thanks to the layered structure of TiN/semi‐rGO, improving overall solar energy utilization. Owing to the enhanced absorption and unique layered nanostructure with strong interfacial interaction, the optimal sample of TiN/semi‐rGO‐25% absorber achieves a high and stable water evaporation rate of ≈1.76 kg m−2 h−1 with an energy efficiency as high as 99.1% under 1 sun illumination. Furthermore, this plasmonic TiN/semi‐rGO absorber is capable of producing high‐quality freshwater from sustainable seawater desalination and wastewater purification processes.

Submarine discharge of underground waters: research experience, еxploration practices, methods and technologies for possible use

In view of the need to solve problems related to the population's access to sufficient drinking water, the search for submarine discharge zones is currently the most important economic task. Infiltration waters generated within the land, being filtered through bottom sediments, are directed to the seas and oceans and are irretrievably lost for practical use. According to numerous data on the dynamics of underground water supply systems, the movement of underground flows in coastal areas under undisturbed conditions is always directed towards the sea, where discharge is carried out. Infiltration waters flowing from the land to the seabed are predominantly distributed in the shelf zone, but under favorable conditions (tectonic disturbances, paleo-river beds, etc.) their flows can reach the continental slope, so significant areas of the ocean shelf deserve to be explored for fresh and slightly salty, brackish water. In some countries, they are already used to provide water supply. The article assesses the feasibility of practical use of subaquatic waters using specific examples. It analyzes hydrogeological potential, economic factors, and presents technical concepts for water intake, transportation, and treatment. Based on these factors, we are analyzing the possibility of replacing the seawater desalination process with its extraction from submarine underground horizons on the shelf. The article provides a comparative assessment of energy consumption obtained from fossil fuels in the process of seawater desalination and its extraction from underwater horizons. The material presented in the article shows that there are no insurmountable obstacles to the use of submarine discharge waters as an additional source of drinking water.

Optimization of pilot-scale re-mineralization by calcite dissolution using sulfuric acid for seawater desalination processes

Desalinated water produced using reverse osmosis (RO) membranes must be re-mineralized with alkali ions before being supplied as drinking water.

Study of microbial desalination cell performance with different saline streams: Analysis of current efficiency and freshwater production

Microbial desalination cell (MDC) is a sustainable and energy-self-sufficient technology that simultaneously treats wastewater, produces electric energy, and desalinates water in a single device. The optimal desalination process depends on the potential generated in the system, which is mainly limited by cathode reaction, high external load values used, initial salinity of saline stream, or other conditions such as anolyte buffer concentration. As transport processes (i.e., migration and diffusion) in the device overlap under such conditions, it is difficult to identify the factors that affect desalination performance. Most of the existing MDC studies have used oxygen reduction (at neutral pH) as a cathode reaction limiting the performance. The removal of the cathode reaction limitation could help to clarify the operation of the MDC and identify different transport phenomena and their influence on the performance (current efficiency, freshwater production, and salt removal rate). This study presents a systematic analysis of a laboratory-scale MDC (cross-section 100 cm2, batch mode) behaviour under different initial saline concentrations from slightly brackish water (1.3 g L−1 NaCl) to seawater (40 g L−1 NaCl) without limitation in the desalination process (i.e., using a low value of external resistance and potassium ferricyanide as a liquid catholyte). For each initial salinity, the parameters of wastewater treatment capacity, energy and freshwater production are discussed and compared with the literature. The values of freshwater production between 0.5 and 10.6 L m−2 h−1 for each initial saline concentration in the saline compartment are achieved with optimal current efficiency values (80–100%). Additionally, the influence of anolyte buffer capacity on current density in the MDC system (from 0.8 to 1.2 mA cm−2) is analysed. Furthermore, the behaviour of the system during a seawater desalination process is discussed in terms of treatment capacity and Coulombic efficiency. This study could help understand the performance of these systems in possible natural saline scenarios where MDC technology can be implemented in the future.

Techno-economic assessment of forward osmosis as a pretreatment process for mitigation of scaling in multi-stage flash seawater desalination process

Thermal desalination processes suffer from the formation of scalants on the heat exchangers of the evaporator unit which negatively affect the process efficiency. This study evaluated the technical and economic feasibility of a pilot-scale forward osmosis (FO) process for the pretreatment of seawater to remove scaling ions before the multi-stage flash (MSF) process. A commercial hollow fiber FO membrane module was used in the pilot plant. The FO pilot plant used real seawater as feed solution and real MSF brine as draw solution. A maximum recovery rate of 27.7 % was achieved using a pressure gradient of 1.0 bar with the feed solution flowing through the membrane bore side and the draw solution flowing through the shell side with a temperature of 40 °C for both feed and draw streams. The FO membrane showed high rejection for scaling ions, where the rejection rate was almost 99 %, 96 %, and 92 % for sulfate, calcium, and magnesium, respectively. The specific power consumption of the FO process was about 0.01 kWh/m3. It was found that the water production cost for the FO process was almost 0.48 $/m3. The sensitivity analysis shows that the water production cost is highly sensitive to the water flux, especially at the lower range of water flux and high membrane cost. FO pretreatment provides a promising and economical solution for mitigating the scaling issue in MSF desalination plants.