Desalination Operations Research Articles

Optimizing Desalination Operations for Energy Flexibility

Optimizing Desalination Operations for Energy Flexibility

Assessment of a solar-powered trigeneration plant integrated with thermal energy storage using phase change materials

This study presents a comprehensive thermodynamic assessment of a trigeneration plant producing electricity, fresh water through multi-effect desalination (MED), and cooling through an absorption refrigeration cycle. The MED and absorption refrigeration systems utilize the rejected heat from the power cycle, driven by concentrated solar power (CSP). Situated in Qatar, the present system leverages the abundant solar irradiance to optimize the efficiency of electricity generation, water desalination, and cooling. The design features parabolic trough collectors with synthetic oil as the heat transfer fluid, direct thermal storage, and a Rankine steam turbine cycle with three turbine stages. The system also incorporates phase change materials (PCMs) based thermal energy storage (TES) to improve the system performance and offset the mismatch between demand and supply. The present system evaluation is based on energy and exergy analyses, while the Aspen Plus is used to simulate the power production and desalination operations, providing detailed insights into its efficiency and potential for large-scale implementation. The proposed system operates with an energy efficiency of 56.72 % and an exergy efficiency of 31.24 %, respectively.

Numerical simulations of the interactions between counterflowing density currents

The collision and interactions between counterflowing density currents frequently occur in nature and engineering practices along the coastal regions. However, the mechanisms and implications of these interactions remain an active research area. In this study, we developed a high-resolution numerical model to simulate the hydrodynamic characteristics of symmetric and asymmetric colliding saline density currents. The aim was to understand the interaction mechanisms, quantify collision parameters, and provide baseline physical insights into the implications of such interactions. The direct numerical simulations reveal that when equal height counterflowing saline density currents collide, the dynamic characteristics of the resulting flow depend on the density difference between the colliding currents, collaborating experimental results. The interaction process initiated mixing and significant vertical motion in the resulting mixed fluid, which attained a maximum rise height of approximately twice that of the colliding currents, thereby enhancing the vertical motion of hypersaline fluid in the ambient column. While the extent of mixing at the collision boundary increases with increasing asymmetry between the colliding currents, a relationship is observed between the buoyancy ratio of the colliding currents and the maximum rise height of the vertically displaced fluid. Given that desalination operations require effective dispersion of brine into the marine environment to minimize local impacts, understanding the collision dynamics of counterflowing saline currents would facilitate improved engineering design and implementation of environmentally compliant coastal management strategies.

A novel two-stage continuous capacitive deionization system with connected flow electrode and freestanding electrode

The desalination of seawater/wastewater utilizing flow-electrode capacitive deionization (FCDI) has received significant interest. However, challenges like the low electrical conductivity of flow electrode and excessive energy consumption have prevented the scaling up of desalination operations. To overcome these issues, this study introduces a new FCDI system termed the two-stage FCDI (TS-FCDI) system, in which desalination modules are equipped with freestanding and flow electrode. The TS-FCDI system offers a graded desalination module design that produces an average salt removal rate (ASRR) of 113 µg cm2·min−1. However, the TS-FCDI system requires substantially reduced infrastructure investment, device size, and energy expenses. Notably, the design allows for the simultaneous operation of freestanding and flow electrode and enables the transport of ions and charges in the electrode region. Experimental evidence from multiple device configurations (CDI, FCDI, and TS-FCDI) supports this claim. Notably, the TS-FCDI system shows about twice the desalination performance over FCDI, with approximately 50 h of single-cycle (SC) operation. This enhancement links the freestanding electrode with the flow electrode, enabling the device to be well-suited for practical applications. The continuous flow of electrode particles in contact with the freestanding electrode initiates secondary ion transport, merging two different types of electrodes to enhance the active space of the electrode, effectively improving ion adsorption performance. In summary, the results of this study indicate the potential of the TS-FCDI system as a suitable desalination technology for scaling up applications.

Effect of design and operation parameters on solar‐driven membrane‐based desalination systems: An overview

AbstractDue to the scarcity of freshwater resources in many arid regions of the world, as well as rapidly growing populations and industrialization, various desalination technologies have been developed and enhanced to improve the performance of saline water purification with high quality. Integrating solar energy technologies with desalination systems would alleviate the running out of fossil fuel sources, reduce costs, and improve energy efficiency. Solar‐powered desalination systems could be a viable and efficient method for treating highly saline water for human consumption. Obtaining reliable and accurate design parameters for such hybrid systems plays a significant role in determining the system performance of solar‐driven desalination systems. The present review provides a comprehensive review of various solar‐driven membrane‐based desalination systems to investigate the impact of design and operation parameters for solar and desalination units on the effectiveness of the hybrid solar/desalination system. Recent advancements in utilizing numerous solar energy sources for desalination are analyzed herein. The economic implications of various membrane desalination operations for different solar energy sources are also discussed. It was revealed that the solar system design parameters, desalination unit characteristics, feed water properties, and climate conditions all affect the functionality and productivity of the membrane‐based solar‐powered desalination system. The feed pressure, number and shape of membranes, and the integrated solar system, all have significant impacts on the performance of the hybrid system. This article provides a pathway for desalination researchers to select the optimal design and operation parameters for hybrid solar‐powered membrane‐based desalination systems. Notably, they are found more feasible and sustainable than traditional desalination processes. Several related conclusions and future perspectives are reported herein.This article is categorized under: Sustainable Energy > Solar Energy

Evaluating groundwater quality for some areas in Zawiya city according to the Libyan and international standards

In this research, some groundwater specifications were evaluated for 5 areas of well water located in different areas in Zawiya city. These areas included (Warshfana, Al-Zawiya Al-Markaz, Dilah, Sayyida Zeinab, South Al-Zawiya), where some of the physical and chemical properties of well water samples were studied and the results were compared with the Libyan standard of 2015 and the specifications of the World Health Organization (WHO). This study showed that the well water samples that were studied are not suitable for human drink because they do not conform to international standards for drinking water, except for the water samples that were collected from the Warshafana area, where it was found that the concentration of total dissolved salts in the water samples collected from the Al-Zawiya Al-Markaz area, Sayyida Zeinab area and the Dilah area fall within a range greater than (1000 ppm). As for the samples from the Dilah region, the salinity level was very high as it is an area close to the sea, and therefore the water needs treatment and desalination operations before it can be used. Keywords: groundwater, physical properties, chemical properties, standard specifications, Zawiya city

High-performance robust graphitic carbon nitride nanosheets embedded membranes for desalination through direct contact membrane distillation

Two-dimensional (2D) graphitic carbon nitride (g-C3N4)-based membranes have recently received widespread attention due to their fantastic separation performance. In the present investigation, for the first time, we assessed the desalination performance of membranes incorporated with g-C3N4 nanosheets through the membrane distillation (MD) process. For this purpose, different concentrations (0–0.06 wt.%) of synthesized nanosheets were embedded within the hydrophobic PVDF matrix by simple phase inversion method. Upon loading 0.03 wt.% g-C3N4, the water contact angle and LEP augmented from 80.5° and 6 bar for the pure PVDF membrane to 95.2° and 8 bar, respectively. Adding the g-C3N4 nanosheets also improved both the tensile strength and the elongation at break by 21.32% and 36.46% than the pristine membrane, respectively. The mixed matrix membranes favorably improved MD performance; so that, 0.03 wt.% g-C3N4 embedded membrane exhibited a flux of 27.63 kg/m2h with an enhancement of 70% relative to its pure counterpart. Continuous testing for up to 24 h filtration of a 3.5 wt.% NaCl solution still showed a stable flux and almost complete salt rejection for the mentioned mixed matrix membrane. The anti-fouling properties of the membranes were also improved by incorporation of the g-C3N4 nanosheets. The 0.03 wt.% gCN embedded membrane recovered about 90% of the original permeation flux after 20 h desalination operations using real seawater as a feed solution. This work holds promise for developing next-generation MD membranes with superior desalination performance in terms of water vapor permeability and salt rejection.

Numerical investigation of capacitive deionization (CDI) with divergent and convergent channels

This research aims to explore the impact of tilted channel configurations of CDI cells on desalination performance. The results reveal that the titled convergent channels have a faster average salt adsorption rate (ASAR) than the regular straight geometry. For desalination operations that end at a quarter of the equilibrium salt adsorption capacity (SAC), the convergent spacer with a slight slope of 1.5 degrees has a 20 % higher ASAR than the typical straight geometry (0.15 mg/g/min for convergent and 0.12 mg/g/min for straight). This gain increases to about 24, 29.5, and 33%, respectively, for slopes of 3.5, 5.5, and 7 degrees, compared to the straight geometry with the same spacer thickness. By looking at the underlying mechanisms, the spacer geometry is found to shift the location of the initial adsorption. This affects how quickly the device outputs the cleaned water. Interestingly, the geometry angle can also affect the location of the depletion zone, so tilted spacers can also affect the behavior during electrode starvation. Specifically, the convergent geometry has the depletion zone in the middle of the electrode instead of the corner near the outlet, as seen for straight and divergent channels. Together, these findings indicate how to construct tilted spacers to enhance CDI performance.

Effects of the Spacer Obstacles on the Capacitive Deionization Performance

The capacitive deionization (CDI) process uses porous electrodes to adsorb electrostatic ions, offering the possibility of efficient desalination of salty water. The purpose of this study is to investigate the effects of obstacles in CDI spacers on charge transfer and adsorption. The results reveal that the adsorption rate of the CDI cells increases remarkably for the obstacle height ratios of h = 0.8 and 0.9 in comparison with the original channel. In contrast, the performance deteriorates for the cells with height ratios of h = 0.3 and 0.6. For desalination operations that end at half the equilibrium salt adsorption capacity (SAC), the CDI channel containing rectangular obstacles covering 80% of the channel, improves the ASAR (0.13 mg g−1 min−1) by 8% compared to the same situation with the original spacer (0.12 mg g−1 min−1). This gain increases to 25% for the barriers covering 90% of the channel height. The results show that as the barrier height is modest, it prevents salt from entering the electrodes, allowing a low concentration zone to be identified adjacent to the barrier inside the electrode. Interestingly, if the barrier height ratio is as high as h = 0.8 and 0.9, the strong vortices facilitate the ions transfer towards the electrode and consequently, more adsorption occurs.

Assessment of Energy Consumption of Brine Discharge from SWRO Plants

The San Pedro del Pinatar I and II desalination plants in Spain were constructed near Posidonia oceanica meadows protected at the national and European level. The environmental impact statement for these plants stipulate that the brine discharge from the plant must not impact the meadows. To this end, a 4790 m submerged outfall was constructed to bypass the lower limit of the seagrass meadows, and a diffuser piece, along with an outfall pumping system, was installed at the end of the outfall. The objective of this paper is to evaluate the economic cost of the energy consumed for the brine discharge evacuation process necessary to comply with environmental requirements. The operating time and power consumption data were obtained from the plant’s monitoring system, while the energy cost was obtained from energy invoices. The computed results show that it is possible to minimize the environmental impacts of brine discharge on the marine environment of an SWRO plant with a low economic cost. The average energy consumption of the reject effluent pumping system ranged from 19.4 to 1239.3 thousand kWh per year, while the average annual energy cost was 49,329 €, which amounts to only 0.56% of the total energy cost for plant operation. The adoption of these measures provide a cost-effective means to meet environmental protection requirements and minimize the environmental impact associated with the discharged brine. As the demand for desalination operations increase, economically and scientifically viable technologies for mitigating environmental impacts are necessary for sustainability in this domain.

Ion Exchange Conversion of Na-Birnessite to Mg-Buserite for Enhanced and Preferential Cu2+ Removal via Hybrid Capacitive Deionization.

Layered manganese oxides (LMOs) have recently been demonstrated to be one of the most promising redox-active material platforms for electrochemical removal of heavy metal ions from solution via capacitive deionization (CDI). However, the impact of interlayer spacing of LMOs on the deionization performance of electrodes in a hybrid capacitive deionization (HCDI) system with an LMO cathode and a carbon anode (i.e., LMO/C electrodes), and their phase transformation behaviors, particularly during the desalination operations, have yet to be extensively evaluated. In this study, we thoroughly evaluate Mg-buserite obtained by ion exchange of fresh Na-birnessite and Na- and K-birnessite as HCDI electrodes to remove copper ions (Cu2+) from saline solutions. Among the three LMO/C electrodes, the Mg-buserite/C (MgB/C) electrodes demonstrate the best deionization performance in terms of salt adsorption capacity (SAC), electrosorption rate, and cycling stability, followed by K-birnessite/C (KB/C) and Na-birnessite/C (NaB/C). More importantly, MgB/C exhibits the highest Cu2+ ion adsorption capacity (IAC) of 89.3 mg Cu2+ per gram electrode materials at a cell voltage of 1.2 V in 500 mg L-1 CuCl2 solution, with an IAC retention as high as 96.3% after 60 charge/discharge cycles. Given that electrosorption of Cu2+ ions is often competed by alkali and alkaline earth metal ions, our data reveal that the MgB/C electrodes demonstrate selectivities of 4.7, 7.7, and 8.1 for Cu2+ over Na+, Ca2+, and Mg2+, respectively. Moreover, X-ray diffraction and spectroscopic analyses show that the enhanced deionization performance and preference for Cu2+ are mainly attributed to the expanded interlayer spacing of LMO minerals. This study provides a promising strategy for tailoring LMO minerals for improving their electrosorption capacity and preference for copper ions from a multivalent-ion solution via an HCDI platform.

Desalination Discharge Influences the Composition of Reef Invertebrate and Fish Assemblages

Large-scale desalination is used increasingly to address growing freshwater demands and climate uncertainty. Discharge of hypersaline brine from desalination operations has the potential to impact marine ecosystems. Here, we used a 7-year Multiple-Before-After-Control-Impact experiment to test the hypothesis that hypersaline discharge from reverse osmosis desalination alters temperate reef communities. Using replicated, video-based, timed searches at eight sites, we sampled fish and invertebrate assemblages before, during, and after the discharge of hypersaline brine. We found that the composition of fish assemblages was significantly altered out to 55 m while the composition of invertebrate assemblages was altered out to 125 m from the outlet during hypersaline discharge. Fish richness and functional diversity increased around the outlet, while the invertebrate assemblages were no less diverse than those on reference reefs. Differences in faunal assemblages between outlet and reference sites during discharging included changes in the frequency of occurrence of both common and rare reef biota. Overall, we found the influence of hypersaline discharge on temperate reef biota to be spatially localized, with the reefs around the outlet continuing to support rich and diverse faunal communities. In some cases, therefore, the marine environmental consequences of large-scale, well-designed, desalination operations may be appropriately balanced against the positive benefits of improved water security.

Development and characterization of LiCl supported composite sorbents for adsorption desalination

• Two innovative composite sorbents were developed for sorption desalination. • Thermodynamic and kinetic performance at material level were deeply investigated. • LiCl/Silica gel composite showed a maximum SDWP higher than 60 m 3 /tonne/day. Adsorption desalination (AD) is an emerging technology to reduce risk of freshwater scarcity, able to use renewable energy and applicable in decentralized areas. Only limited sorbents have been tested experimentally for AD systems. This study developed two composite sorbents based on LiCl as embedded salt and two matrices, namely, silica gel (LiCl@SG_30) and expanded vermiculite (LiCl@EVM_45). The performed analysis figured out how the trade-off between high sorption capacity and good mass transfer caused by their different pore structures influences the desalination operations. The results were compared against a standard microporous Siogel. The sorption isobars indicated that the sorption behavior of LiCl@SG_30 is the combination of silica gel and the embedded LiCl crystals, while for LiCl@EVM_45 is mainly the sorption process of the embedded LiCl crystals. LiCl@EVM_45 reached the highest sorption capacity. The Dubinin-Astakhov equation described the equilibrium capacities of the sorbents. The kinetics coefficient ( k ) was employed to evaluate the sorption rate. Microporous Siogel showed the highest sorption rate, followed by LiCl@SG_30 and LiCl@EVM_45. Finally, predicted specific daily water production (SDWP) were calculated, showing promising features for both LiCl@SG_30 and LiCl@EVM_45, with LiCl@SG_30 achieving SDWP ranging from 43 to 60 m 3 /tonne/day) for the selected conditions.

Spatial extent of desalination discharge impacts to habitat-forming species on temperate reefs

Outlet infrastructure and hypersaline discharge from large-scale desalination operations have the potential to impact marine environments. Here, we present the results of a six-year M-BACI assessment of the impacts of desalination discharge outlet construction and hypersaline effluent on the cover of habitat-forming species on temperate reefs. The construction of the desalination outlet caused a decrease in the cover of Ecklonia radiata (kelp) and an increase in the cover of algal turfs up to 55 m from the outlet. Following the commencement of discharging of hypersaline brine, the impact to E. radiata and algal turfs persisted, but decreased in spatial extent to be less than 25 m from the outlet. Hypersaline discharge was also associated with a significant decline in the cover of sponges in outlet compared to reference sites. Overall, our results demonstrate that the water security benefits from large-scale desalination may sometimes be appropriately balanced against the associated ecological consequences.

Insight into fouling potential analysis of a pilot-scale pressure-assisted forward osmosis plant for diluted seawater reverse osmosis desalination

In recent years, pressure-assisted forward osmosis (PAFO) process has been studied to overcome the low water productivity in FO-RO hybrid seawater desalination. Our research group demonstrated a pilot-scale PAFO-RO plant for seawater desalination operations using secondary treated wastewater and natural seawater. A pretreatment stage of mesh tube filter media (MTF) and cartridge filter (CF) was implemented for a pilot-scale PAFO. In this study, the water quality and fouling index (SDI15 and MFI0.45) of the influent and treated water at each process stage of the plant were measured. For the influent of both wastewater and seawater feature, it showed linear correlations between the concentration of microbial ATP (i.e., an indicator of microbial activity) and MFI0.45. After the PAFO was operated for 76 days, the fouling of the filtration media and the FO membrane was also analyzed. The observation of the fouled membranes by SEM showed that fouling was hardly observed on the side contacting with seawater, but severe bacterial biofilms were observed on the side contacting with wastewater. FT-IR results also confirmed protein-like substances on the membrane surface contacting with wastewater, indicating irreversible fouling. This study suggests that an advanced pretreatment process to remove bacteria and organic matter is essential for the protection of the FO membranes.

The hybridization of thermally-driven desalination processes: The state-of-the-art and opportunities

Water scarcity is a global issue that needs to be urgently addressed to alleviate its adverse impacts on social and economic development. Desalination has been touted as an attractive alternative that can sustainably provide freshwater, particularly when there is no better option to augment water supplies. Tremendous research innovations and evolutions have been made to improve desalination processes in various aspects. Hybridization of two of more desalination processes has been recognized as a promising approach to tackle the inherent disadvantages of conventional desalination processes in regards of energy consumption, water productivity and environmental impacts. While there remains a huge demand for thermal-based desalination particularly in the Middle East region, it is timely to provide a review to look into the progresses made in the hybridization of thermal-based desalination processes. The opportunities for further advancement in the hybridization of thermal-based desalination processes are also proposed. The driving forces for the hybridization of these processes include energy saving, increased freshwater production and improved flexibility in tapping renewable energy. The design and configurations, performances and optimizations have been made in the hybridizations of thermal-thermal or thermal-membrane desalination. Thermal-based hybrid desalination system represents the future trend of commercial scale desalination operations.

Cloud and IoT based smart architecture for desalination water treatment

Increasing water demand and the deteriorating environment has continuously stressed the requirement for new technology and methods to attain optimized use of resources and desalination management, converting seawater into pure drinking water. In this age, the Internet of Things use allows us to optimize a series of previously complicated processes to perform and required enormous resources. One of these is optimizing the management of water treatment. This research presents an implementable water treatment model and suggests smart environment that can control water treatment plants. The proposed system gathers data and analysing to provide the most efficient approach for water desalination operations. The desalination framework integrates smart enabling technologies such as Cloud Portal, Network communication, Internet of Things, Sensors powered by solar energy with ancient water purification as part of seawater's desalination project. The proposed framework incorporates the new-age technologies, which are essential for efficient and effective operations of desalination systems. The implemented desalination dual membrane framework uses solar energy for purifying saline water using ancient methods to produce clean water for drinking and irrigation. The desalination produced 0.47 m3/l of freshwater from a saline concentration of 10 g/l, consuming 8.31 KWh/m3 energy for production from the prototype implementation, which makes desalination process cost effective.

Composite Membranes with Nanofibrous Cross-Hatched Supports for Reverse Osmosis Desalination.

A novel membrane structure composed of cross-hatched electrospun nanofibers is developed. We illustrate that this novel structure allows for much higher water permeability when used as a support for reverse osmosis thin-film composite membranes. Reinforcement and lamination of the aligned nanofibers generates mechanically robust structures that retain very high porosity and low tortuosity when applied to high pressure desalination operations. The cross-hatched nanofiber layers support the polyamide active layer firmly and reduce resistance to water flow due to the high porosity, low tortuosity, high mechanical strength, and minimal thickness of the structures. The nanofiber composite membrane gives a water flux significantly greater than when a traditional support layer is used, at 99 ± 5 m-2 h-1 with NaCl rejection of 98.7% at 15.5 bar.

Surface engineering for anti-wetting and antibacterial membrane for enhanced and fouling resistant membrane distillation performance

With the emergence of membrane fouling as a prominent issue in long-term MD performance, it has become imperative to manufacture superhydrophobic membranes with antibacterial properties. In this study, a novel superhydrophobic and antibacterial membrane is fabricated using trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TPFOS) and titanium dioxide nanoparticles (TiO2-NPs) as chemical modifiers. The virgin PVDF membrane was pre-treated using PEG-co-PMAA, followed by plasma treatment, to enhance the COOH and OH groups on the top layer and promote formation of coordinate bonds on the membrane surface to TiO2. TPFOS was used to impart a superhydrophobic behavior to the titanium-enriched membrane surface. Membrane characteristics were investigated using SEM-EDS, FT-IR, AFM, XPS, porosimetry, and tensile strength analysis. The PVDF/PP-PT/Ti/Si (polyvinylidene difluoride/ coated PEG-co-PMAA-plasma treated/titanium nanoparticles/perfluorooctyl silane) composite membrane showed a superior contact angle of ~152° and a better self-cleaning ability than that of the pristine PVDF membrane. Plasma treatment of the membrane results in increasing the porosity of the membrane by the mechanism of polymer ablation. Furthermore, the superhydrophobic membrane displayed superior performance due to enhanced water flux and improved salt rejection over long-term DCMD operation. It also possessed excellent antibacterial properties, exhibiting a bacterial reduction of ~99% when tested against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This investigation demonstrates a simple approach to design multifunctional membranes showing anti-wetting, anti-bio-fouling, self-cleaning, and robust characteristics in MD desalination operations.

Optimization of backwash parameters for hollow fiber membrane filters used for water purification

Abstract Membrane backwash is one of the most widely used membrane regeneration techniques in large-scale desalination operations and water and wastewater treatment applications. It is necessary in order to enhance membrane life and is critical in managing the cost of pure water. The estimation of optimal backwash conditions is very important for improved hollow fiber membrane (HFM) operations. A unique feature in HFM backwash operations is the lumen side pressure drop, which leads to variation in backwash water flow across the fiber length. In this work, the effect of fiber diameter, membrane structural properties and backwash water pressure and temperature on flow distribution across the membrane length is studied for HFM modules. An analytical model for HFM backwash is developed, and model predictions are compared with measured backwash water flow variation over the fiber length. Experimental results show that the backwash flow variation over the fiber length is minimized by maintaining low backwash water pressure. Simultaneously, minimum backwash flux for effective cleaning may be achieved by increasing backwash water temperature. Homogeneous flow distribution during backwash improves backwash efficiency or forward flow rejuvenation, which can also be achieved by optimizing fiber diameter and membrane permeability. The validated mathematical model may be used for the optimization of backwash operating conditions and HF dimensions to achieve homogeneous backwash flow distribution across the membrane length.