Membrane Desalination Processes Research Articles

Modeling and evaluation of the permeate volume in membrane desalination processes using machine-learning techniques

Machine learning methodologies are gaining significant recognition as an effective approach for tackling and modelling challenges related to membranes. This study delves into the utilization of machine learning algorithms to forecast the quality of reverse osmosis (RO) water. Specifically, we conduct a comparative analysis of four popular algorithms: decision tree, random forest, support vector machine (SVM), and K-nearest neighbours (KNN). Our dataset comprises essential water quality evaluation features such as temperature, pH, and conductivity. Using these features, we train and test our models, evaluating their performance with metrics like accuracy and root-mean-squared error (RMSE). The outcomes indicate that all four algorithms perform admirably in predicting RO water quality, achieving accuracy scores ranging from 80 % to 95 %. Notably, KNN stands out with the highest accuracy score of 95 %, establishing it as the most effective algorithm for this task. Besides its performance, KNN's simplicity of implementation and interpretability make it a pragmatic choice for real-world applications. This study serves as compelling evidence of the potential of machine learning algorithms for forecasting RO water quality, particularly highlighting KNN's effectiveness in this context. To further enhance the accuracy of RO water quality prediction, future research could explore the inclusion of other features or alternative algorithms.

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.

Ionic Hyperbranched Poly(amido-amine)-Incorporated Nanofiltration Membranes for High-Efficiency Dye Desalination.

High-efficiency dye desalination is crucial in the textile industry, considering its importance for human health, safe aquatic ecological systems, and resource recovery. In order to solve the problem of effective separation of univalent salt and ionic dye under the condition of high salt, ionic hyperbranched poly(amido-amine) (HBPs) were synthesized based on a simple and scalable one-step polycondensation method and then incorporated into the polyamide (PA) selective layers to construct charged nanochannels through interfacial polymerization (IP) on the surface of a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane. Both the internal nanopores of HBPs (internal nanochannels) and the interfacial voids between HBPs and the PA matrix (external nanochannels) can be regarded as a fast water molecule transport pathway, while the terminal ionic groups of ionic HBPs endow the nanochannels with charge characteristics for improving ionic dye/salt selectivities. The permeate fluxes and dye/salt selectivities of HBP-TAC/PIP (57.3 L m-2 h-1 and rhodamine B (RB)/NaCl selectivity of 224.0) and HBP-PS/PIP (63.7 L m-2 h-1 and lemon yellow (LY)/NaCl selectivity of 664.0) membranes under 0.4 MPa operation pressure are much higher than PIP-only and HBP-NH2/PIP membranes. At the same time, this project also studied the membrane desalination process in a simulated high-salinity dye/salt mixture system to provide a theoretical basis and technical support for the actual dye desalination process.

Insights into dynamic evolution of combined scaling-biofouling in reverse osmosis

Although extensive research has focused on individual membrane fouling, there is still a lack of studies regarding combined scaling-biofouling, which is more commonly encountered in practical membrane desalination processes due to the coexistence of inorganic scalants and microorganisms. To our best knowledge, it is the first study that elaborated the dynamic evolution of combined scaling-biofouling in the reverse osmosis (RO) cross-flow filtration process, compared with gypsum scaling and biofouling alone. The results indicated that scaling ions (35 mM CaCl2 + 20 mM Na2SO4) stimulated protein secretion but inhibited that of polysaccharide and total organic carbon (TOC). The gradually formed scaling layer evidently enhanced the hydrophilicity of the fouled membrane, and consequently improved the repulsion of membranes against microbes and the secreted extracellular polymeric substances (EPS), proved by the augmented energy barrier for microbial adhesion through XDLVO interfacial energy analysis, and resulted in the slower flux decline at the later stage of combined scaling-biofouling. In the other perspective, microorganisms and EPS diminished the (020), (021) and (041) facets of gypsum crystals, decreased the crystallinity and size of gypsum crystals, and thus prolonged the formation of inorganic scaling. It was suggested that scaling ions should be effectively controlled through pretreatment as they contributed to more rapid flux decline, as the cleaning efficiency of Ca2+ ions decreased from 84.8 % to 57 % after they combined with EPS, and thus chiefly contributed to reversible membrane fouling resistance. This study fills in the knowledge gap on interactions between gypsum scaling and biofouling during the formation of combined scaling-biofouling in RO filtration, which had significant environmental effects under the strict industrial wastewater discharge standards and zero liquid discharge (ZLD) requirements.

Molecular insights into complexation between protein and silica: Spectroscopic and simulation investigations

The synergistic effect of protein-silica complexation leads to exacerbated membrane fouling in the membrane desalination process, exceeding the individual impacts of silica scaling or protein fouling. However, the molecular-level dynamics of silica binding to proteins and the resulting structural changes in both proteins and silica remain poorly understood. This study investigates the complexation process between silica and proteins—negatively charged bovine serum albumin (BSA) and positively charged lysozyme (LYZ) at neutral pH—using infrared spectroscopy (IR), in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and multiple computational simulations. The findings reveal that both protein and silica structures undergo changes during the complexation process, with calcium ions in the solution significantly exacerbating these alterations. In particular, in situ ATR-FTIR combined with two-dimensional correlation spectroscopy analysis shows that BSA experiences more pronounced unfolding, providing additional binding sites for silica adsorption compared to LYZ. The adsorbed proteins promote silica polymerization from lower-polymerized to higher-polymerized species. Furthermore, molecular dynamics simulations demonstrate greater conformational variation in BSA through root-mean-square-deviation analysis and the bridging role of calcium ions via mean square displacement analysis. Molecular docking and density functional theory calculations identify the binding sites and energy of silica on proteins. In summary, this research offers a comprehensive understanding of the protein-silica complexation process, contributing to the knowledge of synergistic behaviors of inorganic scaling and organic fouling on membrane surfaces. The integrated approach used here may also be applicable for exploring other complex complexation processes in various environments.

Experimental performance analysis for reverse osmosis pilot plant subjected to different brackish salinity spectrum

The main obstacles to reverse osmosis desalination processes are high energy intensity and long-term continuity. Temperature and pressure have the greatest and most significant effects on energy use. The main objectives of the current study are to determine the pressure and temperature-dependent optimal operating parameters for a membrane desalination unit. To determine the ideal operating settings for a membrane unit, the impact of changing pressure and temperature on its performance was investigated. These two elements are closely connected to the energy consumption per cubic meter under various operating situations. The present work is experimentally carried out in a research laboratory for capacity building and future research studies in the desalination field established in the National Center of Water Research – Egypt. This laboratory is Egypt’s first multi-functional Desalination Research Station for seawater, brackish water, and related water treatment areas. The plant is equipped with online instrumentation and Data Acquisition System and 13 sensors for most physical parameters which economically affect membrane performance and desalination processes. These parameters, particularly pressure and temperature, are measured, evaluated and analyzed. According to the findings in this study, feed salinity and feed pressure both have significant impacts.At 13 bar pressure, the maximum salt rejection was 98.8%. When feed pressure is increased from 5 to 13 bars, there is a 73.3% decrease in permeate salinity. Additionally, applying a 13 bar feed pressure to water with a salinity of 1000 ppm results in the best water quality of 12 ppm. The relationship between feed pressure, brine salinity, and membrane water recovery appeared to be approximately linear and positive. More crucially, it was discovered that feed pressure, salinity, and water recovery are all constants for water permeability. A prototype for the maximum pressure (ranges from 15.6 to 10.8) and temperature (ranges from 21 to 35) at which the optimal recovery of the laboratory occurred was developed. Moreover, the developed prototype includes the corresponding permeate TDS and a specific energy for each optimal point.

Current Status and Advancement in Thermal and Membrane-Based Hybrid Seawater Desalination Technologies

Emerging hybrid technologies have better potential than conventional technology for diversifying the desalination industry, which is presently being dominated by thermal and membrane-based desalination. Notwithstanding the technological maturity of the desalination processes, they remain highly energy-intensive processes and have certain disadvantages. Therefore, the hybridization of thermal and membrane desalination processes holds great attention to mitigate limitations of individual processes in terms of energy consumption, quality and quantity of potable water, overall efficiency and productivity. This paper provides an oversight of conventional and developing desalination technologies, emphasizing their existing state and subsequent potential to reduce water scarcity. Conventional hybrid desalination systems (NF-RO-MSF, MED-AD, FO-MED, MSF-MED, RO-MED, RO-MSF and RO-MD) are briefly discussed. This study reveals that the integration of solar thermal energy with desalination has a great potential to substantially reduce greenhouse emissions besides providing the quality and/or quantity of potable water in cost-effective ways. Due to its abundant availability with minimal/no carbon footprint and the ability to generate both thermal and electrical energy, solar energy is considered better than other renewable energy technologies. The findings further suggest that hybrid desalination systems are technically sound and environmentally suitable; however, a significant study of the research process and development is still required to make this technology efficient and economically viable.

Deduction of carbon footprint for membrane desalination processes towards carbon neutrality: A case study on electrodeionization for ultrapure water preparation

Decarbonization of the industrial sector, especially in power generation, is vital for achieving carbon neutrality. The life-cycle greenhouse gas (GHG) emissions, namely carbon footprint, of a technology under the decarbonizing macro-environment should be deduced to reveal further opportunities for GHG reduction. Herein, a case study on ultrapure water (UPW) preparation by electrodeionization (EDI) was investigated through life cycle assessment (LCA) and compared with a conventional mixed-bed ion exchange (MBIX) technology. The carbon footprint of the EDI process was quantified as 1.30 kg CO2-eq/metric ton UPW, which is 27.73 % lower than the MBIX. With a decarbonized power grid and recycling of wasted EDI modules, the carbon footprint will be reduced by 91 %. Meanwhile, the proportion of module production and waste management will increase to 18 %. Thus, we suggest reducing the process energy consumption and improving the current efficiency of the EDI process by process modeling and optimization. With the decarbonization of electricity, the degraded reuse of plastic and the recycling of ion-exchange membranes and resins could be considered. The application of LCA to quantify the carbon footprint and provide suggestions for low-carbon designs could be extended to membrane desalination or industrial processes, supporting the revolution towards carbon neutrality.

A Review of Membrane-Based Desalination Systems Powered by Renewable Energy Sources

The rising demand for clean water and the environmental challenges associated with fossil fuels have encouraged the application of renewable and greener energy systems in desalination. Moreover, the small footprint and high productivity favored the membrane-based process in the water industry. In the past few decades, noticeable work has been performed on the development and applicability of membrane-based desalination processes powered by renewable energy sources such as solar, wind, tidal, and geothermal. Several integrated membrane desalination processes for producing clean water with sustainable and clean energy are introduced. This review details the source and performance efficiencies of existing renewable energy technologies and their application in membrane-based desalination processes, with a special focus on current advancements and challenges. This study reviews the interconnections between water, energy, and the environment and explores future energy-efficient desalination options for energy savings and environmental protection.

A Review On Membrane Desalination Process in Water Treatment

Desalination is being used on a much larger scale as a result of the rising scarcity of freshwater. Desalination plant energy usage, however, continues to be a problem. Inherently appealing, the use of renewable energy sources has been the subject of numerous research. Membrane processes are indeed attracting a great deal of interest due to their economic viability and capacity to be scaled up. This article offers a cutting-edge review of membrane processes related to renewable energies for desalinating seawater and brackish water. Reverse osmosis, membrane distillation, and electrodialysis are examples of membrane processes. They are combined with renewable energies like hydrostatic pressure, waves, solar, wind, and wind. The key findings in this field include principles, plant design and implementation, mathematical models, and economic viability, are presented in this article.

Applications of Helical Versus Straight Hollow Fiber Membranes: A Review

The production of straight and helical hollow fibers plays an important role in developing hollow fiber membrane technology that encompasses a broad range of designs. During the last two decades, scientific studies devoted to straight hollow fibers were more abundant than those focused on helical fibers. Several major applications considering side-by-side testing of these two geometries are discussed in this review. For membrane extraction, desalination, and membrane contactor processes, it is observed that permeability rates are 10%-400 % higher for helical fibers compared to straight fibers. This outcome is justified by the presence of Dean-vortices-induced flow turbulences inherent to the geometry of helical membranes. These conditions give rise to an uptake of mass and heat transfer coefficients and a reduction of temperature and concentration polarization phenomena. Aside from enhanced flow properties, helical hollow fiber bundles tend to be more robust by design, thus exhibiting better resiliency over long service operations than straight bundles. One persistent shortcoming of the helical fibers seems to be an increase in pressure drop. However, this does not always translate into a higher energy consumption – i.e., versus straight bundles. Given the performance advantage, product robustness, and adaptiveness to a broad range of applications, the adoption of helical hollow fiber technology deserves growing support from the membrane community in academic and industrial settings.

Optimization of Integrated Forward – Reverse Osmosis Desalination Processes for Brackish Water

Reverse Osmosis (RO) is a membrane desalination process which considered to be an efficient technology for desalination. However, the performance of RO process is facing some challenges; the most important of them are the energy consumption and fouling problem due to external concentration polarization (ECP). Forward osmosis (FO) is an osmotic-driven membrane desalination process, it exhibits lower energy consumption than pressure driven process like RO. It has been suggested to be coupled with RO in order to reduce salinity and the energy consumption. For this objective, a mathematical model has been designed to optimize the operational conditions for FO, RO and FO-RO hybrid system. Firstly, an individual FO experiment has been conducted using urea and sodium chloride as draw solutions to evaluate the FO performance in both agriculture waste treatment and desalination. Then, a modeling approach of an individual FO process has been investigated with considering water flux, solute flux and concentration polarization. In addition, the performance of FO-RO integrated system was compared with conventional RO process in terms of energy consumption, permeate quantity, quality and solute flux. The results of modeling calculations showed that the feed solution concentration, draw solution concentration and concentration polarization are very important factors that affect the overall performance. In addition, it indicated a good performance of individual FO process. Moreover, it revealed increase in both water productivity and permeate quality and a significant decline in energy consumption upon using the efficient FO-RO hybrid system to about 0.9 kWh/m3. Consequently, it offered high energy saving ranged between 87.57% and 87.81%, which confirmed that FO/RO integrated system is more energy efficient than the RO process only.

Novel approach to surface functionalization of mullite-kaolinite hollow fiber membrane using organosilane-functionalized Co3O4 spider web-like layer deposition for desalination using direct contact membrane distillation

This work investigated a novel omniphobic mullite ceramic hollow fiber membrane (MCHFM) with low fouling and wetting propensity for use in direct contact of membrane desalination (MD) processes. The MCHFM was surface-coated with a spider web-like (SWL) cobalt oxide (Co3O4) rough layer via hydrothermal method at different reaction time (10, 13, 16, and 19 h) before a fluorination step using 1H,1H,2H,2H-perfluorodecyltriethoxysilane (97%) (FAS-17). After surface modification, the synthesized super hydrophilic membrane became highly repellent to water and other low surface tension liquids such as olive oil and engine oil with 32 and 31 mN/m of force, respectively. The surface-modified omniphobic membrane showed super-omniphobic properties towards engine oil at 154°, deionized water at 165°, and near superomniphobicity at 142.1° towards olive oil. The hydrothermal reaction time of the omniphobic membranes was studied using the DCMD test at 60 °C, while utilizing 30 g/L of NaCl and 8 mg/L of humic acid as feed. It was found that the hydrothermal reaction time at 16 h/FAS (Hy-16h/FAS) achieved a long-term stability as the rejection rate and water flux values were relatively constant (99.99%) and 22.8 kg/m2.h for about 4.3 h of the MD process. SEM analysis showed no fouling on the surface modified membrane. This was attributed to the Co3O4 spider web-like particles, which achieved superior anti-fouling properties. This implied the suitability of the fabricated omniphobic MCHFM with a SWL structure for DCMD and seawater desalination, in spite of organic contaminants.

Electrospun nanofibrous membranes as promising materials for developing high-performance desalination technologies

Rising population, together with rapid industrial development, are making freshwater shortage an ever-increasing crisis globally. In addition to the conventional strategy such as water reuse, desalination has proven to be an effective method to meet this requirement, especially membrane-based desalination technology. Besides the conventional reverse osmosis (RO) and nanofiltration (NF) desalination, other membrane-based methods such as membrane distillation (MD) and forward osmosis (FO) have also been exploited as promising alternatives. For all the membrane-based desalination, performance of the membrane is the key issue. However, the currently used membranes for the main desalination technologies are all faced with some challenges, e.g., low permeation for RO, low selectivity for NF, wetting for MD, and internal concentrative polarization for FO. Thus, researchers are all pursuing more advanced membranes to meet these challenges. Particularly, developing novel membranes is a promising alternative. Electrospun nanofibrous membranes (ENMs) provide an alternative for various membrane-based desalination thanks to their versatility in tuning membrane morphology, structure, composition, fiber diameter, pore size and pore size distribution, and fiber/membrane functionalization. In this review paper, we discussed the application of ENMs in typical membrane desalination process presented by RO, NF, MD, and FO. We emphasize on the usage of superiorities of ENMs in tackling the problems of the currently used membranes such as low membrane permeability, membrane wetting, and internal concentrative polarization. We also proposed the future directions of ENMs development in developing more advanced membranes for desalination.

Numerical Analysis of Conjugated Heat and Mass Transfer of Helical Hollow Fiber Membrane Tube Bank for Seawater Distillation

A numerical study on the conjugated heat-mass transfer of helical hollow fiber membrane tube bank (HFMTB) for seawater desalination was carried out. Physical and mathematical models of fluid flow, temperature and humidity distribution were constructed to investigate the influences of flow type, Reynolds number, and temperature on the conjugated heat-mass transfer performance of hollow fibers in the distillation membrane module. The conjugated heat-mass transfer characteristics of HFMTB were discussed by utilizing the friction coefficient, Nusselt number (Nu), and Sherwood number (Sh). Results demonstrate that a distillation efficiency enhancement of 29% compared to the straight HFMTB has been detected for four-helical HFMTB configuration, though the friction coefficient of such a module is about 4 times of their straight counterparts. The values of average Nu and Sh numbers are increasing with tube number, which improves distillation efficiency. The effect of flow type has been studied by employing the upstream and downstream flows to the double-helical HFMTB, demonstrating upstream flow type is more conducive to the heat-mass transfer process. Both the outlet air humidity (ω) and distillation efficiency (η) decrease with the air-side Reynolds number (Rea) and inlet air temperature in the helical HFMTB while increasing with the solution-side Reynolds number (ReS) and inlet solution temperature. Overall, the obtained results indicate that helical HFMTB applying upstream flow has great potential to achieve high-performance SGMD for seawater desalination. It is anticipated that the present work can assist in a better understanding of the membrane desalination process in HFMTB and thus provide theoretical suggestions for further optimization and development.

Joule-Heated Layered Double Hydroxide Sponge for Rapid Removal of Silica from Water.

Dissolved silica is a major concern for a variety of industrial processes owing to its tendency to form complex scales that severely deteriorate system performance. In this work, we present a pretreatment technology using a Joule-heated sponge to rapidly remove silica from saline waters through adsorption, thereby effectively mitigating silica scaling in subsequent membrane desalination processes. The adsorbent sponge is fabricated by functionalizing two-dimensional layered double hydroxide (LDH) nanosheets on a porous, conductive stainless-steel sponge. With the application of an external voltage of 4 V, the Joule-heated sponge achieves 85% silica removal and 95% sponge regeneration within 15 min, which is much more efficient than its counterpart without Joule-heating (360 min for silica adsorption and 90 min for sponge regeneration). Material characterization and reaction kinetics analysis reveal that electrostatic interactions and "memory effect"-induced intercalation are the primary mechanisms for silica removal by the LDH nanosheets. Moreover, Joule-heating reduces the boundary layer resistance on nanosheets and facilitates intraparticle diffusion of dissolved silica, thereby increasing silica removal kinetics. Joule-heating also enhances the release of silicate ions during the regeneration stage through exchange with the surrounding anions (OH- or CO32-), resulting in a more efficient sponge regeneration. Pretreatment of silica-rich feedwaters by the Joule-heated sponge effectively reduces reverse osmosis membrane scaling by amorphous silica scale, demonstrating great potential for silica scaling control in a broad range of engineered processes.

Techno-Economic Optimization of a Solar–Wind Hybrid System to Power a Large-Scale Reverse Osmosis Desalination Plant

Solar-wind hybrid systems have grown to become a pivotal option for powering membrane desalination processes, especially because they have zero harmful emissions. In this work, solar photovoltaic (PV) and horizontal wind turbine (HWT) systems were used to drive a reverse osmosis (RO) desalination process to produce large-capacity fresh water. Moreover, an investigation into a hybrid PV–HWT system combined with RO was also conducted. The proposed systems are compared technically and economically with the solar organic Rankine cycle (SORC) for RO. Technical and analytical optimization methods were performed to minimize the unit product cost (USD/m3). The results revealed that photovoltaic-powered RO is recommended over wind energy operations. However, for large capacities, both thermal and wind farms dominate.

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review.

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.

Comparative environmental life cycle assessment of alternative osmotic and mixing dilution desalination system configurations

An environmental life cycle assessment (LCA) methodology was applied to compare the conventional SWRO desalination process to two contemporary low-pressure membrane desalination processes: an osmotic dilution desalination (ODD) and a mixing dilution desalination (MDD). The ODD process combines a forward osmosis (FO) membrane and a low-pressure RO membrane (LPRO) in a hybrid (FO-RO) configuration. The MDD process couples the ultrafiltration (UF) with LPRO in a hybrid UF-RO configuration. SimaPro™ was used to conduct the LCA study. CML environmental impact assessment method was used to evaluate 11 environmental impact categories. Results from LCIA reveal the strong dependency of environmental impacts on the clean in place (CIP) process in dilution desalination systems while the energy flow in the standalone RO shows almost similar levels of dependency of environmental impacts instead of CIP process. Overall, the ODD process with FO-RO hybrid membrane technology has the highest environmental impact. The normalised comparison LCIA indicates that standalone RO has the lowest total environmental impacts as the fossil fuel is considered as the main source of power generator. Compared to conventional SWRO, the MDD process coupled with hybrid UF-RO technology had a lowest contribution to global warming and ozone layer depletion but had higher impacts to marine and aquatic resource depletion. Scenarios substituting the conventional with renewable energy sources to power the water treatment options favoured the MDD process coupled with hybrid UF-RO technology and prove the hybrid UF-RO process as the most environmentally favourable comparing to the conventional SWRO and hybrid FO-RO.

Revealing the brick-laying process of foulants layer in membrane distillation for desulfurization wastewater treatment: Insight into the mineral scaling

Mineral scaling is one key obstacle to membrane distillation (MD) in hypersaline wastewater desalination, but the scaling and fouling mechanism are poorly understood. Addressing this challenge required revealing the foulants layer formation process. In this study, MD was applied for flue gas desulfurization wastewater treatment with a plug flow module, aims at unfolding the foulants accumulation process into three dimensions (3D) space as the flow velocity had significant influence on foulants distribution. Hence, validated offline method was used to detect the formation of foulants layer by SEM-EDS-FTIR-XPS. Mineral scaling was the key fouling mechanism, and the fouling tendency increased along the flow pass by brick-laying process. Hexagonal CaSO4, primarily in the form of α‑calcium sulfate hemihydrate, and lamellate Mg-Si complexes are the leading foulants, acting as “bricks” during the layer-by-layer manufacturing process of scalants. The pioneering foulant, structured by organic matters and Mg-Si complexes, was the key incipient foulant and acted as “concrete”. Heterogeneous nucleation is the primary crystallization mechanism for CaSO4, whereas Mg-Si complexes was formed in bulk. The “brick-laying” process sheds light on the distribution and formation of mineral scaling and membrane fouling in MD, which can be extended to other membrane desalination processes.