Polyelectrolyte-promoted forward osmosis-membrane distillation (FO-MD) hybrid process for dye wastewater treatment

Advances in membrane distillation for wastewater treatment: Innovations, challenges, and sustainable opportunities

Water pollution and the growing demand for zero liquid discharge solutions have driven the development of advanced wastewater treatment technologies. Membrane distillation (MD) is a promising thermal-based process capable of treating high-salinity brines and wastewater. This review provides an in-depth analysis of MD configurations, operating principles, and membrane characteristics while addressing key challenges such as fouling and pore wetting which hinder large-scale implementation. To overcome these limitations, various membrane fabrication and modification strategies, including physical and chemical approaches, have been explored. The integration of MD with other processes (hybrid MD) for wastewater treatment is also examined. A comprehensive discussion on the mechanisms of organic, inorganic, and biological fouling and their impact on MD performance is presented. Additionally, recent advancements in antifouling strategies, including surface modifications, novel materials, and operational optimizations, are reviewed. Furthermore, the review critically analyzes membrane wetting, its governing mechanisms, and mitigation techniques. By summarizing the current challenges and future prospects, this work provides valuable insights into improving MD performance for practical applications. The findings serve as a foundation for further research and technological advancements in the field of wastewater treatment using MD.

The role of membrane technology in palm oil mill effluent (POME) decontamination: Current trends and future prospects

This article reviews the role of membrane systems in treating palm oil mill effluent (POME), a waste generated by the palm industry. The review focuses on various membrane systems such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), highlighting their effectiveness in removing pollutants and recovering water. Special attention is given to hybrid systems integrating membrane bioreactors (MBRs) and other advanced processes to enhance fouling control, improve water quality, and promote sustainability. Several case studies and quantitative data have demonstrated the reduction of chemical oxygen demand (COD), total suspended solids (TSS), and biological oxygen demand (BOD), illustrating the impact of these technologies. This comprehensive review also explores recent advancements, such as the integration of Zero Liquid Discharge (ZLD) processes, providing insights into the benefits and challenges of membrane technology for POME treatment. This article aims to inform future research and guide industrial applications toward more sustainable and efficient wastewater management in the palm oil industry.

Graphene Membrane for Water-Related Environmental Application: A Comprehensive Review and Perspectives

Graphene-based materials can be potentially utilized for separation membranes due to their unique structural properties such as precise molecular sieving by interlayer spacing or pore structure and excellent stability in harsh environmental conditions. Therefore, graphene-based membranes have been extensively demonstrated for various water treatment applications, including desalination, water extraction, and rare metal ion recovery. While most of the utilization has still been limited to the laboratory scale, emerging studies have dealt with scalable approaches to show commercial feasibility. This review summarizes the recent studies on diverse graphene membrane fabrications and their environmental applications related to water-containing conditions in addition to the molecular separation mechanism and critical factors related to graphene membrane performance. Additionally, we discuss future perspectives and challenges to provide insights into the practical applications of graphene-based membranes on the industrial scale.

Recycling scale inhibitor wastes into pH-responsive complexes to treat wastewater produced from spent lithium-ion battery disposal

A large amount of organophosphorus-containing wastewater is produced in spent lithium-ion battery disposal. Forward osmosis (FO) offers unique advantages in purifying this kind of wastewater if suitable draw solutes - the core of FO technology, are available. Herein we synthesize several pH-sensitive zinc complexes, namely ZnATMP-iNa (i = 0, 1, 2, 3, 4), from ZnSO4 and amino tris(methylene phosphonic acid) (ATMP) obtained from scale inhibitor wastes for organophosphorus-containing wastewater remediation. Among these ZnATMP-iNa, ZnATMP-3Na best meets the standards of an ideal draw solute. This makes ZnATMP-3Na outperform other reported draw solutes. 0.6 M ZnATMP-3Na produces a water flux of 12.7 LMH, 136 % higher than that of NaCl and a solute loss of 0.015 g/L, lower than that of NH4HCO3 (0.83 g/L). In organophosphorus-containing wastewater treatment, ZnATMP-3Na has higher water recovery efficiency (8.3 LMH) and sustainability than NaCl and NH4HCO3, and is sufficient to handle large quantities of wastewater. Remarkably, the pH-responsive property allows ZnATMP-3Na to be readily recovered through pH-control and reused in FO. The ionic property, expanded cage-like structure and easy-recycling make ZnATMP-3Na achieve sustainable FO separation and superior to other draw solutes. This study provides inspiration for draw solute design from wastes and extends FO application to organophosphorus-containing wastewater remediation.

Progress in membrane distillation processes for dye wastewater treatment: A review

Textile and cosmetic industries generate large amounts of dye effluents requiring treatment before discharge. This wastewater contains high levels of reactive dyes, low to none-biodegradable materials and chemical residues. Technically, dye wastewater is characterised by high chemical and biological oxygen demand. Biological, physical and pressure-driven membrane processes have been extensively used in textile wastewater treatment plants. However, these technologies are characterised by process complexity and are often costly. Also, process efficiency is not achieved in cost-effective biochemical and physical treatment processes. Membrane distillation (MD) emerged as a promising technology harnessing challenges faced by pressure-driven membrane processes. To ensure high cost-effectiveness, the MD can be operated by solar energy or low-grade waste heat. Herein, the MD purification of dye wastewater is comprehensively and yet concisely discussed. This involved research advancement in MD processes towards removal of dyes from industrial effluents. Also, challenges faced by this process with a specific focus on fouling are reviewed. Current literature mainly tested MD setups in the laboratory scale suggesting a deep need of further optimization of membrane and module designs in near future, especially for textile wastewater treatment. There is a need to deliver customized high-porosity hydrophobic membrane design with the appropriate thickness and module configuration to reduce concentration and temperature polarization (CP and TP). Also, energy loss should be minimized while increasing dye rejection and permeate flux. Although laboratory experiments remain pivotal in optimizing the MD process for treating dye wastewater, the nature of their time intensity poses a challenge. Given the multitude of parameters involved in MD process optimization, artificial intelligence (AI) methodologies present a promising avenue for assistance. Thus, AI-driven algorithms have the potential to enhance overall process efficiency, cutting down on time, fine-tuning parameters, and driving cost reductions. However, achieving an optimal balance between efficiency enhancements and financial outlays is a complex process. Finally, this paper suggests a research direction for the development of effective synthetic and natural dye removal from industrially discharged wastewater.

Innovative biopolyelectrolytes-based technologies for wastewater treatment

Developing eco-friendly, cost-effective, and efficient methods for treating water pollutants has become paramount in recent years. Biopolyelectrolytes (BPEs), comprising natural polymers like chitosan, alginate, and cellulose, have emerged as versatile tools in this pursuit. This review offers a comprehensive exploration of the diverse roles of BPEs in combating water contamination, spanning coagulation-flocculation, adsorption, and filtration membrane techniques. With ionizable functional groups, BPEs exhibit promise in removing heavy metals, dyes, and various pollutants. Studies showcase the efficacy of chitosan, alginate, and pectin in achieving notable removal rates. BPEs efficiently adsorb heavy metal ions, dyes, and pesticides, leveraging robust adsorption capacity and exceptional mechanical properties. Furthermore, BPEs play a pivotal role in filtration membrane techniques, offering efficient separation systems with high removal rates and low energy consumption. Despite challenges related to production costs and property variability, their environmentally friendly, biodegradable, renewable, and recyclable nature positions BPEs as compelling candidates for sustainable water treatment technologies. This review delves deeper into BPEs' modification and integration with other materials; these natural polymers hold substantial promise in revolutionizing the landscape of water treatment technologies, offering eco-conscious solutions to address the pressing global issue of water pollution.

Recent advances in innovative osmotic membranes for resource enrichment and energy production in wastewater treatment

Wastewater is a valuable resource that we can no longer afford to overlook. By recovering the nutrients and metals it contains and generating renewable energy, we can not only meet the rising demands for natural resources but also create a more sustainable and resilient future. Forward osmosis (FO) membranes are one of the most intriguing resource recovery process technologies because of their high organic retention, economical energy usage, and straightforward operation. However, the widespread adoption of FO membranes on a full-scale basis is hindered by several issues with previous membrane products. These include limited selectivity to different types of ions, insufficient water flux, and high susceptibility to membrane fouling during extended periods of operation. Hence, it is essential to either invent new FO membranes or modify the existing ones. The objective of this work is to provide a comprehensive and organized review of up-to-date advancements in the development of innovative osmotic membrane (IOM) materials for resource recovery (RR) and energy production (EP). The paper covers several aspects, including the limitations of current osmotic membrane technologies, a review of new membranes specifically designed for effective RR/EP, their applications in various industrial fields, integrated IOM systems, recent improvements in IOM fabrication processes using artificial intelligence, and a discussion of the challenges and prospects of the potential research. In general, recently developed IOMs have proven to be highly efficient in recovering organics (>99 %), nutrients (>86 %), and precious metals (>90 %). These new membranes have also demonstrated an ability to effectively harvest osmotic energy (with power output ranging from 6 to 38 W/m2) by applied pressure in the range of 8 to 30 bar. These findings suggest that IOMs is promised for efficient resource recovery and renewable energy production.

Carbon nanotubes buckypapers: A new frontier in wastewater treatment technology

Occurrence of contaminants in water is one of the major global concerns humanity is still facing today: most of them are extremely toxic and dangerous for human health, obliging their removal for a proper and correct process of sanitation. Among wastewater treatment technologies, in the view of development of sustainable and environmentally friendly processes, membrane adsorption has proved to be a fast and simple method in the removal of pollutants, offering great contaminants recovery percentages, fast adsorbent regeneration and recycle, and easy scale-up. Due to their large surface area and tunable chemistry, carbon nanotubes (CNTs)-based materials revealed to be extraordinary adsorbents, exceeding by far performances of ordinary organic and inorganic membranes such as polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, ceramics, currently employed in membrane technologies for wastewater treatment. In consideration of this, the review aims to summarize recent developments in the field of carbon nanotubes-based materials for pollutants recovery from water through adsorption processes. After a brief introduction concerning what adsorption phenomenon is and how it is performed and governed by using carbon nanotubes-based materials, the review discusses into detail the employment of three common typologies of CNTs-based materials (CNTs powders, CNTs-doped polymeric membranes and CNTs membranes) in adsorption process for the removal of water pollutants. Particularly focus will be devoted on the emergent category of self-standing CNTs membranes (buckypapers), made entirely of carbon nanotubes, exhibiting superior performances than CNTs and CNTs-doped polymeric membranes in terms of preparation strategy, recovery percentages of pollutants and regeneration possibilities. The extremely encouraging results presented in this review aim to support and pave the way to the introduction of alternative and more efficient pathways in wastewater treatment technologies to contrast the problem of water pollution.

Review of Hybrid Membrane Distillation Systems

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested.

Biofouling mechanism and cleaning procedures for Spirulina platensis as an organic fertilizer draw solution

The forward osmosis (FO) desalination process has recently acknowledged a lot of attention as a promising solution for reducing the disadvantages of existing desalination systems. This work aimed to investigate the effect of a selected liquid organic fertilizer a novel draw solution produced from "microalgae Spirulina platensis" on the biofouling mechanism of FO membrane. Different draw solution (DS) concentrations ranging 240-480 g/L were examined, obtained water flux ranging from 6.5 to 3.4 Lm2h-1. A high flux decline was observed when using higher DS concentrations due to fouling layer accumulated throughout the membrane area which lowers the effective osmotic pressure difference. Different cleaning strategies were examined. The biofouled membrane was cleaned on-line with deionized water (DI) and externally using ultrasound (US) and HCl. Baseline experiments were done to investigate the efficiency of the cleaning strategies. After cleaning using the deionized water (DI) water, it was found that the water flux progressed from 3.4 to 7 Lm2h-1, while when using acid cleaning the flux recovered to 15 Lm-2h-1. The efficacy and amount of foulant removed by each cleaning stage were assessed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Optimization and prediction of lead removal from aqueous solution using FO-MD hybrid process: Statistical and artificial intelligence analysis

Heavy metals (HMs) has become one of the most serious pollutants that are harmful to the environment and ecology. This paper focused on the removal of lead contaminant from wastewater by forward osmosis-membrane distillation (FO-MD) hybrid process using seawater as draw solution. Modeling, optimization, and prediction of FO performance are developed using complementary approach based on response surface methodology (RSM) and an artificial neural network (ANN). FO process optimization using RSM revealed that under initial lead concentration of 60 mg/L, feed velocity of 11.57 cm/s and draw velocity of 7.66 cm/s, FO process achieved highest water flux of 6.75 LMH, lowest reverse salt flux of 2.78 gMH and highest lead removal efficiency of 87.07%. Fitness of all models was evaluated based on determination coefficient (R²) and mean square error (MSE). Results showed highest R² value up to 0.9906 and lowest RMSE value up to 0.0102. ANN modeling generates the highest prediction accuracy for water flux and reverse salt flux, while RSM produces the highest prediction accuracy for lead removal efficiency. Subsequently, FO optimal conditions are applied on FO-MD hybrid process using seawater as draw solution and evaluate their performance to simultaneously remove lead contaminant and desalination of seawater. Results displays that FO-MD process shows a highly efficient solution to produce fresh water with almost free heavy metals and very low conductivity.

Polyelectrolyte and polyelectrolyte complex-incorporated adsorbents in water and wastewater remediation - A review of recent advances

In recent years, polyelectrolyte-incorporated functional materials have emerged as novel adsorbents for effective remediation of pollutants in water and wastewater. Polyelectrolytes (PEs) are a special class of polymers with long chains of repeating charged moieties. Polyelectrolyte complexes (PECs) are obtained by mixing aqueous solutions of oppositely charged PEs. Herewith, this review discusses recent advances with respect to water and wastewater remediation using PE- and PEC-incorporated adsorbents. The review begins by highlighting some water resources, their pollution sources and available treatment techniques. Next, an overview of PEs and PECs is discussed, highlighting the evolving progress in their processing. Consequently, application of these materials in different facets of water and wastewater remediation, including heavy metal removal, precious metal and rare earth element recovery, desalination, dye and emerging micropollutant removal, are critically reviewed. For water and wastewater remediation, PEs and PECs are mostly applied either in their original forms, as composites or as morphologically-tunable complexes. PECs are deemed superior to other materials owing to their tunability for both cationic and anionic pollutants. Generally, natural and semi-synthetic PEs have been largely applied owing to their low cost, ready availability and eco-friendliness. Except dye removal and desalination of saline water, application of synthetic PEs and PECs is scanty, and hence requires more focus in future research.

Introduction of poly(acrylic acid) sodium into traditional draw solution to enhance its driving capacity in forward osmosis process

In this study, poly(acrylic acid) sodium (PAA-Na) salt was selected as representative polymer additive and the effect on forward osmosis (FO) performance of traditional draw solute NaCl was investigated. Results showed that PAA-Na increased water flux in both FO and PRO mode at 25 °C (up to 50%). Water flux and specific RSF firstly increased and then kept stable with the increasing concentration of PAA-Na additive. However, PAA-Na cannot enhance water permeation effectively at 35 and 45 °C. PAA-Na influenced FO performance by (1) increasing membrane hydrophilicity, which can increase water permeation, and was dominant at low temperature, and (2) causing pore-clogging, leading water flux decline, which was significant at high temperature. Furthermore, the influence of PAA-Na was compared with another polymer PAM and divalent salts MgCl₂. The addition of PAM increased water flux slightly (lower than 25%), but increased RSF at the same time, due to the negative charge. Although MgCl₂ decreased RSF and kept water flux fixed, its role was not obvious. In all, PAA-Na had advantages to improve FO performance.

Effect of the Alkyl Chain Length on Assessment as Thermo-Responsive Draw Solutes for Forward Osmosis

A series of thermo-responsive tetrabutylphosphonium 1-alkanesulfonates (abbreviated as [P₄₄₄₄][C _n S], n = 6, 8, 10, and 12), where n is the number of carbon atoms in the alkyl group on the 1-alkanesulfonate anion, were prepared by an ion-exchange reaction to investigate their potential ability toward the application of draw solutes in forward osmosis (FO). We systematically studied the recovery properties and FO performance of [P₄₄₄₄][C _n S]. This series exhibited lower critical solution temperature (LCST) characteristics, which offer a clear advantage of being energy-efficient for recovering draw solutes; however, [P₄₄₄₄][C₆S] was only observed at 20 wt %. The LCSTs of the 20 wt % [P₄₄₄₄][C₆S], [P₄₄₄₄][C₈S], [P₄₄₄₄][C₁₀S], and [P₄₄₄₄][C₁₂S] draw solutions were approximately 83, 54, 49, and 56 °C, respectively. Moreover, when the orientation of the active layer was heading toward the draw solution (AL-DS mode), the water and reverse solute flux of [P₄₄₄₄][C₁₀S] were about 1.58 LMH and 0.81 gMH, respectively, at 20 wt % aqueous solutions. When the membrane was used in the active layer facing the feed solution (AL-FS) system, the water and reverse solute flux of [P₄₄₄₄][C₁₀S] were approximately 0.71 LMH and 0.38 gMH, respectively, at 20 wt % aqueous solutions. Thus, this study is the first to examine the structural transformations of the bulkier alkyl group on the sulfonate anion moiety and its feasibility as the new draw solute for the FO system.

Preparation and characterization of polysulfone-polyurethane membranes for recovery of simulated wastewater from industrial textile processes

Techniques using membranes for the treatment of wastewaters usually promote higher quality of treated water when compared to other processes. Among them, pervaporation has advantages in terms of selectivity in addition to low working pressure, which can prevent clogging problems. Polysulfone and polyurethane have complementary characteristics and are interesting in the context of membranes for industrial applications. In this sense, the aim of this work was to prepare and characterize polysulfone/polyurethane-based membranes and tested them with a simulated wastewater containing the reactive black dye and sodium chloride by pervaporation. In their manufacture, thermal treatment (at 60°C) and photo-radiation treatment (using ultraviolet light) were also applied. The characterizations were performed using different analytical tools. In general, it was possible to verify that all membranes have a dense layer. The thermal analysis allowed to define that the indicated working temperature is below 50°C. With respect to the simulated wastewater treatment, all membranes reached 100% selectivity. Concerning the saline solution, the mean selectivity was around 98.5%. Moreover, the permeate flow values were within the range presented by commercial membranes ranging from 1.6 to 2.4 kg m^-2 h^-1. Although for the photoirradiated membranes the photo-graft reaction has occurred, among all membranes, the blend without any treatment stood out from the others, presenting the highest permeate flow of the simulated wastewater. Finally, the results reveal that these membranes are capable of recovering wastewater from textile processes, in addition to having the potential to remove salts from water through the pervaporation process.Highlights Polysulfone/polyurethane-based membranes were not yet evaluated for wastewater recovery.Modifications in the membrane characteristics promoted variations in the permeate flow.Changes in physical-chemical properties of membrane as a result of a photoinitiation reaction.Removal efficiency achieved was 100% for reactive black dye and 98.5% for sodium chloride.A new way of performing pervaporation on the recovery of aqueous solutions.

Temperature Effects of MD on Municipal Wastewater Treatment in an Integrated Forward Osmosis and Membrane Distillation Process

An integrated forward osmosis (FO)-membrane distillation (MD) process is promising for the treatment and resource recovery from municipal wastewater. As higher temperature is applied in MD, it could affect the performance of both FO and MD units. This study aimed to investigate the effects of the type of draw solution (DS) and feed solution (FS) such as ammonium solution or municipal wastewater containing ammonium at higher temperatures on membrane treatment performance. It is found that higher FS and DS temperatures resulted in a higher water flux and a higher RSF with either NaCl or glucose as DS due to the increased diffusivity and reduced viscosity of DS. However, the water flux increased by 23–35% at elevated temperatures with glucose as DS, higher than that with NaCl as DS (8–19%), while the reverse solute flux (RSF) increase rate with NaCl as DS was two times higher than that with glucose as DS. In addition, the use of NaCl as DS at higher temperatures such as 50 and FS at 42 °C resulted in increased forward ammonium permeation from the FS to the DS, whereas ammonium was completely rejected with glucose as DS at all operating temperatures. Reducing pH or lowering the temperature of DS could improve ammonium rejection and minimize ammonia escape to the recovered water, but extra cost or reduced MD performance could be led to. Therefore, the results suggest that in an integrated FO-MD process with DS at higher temperatures such as 50 °C, glucose is better than NaCl as DS. Furthermore, a simplified heat balance estimation suggests that internal heat recovery in the FO-MD system is very necessary for treating municipal wastewater treatment. This study sheds light on the selection of DS in an integrated FO-MD process with elevated temperature of both FS and DS for the treatment of wastewater containing ammonium. In addition, this study highlights the necessity of internal heat recovery in the integrated FO-MD system.

Water Recovery from Bioreactor Mixed Liquors Using Forward Osmosis with Polyelectrolyte Draw Solutions

This paper reports on the use of forward osmosis (FO) with polyelectrolyte draw solutions to recover water from bioreactor mixed liquors. The work was motivated by the need for new regenerative water purification technologies to enable long-duration space missions. Osmotic membrane bioreactors may be an option for water and nutrient recovery in space if they can attain high water flux and reverse solute flux selectivity (RSFS), which quantifies the mass of permeated water per mass of draw solute that has diffused from the draw solution into a bioreactor. Water flux was measured in a direct flow system using wastewater from a municipal wastewater treatment plant and draw solutions prepared with two polyelectrolytes at different concentrations. The direct flow tests displayed a high initial flux (>10 L/m2/h) that decreased rapidly as solids accumulated on the feed side of the membrane. A test with deionized water as the feed revealed a small mass of polyelectrolyte crossover from the draw solution to the feed, yielding an RSFS of 80. Crossflow filtration experiments demonstrated that steady state flux above 2 L/m2·h could be maintained for 70 h following an initial flux decline due to the formation of a foulant cake layer. This study established that FO could be feasible for regenerative water purification from bioreactors. By utilizing a polyelectrolyte draw solute with high RSFS, we expect to overcome the need for draw solute replenishment. This would be a major step towards sustainable operation in long-duration space missions.

Membrane Distillation for Wastewater Treatment: A Mini Review

Water serves as an indispensable part of human life and production. On account of the overexploitation of traditional water sources, the demand for wastewater recycling is expanding rapidly. As a promising water treatment process, membrane distillation (MD) has been utilized in various wastewater treatments, such as desalination brine, textile wastewater, radioactive wastewater, and oily wastewater. This review summarized the investigation work applying MD in wastewater treatment, and the performance was comprehensively introduced. Moreover, the obstructions of industrialization, such as membrane fouling, membrane wetting, and high energy consumption, were discussed with the practical investigation. To cope with these problems, various strategies have been adopted to enhance MD performance, including coupling membrane processes and developing membranes with specific surface characteristics. In addition, the significance of nutrient recovery and waste heat utilization was indicated.

pH-Responsive Polyoxometalates that Achieve Efficient Wastewater Reclamation and Source Recovery via Forward Osmosis

Forward osmosis (FO) has been increasingly used for water treatment. However, the lack of suitable draw solutes impedes its further development. Herein, we design pH-responsive polyoxometalates, that is, (NH₄)₆Mo₇O₂₄ and Na₆Mo₇O₂₄, as draw solutes for simultaneous water reclamation and resource recovery from wastewater via FO. Both polyoxometalates have a cage-like configuration and release multiple ionic species in water. These characteristics allow them to generate high osmotic pressures to drive the FO separation efficiently with negligible reverse solute diffusion. (NH₄)₆Mo₇O₂₄ and Na₆Mo₇O₂₄ at a dilute concentration (0.4 M) produce water fluxes of 16.4 LMH and 14.2 LMH, respectively, against DI water, outperforming the frequently used commercial NaCl and NH₄HCO₃ draw solutes, and other synthetic materials. With an average water flux of 10.0 LMH, (NH₄)₆Mo₇O₂₄ reclaims water from the simulated glutathione-containing wastewater more efficiently than Na₆Mo₇O₂₄ (9.1 LMH), NaCl (3.3 LMH), and NH₄HCO₃ (5.6 LMH). The final glutathione treated with (NH₄)₆Mo₇O₂₄ and Na₆Mo₇O₂₄ remains intact but that treated with NaCl and NH₄HCO₃ is either denatured or contaminated owing to their severe leakage in FO. Remarkably, both polyoxometalates are readily recycled by pH regulation and reused for FO. Polyoxometalate is thus proven to be an appropriate candidate for FO separation in wastewater reclamation and resource recovery.

Persistent Micelle Corona Chemistry Enables Constant Micelle Core Size with Independent Control of Functionality and Polyelectrolyte Response

Polymer micelles have found significant uses in areas such as drug/gene delivery, medical imaging, and as templates for nanomaterials. For many of these applications, the micelle performance depends on its size and chemical functionalization. To date, however, these parameters have often been fundamentally coupled since the equilibrium size of a micelle is a function of the chemical composition in addition to other parameters. Here, we demonstrate a novel processing pathway allowing for the chemical modification to the corona of kinetically trapped "persistent" polymer micelles, termed Persistent Micelle Corona Chemistry (PMCC). Judicious planning is crucial to this size-controlled functionalization where each step requires all reagents and polymer blocks to be compatible with (1) the desired chemistry, (2) micelle persistency, and (3) micelle dispersion. A desired functionalization can be implemented with PMCC by pairing the synthetic planning with polymer solubility databases. Specifically, poly(cyclohexyl methacrylate-b-(diethoxyphosphoryl)methyl methacrylate) (PCHMA-b-PDEPMMA) was prepared to combine a glassy-core block (PCHMA) for kinetic control with a block (PDEPMMA) that is able to be hydrolyzed to yield acid groups. The processing sequence determines the resulting micelle size distribution where the hydrolyzed-then-micellized sequence yields widely varying micelle dimensions due to equilibration. In contrast, the micellized-then-hydrolyzed sequence maintains kinetically trapped micelles throughout the PMCC process. Statistically significant transmission electron microscopy (TEM) measurements demonstrate that PMCC uniquely enables this functionalization with constant average micelle core dimensions. Furthermore, these kinetically trapped micelles also subsequently maintain constant micelle core size when modifying the Coulombic interactions of the micelle corona via pH changes.

Integrated photocatalysis-adsorption-membrane separation in rotating reactor for synergistic removal of RhB

A synergistic system of integrated photocatalysis-adsorption-membrane separation in a rotating reactor was designed. The composite membrane was prepared via filtration process under vacuum, and it was composed of graphene oxide (GO) acted as the separation membrane, activated carbon (AC) as the adsorbent and Ag@BiOBr as the photocatalyst, respectively. In this Ag@BiOBr/AC/GO membrane system, rotation of the membrane could avoid the light-shielding effect from organic color pollutants to achieve the complete removal of pollutants. More importantly, the synergistic effect among photocatalysis, adsorption and membrane separation in rotating reactor was significant for the efficient removal of rhodamine B (RhB). In the Ag@BiOBr/AC/GO composite membrane, GO membrane layer could reject the organic molecular by the assistance of AC layer with efficient adsorption capacity, and Ag@BiOBr at outer layer could photodegrade the organics under visible light irradiation. The photocatalysis process could solve the problem of membrane fouling and adsorption could assist GO membrane for stopping the permeation of pollutants. Meanwhile, GO membrane was not only beneficial for catalyst recovery, but also could concentrate the pollutants via the membrane separation to accelerate the photocatalytic degradation. At the same time, both the photocatalysis degradation and membrane separation could promote the adsorption ability of AC. This synergistic system showed the significant potential for the practical application in the future.

Adsorption of Malachite Green and Alizarin Red S Dyes Using Fe-BTC Metal Organic Framework as Adsorbent

Synthetic organic dyes are widely used in various industrial sectors but are also among the most harmful water pollutants. In the last decade, significant efforts have been made to develop improved materials for the removal of dyes from water, in particular, on nanostructured adsorbent materials. Metal organic frameworks (MOFs) are an attractive class of hybrid nanostructured materials with an extremely wide range of applications including adsorption. In the present work, an iron-based Fe-BTC MOF, prepared according to a rapid, aqueous-based procedure, was used as an adsorbent for the removal of alizarin red S (ARS) and malachite green (MG) dyes from water. The synthesized material was characterized in detail, while the adsorption of the dyes was monitored by UV-Vis spectroscopy. An optimal adsorption pH of 4, likely due to the establishment of favorable interactions between dyes and Fe-BTC, was found. At this pH and at a temperature of 298 K, adsorption equilibrium was reached in less than 30 min following a pseudo-second order kinetics, with k″ of 4.29 × 10⁻³ and 3.98 × 10⁻² g∙mg⁻¹ min⁻¹ for ARS and MG, respectively. The adsorption isotherm followed the Langmuir model with maximal adsorption capacities of 80 mg∙g⁻¹ (ARS) and 177 mg∙g⁻¹ (MG), and K_L of 9.30·10³ L∙mg⁻¹ (ARS) and 51.56·10³ L∙mg⁻¹ (MG).

Forward osmosis with direct contact membrane distillation using tetrabutylphosphonium p-toluenesulfonate as an effective and safe thermo-recyclable osmotic agent for seawater desalination

A phosphonium-based ionic liquid (IL) with lower critical solution temperature (LCST) property was assessed as a reusable draw solution (DS) for forward osmosis (FO). Tetrabutylphosphonium p-toluenesulfonate ([P4444]TsO) was successfully synthesized by neutralization reaction. Characterization results reveal its ability to generate sufficient osmotic pressure (14-68 bars for 0.5-2 M DS) to create a gradient across the FO membrane. Its thermal, physico-chemical and other colligative properties are favorable for its application as an osmotic agent. The LCST behavior of [P4444]TsO was found reversible and its phase separation from water can be done above its cloud point temperature T_c ∼57 °C. In vitro cytotoxicity tests from LDH and MTT assay reveal that it can be safely used as DS at an effective concentration EC₃₀ ∼57 mg L^-1 as its non-toxic level. Results from FO operations demonstrate that 2 M [P4444]TsO DS can effectively treat saline feed like seawater (0.6 M NaCl) with reasonable J_v = 1.35 ± 0.15 L m^-2h^-1, low J_s = 0.0038 ± 0.00049 mol m^-2h^-1, and considerably low specific solute flux (J_s/J_v ∼ 0.0028 mol L^-1). After FO, ∼98% of [P4444]TsO was precipitated by heating the DS at 60 °C and conveniently reused with consistent FO performance. Direct contact membrane distillation (DCMD) was found effective in removing the residual 2% [P4444]TsO in the DS supernatant to finally produce high-quality effluent with concentrations way below the EC₃₀ limit. Cost estimates for the entire process reveal the potential of FO combined with thermo-cyclic [P4444]TsO regeneration with DCMD for desalination application.

The Water Flux Dynamic in a Hybrid Forward Osmosis-Membrane Distillation for Produced Water Treatment

Standalone membrane distillation (MD) and forward osmosis (FO) have been considered as promising technologies for produced water treatment. However, standalone MD is still vulnerable to membrane-wetting and scaling problems, while the standalone FO is energy-intensive, since it requires the recovery of the draw solution (DS). Thus, the idea of coupling FO and MD is proposed as a promising combination in which the MD facilitate DS recovery for FO-and FO acts as pretreatment to enhance fouling and wetting-resistance of the MD. This study was therefore conducted to investigate the effect of DS temperature on the dynamic of water flux of a hybrid FO-MD. First, the effect of the DS temperature on the standalone FO and MD was evaluated. Later, the flux dynamics of both units were evaluated when the FO and DS recovery (via MD) was run simultaneously. Results show that an increase in the temperature difference (from 20 to 60 °C) resulted in an increase of the FO and MD fluxes from 11.17 ± 3.85 to 30.17 ± 5.51 L m-2 h-1, and from 0.5 ± 0.75 to 16.08 L m-2 h-1, respectively. For the hybrid FO-MD, either MD or FO could act as the limiting process that dictates the equilibrium flux. Both the concentration and the temperature of DS affected the flux dynamic. When the FO flux was higher than MD flux, DS was diluted, and its temperature decreased; both then lowered the FO flux until reaching an equilibrium (equal FO and MD flux). When FO flux was lower than MD flux, the DS was concentrated which increased the FO flux until reaching the equilibrium. The overall results suggest the importance of temperature and concentration of solutes in the DS in affecting the water flux dynamic hybrid process.

Seawater Desalination: A Review of Forward Osmosis Technique, Its Challenges, and Future Prospects

Currently over 845 million people are believed to be living under severe water scarcity, and an estimated 2.8 billion people across the globe are projected to come under serious water scarcity by the year 2025, according to a United Nations (UN) report. Seawater desalination has gained more traction as the solution with the most potential for increasing global freshwater supplies amongst other solutions. However, the economic and energy costs associated with the major desalination technologies are considered intrinsically prohibitive largely due to their humongous energy requirements alongside the requirements of complex equipment and their maintenance in most cases. Whilst forward osmosis (FO) is being touted as a potentially more energy efficient and cost-effective alternative desalination technique, its efficiency is challenged by draw solutes and the draw solutes recovery step in FO applications alongside other challenges. This paper looks at the present situation of global water scarcity, and a brief leap into the major desalination technologies employed. A closer look at the key drivers of FO as a seawater desalination technique in their individual domain and its outlook as an technology are further highlighted.

Dye synthetic solution treatment by direct contact membrane distillation using commercial membranes

The reuse of treated dyeing wastewater has become a viable option to minimizing water scarcity problems and environmental impacts in the textile industry. The potentiality of commercial flat sheet membranes of polytetrafluoroethylene (PTFE) and polypropylene (PP) in direct contact membrane distillation (DCMD) for dye synthetic solution treatment has been explored in this work. DCMD is interesting for the textile industry since a recovery of heat by hot dyeing wastewater for thermal energy is possible. Moreover, DCMD enables water and dye reclamation with possible reuse in the textile process. The commercial availability of membranes may expedite the DCMD commercialization in the textile industry. Experiments were conducted in a laboratory-scale circulating unit with synthetic solutions containing reactive or disperse dye. High mean permeate flux up to 18.8 kg m^-2 h^-1 with complete colour rejection was obtained. The dyes tested in this study are not able to completely wet the membranes and the increase of the permeate flux when compared to distilled water is attributed to electrostatic interactions between the dyes and the membranes. Moreover, a partial wetting reduced vapour diffusion path and the permeate flux was increased. PP membrane showed higher performance due to higher porosity when compared to the PTFE membrane. In addition, an influence of dye class on permeability was observed. The results were promising when compared to other studies, which used commercial or lab-scale membranes.

Feasibility of concentrating textile wastewater using a hybrid forward osmosis-membrane distillation (FO-MD) process: Performance and economic evaluation

The forward osmosis-membrane distillation (FO-MD) hybrid process has shown great promise in achieving zero liquid discharge in the textile industry, recovering valuable dye molecules while producing large amounts of clean water. However, the progress of this technology seems to have stagnated with the direct coupling of commercial asymmetric FO and MD membranes, because water management in the system is found to be rather complicated owing to the processing of the different membranes. Herein, we propose, for the first time, an FO-MD hybrid process using a custom-made self-standing and symmetric membrane and a hydrophobic polytetrafluoroethylene membrane in the FO and MD units, respectively. Three types of operation modes were investigated to systematically study the process performance in the concentration treatment of model textile wastewater; two commercial FO membranes were also tested for comparison. Owing to its low fouling propensity and lack of an internal concentration polarization effect, the water transfer rate of our symmetric FO membrane quickly reaches equilibrium with that in the MD unit, resulting in continuous and stable operation. Consequently, the hybrid process using the symmetric FO membrane was found to consume the least energy, as indicated by its lowest total cost in both lab- and large-scale systems. Overall, our study provides a new strategy for using a symmetric FO membrane in the FO-MD hybrid process and highlights its great potential for use in the treatment of textile wastewater.

A pH-responsive supramolecular draw solute that achieves high-performance in arsenic removal via forward osmosis

A pH-responsive, charge switchable piperazine derivative, 1,4-bis(3-propane- sulphonate sodium)-piperazinediethanesulfonic acid disodium-sulfate (4), has been designed via a stepwise synthesis and proposed as a draw solute to remove arsenics (As^III, As^V) from water through forward osmosis (FO). Having multiple sulfonic groups, 4 generates a high osmotic pressure and produces a water flux as high as 58.4 LMH at a dilute concentration (0.24 M), surpassing most of the existing draw solutes in water transfer rate under the similar experimental conditions. Compound 4 at 0.24 M yields a water flux of 52.9 LMH with a 100% As^V rejection, and 57.8 LMH with a 96.0% As^III rejection when 50 ppm As^V or As^III as the corresponding feed, manifesting the best performance in arsenic removal and concurrent water recovery efficiency. Remarkably, being a polymeric configuration in water, 4 has a negligible solute loss in the FO process. 4 can be readily regenerated for reuse in FO by precipitation from its solution through acidification. The abundance in ionic groups and the pH-responsive property coupled with a supramolecular configuration make 4 an ideal draw solute for FO wastewater treatment.

Application of volume retarded osmosis - Low pressure membrane hybrid process for recovery of heavy metals in acid mine drainage

Recovery of heavy metals in acid mine drainage (AMD) such as Mn, Fe, Cu, Zn, As, Cd and Pb was evaluated using volume retarded osmosis and low-pressure membrane (VRO-LPM) process. In VRO-LPM process, the draw solution (DS) is regenerated by the naturally generated pressure, giving its economic value. Ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) and Poly (sodium-4-styrenesulfonate, PSS-Na) were used and compared to determine more suitable DS in heavy metal recovery from the AMD. Forward osmosis (FO) and nanofiltration (NF) membrane were employed in VRO-LPM process, due to the low EDTA-4Na rejection (about 50%) in ultrafiltration (UF) process. For the FO part in the VRO-LPM process, PSS-Na had flux values of 0.12, 0.11 and 0.05 L m^-2 h^-1 and at osmotic pressure of 8.9, 12 and 13 bar, respectively. Unlike the flux values, the RSF of PSS remained at 0.01 mmol h^-1 at all osmotic pressures. For EDTA-4Na, the flux values were 0.10, 0.06 and 0.04 L m^-2 h^-1, which are relatively higher than those of PSS-Na; and the RSF values were 0.1, 1.2, 2.2 mmol h^-1, which are higher compared to those of PSS-Na. Unlike PSS-Na, RSF for EDTA-4Na increased as the concentration increases. In the NF part of the VRO-LPM process, PSS-Na had higher water flux and rejection than EDTA-4Na, and the flux and rejection both decreased with concentration for both PSS-Na and EDTA-4Na. The overall rejection in VRO-LPM process was over 95% for all heavy metal ions. Therefore, VRO-LPM process has proven its ability to be used in AMD treatment for heavy metal removal.

Synthesis of Poly-Sodium-Acrylate (PSA)-Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions

The synthesis of magnetic nanoparticles (MNPs) coated with hydrophilic poly-sodium-acrylate (PSA) ligands was studied to assess PSA-MNP complexes as draw solution (DS) solutes in forward osmosis (FO). For MNP-based DS, the surface modification and the size of the MNPs are two crucial factors to achieve a high osmolality. Superparamagnetic nanoparticles (NP) with functional groups attached may represent the ideal DS where chemical modifications of the NPs can be used in optimizing the DS osmolality and the magnetic properties allows for efficient recovery (DS re-concentration) using an external magnetic field. In this study MNPs with diameters of 4 nm have been prepared by controlled chemical co-precipitation of magnetite phase from aqueous solutions containing suitable salts of Fe²⁺ and Fe³⁺ under inert atmosphere and a pure magnetite phase could be verified by X-ray diffraction. Magnetic colloid suspensions containing PSA-coated MNPs with three different molar ratios of PSA:MNP = 1:1, 1:2 and 1:3 were prepared and assessed in terms of osmotic pressure, aggregation propensity and magnetization. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of PSA on coated MNPs and pristine PSA-MNPs with a molar ratio PSA:MNP = 1:1 exhibited an osmotic pressure of 30 bar. Molar ratios of PSA:MNP = 1:2 and 1:3 lead to the formation of less stabile magnetic colloid solutions, which led to the formation of aggregates with larger average hydrodynamic sizes and modest osmotic pressures (5.5 bar and 0.2 bar, respectively). After purification with ultrafiltration, the 1:1 nanoparticles exhibited an osmotic pressure of 9 bar with no aggregation and a sufficient magnetization of 25 emu/g to allow for DS regeneration using an external magnetic field. However, it was observed that the amount of PSA molecules attached to the MNPs decreased during DS recycling steps, leaving only strong chelate-bonded core-shell PSA as coating on the MNPs. This demonstrates the crucial role of MNP coating robustness in designing an efficient MNP-based DS for FO.