Water and Wastewater Treatment Systems by Novel Integrated Membrane Distillation (MD)

Advanced membrane-based high-value metal recovery from wastewater

Considering the circular economy and environmental protection, sustainable recovery of high-value metals from wastewater has become a prominent concern. Unlike conventional methods featuring extensive chemicals or energy consumption, membrane separation technology plays a crucial role in facilitating the sustainable and efficient recovery of valuable metals from wastewater due to its attractive features. In this review, we first briefly summarize the sustainable supply chain and significance of sustainable recovery of aqueous high-value metals. Then, we review the most recent advances and application potential in promising state-of-the-art membrane-based technologies for recovery of high-value metals (silver, gold, rhenium, platinum, ruthenium, palladium, iridium, osmium, and rhodium) from wastewater effluents. In particular, pressure-based membranes, liquid membranes, membrane distillation, forward osmosis, electrodialysis and membrane-based hybrid technologies and their mechanism of high-value metal recovery is thoroughly discussed. Then, engineering application and economic sustainability are also discussed for membrane-based high-value metal recovery. The review finally concludes with a critical and insightful overview of the techno-economic viability and future research direction of membrane technologies for efficient high-value metal recovery from wastewater.

Progress in the Sustainable Development of Biobased (Nano)materials for Application in Water Treatment Technologies

Water pollution remains a widespread problem, affecting the health and wellbeing of people around the globe. While current advancements in wastewater treatment and desalination show promise, there are still challenges that need to be overcome to make these technologies commercially viable. Nanotechnology plays a pivotal role in water purification and desalination processes today. However, the release of nanoparticles (NPs) into the environment without proper safeguards can lead to both physical and chemical toxicity. Moreover, many methods of NP synthesis are expensive and not environmentally sustainable. The utilization of biomass as a source for the production of NPs has the potential to mitigate issues pertaining to cost, sustainability, and pollution. The utilization of biobased nanomaterials (bio-NMs) sourced from biomass has garnered attention in the field of water purification due to their cost-effectiveness, biocompatibility, and biodegradability. Several research studies have been conducted to efficiently produce NPs (both inorganic and organic) from biomass for applications in wastewater treatment. Biosynthesized materials such as zinc oxide NPs, phytogenic magnetic NPs, biopolymer-coated metal NPs, cellulose nanocrystals, and silver NPs, among others, have demonstrated efficacy in enhancing the process of water purification. The utilization of environmentally friendly NPs presents a viable option for enhancing the efficiency and sustainability of water pollution eradication. The present review delves into the topic of biomass, its origins, and the methods by which it can be transformed into NPs utilizing an environmentally sustainable approach. The present study will examine the utilization of greener NPs in contemporary wastewater and desalination technologies.

Performances of PTFE and PVDF membranes in achieving the discharge limit of mixed anodic oxidation coating wastewaters treated by membrane distillation

The mixed wastewater generated by anodic oxidation coating facilities contains high levels of various contaminants, including iron, aluminum, conductivity, chemical oxygen demand (COD), and sulfate. In this study, the effectiveness of the membrane distillation (MD) process using polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes was investigated to treat mixed wastewater from an anodized coating factory. The results indicate that both hydrophobic membranes effectively removed targeted contaminants. However, the PTFE membrane achieved higher removal efficiencies, with over 99% removal of sulfate, conductivity, iron, and aluminum, 85.7% of COD, and 86% of total organic carbon (TOC). In contrast, the PVDF membrane exhibited a significant decline in removal efficiency as the temperature increased and performed well only at lower feed temperatures. The PTFE membranes outperformed the PVDF membranes in treating chemically intensive anodic oxidation wastewaters. This superiority can be attributed to the PTFE membrane's morphology and structure, which are less influenced by feed water temperature and chemicals. Additionally, its slippery surface imparts anti-adhesion properties, effectively preventing membrane fouling, and maintaining the treated water quality and flux for longer operation time.

Methanol recovery: potential of nanolaminate organic solvent nanofiltration (OSN) membranes

Researchers have made a significant breakthrough by merging the energy-saving attribute of organic solvent nanofiltration (OSN) with the remarkable solvent permeance and solute rejection of two-dimensional (2D) laminated membranes. This innovative approach brings forth a new era of sustainable and cost-effective separation techniques, presenting a promising solution to the issue of industrial solvents contaminating the environment. This development paves the way for new opportunities in building a sustainable future. Specifically, our mini-review has cast a spotlight on the separation and recovery of methanol-a solvent abundantly used in industrial processes. We systematically evaluated a diverse array of free-standing 2D nanolaminate OSN membranes. The analysis encompasses the assessment of pure methanol permeance, solute rejection capabilities, and the simultaneous evaluation of methanol permeance and solute rejection performance. Notably, this study sheds light on the considerable potential of 2D laminated OSN membranes in revolutionizing separation processes for the industrial use of methanol.

A review of the development in shale oil and gas wastewater desalination

The development of the shale oil and gas extraction industry has heightened concerns about shale oil and gas wastewater (SOGW). This review comprehensively summarizes, analyzes, and evaluates multiple issues in SOGW desalination. The detailed analysis of SOGW water quality and various disposal strategies with different water quality standards reveals the water quality characteristics and disposal status of SOGW, clarifying the necessity of desalination for the rational management of SOGW. Subsequently, potential and implemented technologies for SOGW desalination are reviewed, mainly including membrane-based, thermal-based, and adsorption-based desalination technologies, as well as bioelectrochemical desalination systems, and the research progress of these technologies in desalinating SOGW are highlighted. In addition, various pretreatment methods for SOGW desalination are comprehensively reviewed, and the synergistic effects on SOGW desalination that can be achieved by combining different desalination technologies are summarized. Renewable energy sources and waste heat are also discussed, which can be used to replace traditional fossil energy to drive SOGW desalination and reduce the negative impact of shale oil and gas exploitation on the environment. Moreover, real project cases for SOGW desalination are presented, and the full-scale or pilot-scale on-site treatment devices for SOGW desalination are summarized. In order to compare different desalination processes clearly, operational parameters and performance data of varying desalination processes, including feed salinity, water flux, salt removal rate, water recovery, energy consumption, and cost, are collected and analyzed, and the applicability of different desalination technologies in desalinating SOGW is qualitatively evaluated. Finally, the recovery of valuable inorganic resources in SOGW is discussed, which is a meaningful research direction for SOGW desalination. At present, the development of SOGW desalination has not reached a satisfactory level, and investing enough energy in SOGW desalination in the future is still necessary to achieve the optimal management of SOGW.

Techno-Economic Analysis of Vacuum Membrane Distillation for Seawater Desalination

Seawater desalination is an affordable and viable solution to the growing freshwater scarcity problem in water scarce regions. The current study focuses on cost analysis of Vacuum Membrane Distillation (VMD) setup for removing salts from water. The membrane used in the flat sheet VMD module was Polytetrafluoroethylene (PTFE) with 250 mm × 200 mm dimensions and 165 µm thickness. The experiments were carried out with variations in parameters such as velocity, pressure, concentration, and temperature. For the cost analysis, the operational, maintenance, instrumentation, and capital cost of the lab model was considered and then upscaled. A range of experiments was performed for NaCl and KCl under variations of operating parameters. It was noted that, for the NaCl solution, the increase in temperature from 50 °C to 70 °C doubled the permeate flux. However, for the conditions tested, the concentration shift from 0.25 M to 0.75 M decreased the permeate flux by 1.4% because the increase in ion concentrations along the membrane lowers the vapor pressure, restricting the permeate flux. The results trend for the KCl solution was similar to the NaCl; at temperature T1, it was noted that increased concentration from 0.25 M to 0.75 M significantly reduces the permeate flow. The reduction in permeate flow was nonlinear for a given pressure 30 kPa and velocity 5.22 m/s, but linear for all other variables. It was also observed that with an increase in temperature from 60 °C to 70 °C, the permeate flux for concentration 0.25 M was 49% for all the combinations of pressure and velocity. In addition, permeate flow increased 53% from temperature 50 °C to 60 °C and 49% from temperature 60 °C to 70 °C for both the solutions at a concentration of 0.25 M. This shows that the temperature also had a profound impact on the permeate flux. The economic analysis and market survey shows that the cost of clean water at the lab level was high which can be significantly reduced using a large-scale setup providing 1,000,000 L/H of distilled water.

Recent advances and prospects in electrochemical coupling technologies for metal recovery from water

With the development of our society, the desire to recover valuable metal resources from metal-containing wastewaters or natural water bodies is becoming increasingly stronger nowadays. To overcome the limitations of single techniques, coupling technologies with synergistic effects are attracting increasing attention regarding metal resource recovery from water with particular interest in electrochemical coupling technologies in view of the advantages of electrochemical methods. This state-of-the-art review comprehensively presented the mechanisms and performance of electrochemical coupling systems for metal recovery from water. To give a clear overview of current research trends, technologies coupled with electrochemical processes can be categorized into six main types: electrochemical techniques, membrane modules, adsorption/extraction techniques, sonication technologies, energy supply techniques and others. The electrochemical coupling system has shown synergistic advantages (e.g., improving metal recovery efficiency, reducing energy consumption) over single technologies. We then discuss the remaining challenges, present corresponding solutions, and put forward future directions for current electrochemical coupled systems towards metal recovery. This review is conducive to broadening the potential applications of electrochemical coupling processes for metal recovery and sustainable water treatment.

Combination of chemical coagulation and membrane-based separation for dairy wastewater treatment

An important factor resulted from the ascension of the milk and milk-based by-products production is many effluents directly released into the environment. The main objective of this study was to evaluate the efficiency of the combination of the chemical coagulation, with ferric chloride as a coagulant, and the membrane separation processes (MSP) and reverse osmosis (RO) processes in the treatment of effluents from a powdered milk dairy industry. To evaluate the effectiveness of the integration of these mechanisms, the characterization of the effluents was carried out through Total Nitrogen (Ntotal), Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), color, pH, and turbidity analysis. Regarding the treatments with ferric chloride, the Ntotal removal was up to 55.7% (concentration of 1.2 g L- 1) and the color up to 50% (0.7 g L- 1). For the MSP and RO treatments, the color removal was up to 100% (1st RO), turbidity up to 100% (1st RO), COD up to 98.7% (3rd RO), and TOC up to 96.7% (3rd RO). Finally, the integration of the chemical coagulation and MSP processes was efficient for the treatment of dairy industry wastewater and provides the return of water in appropriate characteristics according to legislation.

Technological advancements in the use of ionic liquid- membrane systems for CO2 capture from biogas/flue gas - A review

Carbon capture has become a very important method for curbing the problems associated with the release of carbon dioxide into the atmosphere, which in turn has detrimental effects on the planet and its inhabitants. Ionic liquids and membrane separation have been explored in this review paper as effective means of capturing carbon dioxide. An innovative approach to CO₂ capture is the use of Ionic liquids (ILs) since they exhibit certain significant traits such as good stability (thermal, mechanical and chemical), inflammability and high absorptive capacities. Ionic liquids (ILs) are widely regarded as nontoxic substances. Viscosity and thermal degradation of ILs at temperatures slightly above 100 °C are the major disadvantages of ILs. Membrane separation is a technique used for the effective separation of substances by materials bearing holes in a continuous structure. Membrane technology has gained significant improvements, over the years. Several ILs and membrane systems were considered in this work. Their weaknesses, strengths, permeability, selectivity, operating conditions and carbon capture efficiencies, were all highlighted in order to gain a good perspective on ways by which the individual systems can be improved upon. The study considered several polymer-Ionic liquid hybrid materials as viable options for CO₂ capture from a post-combustion process. Different ILs were scrutinized for possible integration in membranes by taking full advantage of their individual properties and harnessing their tune-able characteristics in order to improve the overall carbon capture performance of the system. Several options for improving the mechanical, chemical, and thermal stabilities of the hybrid systems were considered including the use of cellulose acetate membrane, nanoparticles (graphene oxide powder) alongside potential ionic liquids. Doping membranes with ILs and nanoparticulates such as graphene oxide serves as a potential method for enhancing the CO₂ capture of membranes and this review provides several evidences that serve as proofs for this concept.

Method of purification of post-production condensates from polyester polyol production

Nowadays, the topics of closed-loop and eco-design are raised very often, especially in the chemical industry. To combine development with these trends, Purinova Sp. z o.o. has focused on pursuing the closed-loop use of post-production condensate from polyester polyols production. To this end, purification and distillation processes have been adapted, both at the laboratory and production scale, to receive treated condensate with decreased Chemical Oxygen Demand (COD) index. The method involves connected purification of production condensate by returning condensate to the top of the distillation column during polycondensation and two stages distillation system afterwards. The method allows for decreasing COD index and contents of diethylene glycol and 1,4-dioxane. The resulting technology has consequently allowed the use of tailored distillation in the purification of post-production condensates in the production of polyester polyols. Furthermore, the quality of the condensate obtained allowed it to be used in the closed loop of the production plant.

Pollution and Cleaning of PDMS Pervaporation Membranes after Recovering Ethyl Acetate from Aqueous Saline Solutions

The removal of volatile organic compounds (VOCs) from wastewater containing nonvolatile salts has become an important and interesting case of the application of the pervaporation (PV) process. The aim of this study was to evaluate the influence of salts on the PV removal of ethyl acetate from wastewater using a polydimethylsiloxane (PDMS) membrane. The fouled membrane was then characterized via scanning electron microscopy–energy-dispersive X-ray analysis (SEM–EDX) to investigate salt permeation. The membrane backflushing process was carried out by periodically flushing the permeate side of the tubular membrane. The results demonstrated that salts (NaCl and CaCl₂) could permeate through the PDMS membrane and were deposited on the permeate side. The presence of salts in the feed solution caused a slight increase in the membrane selectivity and a decrease in the permeate flux. The flux decreased with increasing salt concentration, and a notable effect occurred at higher feed-salt concentrations. A permeate flux of up to 98.3% of the original flux was recovered when the permeation time and backflushing duration were 30 and 5 min, respectively, indicating that the effect of salt deposition on flux reduction could be mitigated. Real, organic, saline wastewater was treated in a pilot plant, which further verified the feasibility of wastewater PV treatment.

The Impact of Operational Parameters on Polypropylene Membrane Performance during the Separation of Oily Saline Wastewaters by the Membrane Distillation Process

In the present study, membrane distillation (MD) was applied for the treatment of oily saline wastewaters produced on ships sailing the Baltic Sea. For comparison purposes, experiments were also carried out with model NaCl solutions, the Baltic Seawater and oil in water emulsions. The commercial Accurel PP V8/2 membranes (Membrana GmbH, Germany) were used. In order to investigate the impact of the operational parameters on the process performance, the experiments were conducted under various values of the feed flow velocity (from 0.03 to 0.12 m/s) and the feed temperature (from 323 to 343 K). The obtained results highlight the potential of PP membranes application for a stable and reliable long-term treatment of oily wastewater. It was demonstrated that the permeate flux increased significantly with increasing feed temperature. However, the lower temperature ensured the limited scaling phenomenon during the treatment of oily wastewaters. Likewise, increasing the feed flow velocity was beneficial to the increase in the flux. Moreover, it was found that performing a cyclic rinsing of the module with a 3% HCl solution is an effective method to maintain a satisfactory module performance. The present study sheds light on improving the MD for the treatment of oily wastewaters.

Slippery membrane surface tuning with polypropylene coating to treat real aquaculture wastewater in membrane distillation

Surging growth of aquaculture industry has alarmed the public when the wastewater discharged had an adverse effect on the environment. This current study is a pioneer in the use of membrane distillation (MD) to treat real aquaculture wastewater. In addition to excellent hydrophobicity, the slippery surface of membrane used for MD is another key factor that enhances the performance of MD. The slippery surface of the membrane was tuned by layering high-viscosity and low-viscosity polypropylene (PP) polymers on the electrospun membrane by solvent-exchanged method. While the high-viscosity PP coating (PP/HV) rendered the membrane surface slippery, the low-viscosity PP coating (PP/LV) caused the fish farm wastewater to have stick-slip movement on the membrane surface. In the long-term 70-hour direct contact membrane distillation (DCMD) separation, PP/HV and PP/LV membranes can perfectly eliminate the undesirable components in the fish farm wastewater. The PP/HV membrane has registered a flux of 19.1 kg/m²·h, while the flux of PP/LV membrane was only 7.3 kg/m²·h. The PP/HV membrane also showed excellent anti-scaling properties in relative to the PP/LV membrane. This is because the PP/HV membrane promotes effortless gliding of the feed water along the surface of the membrane, while the surface of the PP/LV membrane has a static water boundary. Therefore, it can be concluded that the application of MD using the membrane coated with high-viscosity PP polymer is a feasible technology for the treatment of aquaculture wastewater.

Non-solvent Flux Augmentation of an LDPE-Coated Polytetrafluoroethylene Hollow Fiber Membrane for Direct Contact Membrane Distillation

Membrane distillation (MD) is a thermal technology for the desalination process that requires a hydrophobic microporous membrane to ensure that the membrane can maintain the liquid-vapor interface. This work aims to enhance the water permeation flux of the previously coated membrane by modifying the surface of the polytetrafluoroethylene hollow fiber (PTFE HF) membrane with a selected non-solvent such as acetone, cyclohexanone, and ethanol in low-density polyethylene as a polymeric coating solution. However, the modification using acetone and cyclohexanone solvents was unsuccessful because a reduction in membrane hydrophobicity was observed. The modified PTFE HF membrane with ethanol content exhibits high wetting resistance with a high water contact angle, which can withstand pore wetting during the direct contact MD process. Since MD operates under a lower operating temperature range (50-90 °C) compared to the conventional distillation, we herein demonstrated that higher flux could be obtained at 7.26 L m^-2 h^-1. Thus, the process is economically feasible because of lower energy consumption. Performance evaluation of the modified PTFE HF membrane showed a high rejection of 99.69% for sodium chloride (NaCl), indicating that the coated membrane preferentially allowed only water vapor to pass through.

Laboratory Scale Evaluation of Fertiliser Factory Wastewater Treatment through Membrane Distillation and Reverse Osmosis

The incumbent water stress scenario imposes wastewater valorisation to freshwater, promoting technology for its effective treatment. Wastewater from fertiliser factories is quite problematic because of its relevant acidity and solute content. Its treatment through vacuum membrane distillation (VMD) was evaluated through laboratory scale tests at 40 °C and 25 mbar vacuum pressure with polytetrafluoroethylene and polypropylene flat-sheet porous membranes. The wastewater from a partially disused Italian industrial site was considered. VMD distillate fluxes between 22 and 57.4 L m^-2 h^-1 (LMH), depending on the pore size of the membranes, along with very high retention (R > 99%) for anions (Cl^-, NO₃^-, SO₄^2-, PO₄^3-), NH₄⁺, and chemical oxygen demand (COD) were observed. Laboratory scale reverse osmosis (RO) tests at 25 °C and increasing of the operating pressure (from 20 bar to 40 bar) were carried out with a seawater desalination membrane for comparison purposes. Permeability values around 1.1 LMH/bar almost independently of the operating pressure were observed. Lower retentions than those measured from VMD tests were found. Finally, for any given RO operating pressure, the flux recovery ratio (FRR) calculated from permeate fluxes measured with pure water before and after wastewater treatment was always much lower that evaluated for VMD membranes.

Membrane Distillation for the Production of Pharmaceutical-Grade Water-Investigation into the Application of AGMD and VMD

The production of pharmaceutical ingredients, intermediates and final products strongly depends on the utilization of water. Water is also required for the purification and preparation of reagents. Each specific application determines the respective water quality. In the European Union, the European Pharmacopeia (Ph. Eur.) contains the official standards that assure quality control of pharmaceutical products during their life cycle. According to this, the production of water for pharmaceutical use is mainly based on multi-stage distillation and membrane processes, especially, reverse osmosis. Membrane distillation (MD) could be an alternative process to these classical methods. It offers advantages in terms of energy demand and a compact apparatus design. In the following study, the preparation of pharmaceutical-grade water from tap water in a one-step process using MD is presented. Special emphasis is placed on the performance of two different module designs and on the selection of optimum process parameters.

A novel thermophilic anaerobic granular sludge membrane distillation bioreactor for wastewater reclamation

Membrane distillation (MD) has a high heat requirement. Integrating MD with thermophilic bioreactors could remedy this problem. A laboratory-scale thermophilic anaerobic granular sludge membrane distillation bioreactor (ThAGS-MDBR) was used to treat wastewater with a high organic loading rate (OLR). Waste heat from ThAGS was used directly for the MD process to reduce energy consumption. The result demonstrated that the ThAGS-MDBR system achieved a high-efficiency removal of chemical oxygen demand (more 99.5%) and NH₄⁺-N (96.4%). Furthermore, the highest methane production from the proposed system was 332 mL/g COD_removed at OLR of 16 kg COD/m³/day. Specifically, an aggregate of densely packed diverse microbial communities in anaerobic granular sludge was the main mechanism for the enhancement of bioreactor tolerance with environmental changes. High-quality distillate water from ThAGS-MDBR was reclaimed in one step with total organic carbon less than 1.7 mg/L and electrical conductivity less than 120 μS/cm. Furthermore, the result of the DNA extraction kit recorded that Methanosaeta thermophila was a critical archaea for high COD removal and bioreactor stability.

Removal and Recovery of Methyl Tertiary Butyl Ether (MTBE) from Water Using Carbon Nanotube and Graphene Oxide Immobilized Membranes

Methyl tert-butyl ether (MTBE) is a widely used gasoline additive that has high water solubility, and is difficult to separate from contaminated ground and surface waters. We present the development in functionalized carbon nanotube-immobilized membranes (CNIM-f) and graphene oxide-immobilized membranes (GOIM) for enhanced separation of MTBE via sweep gas membrane distillation (SGMD). Both types of modified membranes demonstrated high performance in MTBE removal from its aqueous mixture. Among the membranes studied, CNIM-f provided the best performance in terms of flux, removal efficiency, mass transfer coefficients and overall selectivity. The immobilization f-CNTs and GO altered the surface characteristics of the membrane and enhanced partition coefficients, and thus assisted MTBE transport across the membrane. The MTBE flux reached as high as 1.4 kg/m² h with f-CNTs, which was 22% higher than that of the unmodified PTFE membrane. The maximum MTBE removal using CNIM-f reached 56% at 0.5 wt % of the MTBE in water, and at a temperature of 30 °C. With selectivity as high as 60, MTBE recovery from contaminated water is very viable using these nanocarbon-immobilized membranes.