Membrane Distillation Crystallization Research Articles

Environmentally Friendly Photothermal Membranes for Halite Recovery from Reverse Osmosis Brine via Solar-Driven Membrane Crystallization.

Modern society and industrial development rely heavily on the availability of freshwater and minerals. Seawater reverse osmosis (SWRO) has been widely adopted for freshwater supply, although many questions have arisen about its environmental sustainability owing to the disposal of hypersaline rejected solutions (brine). This scenario has accelerated significant developments towards the hybridization of SWRO with membrane distillation-crystallization (MD-MCr), which can extract water and minerals from spent brine. Nevertheless, the substantial specific energy consumption associated with MD-MCr remains a significant limitation. In this work, energy harvesting was secured from renewables by hotspots embodied in the membranes, implementing the revolutionary approach of brine mining via photothermal membrane crystallization (PhMCr). This method employs self-heating nanostructured interfaces under solar radiation to enhance water evaporation, creating a carefully controlled supersaturated environment responsible for the extraction of minerals. Photothermal mixed matrix photothermal membranes (MMMs) were developed by incorporating graphene oxide (GO) or carbon black (CB) into polyvinylidene fluoride (PVDF) solubilized in an eco-friendly solvent (i.e., triethyl phosphate (TEP)). MMMs were prepared using non-solvent-induced phase separation (NIPS). The effect of GO or GB on the morphology of MMMs and the photothermal behavior was examined. Light-to-heat conversion was used in PhMCr experiments to facilitate the evaporation of water from the SWRO brine to supersaturation, leading to sodium chloride (NaCl) nucleation and crystallization. Overall, the results indicate exciting perspectives of PhMCr in brine valorization for a sustainable desalination industry.

Integration of seeding-induced crystallization with microbubble aeration for membrane fouling and wetting control in vacuum membrane distillation

In this work, a bench-scale vacuum membrane distillation crystallization (VMDC) system coupled with microbubble aeration (MBA) was developed for treating high-salinity feed brine. Herein, the effect of seeding dose on membrane fouling and wetting control in the VMDC system was studied by using synthetic saturated calcium sulfate solution. The results showed that introducing gypsum seeds at a dose of 0.5 g/L effectively restricted membrane fouling and wetting. Subsequently, seeding-induced crystallization coupled with MBA was employed to investigate the control effect on membrane fouling and wetting during VMDC with simulated high-salinity feed brine treatment. As 0.5 g/L gypsum seeds were directly added at 7 h in the VMDC experiment while employing MBA, membrane fouling and wetting were effectively controlled. Finally, the mechanism behind the control of membrane fouling and wetting was elucidated during VMDC operation by integrating seeding-induced crystallization with MBA. This could be ascribed to the synergic effect of gypsum seeds and microbubbles in bulk solution. In brief, this work offers a promising approach to control membrane fouling and wetting during concentrating high-salinity wastewater by VMD.

Seeded membrane distillation crystallization for hypersaline brine treatment

Abstract Brine evaporation and crystallization are energy- and equipment-intensive technologies commonly used in industries. Alternatively, membrane distillation (MD) has shown ability for concentrating different saline solutions. However, there is a limited understanding of the impact of these solutions on the scaling and wetting behavior. To address this knowledge gap and reduce costs and energy consumption, we investigated a novel method called ‘seeded near-zero liquid discharge membrane crystallization’ (NZLDMC). This approach combines MD and crystallization in a single apparatus, reducing capital and operating costs while improving sustainability. Our study focused on applying seeding processes at NZLDMC for concentrating synthetic mono- and multi-salt solutions with a salinity of 300 g/L and a real salt solution. We investigated the effects of salt crystals and seeds on membrane performance under different operating conditions. Our findings indicate that seeding crystal technology leads to high yield and long-term stability, thereby offering the potential in industries and municipal water treatment to fractionate salt in multi-salt solutions and obtain purified water simultaneously.

Performance of membrane distillation assisted crystallization and crystal characteristics for resource recovery from desalination brine

Membrane distillation crystallization (MDC) has been widely studied in recent year for its potential for resource recovery from desalination brine with high concentrations. In this study, crystal samples produced from a bench-scale MDC system have been analysed for crystal morphology, crystal purity and crystal size distribution (CSD). In addition, orthogonal fractional factorial (OFF) experimental design has been introduced to evaluate the influence of various operating conditions on the crystal size and CSD. Feed temperature (40 to 60 °C), crystallization time (60 to 180 min) and the feed composition have been used as the control factors. The results show that the MD in the MDC system maintains a consistent flux of 1.32 to 4.2 kg/m2·h across various feed compositions; higher feed temperatures led to the formation of larger crystal clusters, while longer crystallization time yielded more cubic-shaped crystals; an overall NaCl purity exceeding 99.08 % has been achieved throughout all the experiments; and the increased feed temperature and prolonged crystallization time results in a narrower CSD. The result of OFF experimental design identifies feed temperature as the dominant factor affecting crystal size and CSD. However, the presence of impurities in the feed water could pose challenge to the thermal stability and longevity of the membrane.

Valorization of acid mine drainage into potable water and valuable minerals through membrane distillation crystallization

Owing to the rise in population growth and demands for the current living standards, mineral and water resources are depleting at the alarming rate. Also, the mineral–water-energy nexus raises a concern of high-quality water and mineral production at low costs. Membrane distillation crystallization (MDC) has emerged as a promising technology capable of simultaneous water and mineral recovery from wastewater or industrially discharged brines. Herein, the MDC was evaluated for recovery of water and precious minerals from acid mine drainage discharged from the mine tailings. High quality fresh water with 99.9 % salt rejection and permeate flux of 2.32 kg·m−2·h−1 was recovered at 52 °C feed inlet temperature. Also, feed temperatures were varied to determine their impact on mineral crystal morphology, size distribution and growth rate. Predominantly recovered minerals were gypsum, manganese fluoride, potassium iron oxide, nickel oxide hydroxide, sodium sulphate and dihydrogen sulphate. Orthorhombic crystal structure of mineral salts was attained at low feed inlet temperature (34 °C). Higher feed inlet temperatures (i.e. 41° C and 52° C) promoted co-crystallization giving rise to orthorhombic polymorph structures. Narrow crystal size distribution was reported at low water recovery factor (initial growth) for all temperatures. However, the particle size distribution broadened as the recovery factor increased. The crystal sizes ranged from 3.91 ± 0.97 µm to 14.04 ± 3.31. Remarkably, crystal growth rate increased with an increase in feed inlet temperature. These findings open a research direction towards economic recovery of mineral and water to supplement the existing shortages. With a myriad of crystals obtained from the MDC process, an additional operational unit is required to selectively recover high economic minerals.

Membrane Distillation-Crystallization for Sustainable Carbon Utilization and Storage.

Anthropogenic greenhouse gas emissions from power plants can be limited using postcombustion carbon dioxide capture by amine-based solvents. However, sustainable strategies for the simultaneous utilization and storage of carbon dioxide are limited. In this study, membrane distillation-crystallization is used to facilitate the controllable production of carbonate minerals directly from carbon dioxide-loaded amine solutions and waste materials such as fly ash residues and waste brines from desalination. To identify the most suitable conditions for carbon mineralization, we vary the membrane type, operating conditions, and system configuration. Feed solutions with 30 wt % monoethanolamine are loaded with 5-15% CO2 and heated to 40-50 °C before being dosed with 0.18 M Ca2+ and Mg2+. Membranes with lower surface energy and greater roughness are found to more rapidly promote mineralization due to up to 20% greater vapor flux. Lower operating temperature improves membrane wetting tolerance by 96.2% but simultaneously reduces crystal growth rate by 48.3%. Sweeping gas membrane distillation demonstrates a 71.6% reduction in the mineralization rate and a marginal improvement (37.5%) on membrane wetting tolerance. Mineral identity and growth characteristics are presented, and the analysis is extended to explore the potential improvements for carbon mineralization as well as the feasibility of future implementation.

Resource recovery from acid mine drainage in membrane distillation crystallization

Acid mine drainage (AMD) remains a global threat with no exception to South African water bodies and the environment. It promotes environmental challenges with emerging concerns on water security and drinking water pollution. This study evaluated membrane distillation crystallization (MDC) towards resource recovery from AMD. To ensure high process performance, polyvinylidene fluoride (PVDF) membranes evaluated in the current study were modified using hydrophobic nanoparticle additives and compared with PTFE-20 reference membrane. The produced permeate flux of PTFE-20 reference membranes and M4 (fSiO2NPs-modified membrane) were 2.426 kg m-2·h-1 and 1.459 kg m-2·h-1, respectively. Similarly, salt rejections were 99.96% and 97.52%, respectively. Based on single crystal x-ray diffraction and scanning electron microscopy analysis, MDC predominantly produced monoclinic gypsum (CaSO4.2H2O) with the C2/c space group. Also, crystal properties obtained in fSiO2NPs-modified and PTFE-20 reference membranes were comparable. Though a considerable amount of gypsum was obtained, membrane surfaces were characterized by traces of salt deposit, with possible membrane scaling leading to performance deterioration. The permeate conductivity increased rapidly at the highest water recovery factor, indicating membrane wetting caused by scaling.

Application of the electrical localized heating method in direct contact Membrane Distillation Crystallization process

Membrane Distillation Crystallization (MDCr) was the latest technology which shows great ability in the salt recovery area, but its practical application is currently confined to the laboratory due to the energy loss during long hydraulic circulation, and the high energy consumption caused by the long-term thermal requirements of the feed solution. In this study, the electric heating method was applied in the MDCr system as a potential candidate to increase the solution temperature and enhance the thermal efficiency. Compared to the normal water bath heating, the electrothermal MDCr system exhibited better permeate flux performance, higher thermal efficiency and high controllability. Additionally, the permeate flux decline under the control of AC 20 V was 11.1 %, which was far below the flux drop of 31.6 % obtained by the water bath method. Noticeably, the accumulation of NaCl crystals on the membrane was greatly alleviated according to the in-situ monitor of OCT due to the constant ion migration responding to the electric field within the conducting membrane. We hold the belief that this electrothermal direct contact MDCr system has a promising potential in the treatment of saline wastewater, building an effective foundation for efficient and energy-saving electrical heating MDCr systems.

Recovery of Pure Water, Salicylic Acid Crystals, and Paracetamol using PVDF-MWCNT Membranes by Membrane Distillation-crystallization

Membrane distillation-crystallization (MDC) is presented as a novel technique in the treatment of waste concentrated water which produces valuable crystals along with pure water. In the present study, multi-walled carbon nanotubes (MWCNT)/polyvinylidene fluoride (PVDF) flat sheet membranes were prepared via the wet phase inversion method and applied in MDC for the treatment of pharmaceutical waste. The pure and modified membrane surface properties are characterized with the help of SEM, FTIR, and contact angle measurement. The present work reported the effect of MWCNT content and feed temperature on the MDCperformance and measured pure water flux and pharmaceutical compounds recovery. The observed maximum permeate flux and crystal recovery for Salicylic acid system was 5.5 kg/m2h and 50%, respectively for PVDF+0.5% CNT membrane and 5 kg/m2h and 48%, respectively for pure PVDF. Also, for paracetamol system it was 3.9 kg/m2h and 41% for PVDF +0.5% CNT membrane and 3.5 kg/ m2h and 38% for pure PVDF. Obtained results show that MDC has good potential in treating pharmaceutical waste.

Thermodynamics Analysis of a Membrane Distillation Crystallization Ion Recovery System for Hydroponic Greenhouses Assisted with Renewable Energy

Sustaining agricultural demands is a typical problem, particularly in locations afflicted by the scarcity of fresh water, poor farming soil, and hot weather. The main goal of this study is to perform a thermodynamic analysis of an integrated multigeneration system containing a direct contact membrane distillation crystallization system that recovers beneficial hydroponic farming nutrients from seawater using renewable energy resources. A parametric study is carried out to determine the impacts of various factors on the system, such as changing the rate of mass flow rate, recovery ratio, and salinity. This study proposes a novel sustainable multigeneration system for seawater desalination and ions recovery using the direct contact membrane distillation crystallization system to provide the hydroponic solution and greenhouse ventilation using the dual evaporator vapor compression refrigeration system. With overall exergy efficiency and energy efficiency of 41.40%, and 39.80%, respectively, the system requires about 1182.69 kW and 5314.6 kW of electrical and thermal power in total, respectively, to desalinate 5 kg/s of seawater and recover 170 mg/s of Sulfate (SO4), 81.28 mg/s of Magnesium (Mg), 25.48 mg/s of Calcium (Ca), and 24.16 mg/s of Potassium (K), yielding about 4.4 kg/s of a hydroponic solution, and ventilating 25 greenhouses with a volume of 600 m3 of single greenhouse.

Membrane distillation crystallization for water and mineral recovery: The occurrence of fouling and its control during wastewater treatment

Membrane distillation crystallization (MDC) is an emerging technology envisaged to manage challenges affecting the desalination industry. This technology can sustainably treat concentrated solutions of produced water and industrially discharged saline wastewater. Simultaneous recovery of clean water and minerals is achieved through the integration of crystallization to membrane distillation (MD). MDC has received vast research interest because of its potential to treat hypersaline solutions. However, MDC still faces challenges in harnessing its industrial applications. Technically, MDC is affected by fouling/scaling and wetting thereby hindering practical application at the industrial level. This study reviews the occurrence of membrane fouling and wetting experienced with MDC. Additionally, existing developments carried out to address these challenges are critically reviewed. Finally, prospects suggesting the sustainability of this technology are highlighted.

Boron removal and recovery via vacuum assisted air gap membrane distillation-crystallization (VAGMD-C): A pilot-scale study

Boron is an essential element that is widely used in many industries. Due to its importance, it is beneficial to recover boron from water streams. The concentrate stream contains high boron content and is the major obstacle for membrane processes, due to its high salinity and contaminant content. Since membrane distillation (MD) can be used successfully to treat highly concentrated waters, the pilot scale vacuum-assisted air gap MD (VAGMD) unit was investigated in this study and boron removal efficiency from raw water and RO concentrate was evaluated. This operation was carried out with different recovery ratios through flow rate, conductivity, pressure and removal efficiencies and presented in this study. After the VAGMD operation the crystallization process was applied and up to 43.9 % B2O3 concentrated boron crystals were obtained.

Modelling and simulation of flux prediction and salinity variation in direct contact membrane distillation for seawater desalination and brine treatment

As one of the state-of-art desalination technologies, membrane distillation (MD) has been widely studied in recent years. In order to better control the performance of the MD, a new model that can predict the membrane surface temperatures, permeate flux as well as salinity variation with the operating time has been proposed in this study. Using the model, impacts of operating parameters such as bulk temperature, flow rate, different membrane materials and feed salinity on the permeate flux as well as the efficiency of driving force were simulated. The results of the simulations indicate that feed temperature, feed flow rate and membrane pore size have the most significant influence on the permeate flux. However, the feed and permeate flow rates have the highest impacts on the temperature polarization coefficient (TPC) which has the highest value of 0.68 under certain conditions. Besides, the simulations predicted that the water recovery from the MD for the seawater and the desalination brine at the saturation point of NaCl to be 86.8 % and 72.1 %, respectively. Finally, the salinity variations with operating time were also simulated and the new model would be vital for the salinity control in desalination processes such as membrane distillation crystallization.

Water recovery assessment from hypersaline lithium-rich brines using Membrane Distillation-Crystallization

The current lithium extraction from hypersaline salt-lake brines is causing concerns, mainly due to the evaporation and loss of around 90 % of the water contained in the brines, tensioning the relationship between communities and industrial companies located in zones with a severe water scarcity. This study assesses the water recovery from synthetic hypersaline brines - mimicking the contents variability of Na, K, and Mg - using a Membrane Distillation-Crystallization process. An evaluation of the operational parameters of the process, such as feed temperature, flowrate and water activity was carried-out using a Response Surface Methodology. Final validation was performed to assess the process performance by comparing a real brine from Maricunga salt-lake (Chile) and a synthetic brine. An average flux of around 3.5 kg/m2 h at 60 °C brine feed temperature was obtained for real and synthetic brines, achieving a high quality recovered freshwater (electrical conductivity <40 μS/cm) and low contents of ions.

Osmotic Membrane Distillation Crystallization of NaHCO3

A new crystallization process for sodium bicarbonate (NaHCO3) was studied, proposing the use of osmotic membrane distillation crystallization. Crystallization takes place due to the saturation of the feed solution after water evaporation on the feed side, permeating through the membrane pores to the osmotic side. The process operational parameters, i.e., feed and osmotic velocities, feed concentration, and temperature were studied to determine the optimal operating conditions. Regarding the feed and osmotic velocities, values of 0.038 and 0.0101 m/s, respectively, showed the highest transmembrane flux, i.e., 4.4 × 10−8 m3/m2·s. Moreover, study of the temperature variation illustrated that higher temperatures have a positive effect on the size and purity of the obtained crystals. The purity of the crystals obtained varied from 96.4 to 100% In addition, the flux changed from 2 × 10−8 to 7 × 10−8 m3/m2·s with an increase in temperature from 15 to 40 °C. However, due to heat exchange between the feed and the osmotic solutions, the energy loss in osmotic membrane distillation crystallization is higher at higher temperatures.

Recovery of CaSO4 and NaCl from sub-soil brine using CNT@MOF5 incorporated poly(vinylidene fluoride-hexafluoropropylene) membranes via vacuum-assisted distillation

The recovery of salts from sub-soil brine can fulfil the demand for the salts and chemicals for the industries and mitigate the problem of fresh water at the same time. This study reported the performance of a vacuum-assisted membrane distillation crystallization (VMDCr) for CaSO4 and NaCl salts recovery from sub-soil brine. The facile one-step synthesis of porous MOF5 and CNT@MOF5 composites was also reported. Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) mixed matrix flat-sheet membranes incorporated with 1 wt% of MOF5 and CNT@MOF5 were used for VMDCr. The membranes and materials were characterized by scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) analyses. The incorporation of CNTs to MOF5 did not affect the MOF5 crystallinity, confirmed by XRD and FT-IR. The MOF5 and CNT@MOF5 incorporated PVDF-HFP matrix membranes (designated as M-ZM and M-CZM, respectively) showed rough and porous morphology. Moreover, the M-CZM showed improved porosity and number of pores than the M-ZM membrane. As a result, M-CZM produced 2.1 times the flux than the pristine PVDF-HFP membrane facilitating faster crystallization. In the density span of 15.83°Be' to 24.5°Be', CaSO4 precipitated over the membrane surface, and complete precipitation of CaSO4 was achieved once the feed (sub-soil brine) reached 24.5°Be'. NaCl crystals started forming on the membrane surface after the density of the feed reached 25°Be'. The NaCl salt precipitated completely once the sub-soil brine density reached 28.5°Be'. The SEM and XRD analyses of the recovered monoclinic CaSO4 and cubic NaCl crystals revealed their good geometrical and high purity. This study concludes that the M-CZM membrane can improve the membrane properties for faster salt crystallization from sub-soil brine.

Evaluation of the performance of ultrasound-assisted membrane distillation crystallization process for water and sodium chloride recovery in hypersaline solution

A large amount of high saline solutions has been generated in various industries and management of hypersaline solutions is a critical issue. Membrane distillation (MD) integrated with crystallization (MDC) technology is a promising approach in the treatment of hypersaline solutions, while membrane scaling is still problematic. Herein, MDC assisted by ultrasound (US) was proposed to deal with 25.93 wt% NaCl solution, and the performance of four processes including MD, US + MD, MDC and US + MDC were systematically evaluated. Results showed that ultrasound and crystallization could effectively alleviate membrane fouling and the operation time was extended from 80 min to over 245 min. Compared with MD process, the weight of crystals on the membrane surface was significantly reduced in the presence of US or / and crystallization (by 61.24%–98.63%) while the water recovery rate increased by 122% with the help of ultrasound. Crystal characteristic analysis demonstrated that the average crystal size was narrow in crystallizer of US + MDC process, successfully verifying the stability and feasibility of the system. The superiority of US + MDC process was further confirmed by scanning electron microscopy — energy dispersive spectroscopy observation. Moreover, higher mechanical strength and more stable surface tension showed that US + MDC process had a potential application in treating hypersaline solution.

Membrane Distillation-Crystallization for inland desalination brine treatment

Membrane distillation crystallization (MDC) is a promising technique for treatment of inland desalination brines due to its ability to recover clean water and solid salts. The MDC system developed in this study used a six-tray cascading crystallizer with extended mesh surfaces to provide nucleation sites and support for crystal growth. Sodium chloride (NaCl), potassium chloride (KCl), and sodium nitrate (NaNO3) brines were used to investigate clean water and solid salt recovery using MDC, as well as brine volume reduction. When compared to MD alone, MDC achieved higher water and solid salt recovery under the same operating conditions, resulting in greater reductions in brine volume, while retaining > 99.8% rejection for all three salt species. Solid salts were recovered from all three feed solutions, with NaNO3 feed solution, which has the strongest temperature-solubility relationship, having the highest yield (126.55 ± 6.65 g).

An innovative hollow fiber vacuum membrane distillation-crystallization (VMDC) coupling process for dye house effluent separation to reclaim fresh water and salts

The discharge of dyeing wastewater has become one of the important restrictive factors for the green manufacturing and sustainable development of textile industry. Realizing the maximum reuse of dyeing wastewater resources is an efficient solution. Vacuum membrane distillation crystallization (VMDC) coupling process can separate and recover the components such as fresh water and salts (mordants) in dyeing wastewater as well as achieve the concentration of the valuable substances (dyes) simultaneously. In this study, hollow fiber VMDC coupling process was developed for the treatment of saline dye solution to recover the inorganic salt (mordant Al(NO3)3) and fresh water while realize the high-multiple concentration of dyes (Congo red, CR). High-performance hydrophobic PVDF hollow fiber porous membrane was prepared by the dry-jet wet-spinning technique and used in the VMDC process. The VMDC process in one cycle was optimized, including MD section, crystallization and membrane cleaning process. Variations of MD separation performance including permeate water flux and solute rejection of PVDF hollow fiber membrane for CR and Al(NO3)3 with operating time was determined by the vacuum membrane distillation (VMD) experiment. A three-cycle VMDC process was developed and the variations of MD separation performance and crystal yield in each VMDC cycle were investigated. In each VMDC process, the rejection of CR and Al (NO3) 3 by hollow fiber MD can be maintained above 99%. With the extension of VMDC operating time, the gradually decreased water flux can be recovered by around 90% through the combined cleaning method of NaOH and absolute ethanol (abs). In the three-cycle of VMDC process, 42.5, 32.5 and 9.8% of water were recovered from the feed solution with a total recovery ratio of 84.8%. In the second and third VMDC cycles, 48.0 and 21.5% of the salts in the saline dye solution were obtained with a total salt recovery ratio of 69.5%. An estimation of economic cost was also made to evaluate the economic feasibility of the proposed MDC process for its practical application. Hollow fiber VMDC coupling process was proved to be a simultaneously efficient separation method of saline dye solution.

Enhanced anti-wetted PVDF membrane for pulping RO brine treatment by vacuum membrane distillation

Large amounts of lignin, hemicellulose, organic matter and inorganic salts are present in pulping and papermaking wastewater. Therefore, the treatment and discharge of pulping wastewater are important issues. We have designed and developed the world's first zero liquid discharge (ZLD) system for it based on pretreatment-membrane-evaporative crystallization integrated technologies. However, for the treatment of high salt reverse osmosis (RO) brine, there are still challenges that need to be addressed. In this work, the feasibility of using a membrane distillation crystallization (MDC) process to treat high saline RO brine was investigated. Two different coating materials, Hyflon AD 40H and perfluoropolyether (PFPE), were applied to improve the membrane surface hydrophobicity for stable and efficient performance. After modification, the water contact angle was up to 138.4o and 157.7o for Hyflon/polyvinylidene fluoride (PVDF) and PFPE/PVDF composite membranes, respectively. Moreover, the PFPE/PVDF membrane showed a higher repellency toward RO brine, which is better for the following MDC treatment. During the MDC progress using composite PFPE/PVDF membranes, the salt crystals precipitated and gradually accumulated. More importantly, the final NaCl purity can be up to 94%. Therefore, it is hopeful to improve of the existing ZLD system by MDC operation.