Analysis of Membrane Distillation Crystallization System for High Salinity Brine Treatment with Zero Discharge Using Aspen Flowsheet Simulation

Exploiting the potential of a novel "in-situ latent heat recovery" in hollow-fiber vacuum membrane distillation process for simultaneously improved water production and energy efficiency

Thermal driven membrane distillation (MD) technology is a promising method for purifying & recovering various salty (especially high salty) or contaminated wastewaters with low-grade heat sources. However, the drawbacks of "high energy consumption" and "high cooling water consumption" pose special challenges for the future development of this technology. In this article, we report an innovative strategy called "in-situ heat transfer", which is based on the jacketed structure composed of hollow fiber membranes and capillary heat exchange tubes, to simplify the migration steps of condensation latent heat in MD heat recovery process. The results indicate that the novel heat recovery strategy exhibits higher growth rates both in the flux and gained output ratio (47.4 % and 173.1 %, respectively), and further reduces the system's dependence on cooling water. In sum, under the control of the "in-situ heat transfer" mechanism, the functional coupling of "vapor condensation (exothermic)" and "feed evaporation (endothermic)" in limited-domain space is an attractive alternative solution, because it eliminates the disadvantages of the imbalance between heat supply and demand in traditional heat recovery methods. Our research may facilitate the development of MD heat recovery modules for industrial applications, which will help to further achieve the goal of energy saving and emission reduction.

Salinity impacts on humidification dehumidification (HDH) desalination systems: review

The use of humidification-dehumidification water desalination technology has been shown to be a practical means of meeting the demand for freshwater. The aim of this review is to investigate the impact of salinity on HDH techniques that have various benefits in terms of both economics and the environment, including the capacity to operate at low temperatures, utilize sustainable energy sources, the need for low maintenance, and straightforward construction requirements. Also, in this review, it is observed that the HDH system's components are strong and capable of treating severely salinized water. It can treat water in an appropriate way than other desalination technologies. This technology has recently been commercialized to treat highly salinized generated water. However, more research is needed to determine how salinity affects HDH productivity. According to several research investigations, while the specific thermal energy consumption increased considerably and the productivity of water per unit of time decreased significantly as the salt mass percentage grew, the purity of clean water did not suffer. The rejected brine must be reduced by increasing the total water recovery ratio in the HDH system. Through this review, it was found that brine control is becoming increasingly important in the water processing industry. ZLD systems, which aim to recover both freshwater and solid salts, can be a viable replacement for disposal methods. Finally, through this reviewer, it was concluded that HDH desalination systems may operate with extremely saline water while increasing salinity has a significant influence on system performance.

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.

The advent of thermoplasmonic membrane distillation

Freshwater scarcity is a vital societal challenge related to climate change, population pressure, and agricultural and industrial demands. Therefore, sustainable desalination/purification of salty/contaminated water for human uses is particularly relevant. Membrane distillation is an emerging hybrid thermal-membrane technology with the potential to overcome the drawbacks of conventional desalination by a synergic exploitation of the water-energy nexus. Although membrane distillation is considered a green technology, efficient heat management remains a critical concern affecting the cost of the process and hindering its viability at large scale. A multidisciplinary approach that involves materials chemistry, physical chemistry, chemical engineering, and materials and polymer science is required to solve this problem. The combination of solar energy with membrane distillation is considered a potentially feasible low-cost approach for providing high-quality freshwater with a low carbon footprint. In particular, recent discoveries about efficient light-to-heat conversion in nanomaterials have opened unprecedented perspectives for the implementation of sunlight-based renewable energy in membrane distillation. The integration of nanofillers enabling photothermal effects into membranes has been demonstrated to be able to significantly enhance the energy efficiency without impacting on economic costs. Here, we provide a comprehensive overview on the state of the art, the opportunities, open challenges and pitfalls of the emerging field of solar-driven membrane distillation. We also assess the peculiar physicochemical properties and synthesis scalability of photothermal materials, as well as the strategies for their integration into polymeric nanocomposite membranes enabling efficient light-to-heat conversion and freshwater.

An Ultrahigh-Flux Nanoporous Graphene Membrane for Sustainable Seawater Desalination using Low-Grade Heat

Membrane distillation has attracted great attention in the development of sustainable desalination and zero-discharge processes because of its possibility of recovering 100% water and the potential for integration with low-grade heat, such as solar energy. However, the conventional membrane structures and materials afford limited flux thus obstructing its practical application. Here, ultrathin nanoporous graphene membranes are reported by selectively forming thin graphene layers on the top edges of a highly porous anodic alumina oxide support, which creates short and fast transport pathways for water vapor but not liquid. The process avoids the challenging pore-generation and substrate-transfer processes required to prepare regular graphene membranes. In the direct-contact membrane distillation mode under a mild temperature pair of 65/25 °C, the nanoporous graphene membranes show an average water flux of 421.7 L m^-2 h^-1 with over 99.8% salt rejection, which is an order of magnitude higher than any reported polymeric membranes. The mechanism for high water flux is revealed by detailed characterizations and theoretical modeling. Outdoor field tests using water from the Red Sea heated under direct sunlight radiation show that the membranes have an average water flux of 86.3 L m^-2 h^-1 from 8 am to 8 pm, showing a great potential for real applications in seawater desalination.

Membrane distillation crystallization technology for zero liquid discharge and resource recovery: Opportunities, challenges and futuristic perspectives

Water resources are getting limited, which emphasises the need for the reuse of wastewater. The conventional waste(water) treatment methods such as reverse osmosis (RO) and multi-effect distillation (MED) are rendered limited due to certain limitations. Moreover, the imposition of stringent environmental regulations in terms of zero liquid discharge (ZLD) of wastewater containing very high dissolved solids has assisted in developing technologies for the recovery of water and useful solids. Membrane distillation crystallization (MDCr) is an emerging hybrid technology synergising membrane distillation (MD) and crystallization, thus achieving ZLD. MDCr technology can be applied to desalinate seawater, treat nano-filtration, and RO reject brine and industrial wastewater to increase water recovery and yield useful solids. This manuscript focuses on recent advances in MDCr, emphasizing models that account for application in (waste)water treatment. MDCr has dual benefits, first the environmental conservation due to non-disposal of wastewater and second, resources recovery proving the proverb that waste is a misplaced resource. Limitations of standalone MD and crystallization are discussed to underline the evolution of MDCr. In this review, MDCr's ability and feasibility in the treatment of industrial wastewater are highlighted. This manuscript also examines the operational issues, including crystal deposition (scaling) on the membrane surface, pore wetting phenomenon and economic consequences (energy use and operating costs). Finally, opportunities and future prospects of the MDCr technology are discussed. MDCr technology can amplify natural resources availability by recovering freshwater and useful minerals from the waste stream, thus compensating for the relatively high cost of the technology.

Brine treatment technologies towards minimum/zero liquid discharge and resource recovery: State of the art and techno-economic assessment

In the framework of minimum liquid discharge (MLD) or zero liquid discharge (ZLD), sustainable brine management can be achieved via appropriate hybrid treatment technologies that provide water reuse, resource recovery, energy recovery and even freshwater production. This paper reviews the state of the art brine treatment technologies targeting MLD/ZLD and resource recovery and highlights their advantages and limitations. The right combination of treatment processes can add a high value to the brine management and shift the focus from removal to recovery and reuse point and help to adopt a more circular economy approach. ZLD technologies targets 100% water recovery using both membrane- and thermal-based technologies, while they are often hindered by high cost and intensive energy requirement. Meanwhile, the recovery of salts and other resources can partially compensate the operation cost of ZLD processes. MLD is a promising option that achieves up to 95% water recovery by using mainly membrane-based technologies. At this point, feasibility assessment is important to assess the environmental and economic sound of technologies. In the second part, we provide a techno-economic assessment of the most common technologies to provide possible benefits on a desalination plant. In the latter sections, innovative brine treatment schemes are discussed aiming MLD/ZLD, while resource recovery from brine and possible valorization routes of the recovered materials are highlighted to help to reduce the overall costs of the plants and to reach the targets of circular economy.

A novel zero-liquid discharge desalination system based on the humidification-dehumidification process: A preliminary study

As a byproduct of desalination plants, brine is increasingly becoming a threat to the environment, and the design of zero-liquid discharge (ZLD) systems is gaining increasing attention. Existing ZLD systems are limited by a high energy intensity and high plant costs of their crystallizers. This study proposes a novel crystallization method based on the humidification-dehumidification (HDH) process, which exhibits the advantages of a low energy consumption, low component costs and a reduced scaling and fouling potential. A simple experimental setup is first designed to demonstrate the feasibility of the proposed system. Brine concentration and salt crystallization are successfully achieved with air heated to 40 °C as the heat source. Afterwards, a thermo-economic analysis is conducted for the whole system. The specific thermal energy and electricity consumption levels are found to range from 700-900 and 5-11 kJ, respectively, per kg of feed brine. The energy consumption is 56% lower than that of a conventional evaporative crystallizer, and the initial plant cost is reduced by 58%.

Cane sugar crystallization using submerged vacuum membrane distillation crystallization (SVMDC)

The performance of Submerged Vacuum Membrane Distillation and Crystallization (SVMDC) for cane sugar concentration and crystallization was investigated in this study. Using hollow fiber membrane, the effect of operation parameters, such as feed concentration, feed temperature, and feed agitation were evaluated against the permeate flux. Following the operation parameters optimization, long-term SVMDC tests were performed using cane sugar model solution and raw sugarcane juice as the feed. Porous fouling layer was formed in test using cane sugar model solution which led to membrane fouling and wetting. However, sugar crystals were successfully formed in this test, despite under-saturated final feed concentration of 73.3°Brix. This indicated the occurrence of heterogeneous crystallization in the feed solution, that was induced by the sugar crystals detached from the membrane surface. In test using raw sugarcane juice as the feed, extremely low flux was observed due to the presence of impurities. However, membrane wetting did not occur as the implication of weak drag force occurred due to the low permeate flux. In this test, there was no observable crystal formed as the final feed concentration was much lower than the saturation concentration. In addition, the impurities hindered the interaction of sucrose molecules and disrupted crystal growth.

Long-Running Comparison of Feed-Water Scaling in Membrane Distillation

Membrane distillation (MD) has shown promise for concentrating a wide variety of brines, but the knowledge is limited on how different brines impact salt scaling, flux decline, and subsequent wetting. Furthermore, past studies have lacked critical details and analysis to enable a physical understanding, including the length of experiments, the inclusion of salt kinetics, impact of antiscalants, and variability between feed-water types. To address this gap, we examined the system performance, water recovery, scale formation, and saturation index of a lab-scale vacuum membrane distillation (VMD) in long-running test runs approaching 200 h. The tests provided a comparison of a variety of relevant feed solutions, including a synthetic seawater reverse osmosis brine with a salinity of 8.0 g/L, tap water, and NaCl, and included an antiscalant. Saturation modeling indicated that calcite and aragonite were the main foulants contributing to permeate flux reduction. The longer operation times than typical studies revealed several insights. First, scaling could reduce permeate flux dramatically, seen here as 49% for the synthetic brine, when reaching a high recovery ratio of 91%. Second, salt crystallization on the membrane surface could have a long-delayed but subsequently significant impact, as the permeate flux experienced a precipitous decline only after 72 h of continuous operation. Several scaling-resistant impacts were observed as well. Although use of an antiscalant did not reduce the decrease in flux, it extended membrane operational time before surface foulants caused membrane wetting. Additionally, numerous calcium, magnesium, and carbonate salts, as well as silica, reached very high saturation indices (>1). Despite this, scaling without wetting was often observed, and scaling was consistently reversible and easily washed. Under heavy scaling conditions, many areas lacked deposits, which enabled continued operation; existing MD performance models lack this effect by assuming uniform layers. This work implies that longer times are needed for MD fouling experiments, and provides further scaling-resistant evidence for MD.

Recent advances in membrane development for treating surfactant- and oil-containing feed streams via membrane distillation

Membrane distillation (MD) has been touted as a promising technology for niche applications such as desalination of surfactant- and oil-containing feed streams. Hitherto, the deployment of conventional hydrophobic MD membranes for such applications is limited and unsatisfactory. This is because the presence of surfactants and oils in aqueous feed streams reduces the surface-tension of these media significantly and the attachment of these contaminants onto hydrophobic membrane surfaces often leads to membrane fouling and pore wetting, which compromises on the quantity and quality of water recovered. Endowing MD membranes with surfaces of special wettabilities has been proposed as a strategy to combat membrane fouling and pore wetting. This involves the design of local kinetic energy barriers such as multilevel re-entrant surface structures, surfaces with ultralow surface-energies, and interfacial hydration layers to impede transition to the fully-wetted Wenzel state. This review critiques the state-of-the-art fabrication and surface-modification methods as well as practices used in the development of omniphobic and Janus MD membranes with specific emphasis on the advances, challenges, and future improvements for application in challenging surfactant- and oil-containing feed streams.

Recovery of water and minerals from shale gas produced water by membrane distillation crystallization

Shale gas produced water (SGPW) treatment imposes greater technical challenges because of its high concentration of various contaminants. Membrane distillation crystallization (MDC) has a great potential to manage SGPW since it is capable of recovering both water and minerals at high rates, up to near a zero liquid discharge (ZLD) condition. To evaluate the feasibility of MDC for SGPW treatment, MDC performance indicators, such as water recovery rate, solid production rate (SPR) and specific energy consumption (SEC), were systematically investigated, to our knowledge for the first time, by using actual SGPW from Eagle Ford Shale (USA). The main operating parameters including feed cross-flow velocity (CFV) and crystallization temperature (T_Cr) were optimized by performing a series of MDC experiments. The results reported that water and minerals were effectively recovered with 84% of recovery rate and 2.72 kg/m²day of SPR under respective optimal operating conditions. Furthermore, the scale mechanism was firstly identified as limiting factor for MDC performance degradation. Lastly, SEC of MDC was estimated to be as low as 28.2 kWh/m³ under ideal optimal operating conditions. Our experimental observations demonstrated that MDC could sustainably and effectively recover water and mineral with low energy consumption from SGPW by optimizing operating condition.

Membrane Distillation of Meat Industry Effluent with Hydrophilic Polyurethane Coated Polytetrafluoroethylene Membranes

Meat rendering operations produce stick water waste which is rich in proteins, fats, and minerals. Membrane distillation (MD) may further recover water and valuable solids, but hydrophobic membranes are contaminated by the fats. Here, commercial hydrophobic polytetrafluorethylene (PTFE) membranes with a hydrophilic polyurethane surface layer (PU-PTFE) are used for the first time for direct contact MD (DCMD) on real poultry, fish, and bovine stick waters. Metal membrane microfiltration (MMF) was also used to capture fats prior to MD. Although the standard hydrophobic PTFE membranes failed rapidly, PU-PTFE membranes effectively processed all stick water samples to colourless permeate with sodium rejections >99%. Initial clean solution fluxes 5–6 L/m²/h declined to less than half during short 40% water recovery tests for all stick water samples. Fish stick water uniquely showed reduced fouling and up to 78% water recovery. Lost flux was easily restored by rinsing the membrane with clean water. MMF prior to MD removed 92% of fats, facilitating superior MD performance. Differences in fouling between stick waters were attributed to temperature polarisation from higher melt temperature fats and relative proportions to proteins. Hydrophilic coated MD membranes are applicable to stick water processing but further studies should consider membrane cleaning and longer-term stability.

Crystallization techniques in wastewater treatment: An overview of applications

As a by-product of industrial or domestic activities, wastewater of different compositions has caused serious environmental problems all over the world. Facing the challenge of wastewater treatment, researchers have begun to make use of crystallization techniques in wastewater treatment. Crystallization techniques have many advantages, such as high efficiency, energy saving, low costs, less space occupation and so on. In recent decades, crystallization is considered as one of promising techniques for wastewater treatment, especially for desalination, water and salt recovery. It has been widely used in engineering applications all over the world. In this paper, various crystallization techniques in wastewater treatment are summarized, mainly including evaporation crystallization, cooling crystallization, reaction crystallization, drowning-out crystallization and membrane distillation crystallization. Overall, they are mainly used for desalination, water and salt recovery. Their applications, advantages and disadvantages were compared and discussed in detail.

Review: Water recovery from brines and salt-saturated solutions: operability and thermodynamic efficiency considerations for desalination technologies

BACKGROUND

When water is recovered from a saline source, a brine concentrate stream is produced. Management of the brine stream can be problematic, particularly in inland regions. An alternative to brine disposal is recovery of water and possibly salts from the concentrate.

RESULTS

This review provides an overview of desalination technologies and discusses the thermodynamic efficiencies and operational issues associated with the various technologies particularly with regard to high salinity streams.

CONCLUSION

Due to the high osmotic pressures of the brine concentrates, reverse osmosis, the most common desalination technology, is impractical. Mechanical vapor compression which, like reverse osmosis, utilizes mechanical work to operate, is reported to have the highest thermodynamic efficiency of the desalination technologies for treatment of salt-saturated brines. Thermally-driven processes, such as flash evaporation and distillation, are technically able to process saturated salt solutions, but suffer from low thermodynamic efficiencies. This inefficiency could be offset if an inexpensive source of waste or renewable heat could be used. Overarching issues posed by high salinity solutions include corrosion and the formation of scales/precipitates. These issues limit the materials, conditions, and unit operation designs that can be used.

Thermodynamic modelling of a membrane distillation crystallisation process for the treatment of mining wastewater

Membrane distillation (MD) could be applicable in zero liquid discharge applications. This is due to the fact that MD is applicable at high salinity ranges which are generally outside the scope of reverse osmosis (RO) applications, although this requires proper management of precipitating salts to avoid membrane fouling. One way of managing these salts is with MD crystallisation (MDC). This paper focuses on the applicability of MDC for the treatment of mining wastewater by thermodynamically modelling the aqueous chemistry of the process at different temperatures. The paper is based on the typical brine generated from an RO process in the South African coal mining industry and investigates the effect water recovery and operating temperature have on the salts that are predicted to crystallise out, the sequence in which they will crystallise out and purities as a function of the water recovery. The study confirmed the efficacy of using thermodynamic modelling as a tool for investigating and predicting the crystallisation aspects of the MDC process. The key finding from this work was that, for an MDC process, a purer product can be obtained at higher operating temperatures and recoveries because of the inverse solubility of calcium sulphate.

A pervaporation study of ammonia solutions using molecular sieve silica membranes

An innovative concept is proposed to recover ammonia from industrial wastewater using a molecular sieve silica membrane in pervaporation (PV), benchmarked against vacuum membrane distillation (VMD). Cobalt and iron doped molecular sieve silica-based ceramic membranes were evaluated based on the ammonia concentration factor downstream and long-term performance. A modified low-temperature membrane evaluation system was utilized, featuring the ability to capture and measure ammonia in the permeate. It was found that the silica membrane with confirmed molecular sieving features had higher water selectivity over ammonia. This was due to a size selectivity mechanism that favoured water, but blocked ammonia. However, a cobalt doped silica membrane previously treated with high temperature water solutions demonstrated extraordinary preference towards ammonia by achieving up to a 50,000 mg/L ammonia concentration (a reusable concentration level) measured in the permeate when fed with 800 mg/L of ammonia solution. This exceeded the concentration factor expected by the benchmark VMD process by four-fold, suspected to be due to the competitive adsorption of ammonia over water into the silica structure with pores now large enough to accommodate ammonia. However, this membrane showed a gradual decline in selectivity, suspected to be due to the degradation of the silica material/pore structure after several hours of operation.