Anqi, Ali E.; Usta, Mustafa; Krysko, Robert; Lee, Jung Gil; Ghaffour, NorEddine; Oztekin, Alparslan(Journal of Membrane Science, Elsevier BV, 2019-10-25)[Article]
The performance of vacuum membrane distillation (VMD) modules can be optimized through careful selection of design parameters. The present study examines how the addition of cylindrical filaments in the feed channel increases momentum mixing and the overall performance of VMD modules under different operating inlet conditions. Three-dimensional transient Computational Fluid Dynamics (CFD) simulations are conducted using Wall-Adapting Local Eddy-Viscosity (WALE) subgrid-scale Large Eddy Simulation (LES) turbulence model. Local concentration, temperature, and flux are coupled at the membrane surface to predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanisms. The predicted and measured vapor flux agrees reasonably well; validating the employed model. The small-scale eddies induced by the presence of spacer filaments promote mixing in the module, thus the temperature and concentration polarization is alleviated and the water vapor flux is immensely improved. The insertions of filaments in the feed channel increase the water permeate rate by more than 50% at higher feed flow rates and inlet temperatures. The pressure drop by the spacer reduces the allowable module length by one order of magnitude, but the module length increases two folds at feed temperature 80℃. Even though the power consumption of the module containing the filaments is increased, the addition of filaments is strongly recommended since the required power for the process could be supplied from readily available low-grade heat source.
Rehman, Zahid Ur; Fortunato, Luca; Cheng, Tuoyuan; Leiknes, TorOve(Science of The Total Environment, Elsevier BV, 2019-10-24)[Article]
Biofilm formation on membranes in activated sludge membrane bioreactors (MBR), commonly identified as biofouling, is a significant problem for MBR operations. A better understanding of microbial species involved in the biofilm formation is needed to develop anti-biofilm measures. A read-based and genome-resolved shotgun metagenomic approach was applied to characterize the composition and functional potential of the sludge and early stage biofilm microbial communities in an MBR process. Read-based analysis revealed that the prevalence of different phyla are relatively similar in both the sludge and biofilm samples, with Proteobacteria as the most dominant, followed by Chloroflexi, Bacteroidetes and Planctomycetes. However, the relative abundance of these phyla slightly varies between the sludge and biofilm. Phyla such as Actinobacteria, bacterial candidate phyla, Chlamydiae, Cyanobacteria/Melainabacteria and Firmicutes are 2 to 4 times more abundant in the biofilm than in the sludge. At the genus level, genera belonging to Proteobacteria (Legionella, Caulobacter, Sphingomonas, Acinetobacter and Rhizobium), Cyanobacteria (Hassallia), and Spirochaetes (Turneriella) are at least twice more abundant in the biofilm. These genera, especially those belonging to Phylum Proteobacteria, are known to play an important role in the formation of biofilms on surfaces. The Alpha diversity is found slightly higher in the biofilm, compared with sludge samples. Functional classification of reads through the SEED subsystem shows that functional classes such as those involved in the metabolism of various molecules are significantly different in the biofilm and sludge.
A phylogenomic analysis of the six extracted metagenome assembled genomes (MAGs) shows that three MAGs belong to Proteobacteria, and one MAG belong to each of Chloroflexi, Bacteroidetes and Planctomycetes. The relative abundance of the MAG belonging to Alphaproteobacteria is higher in the biofilm. A functional potential analysis of the MAGs reveals their potential to metabolize carbon and nitrogen sources, as well as the prevalence of antibiotic resistance genes.
Obaid, M.; Ghaffour, NorEddine; Wang, Sungrok; Yoon, Myung-Han; Kim, In S.(Separation and Purification Technology, Elsevier BV, 2019-10-21)[Article]
Enhancing the properties and structure of the ultrafiltration (UF) membrane via rational manipulation is important to optimize their perm-selectivity performance. To overcome the permeance-selectivity trade-off of nanocomposite membranes, Zirconium dioxide nanofibers (ZrO2 NFs) was synthesized in nano-micro size and then incorporated into the polysulfone (PSf) membrane. The effect of different concentrations of ZrO2 NFs on the membrane properties and performance were investigated. Compared to the pristine PSf membrane, the nanocomposite membranes exhibited a remarkable enhancement in the physiochemical properties, mechanical properties, and the overall performance. The results showed that the nanocomposite membrane (M3, 0.5% ZrO2 NFs) possesses the highest flexibility and tensile strength (43% higher than the pristine PSf). The enhancement of the wettability and enlarge the pore size (2.6 times increase) of this nanocomposite membrane, resulting in a remarkably heightened the pure water permeability (Jw1; 255.8 L m−2 h−1 bar−1). As a result, it achieved the highest permeability during the filtration of BSA solution with no decline in the BSA rejection. Furthermore, compared to the pristine PSf membrane, all nanocomposite membranes exhibited higher mechanical properties.
This novel strategy of incorporating the nanofibers, instead of nanoparticles, offers significant opportunities to exploit the various inorganic nanofibers in the fabrication of diverse nanocomposite membrane types.
Obaid, M.; Abdelkareem, Mohammad Ali; Kook, Seungho; Kim, Hak-Yong; Hilal, Nidal; Ghaffour, NorEddine; Kim, In S.(Critical Reviews in Environmental Science and Technology, Informa UK Limited, 2019-10-16)[Article]
Research on membrane technology to provide fresh water while considering inextricably linked energy issues has resulted in remarkable accomplishments in the production of membranes, such as thin film composite (TFC) membranes, for relatively low-energy desalination and wastewater reclamation via the forward osmosis (FO) process. Exhaustive and continuous efforts in the enlargement of TFC membranes to achieve an excellent combination of flux and selectivity have revealed a considerable need to fabricate an appropriate substrate. Electrospinning, as a cheap, scalable, and simple technique, is capable of producing electrospun mats with distinctive features. These features make electrospun nanofibers (ENs) a promising substrate for TFC-FO membranes, resulting in tremendous achievements in enhancing membrane performance. Since 2011, rapid progress has been made in applying electrospinning to fabricate ENs substrates for TFC-FO membranes. This paper reviews progress in the fabrication and modification of TFC membranes supported by ENs substrates for FO applications. The theoretical background of FO, discussing the main problems associated with the use of conventional substrates, progress in applying electrospinning to overcome these problems, including breakthrough achievements in ENs substrates for FO, the synthesis and characterization of such substrates, and a comparison of energy consumption between FO and other desalination techniques were covered.
Air Gap Membrane distillation (AGMD) is a thermally driven separation process capable of treating challenging water types, but its low productivity is a major drawback. Membrane fouling is a common problem in many membrane treatment systems, which exacerbates AGMD’s low overall productivity. In this study, we investigated the direct application of low-power ultrasound (8–23 W), as an in-line cleaning and performance boosting technique for AGMD. Two different highly saline feedwaters, namely natural groundwater (3970 μS/cm) and RO reject stream water (12760 μS/cm) were treated using Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes. Theoretical calculations and experimental investigations are presented, showing that the applied ultrasonic power range only produced acoustic streaming effects that enhanced cleaning and mass transfer. Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that ultrasound was capable of effectively removing silica and calcium scaling. Ultrasound application on a fouled membrane resulted in a 100% increase in the permeate flux. Cleaning effects accounted for around 30–50% of this increase and the remainder was attributed to mass transfer improvements. Contaminant rejection percentages were consistently high for all treatments (>99%), indicating that ultrasound did not deteriorate the membrane structure. Scanning Electron Microscopy (SEM) analysis of the membrane surface was used to confirm this observation. The images of the membrane surface demonstrated that ultrasound successfully cleaned the previously fouled membrane, with no signs of structural damage. The results of this study highlight the efficient and effective application of direct low power ultrasound for improving AGMD performance.
Alkali-metal ions, particularly sodium (Na+) and potassium (K+), are the messengers of living cells, governing a cascade of physiological processes through the action of ion channels. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery, but also to detect conditions in the human body that lead to electrolyte imbalance. In this work, conducting polymers are developed that respond rapidly and selectively to varying concentrations of Na+ and K+ in aqueous media. These polymer films, bearing crown-ether-functionalized thiophene units specific to either Na+ or K+, generate an electrical output proportional to the cation type and concentration. Using electropolymerization, the ion-selective polymers are integrated as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changes with respect to the concentration of the ion to which the polymer electrode is selective. Designed as a single, miniaturized chip, the OECT enables the selective detection of the cations within a physiologically relevant range. These electrochemical ion sensors require neither ion-selective membranes nor a reference electrode to operate and have the potential to surpass existing technologies for the detection of alkali-metal ions in aqueous media.
Singh, Yogesh Balwant; Ng, Kim Choon(Journal of Petroleum Science and Engineering, Elsevier B.V., 2019-08-16)[Article]
Scale deposition in the thermal process for desalination is quite inevitable. This study is about scale formation, crystal modification, and prevention mechanism of a tetrapolymer based antiscalant on Red Seawater. Red seawater at concentration factors (CF) of 1.5 and 2.5 was studied under reflux condition at 70 °C and 98 °C respectively for seven hours with 1 ppm, 2 ppm, and 4 ppm concentration of the antiscalant. Eventually, the mechanism of inhibitory action of the antiscalant has been reconnoitered after seawater analysis and imaging the morphological changes in the crystal formation patterns with Scanning electron microscope (SEM). The changes in the values of pH, turbidity and alkalinity (both phenolphthalein alkalinity (PA) and total alkalinity (TA)) were measured to apprehend various fluctuations happening as a result of the addition of antiscalant. The variations in the pH of seawater with antiscalant were in concurrence with the changes in alkalinity and was also reflected in turbidity. These changes explicitly demonstrated the threshold mechanism of scale inhibition. SEM micrographs exhibited distorted round shaped depositions supporting crystal modification mechanism as well. The efficiency and dominance of inhibitory mechanism varied from 2 h to 6 h for the antiscalant and was observed to be directly related to CF of seawater used, the temperature applied, and a dose of antiscalant added.
With an ever-increasing demand in energy, constrained by strict environmental regulations, process development faces stringent design requirements further limited by intrinsic properties of inherent materials. Process hybridization is now considered as an improvement path to several limitations. Complementarity between processes is the essence of the hybridization concept, with the ultimate goal to design more eco-friendly, energy efficient process combinations delivering higher throughputs and boosting the thermodynamic limits of the existing mature technologies. Market size of membrane-based separation processes, widely used in desalination, water treatment and purification, is forecasted to grow significantly in the next decades. While desalination market is mainly shared between thermal processes and reverse osmosis (RO), advanced water treatment and purification rely mostly on membrane technology. Among the large span of available techniques stands membrane distillation (MD), to which a tremendous research effort has been dedicated during the last two decades. Although praised for its numerous advantages, this thermally-driven separation process still cannot withstand large production rates while maintaining energy efficiency. Hybridization of MD with existing technologies and other emerging processes is therefore at the leading edge. This literature review presents the state-of-the-art MD hybrids with different separation processes including RO, pressure retarded osmosis, forward osmosis, mechanical vapor compression, electrocoagulation, electrodialysis, multi-stage flash, multi-effect distillation, crystallization and adsorption with a focus on water production and energy efficiency enhancement. Each of these processes has advantages at the cost of more or less severe drawbacks and its association to MD offers improvement opportunities. Each variant is thoroughly reviewed with major contributions and knowledge gaps highlighted. Perspectives and recommendations are emphasized in each case. Latest developments in MD and its energy consumption and optimization are also reported.
Low pressure membranes, such as ultrafiltration (UF), are widely used in water treatment applications, including the pretreatment of reverse osmosis desalination. UF membranes produce a water of superior quality, in addition to reducing the footprint and the use of chemicals, compared to conventional methods. However, membrane fouling remains a major drawback, and frequent membrane cleanings are required to maintain the flux of water and its quality. Typically, after a series of backwashes using an UF permeate, a chemical cleaning process is applied to fully recover the membrane's permeability. However, frequent chemical cleanings negatively affect the lifetime of the membrane, the environment, and increase operational costs. Here, we introduce a novel cleaning method that uses a solution saturated with CO2 to clean the membranes through the backwash step. As the pressure drops, the CO2 solution becomes supersaturated, and bubbles start to nucleate within the membrane pores and on its surface, resulting in the effective removal of the deposited fouling material. These foulants are further helping the nucleation process as they are considered as imperfection sites with high creation and growth of bubbles. Investigations performed for different synthetic feed solutions of organic compounds (sodium alginate), colloidal matter (silica) and sea salts, at different concentrations, show that our new physical cleaning process using CO2 is more performant than the regular backwash using Milli-Q water. We obtain a 100% flux recovery, in a short time, even under severe irreversible fouling conditions. Based on these results, we conclude that replacing water by a solution saturated with CO2 for the backwash cleaning of filtration membranes provides significant benefits to existing cleaning processes, and represent a promising alternative for improving and lowering the frequency of conventional chemical cleaning methods.
Forward osmosis (FO) is considered as an energy-efficient process for numerous applications. Although its performance is determined by the spatially varied operation factors and the length of the channel, most of the reported simulation studies rely on length-averaged lumped models. Here, we introduce a one-D model based on heat and mass transfer and transport behavior for both bulk draw and feed channel flows. We find prediction results to be in good agreement with two different experimental results at inlet feed temperatures below 25 °C. However, the difference of water flux (Jw) and reverse salt flux (RSF) between measured and predicted data increases when both feed and draw temperatures also increase. Our theoretical simulation study first reveals that the feed temperature near the membrane active layer surface is the main factor for improving water and salt permeabilities. We find that, with a channel width of 0.3 m and a channel length of 2.5 m, Jw and RSF calculated using the length-averaged based lumped model are overestimated by 13.01% and 13.12%, respectively, compared to those obtained using our new spatial variation model. Our study demonstrates that the length-averaged based lumped model is not an appropriate simulation model to predict the performance of large-scale FO modules at lower inlet velocities.
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