Lee, D, Woo, YC, Park, KH, Phuntsho, S, Tijing, LD, Yao, M, Shim, WG & Shon, HK 2020, 'Polyvinylidene fluoride phase design by two-dimensional boron nitride enables enhanced performance and stability for seawater desalination', Journal of Membrane Science, vol. 598.View/Download from: Publisher's site
© 2019 The instability of polyvinylidene fluoride (PVDF) membranes in membrane distillation (MD) for seawater desalination is still a problem, despite the tremendous effort expended to resolve this issue. Here, a simple and feasible approach for improving desalination performance through the incorporation of two-dimensional boron nitride nanosheets (BNNSs) in polyvinylidene fluoride-co-hexafluoropropene (PVDF-co-HFP) electrospun nanofiber membrane (BNs-PH) is proposed as well as demonstrate its origin for fundamental understanding. The BNs-PH membrane exhibits a stable water vapor flux (18 LMH) and superior salt rejection (99.99%), even after operation for 280 h (commercial PVDF: steep decay within 28 h; neat PH: wetting within 4 h). From structural/chemical analyses, the BNNSs play a crucial role in forming favorable phases of the PH polymer crystal structure, inducing a superhydrophobic surface with greater nanoporosity and higher heterogeneity as well as enhanced mechanical properties (increase of UTS: 13.4%; modulus: 1.2%) for long-term operation. Theoretical modeling results of an air-gap MD system are consistent with our experimental results. The approach introduced in this study can be applied to other desalination systems to boost various water treatment applications.
Yao, M, Tijing, LD, Naidu, G, Kim, S-H, Matsuyama, H, Fane, AG & Shon, HK 2020, 'A review of membrane wettability for the treatment of saline water deploying membrane distillation', DESALINATION, vol. 479.View/Download from: Publisher's site
Ren, J, Woo, YC, Yao, M, Lim, S, Tijing, LD & Shon, HK 2019, 'Nanoscale zero-valent iron (nZVI) immobilization onto graphene oxide (GO)-incorporated electrospun polyvinylidene fluoride (PVDF) nanofiber membrane for groundwater remediation via gravity-driven membrane filtration.', The Science of the total environment, vol. 688, pp. 787-796.View/Download from: Publisher's site
Nanoscale zero-valent iron (nZVI), with its high reactivity towards a broad range of contaminants, has been a promising material for groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI to lower the risk of secondary pollution. In this study, we successfully fabricated a PVDF-GO membrane via electrospinning technology and employed the functionalized nanofiber membrane to immobilize nZVI particles. The addition of GO into PVDF nanofibers can both increase the hydrophilicity to improve membrane flux and offer -COOH as a binder to immobilize nZVI particles. PVDF-GO-nZVI membranes with different GO loadings (0%, 0.5%, 1%, 3% of PVDF) were tested with two typical nZVI-targeted contaminants (Cd(II) and trichloroethylene (TCE)) via gravity-driven membrane filtration. The results show that membrane with 1% GO had the best nZVI distribution against the aggregation and a better performance in both Cd removal (100%) and TCE removal (82%). The nZVI membrane had a high flux in gravity-driven filtration at 255 LMH for Cd(II) and 265 LMH for TCE respectively. Generally, the developed PVDF-GO-nZVI electrospun nanofiber membrane had an excellent performance in the gravity-driven membrane filtration system for groundwater remediation.
Ren, J, Yao, M, Woo, YC, Tijing, LD, Kim, J-H & Shon, HK 2019, 'Recyclable nanoscale zerovalent iron (nZVI)-immobilized electrospun nanofiber composites with improved mechanical strength for groundwater remediation', COMPOSITES PART B-ENGINEERING, vol. 171, pp. 339-346.View/Download from: Publisher's site
Yao, M, Ren, J, Akther, N, Woo, YC, Tijing, LD, Kim, S-H & Shon, HK 2019, 'Improving membrane distillation performance: Morphology optimization of hollow fiber membranes with selected non-solvent in dope solution', CHEMOSPHERE, vol. 230, pp. 117-126.View/Download from: Publisher's site
Yao, M, Woo, YC, Ren, J, Tijing, LD, Choi, J-S, Kim, S-H & Shon, HK 2019, 'Volatile fatty acids and biogas recovery using thermophilic anaerobic membrane distillation bioreactor for wastewater reclamation.', Journal of environmental management, vol. 231, pp. 833-842.View/Download from: Publisher's site
The effects of bioreactor temperatures and salinities of an anaerobic membrane distillation bioreactor (anMDBR) on the permeation performance and their potential recovery of bioresources were fully examined in this study. To the best of our knowledge, this is the first study of a lab-scale anMDBR process utilizing sub-merged hollow fiber membranes. The hybrid system utilizing both membrane distillation (MD) and anaerobic bioreactors achieved 99.99% inorganic salt rejection regardless the operation temperatures and high initial flux from (2-4 L m-2 h-1) at 45-65 °C. However, after 7-day operation, the flux dropped by 16-50% proportional to the bioreactor temperatures. It was found that the effects of bioreactor temperatures had strong impacts on both the permeation performance and fouling behavior while salinity had insignificant effect. A compact non-porous fouling layer was observed on the membrane surface from the bioreactor operated at 65 °C while only a few depositions was found on the membrane from 45 °C bioreactor. In the present study, the optimal anMDBR temperature was found to be 45 °C, showing a balanced biogas production and membrane permeation performance including less fouling formation. At this bioreactor temperature (45 °C), the biogas yield was 0.14 L/g CODremoval, while maintaining a methane recovery of 42% in the biogas, similar recovery to those at bioreactor temperatures of 55 and 65 °C. The potential recovery of volatile fatty acids made anMDBR a more economically efficient system, in addition to its lower operation cost and smaller footprint compared with most other technologies for on-site wastewater treatment.
Woo, YC, Kim, Y, Yao, M, Tijing, LD, Cho, J-S, Lee, S, Kim, S-H & Shon, HK 2018, 'Hierarchical Composite Membranes with Robust Omniphobic Surface Using Layer-By-Layer Assembly Technique', ENVIRONMENTAL SCIENCE & TECHNOLOGY, vol. 52, no. 4, pp. 2186-2196.View/Download from: Publisher's site
Yao, M, Woo, YC, Tijing, LD, Choi, JS & Shon, HK 2018, 'Effects of volatile organic compounds on water recovery from produced water via vacuum membrane distillation', Desalination, vol. 440, pp. 146-155.View/Download from: Publisher's site
© 2017 Elsevier B.V. Membrane distillation (MD) has great potentials to treat produced water in energy industries. However, volatile organic compounds (VOCs) existing in the produced water added in the fracking process can hinder the treatment process regarding two aspects: permeate quality and MD flux performance. To address this challenge, this study aims to systematically study the effects of the VOCs on the MD permeation performance and permeate quality, and the mechanism of its penetration. Acetic acid, ethylene glycol, isopropyl alcohol (IPA), and 2-Butoxyethanol (2-BE), which are commonly found in the produced water, were extensively investigated and their impacts were reviewed and compared. Among all the VOCs, 2-BE had the highest mass transfer despite its low vapour pressure and large molecule weight. Some of the VOCs had surfactant properties, which meant they could penetrate the membrane pores easily during MD process. In long-term operation, pore wetting started to appear as the salt rejection was dropping in the MD process, and flux was also decreasing. Based on the results, this study suggested that the strength of surfactant properties and intra-molecular hydrogen bonds between water molecules and VOCs are as significant as vapour pressure for the VOCs in terms of mass transfer efficiency in MD system.
Ren, J, Woo, YC, Yao, M, Tijing, LD & Shon, HK 2017, 'Enhancement of nanoscale zero-valent iron immobilization onto electrospun polymeric nanofiber mats for groundwater remediation', Process Safety and Environmental Protection, vol. 112, no. Part B, pp. 200-208.View/Download from: Publisher's site
© 2017 Institution of Chemical Engineers A new approach that combines nanoscale zero-valent iron (nZVI) with electrospinning technology has been put forward to avoid nZVI agglomeration and a secondary pollution. In this study, to enhance the immobilization of nZVI particles onto the polyacrylic acid (PAA)/polyvinyl alcohol (PVA) electrospun nanofiber mat, mats (M1, M2 and M3) with different PAA/PVA mass ratios (1:1, 2:1 and 3:1) were tested for the immobilization of nZVI particles and their performance of removing contaminants. The results indicate that M3 immobilized the most nZVI particles (48.4 wt% on the mat, ∼2.5 times the figure for previous study) and had the highest removals to methylene blue and Cu(II) ions at 94% and 83.6% respectively, resulting from more free carboxylic groups available on the cross-linked nanofibers as well as a higher porosity into the mat. Therefore, increasing the PAA/PVA ratio is effective to boost the performance of nZVI–PAA/PVA electrospun nanofiber mat, which has a great potential for the application of nZVI-targeted contaminants remediation.
Woo, YC, Tijing, LD, Park, MJ, Yao, M, Choi, JS, Lee, S, Kim, SH, An, KJ & Shon, HK 2017, 'Electrospun dual-layer nonwoven membrane for desalination by air gap membrane distillation', Desalination, vol. 403, pp. 187-198.View/Download from: Publisher's site
© 2015 Elsevier B.V. In the present study, dual-layer nanofiber nonwoven membranes were prepared by a facile electrospinning technique and applied for desalination by air gap membrane distillation (AGMD). Neat single and dual-layer nanofiber membranes composed of a hydrophobic polyvinylidene fluoride-co-hexafluoropropylene (PH) top layer with different supporting hydrophilic layer made of either polyvinyl alcohol (PVA), nylon-6 (N6), or polyacrylonitrile (PAN) nanofibers were fabricated with and without heat-press post-treatment. Surface characterization showed that the active layer (i.e., PH) of all electrospun nanofiber membranes (ENMs) exhibited a rough, highly porous (>80% porosity), and hydrophobic surface (CA>140°), while the other side was hydrophilic (CA<90°) with varying porosity. Heat-pressing the membrane resulted to thinner thickness (from >129μm to <100μm) and smaller pore sizes (<0.27μm). The AGMD experiments in a co-current flow set-up were carried out with constant inlet temperatures at the feed and permeate streams of 60±1.5 and 20±1.5°C, respectively. The AGMD module had a membrane area of 21cm2 and the thickness of the air gap was 3mm. The neat single and dual-layer ENMs showed a water permeate flux of about 10.9-15.5L/m2 h (LMH) using 3.5wt.% NaCl solution as feed, which was much higher than that of a commercial PVDF membrane (~5LMH). The provision of a hydrophilic layer at the bottom layer enhanced the AGMD performance depending on the wettability and characteristics of the support layer. The PH/N6 dual-layer nanofiber membrane prepared under the optimum condition showed flux and salt rejection of 15.5LMH and 99.2%, respectively, which has good potential for AGMD application.
Yao, M, Woo, YC, Tijing, LD, Cesarini, C & Shon, HK 2017, 'Improving nanofiber membrane characteristics and membrane distillation performance of heat-pressed membranes via annealing post-treatment', Applied Sciences, vol. 7, no. 1, pp. 1-11.View/Download from: Publisher's site
© 2017 by the authors. Electrospun membranes are gaining interest for use in membrane distillation (MD) dueto their high porosity and interconnected pore structure however, they are still susceptible towetting during MD operation because of their relatively low liquid entry pressure (LEP). In thisstudy, post-treatment had been applied to improve the LEP, as well as its permeation and saltrejection efficiency. The post-treatment included two continuous procedures: heat-pressing andannealing. In this study, annealing was applied on the membranes that had been heat-pressed.It was found that annealing improved the MD performance as the average flux reached 35 L/m 2 hor LMH ( > 10% improvement of the ones without annealing) while still maintaining 99.99% saltrejection. Further tests on LEP, contact angle, and pore size distribution explain the improvementdue to annealing well. Fourier transform infrared spectroscopy and X-ray diffraction analysesof the membranes showed that there was an increase in the crystallinity of the polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) membrane also, peaks indicating the α phase ofpolyvinylidene fluoride (PVDF) became noticeable after annealing, indicating some βand amorphousstates of polymer were converted into the α phase. The changes were favorable for membranedistillation as the non-polar α phase of PVDF reduces the dipolar attraction force between themembrane and water molecules, and the increase in crystallinity would result in higher thermalstability. The present results indicate the positive effect of the heat-press followed by an annealingpost-treatment on the membrane characteristics and MD performance.
Woo, YC, Kim, Y, Shim, W-G, Tijing, LD, Yao, M, Nghiem, LD, Choi, J-S, Kim, S-H & Shon, HK 2016, 'Graphene/PVDF flat-sheet membrane for the treatment of RO brine from coal seam gas produced water by air gap membrane distillation', JOURNAL OF MEMBRANE SCIENCE, vol. 513, pp. 74-84.View/Download from: Publisher's site
Woo, YC, Lee, JJ, Shim, W-G, Shon, HK, Tijing, LD, Yao, M & Kim, H-S 2016, 'Effect of powdered activated carbon on integrated submerged membrane bioreactor-nanofiltration process for wastewater reclamation', BIORESOURCE TECHNOLOGY, vol. 210, pp. 18-25.View/Download from: Publisher's site
Yao, M, Woo, YC, Tijing, L, Shim, WG, Choi, JS, Kim, SH & Shon, HK 2016, 'Effect of heat-press conditions on electrospun membranes for desalination by direct contact membrane distillation', Desalination, vol. 378, pp. 80-91.View/Download from: Publisher's site
Membrane distillation (MD) is considered as a promising next-generation technology for desalination. However, there is no specific membrane designed and engineered for this application yet. Recently, electrospun polymeric membranes have been widely investigated due to their relatively high porosity, high hydrophobicity and controllable pore size. However, the robustness of such membranes is not guaranteed as they are susceptible to wetting in long-term operation. Heat-press treatment is a simple and effective procedure to improve both morphological and mechanical characteristics of the electrospun membrane. Nevertheless, the heat-press technique is not fully investigated although some conditions are applied to the electrospun membrane in previous researches. In this paper, a comprehensive investigation of the effect of heat-press temperature, pressure and duration on the morphological and mechanical characteristics of electrospun membrane is accomplished. Impressive improvement of mechanical strength and liquid entry pressure (LEP) can be achieved after heat-press treatment on the electrospun membranes. It is also found that temperature and duration play more important roles than pressure in heat-press treatment. In addition, it is ascertained that optimal treatment conditions for heat-press includes temperature at 150 °C, pressure at 6.5 kPa, and duration for 8 h for the present electrospun polyvinylidene fluoride-co-hexafluoropropylene membrane. A decent DCMD permeation flux of 29 LMH and salt rejection of 99.99% can be achieved with the optimally heat-pressed electrospun membranes for desalination at feed and permeate temperatures of 60 and 20 °C, respectively.
Woo, YC, Lee, JJ, Tijing, LD, Shon, HK, Yao, M & Kim, H-S 2015, 'Characteristics of membrane fouling by consecutive chemical cleaning in pressurized ultrafiltration as pre-treatment of seawater desalination', DESALINATION, vol. 369, pp. 51-61.View/Download from: Publisher's site
Tijing, L, Yao, M, Ren, J, Park, C-H, Kim, CS & Shon, H 2019, 'Nanofibers for Water and Wastewater Treatment: Recent Advances and Developments' in Bui, X-T, Chiemchaisri, C, Fujioka, T & Varjani, S (eds), Water and Wastewater Technologies, Springer, Singapore, pp. 431-468.
Woo, YC, Yao, M, Tijing, LD, Lee, S-E & Shon, HK 2018, 'Recent Progress in the Fabrication of Electrospun Nanofiber Membranes for Membrane Distillation' in Advanced Materials for Membrane Fabrication and Modification, CRC Press, pp. 71-100.View/Download from: Publisher's site