A.G. Fane

Nanyang Technological University, Tumasik, Singapore

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Publications (245)731.71 Total impact

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    ABSTRACT: The development of a side-stream reverse osmosis cell, called the ‘canary cell’, to simulate the spiral wound module (SWM) is described. Representative fouling rates and ex-situ membrane autopsies show the capability of the canary cell to simulate the SWM under controlled hydrodynamics and flux conditions. The development of a dimensionless calibration curve allows the canary cell to act as an early warning system with respect to the SWM. The rate of cake thickness increase was also measured by ultrasonic time domain reflectometry coupled to the canary cell and used to monitor membrane fouling and cleaning. For Access, please click on this link. http://authors.elsevier.com/a/1R4JJ2jQ1hkVX
    Desalination 04/2015; 368. DOI:10.1016/j.desal.2015.04.014 · 3.96 Impact Factor
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    ABSTRACT: In this study an on-line feed fouling monitor (FFM) combined with a salt-tracer-response technique (STRT) was used to predict reverse osmosis (RO) fouling under constant flux filtration. The FFM was used to capture foulant loads using a small ‘collection’ ultrafiltration (UF) membrane at the same crossflow hydrodynamics as in the RO experiments. A UF membrane was used in the FFM to decrease the monitoring time and improve the accuracy because it is more responsive to the fouling resistance than an RO membrane. Since the deposits captured by the FFM are potential RO foulants, the resulting information can be used to predict the transmembrane pressure (TMP) rise for the RO membrane. The STRT was used to measure the development of concentration polarization that is important in estimating the cake-enhanced osmotic pressure (CEOP) contribution. A model was developed that includes both the cake resistance and the CEOP effect due to cake formation and was used to predict RO fouling trends. Model foulants were humic acid and colloidal silica. The major focus was on organic fouling by humic acid (20 mg/l) in 2000 mg/l sodium chloride (NaCl) as the ionic background for the RO and FFM fouling experiments. The RO and FFM fouling experiments were conducted at different constant fluxes using the same feed solutions and at the same crossflow velocity (0.1 m/s). The results indicated that higher fluxes cause an increased fouling rate for both RO and the FFM for both types of solute. The CEOP effect, measured by the salt-tracer-response in the RO experiments, was also strongly enhanced by the flux. The model was validated by plotting the predicted RO transmembrane pressure (TMP) as a function of time for different fluxes based on the resistivity from the FFM and the CP obtained from the STRT. For both organic foulants and colloidal silica the results show that the combination of the FFM and salt-tracer-response STRT is a promising method to provide a good estimate of the RO fouling trends. It also underscores the contribution of CEOP to the increase in TMP during RO fouling of saline feeds.
    Journal of Membrane Science 02/2015; 475:433-444. DOI:10.1016/j.memsci.2014.10.043 · 4.91 Impact Factor
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    ABSTRACT: Pore-size distribution determined by evapoporometry of unfouled (dark-shaded) and fouled (light-shaded) polyvinylidine fluoride (PVDF) hollow fiber membranes; fouling involved a constant flux of 70 l/m2 h, concentration of l.0 g/l of bentonite and 20 mg/l of humic acid, and employed a cycle consisting of 15 min of filtration followed by 2 min of backwashing during which the aeration rate was 0.0011 m/s; fouled membranes were observed after the 9th cycle; fouling is seen to cause a marked shift in the pore-size distribution towards smaller pores and a decrease in the average pore diameter from 34.6 nm to 22.5 nm owing to internal pore fouling.
    Journal of Membrane Science 11/2014; 470:334–345. DOI:10.1016/j.memsci.2014.07.042 · 4.91 Impact Factor
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    ABSTRACT: Biofilm development in a spacer-filled reverse osmosis membrane channel can influence both trans-membrane pressure (TMP) and channel pressure drop (ΔPCH). While current pretreatment methods are unable to completely tackle the biofouling problem, more insights are required to provide strategies to minimize the problem. This study examined the role of operating parameters (i.e. flux and crossflow velocity) to minimize biofouling in RO processes. The experiments were conducted with a lab-scale high pressure flat sheet RO reactor where changes in pressure drop along the channel and across the membrane were measured. The impact of biofouling was measured at constant fluxes, where the TMP rise and ΔPCH rise and the biofoulant was quantified as biovolumes of live and dead bacteria on autopsied membrane and spacer samples by confocal laser scanning microscopy (CLSM). The results show that TMP rise increased exponentially with increasing flux, and decreased with increasing crossflow velocity. The channel pressure drop, ΔPCH, increased when either flux or crossflow velocity was increased, and was more dependent on crossflow. The biofoulant volume on the membrane increased with flux and was less dependent on crossflow. The biofoulant associated with the spacer was much less than on the membrane and relatively insensitive to flux or crossflow velocity. The TMP rise could be correlated with the estimated concentration of nutrient at the membrane surface, Cw,N, highlighting the combined roles of flux and crossflow velocity in solute concentration polarization. Previous TMP rise data could also be correlated to the estimated Cw,N values. This observation suggests a biofouling mitigation strategy by controlling both incoming nutrient concentration and operating conditions (flux and crossflow).
    Journal of Membrane Science 10/2014; 467:116–125. DOI:10.1016/j.memsci.2014.04.052 · 4.91 Impact Factor
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    ABSTRACT: Microfiltration (MF) and ultrafiltration (UF) involving colloidal suspensions are often involved in separations, concentration and clarification processes in the food and beverage as well as other industries. The increase in concentration near the membrane surface owing to concentration polarization can cause some part of a colloidal fouling layer to become metastable whereby it can undero a higher order phase transition to a more dense gel. This was confirmed via deadend filtration studies wherein the fouling layer thickness obtained from the transmembrane pressure (TMP) was compared with that determined directly via ultrasonic time-domain reflectometry (UTDR). Whereas entering this metastable state is thermodynamically driven, the transition from a colloidal suspension to a more dense gel is a rate or kinetically driven process. This phase transition is manifest by a marked rate of increase in the TMP that occurs after an filtration time that is dependent on the flux. A ‘threshold transition flux’ is identified below which the time required for the phase transition can be considerably delayed. Since removing this dense gel layer via conventional cleaning protocols is more difficult, determining an operating strategy whereby this transition to a more dense gel can be delayed is clearly of interest for the optimal operation of MF and UF processes. To this end the effects of crossflow velocity, flux, salinity and colloidal silica concentration on this metastability phenomenon are studied for a polyethersulfone UF membrane under crossflow and constant flux conditions. A lower crossflow velocity and higher flux, increased salinity and higher colloidal silica concentration decrease the time required for the transition to a dense gel.
    Journal of Membrane Science 06/2014; 469:174-187. DOI:10.1016/j.memsci.2014.06.020 · 4.91 Impact Factor
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    ABSTRACT: A comparative study of transverse and longitudinal vibrations of submerged hollow fibre membranes for fouling control was carried out in this paper. The same membrane module was adopted in the comparison, and the reactor geometry was identical. The orientation between the vibration and membrane fibre directions was the only difference between the two. The feed suspensions included both inorganic Bentonite and organic yeast suspensions. The results showed that transverse vibrations were generally more effective in terms of fouling reduction even at a very low vibration frequency of 1 Hz, which may be attributed to the separating boundary layers and the associated secondary flows around the cylindrical membrane fibres. The difference between the two orientations was very substantial in Bentonite suspensions, but less so in yeast suspensions due to the main membrane foulants of cell debris in the yeast components which caused the pore blockage of the membrane. A small degree of fibre looseness was found to further improve membrane performance with transverse vibrations in both Bentonite and yeast suspensions due to additional lateral fibre movement. The effect of packing density of the membrane bundle in transverse vibrations was also examined. The results showed that at larger vibration amplitudes, a high packing density of fibres can be operated with little membrane fouling, which indicated that the secondary flow generated could overcome the strong permeate flux competition within the bundle under vibrations. Finally, vibration relaxation was tested experimentally in half-on/off switching mode with the energy reduction due directly to the 50% stoppage. The results showed that a short relaxation time interval was generally more favourable for fouling reduction.
    Journal of Membrane Science 04/2014; 455:83–91. DOI:10.1016/j.memsci.2013.12.042 · 4.91 Impact Factor
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    ABSTRACT: a b s t r a c t Low-field bench-top nuclear magnetic resonance imaging (MRI) has been applied to investigate the hydrodynamics in novel hollow fiber modules with four different configurations of randomly-packed, spacer-knitted, curly and semi-curly fibers, specifically designed for the membrane distillation (MD) process. Imaging, spatially resolved velocity maps and propagators (probability distributions of displacement/velocity) were all acquired in the modules with flow in the shell side. The MRI data were correlated with overall module performance. The results have revealed that the curly configuration exhibited more significant transverse flow and hence enhanced mixing, compared to the randomly packed configuration; this was consistent with an enhanced MD performance in terms of permeation flux. Interestingly, the velocity maps of the spacer-knitted fiber design indicated a significant flow channeling in the center of the module, despite its enhanced MD performance. Fortunately, combined with further investigations on the localized velocity images of this configuration, the acquisition of propagators provided valuable information in revealing the existence of reduced stagnant regions and significant transverse flow at varied operating conditions, which indicated a better overall mixing and hence confirmed its module performance. & 2013 Elsevier B.V. All rights reserved.
    Journal of Membrane Science 02/2014; 451:46-54. DOI:10.1016/j.memsci.2013.09.015 · 4.91 Impact Factor
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    ABSTRACT: In this paper RO colloidal fouling was predicted using an on-line Feed Fouling Monitor (FFM) combined with a monitor based on ultrasonic time domain reflectometry (UTDR) under constant flux filtration. The FFM incorporated the relevant cross-flow hydrodynamics and detected the development of foulant load and resistance from a continuous sample passing over a small UF membrane. A UF membrane was used in the FFM, rather than a RO membrane, because it was more sensitive to fouling resistance and this decreased monitoring time and increased accuracy. The UTDR was coupled to a RO membrane cell to monitor the rate of cake thickness increase, which is the required information for the estimation of cake-enhanced osmotic pressure (CEOP). A model was developed to predict fouling in RO using data from the two monitors and combined both the cake resistance and the CEOP effect due to cake formation. RO and FFM fouling experiments were performed at different constant fluxes using the same feed solutions (200 mg/l SiO2, 2000 mg/l NaCl) and the same cross-flow velocity (0.1 m/s). The results showed that higher fluxes caused an increased fouling rate for both RO and the FFM. The foulant layer thickness measured by UTDR in the RO experiments increased faster at higher applied fluxes and the estimated CEOP effect was also strongly influenced by the flux. The results show that the model, combined with the FFM and UTDR measurements, can provide a good estimation of the RO fouling profile over a range of applied fluxes. This study also underscores the importance of CEOP in contributing to the increase in transmembrane pressure due to colloidal fouling in RO of saline feeds.
    Journal of Membrane Science 12/2013; 448:12-22. DOI:10.1016/j.memsci.2013.06.040 · 4.91 Impact Factor
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    ABSTRACT: This paper aims to design a system that can enable optimal operation of the solar powered Membrane Distillation Bio-Reactor (MDBR) water recycling plant. Optimal operation is described as maximization of the clean water produced while being a self sufficient entity in terms of energy. During periods of adequate solar radiation, the system will optimize production levels. When faced with inadequate sunlight, the system will focus on reserving sufficient energy for the survival of the essential micro-organisms in the MDBR. Hence, uninterrupted plant operation during periods of unfavorable weather entails the management of a back up reserve. These engineering objectives are translated into mathematical functions that can be incorporated into convex optimization problems. The effectiveness of the control framework is demonstrated through simulation.
    Renewable Energy 12/2013; 60:489–497. DOI:10.1016/j.renene.2013.05.035 · 3.36 Impact Factor
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    X Yang, Gq Guan, R Wang, A G Fane
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    ABSTRACT: Membrane distillation (MD) is well recognized as a potential alternative technology for desalination due to the benefits of mild operating temperature with acceptable permeation rate, high salt rejection and low greenhouse gas emissions when operated with available low-grade waste heat or renewable solar/geothermal energy [1]. Most importantly, MD has an attractive advantage over other desalination processes (e.g. reverse osmosis (RO)), as the water permeation rate is not significantly affected by the salt concentration in the brine streams and hence high water recovery could be easily achieved to greatly reduce discharge hazards [2]. A low grade-heat aided MD process provides an attractive green solution for obtaining fresh water. Nevertheless, there is only a handful of literature available on the process enhancement strategies for treating highly concentrated brines using MD [3, 4]. In particular, an integration of MD with a crystallization unit, namely membrane distillation crystallization (MDC), was proposed as a more economic way to treat high salinity RO brines and recover valuable salt crystals [5]. However, widely acknowledged challenges in scaling up MDC production remain as: potential scaling (membrane pore blockage), difficulty in membrane modular scale-up, low process efficiency and unidentified cost and energy consumption. Therefore, to investigate more effective alternatives for increasing the capacity of MD plants for high salinity brine processing, in this study novel concepts of matrix modular arrangements were proposed instead of augmenting membrane area by simply increasing the number of fibers in one single hollow fiber module. Flowsheets of continuous MDC process, which was simulated with 7 % wt NaCl solution as feed brine concentrated up to saturation point (27% wt NaCl solution at a temperature of 60 °C) in a hollow fiber-based MD unit and fed into the crystallizer at a constant temperature of 30 °C, with various matrix modular arrangments were built in Aspen Plus platform. Specifically, a comparative evaluation on the single pilot-scale module and matrix modular configurations (i.e., parallel, series and mixed matrix arrangments of multiple bench-scale modules) was conducted, in terms of the permeation flux, total solid production, specific energy consumption (SEC, energy consumed per kg water production), and overall capital and operation cost.
    International Membrane Science and Technology (IMSTEC); 11/2013
  • Oral presentation at International Membrane Science and Technology Conference (IMSTEC), Melbourne, Australia; 11/2013
  • Oral presentation at IDA World Congress on Desalination and Water Reuse, Tianjin, China; 10/2013
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    ABSTRACT: Monitoring the ‘state of the process’ is particularly useful in fouling control in the reverse osmosis (RO) industry. In this paper, a novel non-invasive method to monitor the fouling process of single and binary foulants on the RO membrane has been studied; that of electrical impedance spectroscopy (EIS). A typical RO crossflow cell was equipped with electrodes to allow in-situ EIS measurement of the fouling process during RO filtration. The EIS signals were converted to Nyquist plots of the negative imaginary impedance versus the real impedance, and used as a convenient means for characterization of fouling. Different forms of the Nyquist plot were obtained for different types of foulant. Also a significant shift in the Nyquist plots for silica, BSA and their mixtures occurred corresponding to the buildup of a foulant layer on the membrane surface. During the early stages of fouling, the Nyquist plots shifted noticeably while the transmembrane pressure (TMP) showed negligible increase. If EIS could perform on-line in plant operation, it could be a sensitive monitoring tool to detect early fouling in RO membrane filtration.
    Journal of Membrane Science 09/2013; 443:45–53. DOI:10.1016/j.memsci.2013.04.047 · 4.91 Impact Factor
  • Oral presentation at 7th IWA Specialized Membrane Technology Conference and Exhibition for Water and Wastewater Treatment and Reuse, Canada; 08/2013
  • International Congress on Membranes and Membrane Processes (ICOM2014); 07/2013
  • Victor Sim, Wang R., Miao T., Fane A.G.
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    ABSTRACT: Pressure Retarded Osmosis (PRO) and Reverse Electrodialysis (RED) are two emerging membrane techniques that can utilize seawater to recover osmotic power from salinity gradients. Although such technologies are indeed at an early stage of development, they have attracted intensive interest worldwide. There are already an osmotic power pilot plant utilizing PRO technique in Norway, and a pilot salt battery plant utilizing RED technique in Netherlands. To appreciate how such demonstration plants would eventually result in sufficient cost reductions to enable broad-scale deployment, it requires understanding of the working principles and the potential challenges facing the techniques. The aims of this article are to introduce fundamental aspects of the PRO and RED techniques, discuss the feasibility and challenges for achieving optimal power density, and provide an overview on the state-of-the-art of the techniques in terms of PRO membrane development, and reducing the internal resistance and enhancing stack design in RED. The likely developments moving ahead in making the technology more mature for broad scale employment are also highlighted.
    Encyclopedia of Membrane Science and Technology, Edited by Hoek E.M.V., Tarabara V.V., 05/2013: chapter Part IV. Membrane Applications; John Wiley & Sons., ISBN: 9781118522318
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    ABSTRACT: Membrane fouling by bacterial biofilms remains a key challenge for membrane-based water purification systems. Here, the optimal biofilm dispersal potential of three nitric oxide (NO) donor compounds, viz. sodium nitroprusside, 6-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hexanamine (MAHMA NONOate) and 1-(hydroxy-NNO-azoxy)-L-proline, disodium salt, was investigated using Pseudomonas aeruginosa PAO1 as a model organism. Dispersal was quantitatively assessed by confocal microscopy [bacterial cells and the components of the extracellular polymeric substances (EPS) (polysaccharides and extracellular DNA)] and colony-forming unit counts. The three NO donor compounds had different optimal exposure times and concentrations, with MAHMA NONOate being the optimal NO donor compound. Biofilm dispersal correlated with a reduction in both bacterial cells and EPS. MAHMA NONOate also reduced single species biofilms formed by bacteria isolated from industrial membrane bioreactor and reverse osmosis membranes, as well as in isolates combined to generate mixed species biofilms. The data present strong evidence for the application of these NO donor compounds for prevention of biofouling in an industrial setting.
    Biofouling 02/2013; 29(2):203-212. DOI:10.1080/08927014.2012.760069 · 3.70 Impact Factor
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    ABSTRACT: Dynamic shear-enhanced filtration through vibration can be an effective method to reduce concentration polarization and membrane fouling in high solids suspension loaded membrane applications such as membrane bioreactors (MBRs). In this approach, the wall shear rate on the membrane surface is one of the most important parameters which can control the fouling in vibrating membrane systems. In the present study, the effects of vibration parameters (i.e., frequency and amplitude) and geometrical parameters (i.e., fibre radius and distance between the fibres in a bundle of fibres) on the wall shear rate at the membrane surface have been studied both analytically and numerically. The analytical solution uses the cylindrical coordinate for the analysis of a vibrating single fibre. The former Cartesian solution for a flat sheet membrane used also for fibres by others, was compared to the new solution. It was found that a relative error of up to 75% can arise comparing the two solutions within a realistic range of hollow fibre diameters. The results also showed that fibres with smaller radii are more effective for the vibrating system. Computational Fluid Dynamics simulations were also performed to examine the optimal configuration and distance between fibres for different configurations. The computational results with two remote fibres were first obtained and compared with the analytical results of a single vibrating fibre. The comparison was satisfactory and shows the compatibility of the modeling and analytical results. Subsequently, the CFD analysis was conducted for a fibre bundle with both staggered and in-line arrangements, and the former was found to be marginally more responsive to vibrations.
    Journal of Membrane Science 02/2013; 429:304–312. DOI:10.1016/j.memsci.2012.11.024 · 4.91 Impact Factor
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    ABSTRACT: In this study, we examine the improvement of fouling control of hollow fibre membranes with mechanical vibrations in the dead-end filtration of an inorganic suspension. Hollow fibres with diameters of 1.7 mm and 2 mm vibrating at moderate frequencies (0–15 Hz) and small amplitudes (0–12 mm) were submerged vertically in a 4 g/L Bentonite solution. Experiments were then conducted at both constant permeate flux and constant suction pressure conditions. The results showed that the membrane performance can be greatly improved when the vibration frequency or the vibration amplitude increases beyond a threshold magnitude. For example, over 90% reduction in the membrane fouling rate was achieved at 8 mm amplitude and 8 Hz frequency vibration compared to no vibration. Experiments were also conducted with 1% and 2% fibre looseness. The results showed that a small looseness can reduce the membrane fouling and increase the permeate flux under vibrations, which can be mainly attributed to the additional lateral movement of the fibres induced by the looseness. A comparison of vibrating the hollow fibres with and without the holding frame was also carried out to determine the effects of turbulence generated by the vibrating holding frame used in the experimental setup. Particle Image Velocimetry (PIV) measurements were performed to quantify the associated turbulence inside the membrane reactors. It was confirmed that the turbulence generated by the vibrating frame was more obvious at a high vibration frequency. However, it had little influence on the membrane filtration performance. Overall, the results from the present study confirm that at moderate frequencies, the cake layer resistance can be reduced substantially by vibration due to the dynamic shear enhancement on the membrane surface.
    Journal of Membrane Science 01/2013; 427:230–239. DOI:10.1016/j.memsci.2012.09.031 · 4.91 Impact Factor
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    ABSTRACT: Based on their unique combination of offering high water permeability and high solute rejection aquaporin proteins have attracted considerable interest over the last years as functional building blocks of biomimetic membranes for water desalination and reuse. The purpose of this review is to provide an overview of the properties of aquaporins, their preparation and characterization. We discuss the challenges in exploiting the remarkable properties of aquaporin proteins for membrane separation processes and we present various attempts to construct aquaporin in membranes for desalination; including an overview of our own recent developments in aquaporin-based membranes. Finally we outline future prospects of aquaporin based biomimetic membrane for desalination and water reuse.
    Desalination 01/2013; 308:34–40. DOI:10.1016/j.desal.2012.07.007 · 3.96 Impact Factor

Publication Stats

8k Citations
731.71 Total Impact Points

Institutions

  • 2005–2015
    • Nanyang Technological University
      • • School of Civil and Environmental Engineering
      • • Institute of Environmental Science and Engineering (IESE)
      Tumasik, Singapore
  • 1981–2010
    • University of New South Wales
      • • UNESCO Centre for Membrane Science and Technology
      • • School of Chemical Engineering
      • • School of Physics
      Kensington, New South Wales, Australia
  • 1994
    • University of South Wales
      Понтиприте, Wales, United Kingdom
  • 1992
    • University of Colorado at Boulder
      Boulder, Colorado, United States