ORCID Profile
0000-0002-1387-7464
Current Organisation
Nanyang Technological University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Elsevier BV
Date: 06-2019
DOI: 10.1016/J.WATRES.2019.03.029
Abstract: Quorum quenching (QQ) is an effective method to control membrane biofouling in aerobic membrane bioreactors (AeMBRs). However, it is not clear if QQ is feasible in an anaerobic membrane bioreactor (AnMBR). In this study, Microbacterium. sp that has QQ capability was embedded in alginate beads, known as QQ beads (QQB), and applied in a lab-scale AnMBR to investigate their potential in fouling control. With the addition of QQB, the operating period of AnMBR-QQB reactor was prolonged by about 8-10 times at constant flux operation before reaching the pre-set maximum transmembrane pressure (TMP). The concentration of Acyl-homoserine lactones (AHLs) in the bulk liquid was significantly higher during the 'TMP jump' period compared to QQB and control phases, while AHLs in the membrane foulants were remarkably lower in QQB phase compared to control phase. Furthermore, a much lower level of soluble microbial production (SMP) was observed in QQB phases. Extracellular polymeric substance (EPS), protein in particular, was reduced by 39.73-80.58% in the cake layer of the membrane from QQB phases. Significant changes of organic functional groups were observed in cake layer from QQB membrane as compared with that from control membrane. At the end of operation, bio-polymer (BP), building blocks (BB) and low molecular weight (LMW) organic matters increased in the foulant from control phases but such increase was not observed in QQB phase. After long-term operation, revival of QQB is required due to the declined activity for AHLs degradation.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Research Publishing Services
Date: 2014
Publisher: Elsevier BV
Date: 06-2016
Publisher: Elsevier BV
Date: 02-2019
Publisher: Elsevier BV
Date: 08-2019
DOI: 10.1016/J.WATRES.2019.05.038
Abstract: Organic fouling is still elusive in seawater reverse osmosis (SWRO) desalination process. Classifying organics in seawater will provide an in-depth understanding of the important fraction on RO fouling. In this study, dissolved organic matter (DOM) in seawater was fractionated and concentrated by membrane technique into three major fractions (i.e., biopolymer fraction, humic substance with building block fraction, and low molecular weight fraction) by their molecular weight (MW) according to the definitions in liquid chromatography with organic carbon detection (LC-OCD) method. Overall recovery of >80% was attained. The isolated organic fractions were compared with common model foulants such as sodium alginate (SA), bovine serum albumin (BSA), and humic acid (HA), in terms of chemical analyses using fluorescence-excitation emission matrix (FEEM) and LC-OCD, as well as their fouling potentials. SWRO fouling experiments were carried out and fouling mechanism was investigated by atomic force microscopy (AFM) method and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Results showed that initial fouling (i.e., foulant-membrane interaction) was the main driver in SWRO organic fouling with biopolymer fraction as the major contributor followed by low molecular weight fraction. In addition, alent ions was found to enhance the RO fouling by increasing the adhesion and cohesion forces between foulant-membrane and foulant-foulant.
Publisher: Informa UK Limited
Date: 03-2013
DOI: 10.1080/08927014.2013.772141
Abstract: Pseudomonas aeruginosa PAO1 wild type and a mucoid derivative (FRD1) which over produces alginate were used to foul reverse osmosis (RO) membranes. When operated at a constant flux, biofilm formation on the RO membrane resulted in a slow rise in transmembrane pressure (TMP) of 22% for the initial four days of operation, followed by a sharp increase of 159% over the following two days. The initial slow increase in TMP was probably due to the formation of a biofilm on the membrane surface, which then accelerated the rate of biofouling through the effect of concentration polarization. At later stages of operation, most of the bacterial biomass consisted of dead cells. The amount of extracellular polymeric substances appeared to correlate positively with the number of dead cells. The results indicate that prolonging the initial stage of slow TMP increase and avoiding the latter stage of accelerated TMP increase would provide a sustainable operation of the RO system. These results suggest that nutrient limitation could reduce biofilm accumulation and delay the increase in TMP.
Publisher: Elsevier BV
Date: 12-2008
Publisher: Elsevier BV
Date: 02-2016
Publisher: Elsevier BV
Date: 10-2015
Publisher: Elsevier BV
Date: 02-2013
Publisher: Informa UK Limited
Date: 03-2013
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 04-2020
DOI: 10.1016/J.CHEMOSPHERE.2019.125569
Abstract: This study compared the performance of an anaerobic fluidized bed membrane bioreactor (AFMBR)-zeolite adsorption-reverse osmosis (RO) system and an anoxic-aerobic MBR-RO system for municipal wastewater reclamation. Both MBR-RO systems were operated in parallel with the same operating conditions. The results showed that the MBR systems achieved excellent organic removals (>95%) and the anoxic-aerobic MBR could also remove ∼57% of soluble total nitrogen. Compared to the aerobic MBR, the AFMBR displayed better membrane performance with less energy consumption, attributed to effective membrane scouring by liquid-fluidized GAC particles. Furthermore, a zeolite column was employed to remove ammonia in the AFMBR permeate, which ensured comparable organic and nitrogen levels in the feeds to RO units in the two processes. Although less organic substances and microbial cells were accumulated on the RO membrane fed with AFMBR-zeolite column effluent, its fouling rate (∼6.5 ± 2.2 bar/day) was significantly greater than that fed with anoxic-aerobic MBR permeate (∼1.1 ± 1.5 bar/day). This may be associated with more severe inorganic colloidal fouling on the RO membrane, illustrated by an electrical impedance spectroscopy fouling monitoring system.
Publisher: Elsevier BV
Date: 03-2019
DOI: 10.1016/J.SCITOTENV.2018.11.068
Abstract: Rainwater recycling has been considered as an alternative cost-effective decentralized water supply. The low cost and effective gravity-driven membrane (GDM) filtration technology has been introduced to treat the rainwater prior use. In this study, we investigated the effects of hydraulic retention time (HRT 27 h, 51 h, and 156 h) and periodic backwash durations (2 min, 5 min, 10 min, and 30 min per 2-3 days' filtration) on the permeate quality, flux and fouling mechanism in lab-scale submerged GDM reactors. Compared to the performance at HRT of 51 h (40% of DOC removal and ~2.9 L/m
Publisher: Elsevier BV
Date: 04-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4EW00073K
Abstract: New thermally responsive ionic liquid draw solutes generate high flux against seawater with substantially reduced electrical energy consumption.
Publisher: Elsevier BV
Date: 05-2018
Publisher: Informa UK Limited
Date: 14-05-2013
Publisher: Elsevier BV
Date: 02-2021
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 02-2018
DOI: 10.1016/J.WATRES.2017.11.013
Abstract: This study examines the feasibility of a novel nanofiltration membrane bioreactor (NF-MBR) followed by reverse osmosis (RO) process for water reclamation at 90% recovery and using an ultrafiltration MBR (UF-MBR)+RO as baseline for comparison. Both MBRs adopted the same external hollow fiber membrane configurations and operating conditions. The collected permeates of the MBRs were subsequently fed to the respective RO systems. The results showed that the NF-MBR (operated at a constant flux of 10 L/m
Publisher: Elsevier BV
Date: 05-2020
Publisher: Elsevier BV
Date: 04-2019
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.BIORTECH.2012.05.016
Abstract: In this study, an interesting phenomenon was observed that when the levels of soluble polysaccharides (SP) and soluble transparent exopolymer particles (sTEP) in the MBR unexpectedly and suddenly increased, the cleaned membranes tended to be more easily fouled compared to the membranes with the initial cake layers formed in a slow TMP increase stage. Foulant analysis indicated great accumulation amounts of SP and sTEP on the cleaned membrane. FT-IR spectra further confirmed that hydroxyl and amide groups in the soluble substances preferred to attach on the cleaned membranes. While, the initially formed cake layers on the membranes played a role to decrease zeta potential of cleaned membranes, which created less interaction with the soluble substances. It suggests that forming loose-structured cake layers on the primary membranes could be thought as an effective membrane fouling control strategy.
Publisher: Elsevier BV
Date: 05-2019
DOI: 10.1016/J.WATRES.2019.01.044
Abstract: In this study, permeate quality, membrane performance, and microbial community in a gravity-driven microfiltration (GDM) reactor and a biofiltration (BF) + GDM reactor for seawater reverse osmosis (RO) desalination pretreatment were compared at both lab-scale and pilot-scale. The presence of BF column was more efficient in removing soluble organic substances by biosorption/biodegradation, leading to superior permeate quality from BF + GDM and subsequently lower RO fouling than GDM. Compared to the biofilm-saturated anthracite media, the granular activated carbon media in BF improved the assimilable organic substances removal in BF + GDM. Although less organic substances and microbial cells were accumulated on the membrane in BF + GDM, its permeate flux was 10-20% lower than GDM. Furthermore, BF lowered the amounts and ersity of prokaryotes (due to less organic substances) and eukaryotes (due to BF media rejection and lacking of prokaryotic preys) in the membrane biofilm of BF + GDM, but did not cause significant shifts of predominant species. Thus, the lower flux in BF + GDM was attributed to the limited predation and movement of eukaryotes in membrane biofilm, which may result in the formation of less porous and compact biofilm layer. The cost analysis indicated that BF + GDM-RO requires 5.2% less operating cost and 1.5% less water production cost than GDM-RO.
Publisher: Elsevier BV
Date: 08-2018
Publisher: Elsevier BV
Date: 04-2008
Publisher: Elsevier BV
Date: 12-2016
Publisher: Elsevier BV
Date: 11-2014
Publisher: Elsevier BV
Date: 2015
Publisher: Informa UK Limited
Date: 02-07-2016
Publisher: CRC Press
Date: 21-04-2017
Publisher: Wiley
Date: 22-04-2009
Publisher: Elsevier BV
Date: 10-2018
Publisher: Elsevier BV
Date: 09-2001
Publisher: American Chemical Society (ACS)
Date: 17-06-2016
Abstract: The development of novel tools for studying the fouling behavior during membrane processes is critical. This work explored optical coherence tomography (OCT) to quantitatively interpret the formation of a cake layer during a membrane process the quantitative analysis was based on a novel image processing method that was able to precisely resolve the 3D structure of the cake layer on a micrometer scale. Fouling experiments were carried out with foulants having different physicochemical characteristics (silica nanoparticles and bentonite particles). The cake layers formed at a series of times were digitalized using the OCT-based characterization. The specific deposit (cake volume/membrane surface area) and surface coverage were evaluated as a function of time, which for the first time provided direct experimental evidence for the transition of various fouling mechanisms. Axial stripes were observed in the grayscale plots showing the deposit distribution in the scanned area this interesting observation was in agreement with the instability analysis that correlated the polarized particle groups with the small disturbances in the boundary layer. This work confirms that the OCT-based characterization is able to provide deep insights into membrane fouling processes and offers a powerful tool for exploring membrane processes with enhanced performance.
Publisher: Elsevier BV
Date: 12-2013
Publisher: Elsevier BV
Date: 02-2021
Publisher: Elsevier BV
Date: 08-2020
Publisher: IWA Publishing
Date: 02-2010
DOI: 10.2166/WST.2010.835
Abstract: Forward Osmosis (FO) is a membrane process that uses the natural osmotic pressure of a concentrated draw solution to extract pure water from a feed stream. The attraction of the FO process is that it uses dense membranes, while operating at ambient pressure. This means that the FO process could potentially produce high quality water with lower energy consumption, as compared to the other desalination or reclamation processes. As FO does not entail the use of hydraulic pressure, FO has been hypothesized to have lower fouling propensity than pressure driven membrane processes. Membrane fouling has significant impact on the operational sustainability and economics of the process. This study examines the possible contributing factors to the slower flux decline observed in FO experiments based on a combined experimental and modelling approach. It was found that these factors could include low water fluxes, use of hydrophilic and smooth membranes, and the effect of internal concentration polarisation that is inherent of FO. It was also found that the transmission of draw solutes from the draw solution into the feed can have significant effect on FO performance.
Publisher: Elsevier BV
Date: 03-2017
DOI: 10.1016/J.WATRES.2016.12.002
Abstract: Spacer design plays an important role in improving the performance of membrane processes for water/wastewater treatment. This work focused on a fundamental issue of spacer design, i.e., investigating the effects of spacer orientations on the fouling behavior during a membrane process. A series of fouling experiments with different spacer orientation were carried out to in situ characterize the formation of a cake layer in a spacer unit cell via 3D optical coherence tomography (OCT) imaging. The cake layers formed at different times were digitalized for quantitatively analyzing the variation in the cake morphology as a function of time. In particular, the local deposition rates were evaluated to determine the active regions where the instantaneous changes in deposit thickness were significant. The characterization results indicate that varying the spacer orientation could substantially change the evolution of membrane fouling by particulate foulants and thereby result in a cake layer with various morphologies the competition between growth and erosion at different locations would instantaneously respond to the micro-hydrodynamic environment that might change with time. This work confirms that the OCT-based characterization method is a powerful tool for exploring novel spacer design.
Publisher: Elsevier BV
Date: 09-2017
Publisher: Elsevier BV
Date: 11-2018
Publisher: Informa UK Limited
Date: 08-2009
DOI: 10.5004/DWT.2009.792
Publisher: Elsevier BV
Date: 07-2015
Publisher: Elsevier BV
Date: 02-2007
Publisher: Elsevier BV
Date: 2007
Publisher: Elsevier BV
Date: 05-2012
Publisher: Elsevier BV
Date: 2020
DOI: 10.1016/J.WATRES.2019.115198
Abstract: The biofouling potential of three isolated dissolved organic fractions from seawater according to their molecular weights (MWs), namely, fractions of biopolymers (F.BP, MW > 1000 Da), humic substances and building blocks (F.HS&BB, MW 350-1000 Da), and low molecular weight compounds (F.LMW, MW F.BP (∼19%) > F.HS&BB (∼8%) AOC/DOC of seawater was ∼20% organic compositions of seawater were BP ∼6%, HS&BB ∼52% and LMW ∼42% LMW accounted for >70% of AOC in seawater. Their impact on SWRO biofouling in term of flux decline rate was in the order of F. LMW (∼30%) > F.BP (∼20%) > F.HS&BB (<10%). Despite being the major organic compound in seawater, HS&BB showed marginal effect on biofouling. The role of indigenous BP was less critical owing to its relatively low concentration. LMW, which was the major AOC contributor, played a significant role in biofouling by promoting microbial growth that contributed to the build-up of soluble microbial products and exopolymeric substances (i.e., in particular BP). Therefore, seawater pretreatment shall focus on the removal of AOC (i.e., LMW) rather than the removal of biopolymer.
Publisher: Elsevier BV
Date: 03-2020
DOI: 10.1016/J.WATRES.2019.115352
Abstract: The impacts of salt accumulation, through adjusting the solid retention time (SRT), in the bioreactor on the bioprocess as well as membrane performance of a high retention nanofiltration membrane bioreactor (NF-MBR) and subsequent reverse osmosis (RO) process for water reclamation are addressed in this study. The build-up of salts (i.e., Ca, Mg, PO
Publisher: American Chemical Society (ACS)
Date: 11-01-2017
Abstract: This study evaluated the effects of salinity on the physiological characteristics of Vibrio sp. B2 and biofilm formation on nanofiltration (NF) membrane coupons used in the high recovery seawater desalination process. The test conditions were at 0.6, 1.2, and 2.4 M sodium chloride (NaCl), equivalent to salinity of seawater, brine at 50% and 75% water recovery, respectively. High salinity inhibited the cell growth rate but increased the viability and bacterial membrane integrity. In addition, protein and eDNA concentrations of salinity-stressed bacteria were increased at 1.2 and 2.4 M NaCl. In particular, protein concentration was linearly correlated with the NaCl concentration. Similarly, less biofilm formation on the NF membrane coupon (without permeation flux) was observed by the salinity-stressed bacteria however, the production of extracellular polymeric substances (EPS) was significantly increased as compared to control, and protein was an influential factor for biofilm formation. This study shows that salinity-stressed bacteria have a high potential to cause biofouling on membrane surface as the bacteria still maintain the cell activity and overproduce EPS. The potential of biofilm formation by the salinity-stressed bacteria has not been reported. Therefore, the findings are important to understand the mechanisms of membrane biofouling in a high salinity environment.
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.CIS.2010.10.007
Abstract: Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of colloidal fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling colloidal fouling of both RO and NF membranes. Major colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for colloidal fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter≪100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF colloidal fouling are also identified in the current paper.
Publisher: Elsevier BV
Date: 2022
Publisher: Elsevier BV
Date: 07-2012
Publisher: Elsevier BV
Date: 03-2019
Publisher: Elsevier BV
Date: 12-2019
DOI: 10.1016/J.SCITOTENV.2019.133719
Abstract: This study investigated the performances of gravity-driven membrane (GDM) reactors integrated with granule activated carbon (GAC) biofilm process for wastewater treatment under different intermittent aeration cycles (intensity and frequency). The results showed the removal efficiencies of dissolved organic carbon, total nitrogen, ammonia were significantly improved under intermittent aeration conditions (~86-87%, ~29-37%, and ~83-99%, respectively) compared to non-aeration condition (~72% and ~18%, and ~17%, respectively). In addition, it was found that the intermittent aeration significantly reduced the cake layer resistance and therefore improved ~130-300% the permeate flux compared to control without aeration. Microbial community analysis indicated that prokaryotic and eukaryotic compositions in the cake layer biofilm were significantly influenced by aeration condition. Lastly, energy consumption analysis revealed that GAC + GDM with shorter aeration period and low aeration intensity could be promising as a decentralized wastewater treatment process in terms of water quality and operating energy.
Publisher: Elsevier BV
Date: 06-2015
Publisher: Elsevier BV
Date: 05-2018
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 02-2013
Publisher: Elsevier BV
Date: 05-2021
Publisher: Elsevier BV
Date: 2012
Publisher: Elsevier BV
Date: 12-2021
DOI: 10.1016/J.WATRES.2021.117818
Abstract: Feed spacers are an essential part of spiral wound modules for reverse osmosis (RO). They create flow channels between membrane sheets and manipulate hydrodynamic conditions to control membrane fouling. In this work, additive manufacturing (Polyjet) was used to print novel sinusoidal spacers with wavy axial filaments connected by perpendicular (ST) or slanted (SL) transverse filaments. When tested with 2 g/L NaCl solution, conventional and SL spacers had similar flux while the ST spacer had about 5-7% lower flux. The pressure losses for ST and SL spacers increased by up to 3 folds depending on the flow condition. In the colloidal silica fouling and biofouling tests, the sinusoidal spacers showed lower membrane permeability decrease of 46% for ST, 41% for SL vs 56% for conventional and 26% for ST, 22% for SL vs 33% for conventional, respectively. Optical coherence tomography images from colloidal silica fouling and confocal images from biofouling tests revealed that fouling patterns were closely associated with the local hydrodynamic conditions. Overall, sinusoidal spacers showed promising results in controlling membrane fouling, but there is potential for further optimizations to reduce channel pressure loss.
Publisher: Elsevier BV
Date: 03-2008
Publisher: MDPI AG
Date: 04-07-2013
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.CHEMOSPHERE.2018.12.066
Abstract: The presence of transparent exopolymer particles (TEP) in water bodies has been related to several adverse impacts in various water treatment processes. In recent years, there have been an increasing number of publications relating to TEP. Unfortunately, this increased interest in TEP measurement has not been accompanied by significant improvement in the analysis method or TEP monitoring. Currently, the most common method to analyze and quantify TEP only allows offline, and often offsite measurement, causing delays and slow response times. This paper introduces an improved method for TEP monitoring using a membrane-based spectrophotometric technique to quantify TEP in various water bodies. The proposed TEP monitor involves a crossflow filtration unit, reagent injection and a spectrophotometer system. The TEP retained on the membrane surface is stained by Alcian blue and the amount deposited is quantified directly using an optic fibre reflectance probe coupled with a spectrophotometer. The novel method shows a linear relationship with various concentrations of Xanthan gum (a model representing TEP). When tested with various water s les, the proposed method was found to correlate well with the conventional method. Several advantages of this novel method are shorter analysis time, increased accuracy, and the potential to be further developed into an online system.
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 2016
Publisher: Elsevier BV
Date: 10-2014
No related grants have been discovered for Tzyy Haur Chong.