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Now showing items 1 - 16 of 70

  • Electrodialysis reversal for industrial reverse osmosis brine treatment

    Zhao, Dandan   Lee, Lai Yoke   Ong, Say Leong   Chowdhury, Prannoy   Siah, Keng Boon   Ng, How Yong  

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  • Brine pre-treatment technologies for zero liquid discharge systems

    Semblante, Galilee Uy   Lee, Jonathan Zhiqiang   Lee, Lai Yoke   Ong, Say Leong   Ng, How Yong  

    The management of brine produced by the reverse osmosis process is challenging due to its high salt and organic content. Limitations in brine disposal options sometimes necessitate the use of zero liquid discharge (ZLD) approach. ZLD systems may include a membrane process which is used to recover water and to further concentrate brine followed by thermal treatment. In such systems, a high-water recovery rate is difficult to achieve due to the early onset of membrane scaling and fouling. Brine pre-treatment is therefore necessary to protect the membrane and facilitate ZLD. Literature shows that the most common brine pre-treatment process, chemical precipitation, is generally costly because of high chemical consumption and hazardous sludge production. Moreover, its performance may be hindered by the temporal fluctuations in brine chemistry and the occurrence of residual antiscalants in the brine. A critical evaluation of alternative pre-treatment options was performed. It was found that electrocoagulation and nanofiltration processes have promising performance in terms of hardness and organic removals. Meanwhile, coagulation and adsorption processes show potential for organic removal. Further studies should be performed on process optimization and cost analysis to determine the feasibility of applying these technologies in ZLD systems.
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  • Denitrification of Nitrate Wastewater using Packed-Bed Columns

    Lee, Lai Yoke   Ong, Say Leong   Ng, Wun Jern  

    Columnar packed-bed (PB) reactors with a specific surface area of 127 m2/m3 were investigated in this study for treating nitrate wastewater. This study demonstrated that a single-stage packed bed was able to achieve total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies higher than 83 and 75%, respectively. The highest achievable TN and COD removal rates were 47.2 g N/m2.d and 158.0 g COD/m2.d, respectively. The substrate removal rate in the PB column was found to follow half-order reaction kinetics, with a reaction coefficient, k, of 53.62 (mg/L)1/2/d. A dual-stage PB system was capable of achieving TN and COD removal efficiencies greater than 99 and 98%, respectively. Effluent TN and COD concentrations less than 6.5 mg NO3--N/L and 50.0 mg COD/L, respectively, were obtained when the dual PB system was used.
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  • Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff

    Xu, Dong   Shi, Xueqing   Lee, Lai Yoke   Lyu, Zhiyang   Ong, Say Leong   Hu, Jiangyong  

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  • RO brine treatment and recovery by biological activated carbon and capacitive deionization process

    Tao, Guihe   Viswanath, Bala   Kekre, Kiran   Lee, Lai Yoke   Ng, How Yong   Ong, Say Leong   Seah, Harry  

    The generation of brine solutions from dense membrane (reverse osmosis, RO or nanofiltration, NF) water reclamation systems has been increasing worldwide, and the lack of cost effective disposal options is becoming a critical water resources management issue. In Singapore, NEWater is the product of a multiple barrier water reclamation process from secondary treated domestic effluent using MF/UF-RO and UV technologies. The RO brine (concentrates) accounts for more than 20% of the total flow treated. To increase the water recovery and treat the RO brine, a CDI based process with BAC as pretreatment was tested. The results show that ion concentrations in CDI product were low except SiO2 when compared with RO feed water. CDI product was passed through a RO and the RO permeate was of better quality including low SiO2 as compared to NEWater quality. It could be beneficial to use a dedicated RO operated at optimum conditions with better performance to recover the water. BAC was able to achieve 15-27% TOC removal of RO brine. CDI had been tested at a water recovery ranging from 71.6 to 92.3%. CDI based RO brine treatment could improve overall water recovery of NEWater production over 90%. It was found that calcium phosphate scaling and organic fouling was the major cause of CDI pressure increase. Ozone disinfection and sodium bisulfite dosing were able to reduce CDI fouling rate. For sustainable operation of CDI organic fouling control and effective organic fouling cleaning should be further studied.
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  • Combination of in situ preconcentration and on-site analysis for phosphate monitoring in fresh waters.

    Li, Weijia   Lee, Lai Yoke   Yung, Lin Yue Lanry   He, Yiliang   Ong, Choon Nam  

    Excess nutrients of phosphorus and nitrogen would lead to adverse impacts on a water body. It is important that their concentrations in a dynamic water ecosystem are measured accurately and constantly for an early warning before occurrences of algal blooms and for environmental management. Nevertheless, on-site measurements by existing technologies are often limited by the inherent sensitivities. In this study, a portable system for dissolved phosphate monitoring in freshwater based on the diffusive gradients in thin films (DGT) technique was developed. A polydiallydimethylammonium chloride (PDA) aqueous solution and a dialysis membrane were used as a binding phase and a diffusive layer in this preconcentration device, respectively. The binding properties of the PDA solution were evaluated in solutions of different pH (3 to 9) and varying concentrations of anions (2.0-20 mM). The amount of phosphates preconcentrated in the devices was measured by ultraviolet-visible (UV) spectroscopy to obtain the concentrations in waters without elution steps. The devices were validated in synthetic river water with good agreement with the theoretical prediction and in natural river water. A system combining this preconcentration device and a compact detection chamber equipped with a pair of light emitting diodes (LED) was studied in lab synthetic solutions for on-site monitoring of phosphate concentrations and their fluctuations. =20
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  • Effect of ferric hydroxide on membrane fouling in membrane bioreactor treating pharmaceutical wastewater

    Huang, Shujuan   Shi, Xueqing   Bi, Xuejun   Lee, Lai Yoke   Ng, How Yong  

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  • Reverse Osmosis Brine from Water Reclamation Plant – Cost Effective Process for Treatment and Recovery

    Lee, Lai Yoke   Ng, How Yong   Ong, Say Leong   Tao, Guihe   Viswanath, Balakrishnan   Kekre, Kiran   Lay, Winson   Seah, Harry  

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  • Ozone-biological activated carbon as a pretreatment process for reverse osmosis brine treatment and recovery

    Lee, Lai Yoke   Ong, Say Leong   Hu, Jiang Yong   Tao, Guihe   Kekre, Kiran   Viswanath, Balakrishnan   Lay, Winson   Seah, Harry  

    Ozonation was used in this study to improve biodegradability of RO brine from water reclamation facilities. An ozone dosage ranging from 3 to 10 mg O-3/L and contact times of 10 and 20 min in batch studies were found to increase the biodegradability (BOD5/TOC ratio) of the RO brine by 1.8-3.5 times. At the same time, total organic carbon (TOC) removal was in the range of 5.3-24.5%. The lab-scale ozone-biological activated carbon (BAC) at an ozone dosage of 6.0 mg O-3/1, with 20-min contact time was able to achieve 3 times higher TOC removal compared to using BAC alone. Further processing with Capacitive Deionization (CDI) process was able to generate a product water with better water quality than the RO feed water, i.e., with more than 80% ions removal and a lower TOC concentration. The ozone-BAC pretreatment has the potential of reducing fouling in the CDI process. (C) 2009 Elsevier Ltd. All rights reserved.
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  • Alternative Immunofluorescent Labeling of Cryptosporidium parvum in Water Samples Using Semiconductor Quantum Dots

    Lee, Lai Yoke   Hu, Jiang Yong   Ong, Say Leong   Ng, How Yong   Wong, Shih Wei   Feng, Yaoyu   Tan, Xiaolan  

    The application of immunofluorescent labeling using quantum dots for detection of inactivated Cryptosporidium parvum oocysts in spiked water samples (reservoir water, treated wastewater effluent, permeate of a membrane bioreactor, and tap water) provided more consistent results compared with the organic fluorophores label. The varying degree of particles present in the different water samples (with turbidity ranging from 0.2 to 6.1 NTU) in nonconcentrated water samples had insignificant interference on the labeled counts (2-sample t-tests, p > 0.236) using the quantum dot label, while the quantum dot label provided an advantage of approximately 50% lower interference in concentrated water samples compared with the organic fluorophores label. Water Environ. Res., 80, 725 (2008).
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  • Integrated pretreatment with capacitive deionization for reverse osmosis reject recovery from water reclamation plant

    Lee, Lai Yoke   Ng, How Yong   Ong, Say Leong   Tao, Guihe   Kekre, Kiran   Viswanath, Balakrishnan   Lay, Winson   Seah, Harry  

    Reverse osmosis (RO) reject recovery from the water reclamation process was demonstrated feasible using an integrated pretreatment scheme followed by the Capacitive Deionization (CDI) process. The RO reject had an average total dissolved solids (TDS) of 1276 +/- 166 mg/L. Water recovery of 85% with water quality comparable with the RO feed was achieved. Pretreatments using biological activated carbon (BAC) and BAC-ultrafiltration (UF) attained total organic carbon (TOC) removal efficiencies of 23.5 +/- 6.0% and 39.9 +/- 9.0%, respectively. Organics removal of RO reject was attributed to simultaneous adsorption and biodegradation in the BAC pretreatment, while further biodegradation in the submerged UF membrane tank provided additional organics removal. Membrane and CDI fouling was reduced by pH adjustment of the pretreated RO reject to approximately 6.5, which prolonged the CDI operation time by at least two times. The CDI process was able to achieve more than 88 and 87% TDS and ion removals, respectively, while PO(4)(3-) and TOC removals were at 52-81% and 5G-63%, respectively. (C) 2009 Elsevier Ltd. All rights reserved.
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  • Alternative Immunofluorescent Labeling of Cryptosporidium parvum in Water Samples Using Semiconductor Quantum Dots

    Lee, Lai Yoke   Hu, Jiang Yong   Ong, Say Leong   Ng, How Yong   Wong, Shih Wei   Feng, Yaoyu   Tan, Xiaolan  

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  • Water treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives

    Xu, Dong   Lee, Lai Yoke   Lim, Fang Yee   Lyu, Zhiyang   Zhu, Hao   Ong, Say Leong   Hu, Jiangyong  

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  • China and the South Sea Dialoguesby Lee Lai To

    Review by: Jason Abbott  

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  • China and the South Sea Dialoguesby Lee Lai To

    Review by: Jason Abbott  

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  • China and the South China Sea Dialoguesby Lee Lai To

    Review by: Ramses Amer  

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