Ong Say Leong
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ceeongsl@nus.edu.sg
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Publication Investigation on gasoline deep desulfurization for fuel cell applications(2005-01) Zhang, J.C.; Song, L.F.; Hu, J.Y.; Ong, S.L.; Ng, W.J.; Lee, L.Y.; Wang, Y.H.; Zhao, J.G.; Ma, R.Y.; CIVIL ENGINEERINGThe effect of adding some amounts of cerium into Zn-Fe-O/Al 2O3 sorbent on its performance of removal of organic sulfur compounds from gasoline by adsorption was studied in this paper. It showed that the ideal compositions for the preparation of Zn-Fe-Ce-O/Al 2O3 consisted of 4.54 wt.% ZnO, 2.25 wt.% Fe 2O3 and 2.5 wt.% CeO2, respectively, shortened as AZFC0.52. Further study indicated that this sorbent could be well regenerated at 250 °C with gas mixtures containing 6.0 vol.% steam+air and 2400 mlh-1ml-1 gas space velocity. At those regenerated conditions and 60 °C adsorption temperature, the AZFC0.52 sorbent had better desulfurization stability, which was confirmed by typical characterization results using BET, XRD and SEM apparatus. This implied that the AZFC0.52 sorbent could be an ideal sorbent for removal of organic sulfur compounds from gasoline. © 2004 Elsevier Ltd. All rights reserved.Publication Post-treatment of banknote printing works wastewater ultrafiltration concentrate(2004-09) Zhang, G.; Liu, Z.Z.; Song, L.F.; Hu, J.Y.; Ong, S.L.; Ng, W.J.; CIVIL ENGINEERINGA novel process of vortex settling and stage-2 ultrafiltration (UF) with alternating feed direction was used to further concentrate the concentrate produced by a stage-1 UF employed for treatment of banknote printing works wastewater. In this post-treatment process, the final concentrate volume for incineration was reduced by 4-5 times while the permeate of the stage-2 UF could be further reused in the banknote printing operation. It was noted vortex settling facilitated settling of the printing ink and the strategy of regularly alternating feed direction in the UF resulted in a higher permeate flux compared to the corresponding flux for operation without alternating feed direction. The hydraulic retention time (HRT) of the vortex settling tank (VST) used in the pilot-scale experiment was 14 min while feed direction to the stage-2 UF was alternated once every hour. Based on the pilot-scale experimental results, a full-scale system was set up. An economic analysis showed that the novel system was a cost-effective option for post-treatment of stage-1 UF concentrate. The treatment system has been successfully implemented at several Chinese banknote printing companies. © 2004 Elsevier Ltd. All rights reserved.Publication Spatial variation of fouling behavior in high recovery nanofiltration for industrial reverse osmosis brine treatment towards zero liquid discharge(Elsevier, 2020-08-15) SONG WEILONG; LEE LAI YOKE; LIU ENYU; SHI XUEQING; ONG SAY LEONG; NG HOW YONG; CIVIL AND ENVIRONMENTAL ENGINEERINGNanofiltration (NF), as a cost-efficient pre-concentrating process, has been incorporated into Zero Liquid Discharge (ZLD) treatment system to improve economic feasibility. However, NF is required to operate with an extremely high recovery rate to achieve ZLD, which could cause severe and complex membrane fouling. Understanding the variation of fouling behavior with increase in recovery rate is crucial for the development of effective fouling control strategy. Spatial variation of fouling behavior in a 3-stage NF used for industrial RO brine treatment towards ZLD was investigated in present study. Distinctive fouling characteristics were observed in each operation stage. Membrane fouling was dominated by organics at lead stage, which could be completely removed via simple base cleaning. Scaling by deposition of bulk crystallization occurred on fouling layer at middle stage, which required a combination of acid and base cleaning for its removal. At the tail stage, more refractory scaling by surface crystallization accompanied by irreversible silica and ferric fouling led to the formation of fouling layer that was resistant to conventional chemical cleaning. Significant humics in preformed fouling layer could have facilitated the occurrence of surface crystallization. Minor elements present in the feed such as silica, humics and iron could cause significant fouling and alter preformed fouling layer that induced more complex and refractory fouling/scaling as recovery rate increased.Publication Adsorption removal of phenol in water and simultaneous regeneration by catalytic oxidation(2005) Wang, Y.H.; Zhang, J.C.; Song, L.F.; Hu, J.Y.; Ong, S.L.; Ng, W.J.; CIVIL ENGINEERINGA series of sorbents were prepared, and their performance on removal of phenol from wastewater was investigated in this study. It indicated that the suitable compositions for the prepared sorbent mainly consisted of 0.5 wt.% PtO, 4.5 wt.% MnO, 1.99 wt.% Fe2O3, and 2.4 wt.% CoO, respectively, and supported on Al2O3, shortened as an APMFC1.2 sorbent, A, P, M, F, C indicated Al2O 3, PtO, MnO, Fe2O2, CoO, respectively, and number 1.2 as the molar ratio of Co. Studies showed that the spent sorbent could be effectively regenerated at 240°C by gas mixtures of 6.0 mol.% steam balanced with air. Multiadsorption-regeneration cycles conducted on APMFC 1.2 sorbent indicated that it had good regenerability at the experimental conditions, and characterized results further confirmed that the APMFC1.2 sorbent had stable structure, which implied APMFC 1.2 sorbent could be a promising sorbent/catalyst to be used in the process of removal of organic compounds in wastewater by adsorption combined with catalytic oxidation methods. © Mary Ann Liebert, Inc.Publication Experimental studies on removal of microcystin-LR by peat(2010) Sathishkumar, M.; Pavagadhi, S.; Vijayaraghavan, K.; Balasubramanian, R.; Ong, S.L.; CIVIL ENGINEERING; DIVISION OF ENVIRONMENTAL SCIENCE & ENGGCyanotoxins have caused worldwide concerns for their eclectic occurrence and toxic effects, which led to an intensive search of cost-effective techniques for their removal from contaminated waters. A range of biomaterials was tested for their efficacy to adsorb a potent cyanotoxin, microcystin-LR (MCLR). Among these sorbents, peat showed the maximum efficacy to sequester MCLR. The BET (Brunauer-Emmett-Teller) surface area of peat was found to be 12.134m2/g. The pH of the reaction media played a significant role in removal of MCLR; maximum adsorption occurred at pH 3. Kinetic studies showed that the adsorption of MCLR onto peat was a rapid process. The adsorption capacity (Qmax) from the Langmuir model was found to be 255.7μg/g at pH 3. Among various desorption media studied, strong alkali (2N NaOH) showed highest desorption (94%). © 2010 Elsevier B.V.Publication Fouling of RO membranes by effluent organic matter (EfOM): Relating major components of EfOM to their characteristic fouling behaviors(2010-03-01) Zhao, Y.; Song, L.; Ong, S.L.; CIVIL ENGINEERINGEffluent organic matter (EfOM) has been considered by many to play an important role in fouling of RO membranes used for wastewater reclamation. However, due to their heterogeneous composition, which is a mixture of structurally complex aquatic humic substances (AHS), soluble microbial products (SMP) or extracellular polymeric substances (EPS) and other poorly defined organic compounds, the fractional component(s) or physical-chemical properties responsible for the fouling phenomenon are still not well understood. This study aims to obtain a better understanding of interactions between fractional components of EfOM and RO membranes and attempts to identify the most influential fraction(s) or physical-chemical properties governing the fouling process. Four EfOM fractions were isolated and fractionated from UF prefiltrated treated effluent based on hydrophobicity and charge characteristics. EPS was extracted from the biological treatment stage to assess their fouling potential on RO membranes via well-controlled laboratory-scale experiments. The individual organic fractions were rigorously characterized in terms of physico-chemical properties. A clear correlation was observed between the physico-chemical properties of EfOM fractions and their fouling potential. Under hydrodynamic and chemical conditions typical of commercial applications, the hydrophilic neutral fraction, mainly composed of small size carbohydrates, resulted in the highest flux decline and exhibited highest affinity towards the membrane. EPS biopolymers, to which great importance has been associated with regard to causing RO organic fouling, resulted in less fouling than hydrophilic carbohydrates. Although EPS biopolymers tended to accumulate on the membrane in much higher quantities, the cake layer formed was found to constitute a much lower resistance towards filtration and has a much lower membrane affinity, probably due to their large molecular sizes. The contribution of AHS and other hydrophilic fractions to membrane fouling was found to be much lower as compared to hydrophilic carbohydrates and EPS biopolymers. © 2009 Elsevier B.V. All rights reserved.Publication Two-stage SBR for treatment of oil refinery wastewater(2004) Lee, L.Y.; Hu, J.Y.; Ong, S.L.; Ng, W.J.; Ren, J.H.; Wong, S.H.; CIVIL ENGINEERINGA two-stage sequencing batch reactor (SBR) system was used for treatment of oily wastewater with COD and oil and grease (O&G) concentrations ranging from 1,722-7,826 mg/L and 5,365-13,350 mg/L, respectively. A suitable start-up protocol was developed using gradual increase in oily wastewater composition with methanol as the co-substrate. This strategy enabled a short acclimation period of 12 days for the sludge in the two-stage SBR to adapt to the oily wastewater. After acclimation, the 1st stage and 2nd stage SBRs were able to achieve COD removals of 47.0 ± 2.4% and 95.3 ± 0.5%, respectively. The 1st stage SBR was able to achieve 99.8 ± 0.1% of O&G removal and effluent O&G from the 1st stage SBR was only 6 ± 2 mg/L. The 2nd stage SBR was used to further remove COD in the effluent from the 1st stage SBR. The final effluent from the 2nd stage SBR had a COD concentration of 97 ± 16 mg/L with no detectable O&G content. Thus, a two-stage SBR system was shown to be feasible for treating high strength oily wastewater to meet the local discharge standards. © IWA Publishing 2004.Publication Improvement of recoveries for the determination of protozoa Cryptosporidium and Giardia in water using method 1623(2004-09) Hu, J.; Feng, Y.; Ong, S.L.; Ng, W.J.; Song, L.; Tan, X.; Chu, X.; CIVIL ENGINEERING; INSTITUTE OF ENGINEERING SCIENCEThe U.S. Environmental Protection Agency has developed method 1623 for simultaneous detection of Cryptosporidium oocysts and Giardia cysts in water. Method 1623 includes four major steps: filtration, immunomagnetic separation (IMS), fluorescent antibody (FA) staining and microscopic examination. It was noted that the recovery levels following IMS-FA and FA staining were high, averaging more than 92.0% and 89.0% for C. parvum oocysts and G. lamblia cysts, respectively. In contrast, when the filtration step was incorporated, the recovery level of C. parvum oocysts declined significantly to 18.1% in seeded tap water, while a relatively high recovery level of 77.2% for G. lamblia cysts could still be achieved. Further study indicated that the recovery level of C. parvum oocysts could be enhanced significantly when an appropriate amount of silica particles was added to a water sample. The recovery level of C. parvum oocysts was affected by particle size and concentration. The optimal silica particle size was determined to be within the range of 5-40 μm, and the corresponding optimal silica concentration was 1.42 g for 10-l tap water. When both G. lamblia cysts and C. parvum oocysts were spiked into the tap water sample containing the optimum amount of silica particles, the average recovery levels of oocysts and cysts were 82.7% and 75.4%, respectively. The results obtained clearly suggested that addition of an appropriate amount of silica particles could improve the recovery level of C. parvum oocysts significantly and yet there was no noticeable deleterious effect on the recovery level of G. lamblia cysts. Further study indicated that the rotation time in the IMS procedure using the Dynal GC-Combo IMS kit (which was recommended in method 1623) was important for G. lamblia cyst detection. In contrast, the recovery level of C. parvum oocysts was not affected by the rotation time. Furthermore, it was found that the recovery levels of C. parvum oocysts using methods 1622 and 1623 were quite close although different IMS kits were used in the two methods. © 2004 Elsevier B.V. All rights reserved.Publication Effect of mean cell residence time on the performance and microbial diversity of pre-denitrification submerged membrane bioreactors(2008-01) Tan, T.W.; Ng, H.Y.; Ong, S.L.; CIVIL ENGINEERING; DIVISION OF ENVIRONMENTAL SCIENCE & ENGGThe effect of mean cell residence time (MCRT) (5, 8.3, 16.7, and 33.3 d) on domestic wastewater treatment performance had been investigated using four bench-scale pre-denitrification submerged membrane bioreactors (MBR) operated in parallel. The 33.3-d MCRT MBR had the lowest microbial activities in terms of specific oxygen uptake rate, specific denitrification rate and observed sludge yield. Excellent COD removal efficiency (more than 95%) and nitrification (more than 97%) were observed in all the four MBRs investigated. Even though high nitrification can be achieved in all the MBRs, total nitrogen (TN) removal efficiency was found to be affected by MCRT with a maximum of 77% at 33.3-d MCRT. Better TN removal efficiency achieved in the 33.3-d MCRT MBR was due to the combined effect of high mixed liquor concentration and lower dissolved oxygen concentration in the recycled mixed liquor. A comparison of terminal-restriction fragment length polymorphisms (T-RFLP) fingerprints based on 16S rRNA and nirS gene revealed that the microbial communities of 5- and 8.3-d MCRT are grouped under the same branch while 16.7- and 33.3-d MCRT are grouped in another branch. T-RFLP based on amoA gene shows that members from the Nitrosomonas genus were more dominant under shorter MCRT operating environment. Clustering analysis did not show any correlation with the organic and nitrogen removal performance obtained in this study. © 2007 Elsevier Ltd. All rights reserved.Publication Calculation of effectiveness factors for spherical shells using shooting technique(1991-11) Wang, C.M.; Ong, S.L.; Ang, K.K.; CIVIL ENGINEERINGStevens et al. (1987) claimed that the orthogonal collocation method is a rapid and efficient technique for calculating effectiveness factors for the rate of chemical or biochemical reaction in spherical porous shells based on Michaelis-Menten kinetics. Stevens (1988) further applied the same method to determine the effectiveness factors for more general forms of Michaelis-Menten kinetics that incorporate the effects of substrate and product inhibitions. The writers, using the shooting method, show that Stevens et al. (1987) and Stevens (1988) soluitions obtained by the collocation method may be inaccurate, and even erroneous in the case in which substrate inhibition is considered in the analysis.