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Yap W.J.,Nanyang Technological University | Zhang J.,Nanyang Technological University | Lay W.C.L.,Public Utilities Board PUB | Cao B.,Nanyang Technological University | And 2 more authors.
Bioresource Technology | Year: 2012

In the last few years, extensive research has been dedicated to development of a novel osmotic membrane bioreactor (OMBR), which combines high-retention osmotic separation and biological reactions in a single vessel. Although promising results have been reported in the literature, some challenges associated with applications of OMBR remain unresolved at the present stage of development, including lack of a high performance forward osmosis (FO) membrane, identification of an ideal draw solute and effect of salt accumulation on biological activity. Therefore, this paper attempts to provide a comprehensive review of state of the art of OMBR for water and wastewater reclamation. © 2012 Elsevier Ltd.

Ong G.S.,Public Utilities Board PUB | Kalyanaraman G.,Public Utilities Board PUB | Wong K.L.,Public Utilities Board PUB | Wong T.H.F.,Monash University
WSUD 2012 - 7th International Conference on Water Sensitive Urban Design: Building the Water Sensitive Community, Final Program and Abstract Book | Year: 2012

Active, Beautiful and Clean Waters, (ABC Waters) Programme is a long term strategic programme by PUB that aims to transform utilitarian canals, drains and reservoirs in Singapore into clean flowing rivers, lakes and streams that blend naturally into the urban environment. A key strategy of the programme is to adopt "ABC Waters Management" which entails detaining and treating stormwater runoff closer to source using green features to achieve sustainable stormwater management. In respect to this, PUB has implemented several pilot projects to demonstrate the efficacy of ABC Waters design features like bioretention systems, constructed wetlands in tropical climate. The first bioretention system built in Singapore in 2008 is a 240m 2 rain garden retrofitted in a residential estate to capture and treat runoff from the adjacent area. The rain garden has since gained popularity in Singapore. Upon completion of the project, a detailed hydrological and water quality monitoring was undertaken to test the performance of this system. The monitoring results indicate that the Balam Rain garden operates well within its design capability. The anoxic layer of the rain garden has found to enhance nitrogen removal. This paper presents the details, inferences and results of the monitoring study of this bioretention system.

You L.,National University of Singapore | Nguyen V.T.,Public Utilities Board PUB | Pal A.,National University of Singapore | Chen H.,National University of Singapore | And 3 more authors.
Science of the Total Environment | Year: 2015

Previous studies showed the presence of multiple emerging organic contaminants (EOCs) in urban surface waters of Singapore even though there are no obvious direct wastewater discharges. In this study, we investigated the occurrence and distribution of 17 pharmaceuticals and personal care products (PPCPs) and endocrine disruptive compounds (EDCs) in a tropical urban catchment of Singapore. Monthly samples were collected from a reservoir and its 5 upstream tributaries during a 16-month period. Analysis of samples showed all sites had measurable PPCP and EDC concentrations, with caffeine (33.9-2980. ng/L), salicylic acid (5-838. ng/L), acetaminophen (<. 4-485.5. ng/L), BPA (<. 2-919.5. ng/L) and DEET (13-270. ng/L) being the most abundant. Marked differences in concentrations of target analytes between the reservoir and upstream tributaries were observed, and were tentatively attributed to the spatial differences in source inputs, water dilution capacity as well as natural attenuation of EOCs. Significant correlations between EOCs and conductivity, dissolved oxygen, chlorophyll a, turbidity, nutrients and cumulative precipitation were observed. These factors appeared to affect the distribution and attenuation of EOCs, depending on their physicochemical properties. Rainfall also influenced the temporal distribution of caffeine, BPA, triclosan, fipronil and DEET in the reservoir. Ecological risk assessment showed that caffeine, acetaminophen, estrone, BPA, triclosan and fipronil may warrant further survey. In particular, BPA levels exceeded the literature-based Predicted No-Effect Concentration (PNEC) value, highlighting the need for source control and/or water remediation in this urban catchment. © 2015 Elsevier B.V.

Nguyen T.V.,Public Utilities Board PUB | Reinhard M.,National University of Singapore | Reinhard M.,Stanford University | Chen H.,National University of Singapore | Gin K.Y.-H.,National University of Singapore
Environmental Science and Pollution Research | Year: 2016

Transport and fate of perfluoro- and polyfluoroalkyl substances (PFASs) in an urban water body that receives mainly urban runoff was investigated. Water, suspended solids, and sediment samples were collected during the monsoon (wet) and inter-monsoon (dry) season at different sites and depths. Samples were analyzed for C7 to C12 perfluoroalkyl carboxylate homologues (PFCAs) (PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA), perfluorohexane, perfluorooctane, and 6:2-fluorotelomer sulfonate (PFHxS, PFOS, and 6:2FtS, respectively), perfluorooctane sulfonamide (FOSA), N-ethyl FOSA (sulfluramid), N-ethyl sulfonamidoethanol (N-EtFOSE), and N-methyl and N-ethyl sulfonamidoacetic acid (N-EtFOSAA and N-MeFOSAA, respectively). Concentrations in wet samples were only slightly higher. The sum total PFAS (ΣPFAS) concentrations dissolved in the aqueous phase and sorbed to suspended solids (SS) ranged from 107 to 253 ng/L and 11 to 158 ng/L, respectively. PFOA, PFOS, PFNA, PFHxS, and PFDA contributed most (approximately 90 %) to the dissolved ΣPFASs. N-EtFOSA dominated the particulate PFAS burden in wet samples. KD values of PFOA and PFOS calculated from paired SS and water concentrations varied widely (1.4 to 13.7 and 1.9 to 98.9 for PFOA and PFOS, respectively). Field derived KD was significantly higher than laboratory KD suggesting hydrophobic PFASs sorbed to SS resist desorption. The ΣPFAS concentrations in the top sedimentary layer ranged from 8 to 42 μg/kg and indicated preferential accumulation of the strongly sorbing long-chain PFASs. The occurrence of the metabolites N-MeFOSAA, N-EtFOSAA and FOSA in the water column and sediments may have resulted from biological or photochemical transformations of perfluorooctane sulfonamide precursors while the absence of FOSA, N-EtFOSA and 6:2FtS in sediments was consistent with biotransformation. © 2016 Springer-Verlag Berlin Heidelberg

Chen H.,National University of Singapore | Reinhard M.,National University of Singapore | Nguyen V.T.,Public Utilities Board PUB | Gin K.Y.H.,National University of Singapore
Chemosphere | Year: 2016

Uncertainty about the extent to which contaminant sorption by suspended solids and bed sediments is irreversible is a major impediment for modeling and managing the water quality of surface water resources. This study examined reversible and irreversible sorption of several perfluorinated compounds (PFCs) to bed sediments from an urban reservoir. PFCs investigated include C4, C6, C8, C9 and C10 perfluoroalkanoate homologues (PFBA, PFHxA, PFOA, PFNA and PFDA, respectively) and perfluorooctane and hexane sulfonate (PFOS and PFHxS, respectively). Although sorption branches of the PFOS, PFNA and PFDA isotherms were nearly linear (implying a partitioning-like process), desorption experiments indicated that a fraction of the sorbed PFCs were entrapped and resistant to desorption. The hysteretic desorption branches were approximately linear. Irreversibility increased with chain length and was nearly complete for PFDA (thermodynamic irreversibility index (TII) 0.98). For the weakly sorbing PFOA and PFHxS, sorption was largely reversible. Data suggest that (1) for the strongly sorbing PFCs, e.g. PFNA, PFDA and PFOS, bed sediments acted predominantly as irreversible sinks, (2) aqueous concentrations of the moderately sorbing PFCs (PFOA and PFHxS) are buffered by reversibly sorbing suspended solids, and (3) the short-chain PFCs (PFBA and PFHxA) are not significantly sorbed and therefore not expected to be significantly influenced by sediment transport. Situations in which highly contaminated particles entering relatively clean water bodies, equilibrium is approached from the reverse (desorption) direction. For irreversibly sorbed contaminants field-based KD values will be higher than the KD values derived from laboratory sorption data obtained from forward sorption experiments. © 2015 Elsevier Ltd.

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