Technology and Water Quality Office

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Rezaeinejad S.,National University of Singapore | Vergara G.G.R.V.,National University of Singapore | Woo C.H.,Technology and Water Quality Office | Lim T.T.,Technology and Water Quality Office | And 2 more authors.
Water Research | Year: 2014

An assessment of the occurrence and concentration of enteric viruses and coliphages was carried out in highly urbanized catchment waters in the tropical city-state of Singapore. Target enteric viruses in this study were noroviruses, adenoviruses, astroviruses and rotaviruses. In total, 65 water samples were collected from canals and the reservoir of the Marina catchment on a monthly basis over a period of a year. Quantitative PCR (qPCR) and single agar layer plaque assay (SAL) were used to enumerate target enteric viruses and coliphages in water samples, respectively. The most prevalent pathogen were noroviruses, detected in 37 samples (57%), particularly norovirus genogroup II (48%), with a mean concentration of 3.7×102 gene copies per liter. Rotavirus was the second most prevalent virus (40%) with a mean concentration of 2.5×102GC/L. The mean concentrations of somatic and male-specific coliphages were 2.2×102 and 1.1×102PFU/100ml, respectively. The occurrence and concentration of each target virus and the ratio of somatic to male-specific coliphages varied at different sampling sites in the catchment. For sampling sites with higher frequency of occurrence and concentration of viruses, the ratio of somatic to male-specific coliphages was generally much lower than other sampling sites with lower incidences of enteric viruses. Overall, higher statistical correlation was observed between target enteric viruses than between enteric viruses and coliphages. However, male-specific coliphages were positively correlated with norovirus concentrations. A multi-level integrated surveillance system, which comprises the monitoring of bacterial indicators, coliphages and selected enteric viruses, could help to meet recreational and surface water quality criteria in a complex urbanized catchment. © 2014 Elsevier Ltd.


Vergara G.G.R.V.,National University of Singapore | Goh S.G.,National University of Singapore | Rezaeinejad S.,National University of Singapore | Chang S.Y.,Technology and Water Quality Office | And 2 more authors.
Water Research | Year: 2015

This study aimed to evaluate the relationship between FRNA coliphages (FRNA GI to GIV) and human enteric viruses (human adenoviruses, HAdV, astroviruses, AstV, noroviruses, NoV, and rotaviruses, RoV) in a tropical urban freshwater catchment. Positive associations between human-specific coliphages and human viral pathogens substantiate their use as viral indicators and in microbial source tracking. Reverse transcription qPCR was used to measure the concentrations of viruses and FRNA coliphages in concentrated water samples. Environmental water samples were also analyzed for male-specific (F+) and somatic (Som) coliphages using plaque assay. The most abundant enteric virus was NoV (55%) followed by HAdV (33%), RoV (33%), and AstV (23%), while the most abundant FRNA genogroup was GI (85%) followed by GII (48%), GIV (8%) and GIII (7%). Concentrations of human-specific coliphages FRNA GII were positively correlated with NoV, HAdV, RoV, AstV, F+ and Som (τ=0.5 to 0.3, P<0.05) while concentrations of animal-specific coliphages FRNA GI were negatively correlated with HAdV and RoV (τ=-0.2, P<0.05). This study demonstrates statistical relationships between human-specific coliphages and a suite of human enteric viruses in the environment. © 2015 Elsevier Ltd.


Loke L.H.L.,National University of Singapore | Clews E.,National University of Singapore | Low E.,Technology and Water Quality Office | Belle C.C.,National University of Singapore | And 3 more authors.
Aquatic Biology | Year: 2010

Reliable quantitative methods for sampling invertebrate communities are critical for effective freshwater biomonitoring. We tested a range of devices and protocols for sampling benthic macroinvertebrates in shallow tropical lakes; this is the first time this has been attempted in Southeast Asia. First, a pilot study to identify a suitable artificial substrate and colonisation period was conducted. Coconut brushes combined with split palm fronds attracted the greatest macroinvertebrate abundance and richness. A colonisation period of 4 wk was sufficient to capture the key macroinvertebrate families and orders. Second, the sampling efficiencies of 7 artificial substrate sampler designs and 2 hydraulic suction devices were compared in rocky and soft-sediment littoral habitats of a reservoir in Singapore. Among the 9 different sampling techniques tested, the samplers containing coconut brushes and split palm fronds again were the most effective at capturing the greatest total abundance and family richness of benthic macroinvertebrates. Variation in community structure among sampler types was largely explained by the abundance of Chironomidae and Polymitarcyidae (Ephemeroptera). Results were similar between sites dominated by 'rocky' and 'vegetated' littoral habitats. This project identified a sampling device suitable for biomonitoring Singapore's lentic environment, with protocols likely to apply to shallow tropical lentic systems elsewhere. © Inter-Research 2010.


PubMed | National University of Singapore, University of North Carolina at Chapel Hill and Technology and Water Quality Office
Type: | Journal: Water research | Year: 2014

An assessment of the occurrence and concentration of enteric viruses and coliphages was carried out in highly urbanized catchment waters in the tropical city-state of Singapore. Target enteric viruses in this study were noroviruses, adenoviruses, astroviruses and rotaviruses. In total, 65 water samples were collected from canals and the reservoir of the Marina catchment on a monthly basis over a period of a year. Quantitative PCR (qPCR) and single agar layer plaque assay (SAL) were used to enumerate target enteric viruses and coliphages in water samples, respectively. The most prevalent pathogen were noroviruses, detected in 37 samples (57%), particularly norovirus genogroup II (48%), with a mean concentration of 3.7 10(2) gene copies per liter. Rotavirus was the second most prevalent virus (40%) with a mean concentration of 2.5 10(2) GC/L. The mean concentrations of somatic and male-specific coliphages were 2.2 10(2) and 1.1 10(2) PFU/100 ml, respectively. The occurrence and concentration of each target virus and the ratio of somatic to male-specific coliphages varied at different sampling sites in the catchment. For sampling sites with higher frequency of occurrence and concentration of viruses, the ratio of somatic to male-specific coliphages was generally much lower than other sampling sites with lower incidences of enteric viruses. Overall, higher statistical correlation was observed between target enteric viruses than between enteric viruses and coliphages. However, male-specific coliphages were positively correlated with norovirus concentrations. A multi-level integrated surveillance system, which comprises the monitoring of bacterial indicators, coliphages and selected enteric viruses, could help to meet recreational and surface water quality criteria in a complex urbanized catchment.


Qin J.-J.,Technology and Water Quality Office | Chen S.,Nanyang Technological University | Oo M.H.,Technology and Water Quality Office | Kekre K.A.,Technology and Water Quality Office | And 2 more authors.
Water Science and Technology | Year: 2010

Concentration polarization (CP) is an important issue in forward osmosis (FO) processes and it is believed that the coupled effect of dilutive internal CP (DICP) and concentrative external CP (CECP) limits FO flux. The objective of this study was to distinguish individual contribution of different types of DICP and CECP via modeling and to validate it by pilot studies. The influence of DICP/CECP on FO flux has been investigated in this study. The CP model presented in this work was derived from a previous study and evaluated by bench-scale FO experiments. Experiments were conducted with drinking water as the feed and NaCl/MgSO4 as draw solutions at different concentrations and velocities. Modeling results indicated that DICP contributed to a flux reduction by 99.9% for 0.5M NaCl as a draw solution although the flow pattern of both feed and draw solutions was turbulent. DICP could be improved via selection of the draw solution. The modeling results were well fit with the experimental data. It was concluded that the model could be used for selection of the draw solution and prediction of water flux under similar situation. A draw solution with greater diffusion coefficient or a thinner substrate of an asymmetric FO membrane resulted in a higher flux. © IWA Publishing 2010.


Cornelissen E.R.,KWR Watercycle Research Institute | Harmsen D.J.H.,KWR Watercycle Research Institute | Beerendonk E.F.,KWR Watercycle Research Institute | Qin J.J.,Technology and Water Quality Office | Kappelhof J.W.M.N.,Waternet
Journal of Water Reuse and Desalination | Year: 2011

Forward osmosis (FO) is a concentration driven membrane process which recently gained an increase in attention due to the development of improved FO membranes. Most of the currently available data on FO research is obtained on small laboratory-scale set-ups, thereby overlooking the effects of scaling-up to pilot or full-scale size. In this paper, FO experiments are carried out with a 10.16 cm (4-in) spiral wound FO (SWFO) Hydration Technologies Innovations (HTI) module. The performance of the SWFO module was investigated during daily experiments and the influence of two types of draw solutions (NaCl and MgCl2) was evaluated and compared to data from lab-scale FO research. Furthermore, the difference between fixed draw solution concentration and draw solution dilution was studied for both draw solutions. Salt flux was determined from the increase in: (i) conductivity; and (ii) individual ion concentration in the feed vessel. Water and salt flux values from laboratory-scale membrane FO experiments were similar but slightly lower than that of the SWFO module in the fixed draw solution concentration experiments (respectively 5 L/m2h and 3 g/m2h for 0.5 M NaCl). Salt flux values obtained from individual ion measurements were lower and more accurate compared to that determined by conductivity measurements. © IWA Publishing 2011.


Qin J.-J.,Technology and Water Quality Office | Oo M.H.,Technology and Water Quality Office | Kekre K.A.,Technology and Water Quality Office | Seah H.,Technology and Water Quality Office
Water Science and Technology: Water Supply | Year: 2010

This paper focuses on the systematic approach adopted towards optimizing the salt consumption when using direct-osmosis - high-salinity (DO-HS) cleaning method for RO membranes in water reuse application. Trials were carried out on a pilot RO system with a capacity of 50m 3/day. Initially, proof of concept for the DO-HS method in water reuse application was established wherein the profile of osmotic driving force for DO backwash, DO backwash flow during HS injection, removal of foulants with DO-HS treatment and lower RO fouling rate with the DO-HS method were demonstrated. 6 months of trials further demonstrated that RO membrane fouling rate and CIP frequency could be significantly reduced with the DO-HS method and there was no impact on the performance of RO membranes. Further trials were carried out focusing of salt requirements and it was found that salt injection duration could be reduced by 68% while the 48-h interval of salt injection was not recommended. Currently, the salt consumption has been reduced from the initial at 0.5 ton to the current at 0.16 ton as per 10,000m 3/day production. The study is ongoing to achieve the target of 0.05 ton for ease of operation. © IWA Publishing 2010.


Qin J.-J.,Technology and Water Quality Office | Kekre K.A.,Technology and Water Quality Office | Oo M.H.,Technology and Water Quality Office | Tao G.,Technology and Water Quality Office | And 4 more authors.
Water Science and Technology | Year: 2010

Preliminary study on a novel osmotic membrane bioreactor (OMBR) was explored. Objective of this study was to investigate the effects of draw solution on membrane flux and air scouring at the feed side on fouling tendency in a pilot OMBR system composing the anoxic/aerobic and forward osmosis (FO) processes. Domestic sewage was the raw feed, FO membrane from HTI and NaCl/MgSO4 draw solutions were used in the experiments. Fluxes of 3 l/m2/h (LMH) and 7.2 LMH were achieved at osmotic pressure of 5 and 22.4 atm, respectively. No significant flux decline was observed at 3 LMH over 190 h and at 7.2 LMH over 150 h when air scouring was provided at the feed side of the membrane. However, without air scouring, the flux at 22.4 atm osmotic pressure declined by 30% after 195 h and then levelled off. The potential advantages of the fouling reversibility with air scouring under the operating conditions of the pilot OMBR and better water quality in OMBR over the conventional MBR were preliminarily demonstrated. © IWA Publishing 2010.


Qin J.-J.,Technology and Water Quality Office | Oo M.H.,Technology and Water Quality Office | Kekre K.A.,Technology and Water Quality Office
Water Science and Technology: Water Supply | Year: 2010

We have demonstrated a novel backwash cleaning technique of direct osmosis (DO)-high salinity (HS) for reverse osmosis (RO) fouling control in water reuse. An UF-RO pilot system was continuously (24-h) operated on site with the secondary effluent as the feed over 4 months. The RO plant was run at 75% recovery and at the membrane flux of 17 lm-2 h-1 (LMH) to simulate the full scale NEWater production when DO-HS treatment was conducted once per day and five times per week during the last two months. Permeability of RO membranes as a function of elapse time of the pilot operation was monitored and compared over different durations. Impact of DO-HS treatment on RO product quality in terms of TOC and conductivity was investigated. It was concluded that the DO-HS treatment preliminarily demonstrated a benefit to low RO fouling rate by 2.5-4 times in 30-60 days without interruption on RO operation and impact on RO product quality. © IWA Publishing 2010.


PubMed | Technology and Water Quality Office
Type: Journal Article | Journal: Water science and technology : a journal of the International Association on Water Pollution Research | Year: 2010

Preliminary study on a novel osmotic membrane bioreactor (OMBR) was explored. Objective of this study was to investigate the effects of draw solution on membrane flux and air scouring at the feed side on fouling tendency in a pilot OMBR system composing the anoxic/aerobic and forward osmosis (FO) processes. Domestic sewage was the raw feed, FO membrane from HTI and NaCl/MgSO4 draw solutions were used in the experiments. Fluxes of 3l/m2/h (LMH) and 7.2LMH were achieved at osmotic pressure of 5 and 22.4atm, respectively. No significant flux decline was observed at 3 LMH over 190h and at 7.2 LMH over 150h when air scouring was provided at the feed side of the membrane. However, without air scouring, the flux at 22.4atm osmotic pressure declined by 30% after 195h and then levelled off. The potential advantages of the fouling reversibility with air scouring under the operating conditions of the pilot OMBR and better water quality in OMBR over the conventional MBR were preliminarily demonstrated.

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