Rajasekhar Balasubramanian
Email Address
ceerbala@nus.edu.sg
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Publication Seven Southeast Asian studies (7 SEAS): Atmospheric supersite in Singapore(2009) Chew, B.N.; Liew, S.C.; Balasubramanian, R.; Yu, L.; Bucholtz, A.; Reid, J.S.; DIVISION OF ENVIRONMENTAL SCIENCE & ENGG; CTR FOR REM IMAGING,SENSING & PROCESSINGThrough collaborations with scientific partners in Taiwan and various Southeast Asian countries such as Indonesia, Malaysia, Philippines, Singapore, Thailand and Vietnam, the Seven SouthEast Asian Studies (7 SEAS) is jointly initiated by NASA's Radiation Science, Tropospheric Chemistry, Air Quality and Oceanography programmes as well as the Office of Naval Research (ONR), the Office of Naval Research - Global (ONRG) and the US State Department in an effort to investigate the complex interactions between aerosols (anthropogenic or natural) and meteorological systems, especially with clouds, and their impacts on air quality in the Southeast Asian region. 7 SEAS is a multi-disciplinary regional science programme which operates with the integrative support of in-situ measurements, remote sensing and scientific modeling. Under the cooperative framework of 7 SEAS, an atmospheric supersite has been established in the National University of Singapore to collect baseline data on air quality and the urban atmosphere as well as information on the transboundary haze during periods of severe biomass burning. The station has a comprehensive suite of instruments to measure the radiometric and meteorological properties of the atmosphere, vertical distribution of aerosols and clouds, and the microphysical and chemical properties of aerosols at the surface. Among the instruments, the on-site Cimel Sunphotometer is part of the world-wide AErosol RObotic NETwork (AERONET) while the Micro Pulse Lidar (MPL) is part of the NASA's growing Micro Pulse Lidar Network (MPLNET).Publication Determination of aldehydes in rainwater using micro-solid-phase extraction and high-performance liquid chromatography(2010-10) Basheer, C.; Pavagadhi, S.; Yu, H.; Balasubramanian, R.; Lee, H.K.; DIVISION OF ENVIRONMENTAL SCIENCE & ENGG; CHEMISTRYA simple and rapid extraction procedure was developed for determining aldehydes in rainwater samples. This extraction technique involved the use of micro-solid-phase extraction in which the sorbent was held within a polypropylene membrane envelope, followed by high-performance liquid chromatographic analysis. Aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and valeraldehyde were used as model compounds. Extraction conditions were optimized. The method linearity ranged between 0.5 and 50μgl-1 with the correlation coefficient of 0.987-0.999. The relative standard deviations (RSDs) of the method ranged from 7 to 12%. Method detection limits were in the range of 0.07-0.15μgl-1, which is lower than those previously reported for solid-phase microextraction combined with gas chromatography-mass spectrometric techniques. The proposed extraction technique was used for determination of aldehydes in rainwater samples to demonstrate the applicability of the method. © 2010 Elsevier B.V.Publication Preparation and characterization of fuel pellets from woody biomass, agro-residues and their corresponding hydrochars(2014-01) Liu, Z.; Quek, A.; Balasubramanian, R.; CIVIL & ENVIRONMENTAL ENGINEERINGTwo types of biofuel pellets were prepared from raw biomass and the corresponding hydrochar. Fuel qualities of the two types of pellets including pellet density, mechanical strength and combustion characteristics were investigated. The results showed that the hydrochar pellets had higher fixed carbon contents, elevated heating values and enhanced mass densities in comparison to those raw biomass pellets. The presence of extractives led to the low tensile strength of biomass pellets, while the formation of liquid bridge and significantly enhanced attractive forces including H-bonding and van der Waal's forces mainly contributed to the strong bonding within the matrix of hydrochar pellets. The hydrochar pellets combusted at elevated temperatures and wide temperature ranges compared to biomass pellets. The high mechanical strength, low moisture uptake and improved combustion property indicated that hydrochar pellets were more suitable than raw biomass pellets as solid biofuels. The present study demonstrated that hydrothermal carbonization (HTC) combined with pelletization provides an alternative for solid biofuel production from biomass resources, especially for the abundant agricultural residues. © 2013 Elsevier Ltd.Publication Insights into lipidomic perturbations in zebrafish tissues upon exposure to microcystin-LR and microcystin-RR(2013-12-17) Pavagadhi, S.; Natera, S.; Roessner, U.; Balasubramanian, R.; CIVIL & ENVIRONMENTAL ENGINEERINGThis work represents the first study of its kind that was conducted to evaluate changes in lipid metabolic networks following a balneation exposure of adult zebrafish to MCLR (microcystin-leucine-arginine) and MCRR (microcystin-arginine-arginine) at a sublethal dose (10 μg L-1) for a period of 30 days. Following the exposure to MCLR and MCRR, gills, liver, intestine, and brain tissues were harvested for metabolite extraction. Extracted metabolites were detected using qTOF-LC-MS (time-of-flight-liquid chromatography-mass spectrometry). Metabolites were identified using Kegg pathways. The identified metabolites are shown on lipid biochemical maps to demonstrate major perturbations in the metabolic machinery. Results showed that most of the metabolic pathways under the lipid class were affected in different tissues of zebrafish following the exposure to MCLR and MCRR (10 μg L -1 for 30 days). The kind and flux of metabolic perturbations varied among different tissues of the organs after the exposure to MCLR and MCRR with the tissues of gills being the most affected. Among the various lipid pathways, cholesterol synthesis was affected significantly as observed from the highest number of perturbed metabolites in that pathway. Cholesterol is responsible for synthesis of steroid hormones and bile acids, which have been recognized as endocrine signaling molecules. Disruption in the synthesis of these compounds following MCLR/MCRR exposure suggests that MCs are capable of causing endocrine disruption among aquatic organisms even under sublethal conditions. Apart from cholesterol synthesis, various other metabolic pathways belonging to the class of essential fatty acids and lipid oxidation were also observed to be perturbed following a balneation exposure of zebrafish to MCLR/MCRR. © 2013 American Chemical Society.Publication Impact of biomass burning on Ocean water quality in Southeast Asia through atmospheric deposition: Field observations(2010) Sundarambal, P.; Balasubramanian, R.; Tkalich, P.; He, J.; CIVIL ENGINEERING; DIVISION OF ENVIRONMENTAL SCIENCE & ENGG; TROPICAL MARINE SCIENCE INSTITUTEAtmospheric nutrients have recently gained considerable attention as a significant additional source of new nitrogen (N) and phosphorus (P) loading to the ocean. The effect of atmospheric macro nutrients on marine productivity depends on the biological availability of both inorganic and organic N and P forms. During October 2006, the regional smoke haze episodes in Southeast Asia (SEA) that resulted from uncontrolled forest and peat fires in Sumatra and Borneo blanketed large parts of the region. In this work, we determined the chemical composition of nutrients in aerosols and rainwater during hazy and non-hazy days to assess their impacts on aquatic ecosystem in SEA for the first time. We compared atmospheric dry and wet deposition of N and P species in aerosol and rainwater in Singapore between hazy and non-hazy days. Air mass back trajectories showed that large-scale forest and peat fires in Sumatra and Kalimantan were a significant source of atmospheric nutrients to aquatic environments in Singapore and SEA region on hazy days. It was observed that the average concentrations of nutrients increased approximately by a factor of 3 to 8 on hazy days when compared with non-hazy days. The estimated mean dry and wet atmospheric fluxes (mg/m2/day) of total nitrogen (TN) were 12.72 ± 2.12 and 2.49 ± 1.29 during non-hazy days and 132.86 ± 38.39 and 29.43 ± 10.75 during hazy days; the uncertainty estimates are represented as 1 standard deviation (1σ) here and throughout the text. The estimated mean dry and wet deposition fluxes (mg/m2/day) of total phosphorous (TP) were 0.82 ± 0.23 and 0.13 ± 0.03 for non-hazy days and 7.89 ± 0.80 and 1.56 ± 0.65 for hazy days. The occurrences of higher concentrations of nutrients from atmospheric deposition during smoke haze episodes may have adverse consequences on receiving aquatic ecosystems with cascading impacts on water quality. © 2010 Author(s).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 Chemical characterization of rainwater at Singapore(2003-06) Hu, G.P.; Balasubramanian, R.; Wu, C.D.; CHEMICAL & ENVIRONMENTAL ENGINEERINGA short term study of the chemical composition of rainwater was carried out from November 1999 to October 2000 in Singapore. The rainwater was typically acidic with a mean pH of 4.2. Sulfate was the most abundant ion and comparable to the results reported for other industrialized regions. The concentrations of major ions (NH4 +, Ca2+, K+, Na+, Mg2+, SO4 2+, NO3 2-, Cl-, HCOO-, CH3COO-) varied monthly. Results show that local meteorological conditions influence the chemical compositions to a significant extent. The pollutants in rainwater were derived from long range and local (industry and traffic) sources. © 2003 Elsevier Science Ltd. All rights reserved.Publication Role of hydrocarbon degrading bacteria Serratia marcescens ACE2 and Bacillus cereus ACE4 on corrosion of carbon steel API 5LX(2011-09-07) Rajasekar, A.; Balasubramanian, R.; Vm Kuma, J.; CIVIL ENGINEERING; CIVIL & ENVIRONMENTAL ENGINEERINGThis paper reports the microbiologically induced corrosion (MIC) and electrochemical behavior of carbon steel (API 5LX) in the presence of hydrocarbon-degrading bacteria Bacillus cereus ACE4 (a Gram-positive bacterium) and Serratia marcescens ACE2 (a Gram-negative bacterium). Weight loss studies and metallographic analysis of the metal API 5LX exposed to a simulated corrosive environment showed that the bacterium ACE4 caused severe pitting corrosion than that of bacterium ACE2. As part of biodegradation studies, the impact of aryl hydrocarbon hydroxylase (AHH) on diesel degradation was investigated along with reduction of total hydrocarbons. It was clearly observed that, during the biodegradation experiment in the presence of B. cereus ACE4, the content of the total hydrocarbons decreased significantly due to their metabolism induced by AHH enzymes when compared to S. marcescens ACE2. Degraded petroleum hydrocarbons (diesel) act as a good nutrient for bacteria, which in turn increases the proliferation of bacteria on the steel and determines the nature of corrosion. Metal oxides such as MnO2 and Fe 2O3 were found as part of the corrosion products, indicating that the ACE4 bacterium is capable of converting the elements on the carbon steel (API 5LX) to their metal oxides and thus accelerating severe pitting corrosion on the surface of the pipeline networks. Overall, the study provides an insight into the microbiologically influenced corrosion of carbon steel API 5LX by two hydrocarbon-degrading bacteria in diesel fuel/water mixtures. © 2011 American Chemical Society.Publication Determination of semi-volatile organochlorine compounds in the atmosphere of Singapore using accelerated solvent extraction(2009-05) He, J.; Balasubramanian, R.; Karthikeyan, S.; Joshi, U.M.; CIVIL ENGINEERING; DIVISION OF ENVIRONMENTAL SCIENCE & ENGGAccelerated solvent extraction (ASE) has been applied to the quantitative extraction of organochlorine compounds (OCs), including organochlorine pesticides (HCHs, DDXs) and polychlorinated biphenyls (PCBs) present in both atmospheric particulate and gaseous phase. Extraction parameters such as the combination of solvents, extraction temperature, and static extraction time were investigated and optimized. Effective extraction can be carried out using a 3:1 mixture of n-hexane and acetone as extraction solvents at 100 °C in 20 min for all the compounds studied. The entire analytical procedure developed in this study proves to be reliable as evident from the analysis of specific surrogate standards with the mean recoveries per sample being greater than 82%. The optimized method was validated using NIST-certified SRM 1649a. Semi-volatile OCs, in the atmosphere of Singapore were quantified using the optimized ASE method together with GC-MS. Total average concentrations of ΣHCHs, ΣDDXs, and ΣPCBs in air samples were 244.9 ± 88.5 pg m-3, 7.7 ± 4.1 pg m-3, and 34.1 ± 19.7 pg m-3, respectively. The distribution of these compounds between the gas and particulate phase is discussed. Possible sources of atmospheric OCs are evaluated based on the molecular ratio of specific compounds and backward air trajectory analysis. © 2009 Elsevier Ltd. All rights reserved.Publication From Module to MOOC: Designing an Interdisciplinary Online Course on the Novel Theme "Microbiomes & Sustainability"(2020-12-08) Rashid, Rafi; Balasubramanian, Rajasekhar; Williams, Rohan; Dr Rafi Rashid; CIVIL AND ENVIRONMENTAL ENGINEERING; LIFE SCIENCES INSTITUTE