Browsing by Author "Subramanium, S. S."

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Development of a digestion technique for the determination of selected heavy metals in soil and sediments
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Wekasinghe, K.; Subramanium, S. S.
The objective of this study was to develop a new method on soil digestion techniques because some metal ions such as Cd, Pb, Cu, Cr and Zn are chelated by many soil-organic matter and complexes are inaccessible using previously studied techniques. This method development as well as the analysis of total contents of Cd, Pb, Cr, Cu and Zn in soil and sediment were conducted in selected areas in Medawachchiya, Sri Lanka which is an area that is mostly affected with Chronic Kidney Disease of unknown etiology. In this regard, the random soil samples were taken from cultivated and uncultivated paddy fields and the banks of the tanks. Sediments were collected randomly from the banks of the tanks. Three different digestion methods were used to analyze the heavy metals in soil to select the best digestion method for heavy metal analysis in soil for further studies. All three digestion methods have different combinations and quantities of concentrated acids (i.e., HNO3 and HCl) and H2O2. The heating methods were varied by using hot plate for one of the techniques (i.e., Gallenkamp) and microwave (i.e., Mars6 microwave digester) for the other two techniques. The digestion timing and temperature programming used are different in the three techniques. The results obtained using the Flame absorption spectrometer (i.e., GBC 2000, SavantAA) were analyzed. The results obtained for each technique were compared. Method spike recovery was conducted for the three methods to compare the difference, accuracy and effectiveness of each digestion processes. The concentration variation of heavy metals were as follows; Cd 1.0 mg/kg - 2.0 mg/kg, Cr 20 mg/kg - 60 mg/kg, Pb 10 mg/kg - 24 mg/kg, Zn 20 mg/kg - 110 mg/kg and Cu had the highest variation 20 mg/kg -170 mg/kg. Variation of the above values occur due to the variation of sample areas and environmental factors surrounding them. Further, the spiked method recovery for Zn suggests that the microwavebased digestion is more suitable for the analysis in soil. Results showed that the concentrations of Cu, Cr, Pb and Zn in soil were recorded within the permissible limits set by WHO. The Method LOD and LOQ suggests that the values obtained for Cd were not on the detectable limits and the use of GFAAS or any other sensitive analytical instrument is required for the analysis.
Model study on the adsorptive removal of nickel and cobalt ions from waste water using clay soil as a natural adsorbent.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Kumarihami, C. A. U. K.; Kulathunga, S.; Subramanium, S. S.
Requirement for developing strategies for employing cost effective and efficient adsorbents for the removal of heavy metals from waste streams has been steadily increasing over the past years. Naturally occurring clay is a cost effective and efficient adsorbent due to its natural abundance, high surface area, porosity and high cation exchange capacity. In Sri Lanka, untreated laboratory waste water which contains toxic heavy metals is released to the environment continuously due to the absence of proper laboratory waste water management strategies. An effective heavy metal adsorption into a particular adsorbent is governed by the factors such as initial metal ion concentration, ionic strength, pH and contact time etc. The present study mainly focused on optimizing pH and contact time to achieve maximum adsorption of Nickel and Cobalt on to clay soil. In this regard, clay soil sampling was carried out at a clay mining site of a brick making facility at Malwana area, followed by the standard soil characterization. The highest cation exchange capacity bearing clay soil was used to prepare the Na+ homoionic clay soil adsorbent. During this study, heavy metals under six different initial concentrations (i.e., 900 mg L-1, 1200 mg L-1, 1500 mg L-1, 1800 mg L-1, 2400 mg L-1 and 3000 mg L-1) were used. Adsorptive removals of Ni2+ and Co2+ by Na+ homoionic clay soil under different pH values (pH 3, pH 7 and pH 11) were studied by conducting single element batch experiments under each initial metal ion concentration in order to determine the effect of pH for the adsorption capacities of Nickel and Cobalt. Similarly, contact time of 1 day, 3 days and 5 days were used to determine the effect of the contact time. Flame atomic absorption spectrophotometry was used for the analysis of metal concentrations. The present study revealed that the nickel and cobalt ion adsorption capacities increase for each initial metal ion concentration upon increasing the pH and the contact time. Ni2+ at initial metal ion concentration of 3000 mg L-1 had the maximum adsorption of 64.09 ± 0.51 mg g-1 at pH 11 for the contact time of 3 days. Co2+ adsorption capacity nearly attained constant after 3 days. The maximum adsorption value of 63.88 ± 0.25 mg g-1 at pH 11 after 3 days was observed for Co2+ at the initial concentration of 3000 mg L-1. Further, for both metal ions, even though there was a significant increment with the increase of pH values, there was no significant difference in the adsorption capacities for the contact time after 3 days. This trend is in good agreement with previous studies carried out on removing of Cu, Pb, Cd and Cr ions using clay soil adsorbents.
Monitoring the accumulation of polycyclic aromatic hydrocarbons in the water bodies around Kelanitissa and Kerawalapitiya power plants in Sri Lanka.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Chandrasiri, H. M. H. B.; Doole, F. T.; Subramanium, S. S.
Polycyclic aromatic hydrocarbons (PAHs) are a group of environmental contaminants which are formed due to natural processes such as forest fires and anthropogenic activities including incomplete combustion of organic matter (eg. wood, carbon, coke, fossil fuel etc.). These ubiquitous contaminants have attracted attention due to their toxicity and carcinogenicity. The Agency for the Toxic Substances and Disease Registry (ATSDR) and the United States Environmental Protection Agency (US EPA) have identified 16 PAHs as priority pollutants based on their health effects. In this study, the water samples which were collected from Sebastian canal near Kelanitissa power plant and Hamilton canal near Kerawalapitiya power plant were extracted using dichloromethane and were analyzed by HPLC with UV-DAD (254 nm) and FLD (excitation at 250 nm, emission at 410 nm) detectors. This study aim to determine the seasonal variation and accumulation trend of the PAH content in water bodies around Kelanitissa and Kerawalapitiya power stations in Sri Lanka. The study revealed the presence of low, medium and high molecular weight PAHs in the water samples obtained from Sebastian canal near Kelanitissa power plant and Hamilton canal near Kerawalapitiya power plant. Total concentration of PAHs in surface water samples obtained from Sebastian canal during rainy season (April 2015), dry season (July 2015) and rainy season (June 2016) were 0.11-1.71 μg/L, 2.36-14.68 μg/L and 6.88 μg/L - 10.05 μg/L, respectively. Furthermore, PAH content in water samples obtained from Hamilton canal during rainy season (April 2015), dry season (July 2015) and rainy season (April 2016) were 0.16-2.74 μg/L, 11.06- 54.89 μg/L and 5.35 - 7.79 μg/L, respectively. As expected, high amount of PAHs were detected during the dry season due to the accumulation. However, the total PAHs in the Sebastian canal during the rainy season of June 2016 has shown a significantly high amount than during the rainy season of April 2015. Also the same trend can be observed in Hamilton canal where high amount of PAHs were detected during the rainy season of April 2016 than during the rainy season of April 2015. This may indicate an accumulation of PAHs with time in the water bodies near the power plants. Further monitoring for longer durations is required to identify the accumulation trend.