Browsing by Author "de Silva, R.C.L."

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Analysis of undergraduate chemistry scores and the study of correlation between G.C.E. Advanced level Z-scores, with undergraduate chemistry scores in the University of Kelaniya
(Sri Lanka Association for the Advancement of Science, 2010) Walgama, C.T.; de Silva, R.C.L.
Atmospheric deposition of Polycyclic Aromatic Hydrocarbons (PAHs) around two metropolitan areas in the western province of Sri Lanka, using moss (Hyophila involuta) as a biomonitor
(Sri Lanka Association for the Advancement of Science, 2015) Jayalath, K.G.; Deeyamulla, M.P.; de Silva, R.C.L.
Background Levels of Heavy Metals in Moss Hyophila Involuta as A Bioindicator Using Four Strict Nature Reserves in Sri Lanka: Sinharaja Rainforest, Knuckles Mountain Range, Horton Plains National Park and Hakgala Mountain Forest
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Jayalath, J.I.K.G.; Deeyamulla, M.P.; de Silva, R.C.L.
Atmospheric deposition of six heavy metals (Zn, Cu, Pb, Ni, Cr and Cd) using the moss Hyophila involuta as a bioindicator was investigated to establish the background levels of heavy metals for different geographical and climatic zones of Sri Lanka. Moss sampling was carried out in four strict nature reserves in different geographical and climatic zones of Sri Lanka, namely Sinharaja rainforest (6°24′–6°27′ N, 80°24′–80°26′ E, 450– 500 m) from wet zone, Knuckles mountain range (7°31′ N, 80°43′ E , 1,000–1,300 m) from intermediate zone, Horton Plains National Park (6°46′–6°48′ N, 80°47′–80°49′ E, 2,000–2,200 m) and Hakgala mountain forest (6°55′ N, 80°48′ E, 1,700–1,800 m) from wet zone and Central highlands using about 10 sampling sites from each location within a month from October to November 2015. Concentrations of heavy metals in moss were analysed by using atomic absorption spectrometer. The atmospheric deposition of heavy metal concentrations in all sampling stations is given for dry weight of moss and the ranges of six elements around four strict nature reserves were 9.58– 65.68, 1.87–9.97, 1.20–10.56, 1.12–7.81, 1.20–10.60 and 0.05–0.36 μg/g for Zn, Cu, Pb, Ni Cr and Cd separately. According to the statistical analysis (one-way ANOVA , p < 0.05), accumulation of Cu, Cr and Cd in moss was not significantly change among four strict nature reserves and accumulation of Ni and Pb in moss was significantly higher around Hakgala mountain forest. Atmospheric deposition of Zn in moss was significantly higher around Knuckles mountain range area than other sampling locations. Therefore background levels of heavy metals in moss can be expressed as as 5.53 (±1.75), 7.23 (±2.11), 4.03 (±1.41), 6.61 (±2.58) and 0.17 (±0.06) μg/g for Cu, Pb, Ni, Cr and Cd respectively for the most of the geographical and climatic zones of Sri Lanka and background levels of Zn can be established as 30.62 (±8.11) and 47.42 (±12.31) μg/g for wet zone including Central highlands and intermediate zone of Sri Lanka respectively.
Comparizon of atmospheric deposition of heavy metals in Kandy and Puttalam areas in Sri Lanka using moss (Hyophila involuta) as a bioindicator: short term study
(Sri Lanka Association for the Advancement of Science, 2013) Jayalath, K.G.; Deeyamulla, M.P.; de Silva, R.C.L.
Effect of addition of EDTA in calcium absorption by mung plants (Vigna radiata)
(Sri Lanka Association for the Advancement of Science, 2016) Ranhoti, M.P.; de Silva, R.C.L.
Effect of EDTA on chromium uptake and translocation of selected, potential phytoextractant wild plants, under contaminated conditions
(Sri Lanka Association for the Advancement of Science, 2014) Tharanga, A.M.D.; de Silva, R.C.L.
The effect of moisture content on the soil organic matter decomposition in Muthurajawela marsh soil – a preliminary study
(Faculty of Graduate Studies, University of Kelaniya, 2015) Sandamali, G.K.A.H.T.; Ubeynarayana, N.J.; de Silva, R.C.L.
Muthurajwela marsh situated along the west coast of Sri Lanka is being highly exploited by the industries to dump their waste. According to the literature a high organic matter content in the marsh (>30%) is having a linear relationship with the soil cation exchange capacity (CEC), making industries to consider the marsh a potential wasteland with a high capacity to hold heavy metal cations. The high CEC of marsh is capable to act as a buffer preventing the surrounding ground water becoming acidic even though the organic soils are acidic. With the accelerated development around the area, various anthropogenic activities have been affecting the moisture content of the soil which may alter the quality of the marsh. In an attempt to investigate the effect of the changing moisture content on the soil properties of the marsh, a preliminary study is been conducted at certain areas in the periphery of the Muthurajawela sanctuary. The observed results are as follows; moisture content of 17.64% to 168.71% (by dry weight) and 36.63% to 84.31% (by wet weight), organic matter content of 5.06% to 57.89% (by dry weight), total CEC of 96 to 696 meq/100g soil, soluble soil pH of 2.10 to 7.91 and exchangeable soil pH of 2.08 to 7.26. Samples from the sites that had very high moisture levels showed higher organic matter contents, low pH values and very high CEC. As the soil moisture decreased, the organic matter levels and the total CEC decreased while the soil pH increased according to the study so far. The study implicates that the moisture content has a significant influence on the organic matter content of the marsh soil and hence is important in monitoring the quality of the marsh. Reduction of the soil moisture due to anthropogenic activities is therefore suggested to be directly affecting the continuity of the organic nature of the soil. Hence the cation exchange capacity and other properties of the soil would be altered making long-term loss of soil moisture putting the wetland system at the risk of losing its ecological performance. Therefore the Muthurajawela marsh needs strict conservation.
Identification of wild plants to phytoextract chromium from polluted terrestrial environments
(Sri Lanka Association for the Advancement of Science, 2013) Liyanage, A.L.L.A.; Jayalath, K.G.; de Silva, R.C.L.; Deeyamulla, M.P.
Optimizing conditions for the electrodeposition of chromium in very diluted aqueous solutions
(Sri Lanka Association for the Advancement of Science, 2011) Sachinthani, K.A.N.; de Silva, R.C.L.
Heavy metal pollution has become one of the major problems in the world. To overcome this problem, we have to minimize the generation of metal waste, while using techniques to treat the already contaminated environment. Phytoextraction is an environmentally friendly remediation method used successfully by several developed countries to treat existing heavy metals. After phytoextraction, heavy metals have to be re-extracted into aqueous solutions to complete the removal process. According to prior studies, these solutions contain heavy metals in very low concentrations (100 – 150 μg dm-3). Electrodeposition is one possible metal recovery method in aqueous solutions having higher metal concentrations. Therefore, the present study investigated the applicability of the electrodeposition technique to recover heavy metals from re-extracted aqueous solutions having relatively low concentrations of the heavy metal. Chromium extraction and the conditions for electrodeposition were also optimized. Model chromium solutions with a concentration of around 100.0 μg dm-3 were used. A three electrode system consisting of platinum, carbon and Ag/AgCl electrodes were used for the electrodeposition. Deposition voltage was supplied with Model 264 V Polarographic Analyzer/ Stripping Voltammeter (Potentiostat). Concentrations were determined with GBC 9 321B Plus Atomic Absorption Spectrophotometer with flame unit. The conditions optimized were deposition voltage, deposition time, temperature, pH and ionic strength and the optimum values were -3.00 V, 20 min, 50o C, 1.0 and 0.5 mol dm-3 respectively. However, the reduction of water occurs at -0.83 V and it may interfere with the electrodeposition at this optimum voltage. The optimization experiments were initially carried out assuming that the conditions were independent of each other. The analysis was repeated by considering their dependency, using sequential simplex optimization method. It was carried out using two conditions, deposition voltage and time. According to the results, the optimum values which were obtained from initial independent optimization studies were proven to be correct. Under the optimum conditions electrodeposition was performed and it resulted a mean percentage weight of 10.7 (±0.4) of chromium deposited.
Phytoextraction of heavy metals in semi-aquatic environments using selected colocasia sp. and wedelia sp.
(Sri Lanka Association for the Advancement of Science, 2008) Perera, M.D.C.S.; de Silva, R.C.L.
This particular study focuses on remediation of heavy metal (Cd2+ and Pb2+) contaminated semi-aquatic environments using two plant species, a Colocasia sp. and a Wedelia sp. which are two common local plants growing under semiaquatic conditions. The main research work involved two experimental setups; the pot experimental setup and the hydroponic solution experimental setup (only for Colocasia sp.). In pot experimental setup a series of plants were allowed to grow for a certain period of time in pots containing varying concentrations of the analyte in soil. Then the plant materials (aerial parts and below ground parts separately) and the corresponding soil samples were digested and analyzed using flame atomic absorption spectrometer (FAAS). In hydroponic solution experimental setup, plants of similar nature were placed in conical flasks containing varying concentrations of the analyte in a hydroponic solution and observed for two weeks. Then the plant materials and the solutions were digested and analyzed using FAAS. The two experimental plants Wedelia sp. and Colocasia sp. have not proven to be suitable candidates for Cd2+ phytoextraction. The maximum tolerable Cd2+ concentration for Wedelia sp. was 450 mg per 1kg of dry soil while that for Pb2+ was 1500 mg kg-1 (after 60 days in soil). This shows that the toxicity of Cd2+ on the Wedelia sp. is higher than the Pb2+ toxicity on the same plant. At 450 mg kg-1 concentration in soil, phytoextracted concentration of Cd2+ was 8.1(±0.4) mg kg-1 while that for Pb2+ was 128.9(±4.6) mg kg-1. The maximum Cd2+ concentration which was tolerated by the Colocasia sp. was less than 10ppm and survived less than a week in hydroponic solution.
Phytoextraction of Lead and Chromium Using Selected Legumes: A Study of Growth and Germination of Plants under Contaminated Conditions
(University of Kelaniya, 2012) Rathnaweera, T.A.D.H.N.; de Silva, R.C.L.
Soil pollution has become a major problem in recent times. Heavy metals make a significant contribution to soil contamination. Phytoextraction is a soil cleanup technology that seeks to exploit the ability of some plants to accumulate high concentrations of heavy metals from the environment and continue to grow. Phytoextraction is an innovative, novel and potentially inexpensive technology and an environmental friendly method. Many studies have been done using plants such as Indian mustard (Brassica juncea )1, maize (Zea mays)2, vetiver grass (vetiveria zizanoids)3. This study was done using a wild plant type locally called “pora wel” (Pueraria phaseoloides) instead of plants consumed by animals and humans. The main objective of this study was to determine whether Pueraria phaseoloides seeds can grow in contaminated environments and also in different types of soils. Germination of Pueraria phaseoloides seeds takes a long time (approximately two years). Several methods to reduce seed dormancy were tested using different types of solutions; water, hot water, diluted acids and concentrated acids. The Pueraria phaseoloides seeds which were treated with concentrated acid method germinated within three days. According to the results, Pueraria phaseoloides can tolerate at even higher Pb concentrations up to 4000 mg/kg of dry soil and Cr concentration - 3500 mg/kg of dry soil. All plants died at higher Pb concentrations (8000 mg/kg of dry soil and 10,000 mg/kg of dry soil). Statistical analysis reveals that there is a reciprocal correlation between the tested parameters; the number of plants which survived, average number of leaves per plant and average plant height with the soil in both heavy metal contaminated soil, which indicates the effect of contaminant on the growth of plants. More than half of the plants (13) survived, out of 25 seeds at 3000 mg/kg of dry soil of Pb concentration. At higher Cr concentrations (6000 mg/kg of dry soil and 8000 mg/kg of dry soil) no plants survived. More than half of seeds (16) out of 25 seeds germinated and grew rapidly at 3500 mg/kg of dry soil Cr concentration. Pueraria phaseoloides plants which were grown in sandy clay loam soil showed higher Pb accumulation compared to plants grown in other soil types tested. The number of plants survived, average number of leaves per plant and average plant height decreased with the increasing of Pb concentration. Soil type did not show significant change on germination and growth of plant. Heavy metal accumulation of Pueraria phaseoloides increased with increasing of heavy metal concentration in the soil. But Cr accumulation is very low when compared to Pb accumulation by plant.
Pilot survey to monitor atmospheric deposition of heavy metals in moss species (Hyophila involuta) in Kurunegala using two different digestion methods
(University of Kelaniya, 2013) Jayalath, K.G.; Deeyamulla, M.P.; de Silva, R.C.L.
Dry ashing digestion is a traditional digestion method used during the sample preparation step in moss biomonitoring studies in Sri Lanka. The aim of this study is to compare dry ashing procedure with the rapid and efficient microwave digestion procedure to validate previous findings. In February 2013, moss species (Hyophila involuta) were collected from Kurunegala and the concentrations of five heavy metals copper, lead, nickel, chromium and cadmium were analyzed by atomic absorption spectrometer followed by two different digestion procedures. The atmospheric deposition of heavy metal concentration in Kurunegala is expressed as dry weight of moss and the ranges of heavy metals were Cu (18.39 μg/g – 23.39 μg/g), Pb (13.66 μg/g – 19.79 μg/g), Ni (8.62 μg/g – 13.65 μg/g), Cr (19.18 μg/g – 30.36 μg/g) and Cd (0.72 μg/g – 0.78 μg/g) in microwave digestion and Cu (14.43 μg/g – 19.43 μg/g), Pb (10.00 μg/g – 15.54 μg/g), Ni (11.00 μg/g – 16.68 μg/g), Cr (16.49 μg/g – 29.03 μg/g) and Cd (0.70 μg/g – 0.80 μg/g) in ash digestion respectively. The metal content of Cu, Pb, Cr and Cd shows higher values in microwave digestion whereas Ni shows higher concentrations in ashing procedure. However, the comparison of two digestion methods (ANOVA, p < 0.05) showed no statistically significant differences in results. The recovery percentages of five heavy metals in two digestion methods were Cu (97.6 ± 0.4 %), Pb (95.9 ± 1.3 %), Ni (97.6 ± 1.6 %), Cr (98.0 ± 1.2 %) and Cd (95.3 ± 4.1 %) in microwave digestion method and Cu (93.1 ± 2.5 %), Pb (92.0 ± 2.7 %), Ni (99.6 ± 2.1%), Cr (97.3 ±1.7 %) and Cd ( 96.8 ± 2.8 %) in ash digestion method separately. The relative standard deviation of readings was less in microwave digestion and further, time required for dry ashing digestion and microwave digestion were 4 hours and 45 minutes respectively. Therefore ashing digestion method is more time consuming than the microwave digestion method without any advantages in terms of digestion efficiency.
Pre-concentration and determination of trace amounts of heavy metals in beverages marketed in Sri Lanka using naturally occurring clay
(Sri Lanka Association for the Advancement of Science, 2014) Weeraratne, K.S.; Jayathilaka, J.M.P.I.; Subramanium, S.S.; de Silva, R.C.L.
The role of washing of moss samples in analysis of heavy metal concentrations in moss biomonitoring studies
(Sri Lanka Association for the Advancement of Science, 2013) Jayalath, K.G.; Deeyamulla, M.P.; de Silva, R.C.L.
Study of Effluents from University Chemistry Laboratories and Development of Possible Methods to Recover Chromium from Laboratory Effluents
(University of Kelaniya, 2012) Gamage, D.G.C.L.; de Silva, R.C.L.
The laboratories of the Department of Chemistry at University of Kelaniya, like any other university chemistry laboratory, generate laboratory effluents daily as a result of their general course of activities. As most of the laboratories are teaching laboratories, the laboratory effluents contain many different types of chemicals (in bulk but known quantities) resulting from the experiments designed for the undergraduate students. These laboratory effluents are discarded through the university drain system without any pre-treatment as the Department does not have a proper disposal mechanism, contributing to environmental pollution. Therefore, paying attention to laboratory waste management strategies has become an important aspect of a healthy lifestyle. In this study, laboratory effluents of the Department of Chemistry, University of Kelaniya were characterized using the characterization parameters: pH, chemical oxygen demand (COD) and heavy metal ion concentrations which are used frequently. For this, laboratory effluent samples were collected from the laboratory classes conducted by the Department in the academic year 2009/2010. According to the results, the laboratory effluents had very acidic and basic pH values (ranging from pH 0.9-10), very high COD values (varying from 40-1600 mg O2/L), and high heavy metal ion concentrations (Cu-298.5 mg/L, Cr-933.6 mg/L, Pb-85.8 mg/L, Ni-3151.0 mg/L). These results suggest that treatment of the laboratory effluents is essential in order to minimize the level of pollutants discharged to the environment by the Department. This study also makes an effort to develop a simple and cost effective treatment method for the heavy metal chromium which is present in the laboratory effluents of the Department of Chemistry, University of Kelaniya, as a model study. Chromium is considered as a major toxic pollutant and it has many adverse effects on environment and human health. Chromium in waste effluents can be removed using the hydroxide precipitation method. By using this method, chromium present in the laboratory effluents was removed with a removal efficiency of 97% - 98%. Therefore, hydroxide precipitation method can be suggested to be used by the Department for removal of chromium from the laboratory effluents as it would be a simple and cost effective method with high efficiency. In order to recover removed chromium from the laboratory effluents, a further purification step was carried out. In this step, waste chromium was converted into barium chromate which can be reused. This purified form gave a satisfactory yield of 75% chromium content. As a suggestion to reduce the amount of chromium discarded as waste by the Department, the possibility of using low concentrated chemical solutions containing chromium for undergraduate experiments has also been proven in this study.
Study of heavy metal adsorption capacities of clays and development of recovery methods to effectively remove and to convert the adsorbed metals into reusable forms
(Sri Lanka Association for the Advancement of Science, 2009) Siriwardana, A.A.G.K.; de Silva, R.C.L.
Synthesis and Characterization of Sodium Cobalt Oxide Nanostructures for Sodium-ion Batteries
(University of Kelaniya, 2012) de Silva, R.C.L.; Perera, V.P.S.
The secondary lithium-ion battery has been widely used in various kinds of personal digital accessories, and is expected to be further spread into larger-sized applications such as power sources of hybrid automobiles. While cathode materials for secondary lithium-ion battery have been so far made mostly from lithium cobalt oxide, the development of substitute materials is essential because of the depletion and increasing prices of lithium and cobalt resources. The sodium-ion secondary battery is an alternative for lithium ion rechargeable battery utilizing mostly abundant sodium which has high electrochemical potential after the lithium. Therefore, in this study we have synthesized sodium cobalt oxide by the solid state reaction of cobalt carbonate and sodium carbonate at 700 C. The product was characterized by X-ray diffraction (XRD) technique. The apparent peaks presented for 2 values of XRD at 16, 33, 38 and 46 degrees matching the sample with the standard confirmed the proper synthesis of sodium cobalt oxide which is the active cathode material of the secondary sodium-ion battery. The average crystal size of the sodium cobalt oxide was found to be 42 nm by using the Scherrer equation for the peak, which appeared at 16 degrees in the XRD. The cathode of sodium-ion battery was fabricated on stainless steel plates by spreading a slurry made grinding sodium cobalt oxide with 5% of carbon black in absolute alcohol and drying at 120 0C. The sodium-ion batteries were fabricated in N2 atmosphere using Na foil as anode and polyester membrane as the separator. The electrolyte was 1M solution of NaClO4 in propylene carbonate. The preliminary studies showed that the cell has discharge capacity of 20 mAhg-1 discharging at current rate of 50 mAg-1. Further studies need to be carried out to test for long cycle life and other battery performance requirements.