Browsing by Author "De Silva, S.M."

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    Determination of potential use of chitosan for the removal of Pb, Fe and Mn in the water samples collected from different areas of Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2015) Farhan, S.; De Silva, S.M.; Rajapakse, C.S.K.
    Water contamination is one of the major concerns in the world. From the beginning of the 21 century, the drinking water sources in the main agricultural regions under reservoir based irrigation of Sri Lanka have been polluted from heavy metals in considerable amounts and exposure to heavy metals can cause a number of health problems, ranging from nausea and stomach discomfort to development of cancers and kidney diseases (Bandara et al.,2008). Although a wide range of physical and chemical processes are available for the removal of heavy metals from natural water bodies, most of these methods are not practicable to developing country like Sri Lanka as they are extremely expensive. In recent years, biosorption has been recognized as an effective method of removal of heavy metal contaminants in surface water as low cost bio- adsorbents are readily available, environmentally friendly, and biodegradable. The bioadsorbent chitosan; deacetylated product of chitin (Gamage et al.,2007) has been used as a bioadsorbent for the removal of toxic/heavy metals from waste water. Depending on the pH of the medium the interaction of metals with chitosan are possibly dominated by adsorption, ion-exchange and chelation. Chitosan has been used to remove heavy metals mainly from industrial wastewater and as a non-toxic flocculent in the treatment of organic polluted wastewater (Shanmugapriya et al., 2011); but little attempt has been made to understand the ability of chitosan to uptake heavy metals in polluted drinking water containing trace amounts (ppb levels) of heavy metals (De Silva et al.,2014). The current study focuses on potential of using chitosan as a low cost, environmentally friendly biosorbent for purification of drinking water contaminated by the low levels of heavy metal pollutants; Pb, Fe and Mn. Methodology Drinking water samples were collected from different areas of the country including Anuradhapura, Nikkawewa, Vavuniya, Trincomalee, Badulla and Kantale. First the basic parameters such as colour, pH and total hardness of the collected water samples were measured and recorded. Then the initial metal ion concentration of Pb, Fe and Mn of acid digested water samples were measured using AAS. Next, all the water samples with initial metal ion concentrations above the permissible limits for drinking water defined by the World Health Organization (WHO) were treated with chitosan as follows. A finely crushed chitosan (0.0250 g) was taken separately into clean dry polypropylene containers. A volume (50.00 mL) of digested water sample was introduced into polypropylene container having chitosan sample. pH of the sample was adjusted to pH 7 using NaOH (0.1 M) and the sample container was stirred at room temperature (29.0 ± 0.5 C) for 2 hours. Control sample was prepared simultaneously with chitosan (0.0250 g) and deionized water (50.00 mL) and pH was adjusted to pH 7. Control sample was also stirred at room temperature (29.0 ± 0.5 C) for 2 hours. After 2 hours stirring period, both sample and control were filtered using filter papers. Filtrates of sample and control were analyzed by AAS to determine the amount of Pb, Fe, and Mn remaining in the solutions after treatment with chitosan. The procedure was carried out in duplicate for each digested drinking water sample. Result and Discussion The pH values of the collected water samples range from 6.53 – 7.31 which were in the range of accepted pH value range (6.5 – 8.5) for drinking water defined by WHO. But hardness in some of the collected water samples had exceeded 250 ppm, the maximum permissible level defined by the Sri Lanka Standards Institution (SLSI) for the drinking water. The Initial metal concentrations in collected water samples, metal concentrations after treatment with chitosan, and percentage metal removal (%) of Pb Fe and Mn are shown in table 1, table 2 and table 3 respectively. The maximum permissible levels for drinking water given by WHO for corresponding metals are shown in table 4.
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    Use of computational method to identify metal binding sites of chitosan as a tool to investigate the interaction mechanism of chitosan and heavy metals
    (Uva Wellassa University of Sri Lanka, 2015) De Silva, S.M.; Rajapakse, C.S.K.
    A bioadsorbent chitosan; a derivative of chitin polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine (Cahyaningrum et al., 2004) was reported by our group to be much effective as a drinking water purification agent as the percent removal of Cd(II), Pb(II) and Cr(VI) from drinking water by chitosan were 94%, 64% and 70% respectively under optimized conditions (De Silva et al., 2014). It is widely known that chitosan can make complexes with certain metal ions as chitosan has different possible binding sites for metals (figure 1). But little attempt has been made to understand the interaction mechanism of chitosan and heavy metals. Hence the aim of this study was to simulate the IR spectrum of chitosan by DFT calculations and to identify the vibrational bands associated with the possible metal binding sites which can be used as a tool to investigate the interaction mechanism of chitosan and heavy metals. Methodology All theoretical calculations reported in this study were carried out by use of the Gaussian 09 program package. Although chitosan is a polymer, a trimer shown in figure 01 was used to represent chitosan in all theoretical studies. First the structural parameters of the optimized structure of the chitosan have been obtained using electron density functional theory (DFT) with the Becke–Lee–Yang–Parr functional (B3LYP) and 6-31G (d) basis set employing in a gas phase model. Then the IR spectrum of the chitosan was simulated by using the computed frequencies of the optimized geometrical configuration of the trimer in gas phase. The experimental FTIR spectrum for chitosan was obtained from a Bruker Alpha-T spectrometer.