International Research Symposium on Pure and Applied Sciences (IRSPAS)
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Item Preparation, characterization and properties of activated carbon derived from rice husk(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Perera, P. L. R. A.; Rajapakse, C. S. K.Rice, the staple food of the Sri Lankans is one of the important crops occupying 34% of the total cultivated area in the country. Thus, rice processing generates a large quantity of rice husk as waste material. The main objective of the present work was to investigate the potential of using this agricultural waste, rice husk as a precursor for the production of low-cost activated carbon (AC) as an adsorbent for the removal of heavy metals (Pb(II), Cd(II) etc.). Therefore, the present study was carried out to evaluate the effect of carbonization time and activating agent on AC production from rice husk and its Pb(II) removal capacity. Cleaned and dried rice husks samples (12.00 g) were separately carbonized at 400 °C under constant nitrogen flow for 60 minutes -150 minutes (60 min, 90 min, 120 min, 150 min) and chemically activated by HCl. The AC yield was calculated in each sample. In order to determine the lead removal percentages (Pb%) of AC derived from rice husk at different carbonized temperatures, first AC samples were added (1.00 g) separately to a Pb(II) standard solution (5.00 mg L-1), stirred for 1 hour at pH 7 at room temperature. The solutions were filtered and the residual Pb was determined by Atomic Absorption Spectrophotometry (AAS). All the experiments were performed in duplicate. Further, the AC with the highest Pb removal capacity was characterized by Scanning Electron Microscopy & Energy Dispersive Spectroscopy (SEM/EDAX), and Fourier Transform Infrared Spectroscopy (FT-IR). Proximate analysis, of the AC were also studied. The percent yield of AC prepared from rice husk with HCl activation, and its corresponding % Pb removal potential were fluctuated with increasing carbonization time. The highest AC yield (20.50%), the highest % Pb removal (93.31%) was observed for the AC prepared by carbonization of rice husk at 400 °C for 120 minutes with HCl activation. The results of the proximate analysis revealed that the ash content, moisture content volatile matter content and fixed carbon content of the AC were 32.47%, 34.94%, 24.20%, and 8.39% respectively. Based on the results, it can be concluded that AC derived from rice husk can be considered as an efficient and cost-effective adsorbent for the removal Pb(II) from wastewaterItem Bench scale fixed-bed column adsorption studies and adsorption modelling: removal of methylene blue from aqueous solutions using glutaraldehyde cross - linked chitosan beads(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Amarasooriya, M. P. N. A.; Rajapakse, C. S. K.As dye-containing waste effluent is a big threat not only to the environment, but also to human life and the economical removal of dyes from wastewater has become an environmental challenge in nowadays. Therefore, this work focuses on the exploration of potential of using physically and chemically modified chitosan, glutaraldehyde cross-linked chitosan beads (GCLCBs) to remove a model dye, methylene blue (MB) from aqueous solutions using bench-scale fixed bed columns. GCLCBs (4.00±0.02 mm in diameter) were prepared by using glutaraldehyde as the cross-linking agent and it was characterized by Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR). FTIR analyses confirmed the cross-linking of chitosan beads with glutaraldehyde. The effects of initial MB concentration (10, 12, 15 mg/L) and inlet flow rate (5, 10, 15 mL/min) at neutral pH and at room temperature (30 ± 2 ºC) on the performance of column packed with GCLCBs were analysed using breakthrough curves. The breakthrough time (Tb), time required for full bed exhaustion (Tt), bed capacity (BC) and length of unused bed (LUB) were determined at each column operating conditions. The highest % MB removal of 72.80% was obtained at initial MB concentration of 10 mg/L and inlet flow rate of 5 mL/min at 6 cm bed height of the adsorbent. The breakthrough time, Tb increased with decreasing inlet flow rate and initial MB concentration. Two kinetic models namely the Thomas model and Yoon – Nelson model were used to predict the column performance and column parameters important in designing large-scale columns in water purification systems. The results revealed that the Thomas rate constant decreased with increasing initial adsorbate concentration and inlet flow rate. The time required to achieve 50% of adsorbate breakthrough (τ) seems to agree quite well with the experimental data (τ experimental) according to the results obtained from Yoon – Nelson model. Both the Thomas and Yoon – Nelson models fitted the experimental data with high regression coefficient values (R2 ~ 1) indicating the validity of both kinetic models for the studied column system. Based on the results it can be concluded that that the GCLCBs could be used as low-cost and environmentally friendly agent for the treatment of dye containing wastewaterItem Bioactive properties of Rambutan (Nephelium lappaceum L.) and Durian (Durio zibethinus Murr.) peel extracts(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Silva, A.G.; Wickramaarachchi, S.; Attanayake, R. N.; Rajapakse, C. S. K.Although these fruits are seasonal, a considerable amount of Rambutan (Nephelium lappaceum L.) and Durian (Durio zibethinus Murr.) fruit residues (mainly peels) are collected each year as waste materials, due to the significant volume of trade of these fruits. Therefore, present work was initiated with the aim of evaluating the impact of these residues lying as waste and possible re-use, by investigating the bioactive properties in peels of rambutan and durian. Methanol extracts of Rambutan and Durian peels were sequentially extracted with hexane, chloroform and methanol. First, methanol extracts of peels were subjected to phytochemical screening following standard procedures and results revealed that rambutan and durian peels were rich in polyphenols, flavonoids, steroids, coumarin, etc. Total phenolic content (TPC) and total flavonoid content (TFC) of methanol extracts of peels were determined using Folin-Ciocalteu and aluminium chloride method, respectively. Results showed that TPC and TFC in methanol extract of durian peels were (11.39 ± 0.49 mg GAE/g dry weight, 257.20 ± 5.14 mg Catechin /g dry weight) higher than those of Rambutan peels (2.73 ± 0.15 mg GAE/g dry weight, 198.00 ± 1.89 mg Catechin /g dry weight). Further, the antioxidant activity of methanol extracts of peels and its fractions were investigated using 1, 1-diphenyl-2-picryl-hydrazyl free radical (DPPH) scavenging assay and the correlation with their TPC and TFC were examined using Pearson’s correlation analysis. The strongest antioxidant activity was observed in hexane fraction of Rambutan peels with IC50 value of 13.49 ± 0.52 μg/mL, and which was lower than that of the control, butylated hydroxytoluene (43.70 ± 0.89 μg/mL). Significant positive correlations were observed between TPC and TFC in fractions of rambutan and durian peels with their DPPH radical scavenging activity indicating that phenolics and flavonoids in rambutan and durian peels may contribute to their strong antioxidant activities. The antimicrobial activity of the extracts of peels and its fractions were assessed by using disc diffusion method against a bacterial species of Staphylococcus aureus and fungal species, Fusarium oxyporum and Aspergillus flavus. The lowest concentration of methanolic extract of durian and rambutan peels that showed an inhibition against Staphylococcus aureus was 31.25 μg/mL. It was also found out that neither peels of rambutan nor durian had antifungal activity against the two selected fungal species. Results revealed that the peels of rambutan and durian are potential sources of antioxidants and antibacterial agentsItem Defluoridation of drinking water using physically and chemically modified chitosan(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Pathirannehe, P. N. S.; Fernando, T. D.; Rajapakse, C. S. K.Depending on the total intake, fluoride (F-) is known to have both beneficial and adverse effects on humans. As the occurrence of the Chronic Kidney Disease of unknown etiology (CKDu) is thought to be linked with excess levels of F- in drinking water, the search for efficient, readily available, more affordable and eco-friendly adsorbents that have defluoridation potential has intensified in recent years. Therefore, the current study focuses on use of chitosan-derived adsorbents, physically and chemically modified chitosan for the removal of F- from drinking water. Physically modified chitosan; chitosan beads (CB), and chemically modified chitosan; protonated glutaraldehyde cross-linked chitosan beads (GCLCB/H+) and protonated glycerol diglycidyl ether cross-linked chitosan beads (GDCLCB/H+) were prepared, and characterized by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope. Batch experiments were conducted to determine the effect of adsorbent dosage, initial F- concentration, pH and contact time on defluoridation capacity of GCLCB/H+ at 30 ± 20C and the defluoridation capacities of different chitosan derivatives were determined under the optimized conditions (adsorbent dosage = 0.6 g, initial F- content =15 mg/L, contact time = 30 min, pH = 7). Further, the adsorption isotherm studies were conducted to understand the F- sorption process. The results revealed that the defluoridation capacities of CB, GCLCB/H+ and GDCLCB/H+ under optimized conditions at 30 ± 20C were 76.04 mg/kg, 576.98 mg/kg and 655.37 mg/kg, respectively and these values were significantly greater than that of unmodified chitosan flakes (44.20 mg/kg). The results indicate that physical and chemical modification of chitosan have enhanced the F- adsorption capacity of chitosan-derived adsorbents. Further, the results of the isotherm experiments indicated that the adsorption process is well fitted to Langmuir and Freundlich isotherm models. Six water samples among the drinking water samples collected around Kirigollewa Grama Niladhari Division in Medawachchiya, have exceeded the permissible level of F- in drinking water as defined by WHO (1.5 mg/L), but were able to successfully reduce to the permissible range by treatment with GDCLCB/H+. The findings of this study demonstrate that chitosan derived adsorbents are efficient and cost-effective candidates to use in removing F- ions from drinking water.Item Simultaneous detection of Pb(II) and Cd(II) in aqueous solutions by UV-visible spectrophotometry(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dikella, D. G. T. N.; Rajapakse, C. S. K.The pollution of water resources due to disposal of metals, especially heavy metals is one of the most concerned environmental issues in the current world. Therefore, detection of these heavy metal ions with rapid, sensitive and accurate analytical tools is important. In recent years, water soluble porphyrins, macrocyclic compounds have gained growing interest as colorimetric agents for heavy metal detection by UV-VIS spectrophotometry. Porphyrins are highly sensitive to metal ions and display new Soret band (~ 400 nm) as well as minor Q bands (500–700 nm) upon metal ion chelation. This property has been widely used for detecting heavy metal ions in aqueous solutions. In this work, the influence of pH, water hardness (Ca(II)) and presence of other foreign ions (Mg(II), Co(II), Al(III), Cr(III), Fe(III), Ba(II), K(I), Mn(II), Sn(II), Ni(II), Zn(II), Bi(III)) for simultaneous detection of Pb(II) and Cd(II) by a porpyrin; 5, 10, 15, 20-tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate); (TMPyP) under the selected experimental conditions were investigated. TMPyP displayed a characteristic Soret band in the UV-Vis spectrum at 422 nm. Upon addition of Pb(II) and Cd(II) into TMPyP, the band at 422 nm was disappeared and new Soret bands were appeared at 474 nm and 444 nm, respectively indicating that these characteristic absorption bands, attributed to corresponding Metal(II)-TMPyP complexes. The lower detection limit (LOD) for Pb(II) and Cd(II) with TMPyP was found to be 0.02 mg/L and 0.01 mg/L, respectively which are considerably below the maximum permissible levels for wastewater discharge according to WHO guidelines. The best pH range for simultaneous detection of Pb(II) and Cd(II) was found to be pH 7 to 9. The water hardness (Ca(II)) and the presence of other foreign ions also had no significant effect on the simultaneous detection of Pb(II) and Cd(II) ions in aqueous solutions. It was possible to remove TMPyP complexes as well as unbound TMPyP successfully using chitosan before discharging the analyzed solutions. The results revealed that the TMPyP can function as a single optical sensor capable of detecting Pb(II) and Cd(II) simultaneously in aqueous solutions in the pH range 7-9.Item A simple and rapid UV-Visible spectrophotometric method for determination of Mercury (II) using TMPyP in aqueous solutions.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Hettiarachchi, A. H .P.; Rajapakse, C. S. K.Even though Mercury and its compounds are known to be extremely toxic they are widely distributed in the environment. The main sources of mercury pollution are coal burning power plants, paper, plastic, electrical, paint, and pharmaceutical industries. Uses of mercury as pesticides also add mercury to the environment. Several analytical methods are available to detect heavy metal ions in environmental water samples and biological samples. However, in recent years significant attention has been focused on porphyrins, as the sensitive sensing reagents for spectrophotometric determination of several metal ions. In this study, a simple, rapid and considerably sensitive UV-Visible spectrophotometric method was developed for determination of Hg(II) using, 5, 10, 15, 20-Tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate); (TMPyP) as the sensing reagent. The effects of pH, water hardness and presence of other metal ions such as Cd(II), Cr(III) and Pb(II) for Hg(II) detection were also examined. Upon addition of Hg(II) ions into an aqueous solution of TMPyP, a new absorption band (Soret band) appeared at 458 nm indicating that, this characteristic absorption band, attributed to Hg(II)-TMPyP complex can be used as a diagnostic absorption for Hg(II) ions. The reaction was very fast and constant absorbance was achieved within 1 min and the system obeys Beer’s law for concentration range of Hg(II) between 0.005 mg L-1 and 70 mg L-1. The detection limit for Hg(II) with TMPyP was determined to be 0.003 mg L-1 which is below the maximum permissible limit (0.005 mg L-1) for wastewater discharge according to EPA effluent discharge standards. The best pH range for Hg(II) detection was found to be pH 7-12. Hg(II) detection was not affected by water hardness. The presence of Mg(II), Cd(II), Cr(III) and Pb(II) ions over a concentration range of 0-100 mg L-1 also had no significant effect on the detection of Hg(II) ions. It was possible to successfully remove Hg(II) - TMPyP complex as well as unbound TMPyP from the aqueous solutions using chitosan, before discharging the analyzed aqueous samples. These results indicated that, TMPyP can be used as a promising optical chemical sensor for the detection of Hg(II) in aqueous solutions with satisfactory sensitivity and selectivity.Item A study on sorption of Cd(II) onto chitosan derivatives.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Samaranayaka, K. A. S.; Rajapakse, C. S. K.Pollution of water sources, specially drinking water sources, is becoming a serious problem in the world today. Unlike organic pollutants, heavy metals are non-biodegradable and even trace amounts of some of the heavy metals such as cadmium is highly toxic and may cause deleterious health effects in humans. In recent years the search for efficient, readily available and more affordable adsorbents that have high metal-binding capacities for the removal of toxic heavy metals in drinking water has intensified and in this research, chemically modified chitosan [cross-linked chitosan beads (CLCB) and physically modified chitosan] and chitosan coated activated carbon (CCAC) were prepared and their sorption properties for Cd(II) uptake were studied. Chitosan derivative CLCB was prepared using glycerol diglycidyl ether as the cross linking agent and composite bio-adsorbent CCAC has been prepared by coating chitosan onto commercially available activated carbon to improve their mechanical strength and metal adsorption ability compared to that of unmodified chitosan. The modified adsorbents were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The equilibrium data were evaluated using Langmuir, and Freundlich isotherms and adsorption equilibrium data of Cd(II) adsorption onto CLCB and CCAC at 30 0C were correlated with the Langmuir isotherm model. The maximum monolayer adsorption capacity; Langmuir constant, qo obtained for adsorption of Cd(II) onto CLCB and CCAC were 79.4 μg/g and 84.0 μg/g, respectively, which were significantly higher than the values for the adsorption of Cd(II) onto unmodified chitosan. The kinetic data were fitted with the pseudo second order model for initial Cd(II) concentrations of 50 μg/L. The findings from this research indicate that the CLCB and CCAC have enhanced Cd(II) sorption abilities compared to that of unmodified chitosan. Therefore, the modified chitosan derivatives could be used as efficient bio-adsorbents to remove Cd(II) from polluted drinking water.Item Evaluation of fungicide resistance of Sclerotinia sclerotiorum causing cabbage white mold in Sri Lanka.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Mahalingam, T.; Somachandra, K. P.; Rajapakse, C. S. K.; Attanayake, R. N.Incidence of severe white mold disease was extensively observed in upcountry commercial cabbage fields of Sri Lanka in early 2014. The pathogen was identified as Sclerotinia sclerotiorum, a nectrophic soil borne fungus that can infect more than 400 plant species worldwide. Chemical control is the most effective method available to date due to lack of complete resistant cabbage varieties. However, improper fungicide applications can lead to the development of fungicide resistant isolates. In Sri Lankan small scale upcountry vegetable production system, more than one crop species is grown per year and most of these crops serve as hosts for the pathogen S. sclerotiorum. Frequent fungicide and pesticide application is also a common practice. Therefore, it was hypothesized that resistant S. sclerotiorum isolates against commonly used fungicides are present in Sri Lankan pathogen population. Objectives of this study were to determine the variation in insensitivities of the pathogen against commonly used fungicides in upcountry vegetable production systems, to search for the presence of resistant isolates and to determine if there are signals of positive cross resistance for the fungicides in Sri Lanka. Pathogen population was tested against three selected fungicides, carbendazim and thiophanate methyl (benzimidazole fungicides) and tebuconazole (triazole group fungicide) using in vitro plate assay. Firstly, a discriminatory concentration, which showed the highest variance in percentage inhibition of mycelial growth of a few randomly selected S. sclerotiorum isolates were determined as 0.25 μg/mL for carbendazim and 0.5 μg/mL for both thiophanate methyl and tebuconazole. Later, all of the 34 isolates were assayed for their insensitivities using fungicide amended PDA at the above concentrations with three replicates per isolate and fungicide unamended PDA plates were used as the control. Colony diameters were measured after 36 hr of incubation and percentage inhibition was calculated. While only 12% of the isolates showed > 50% inhibition for thiophanate methyl, the majority of the isolates (63 %) showed > 50% inhibition for the fungicide, carbendazim. The highest variance observed in percent inhibition of the pathogen population for carbendazim indicated that the pathogen population has the potential to adjust to the challenging environments, in this case fungicide applications. Based on the in-vitro plate assay, thiophanate methyl was found to be the least effective fungicide than the other two. Twelve isolates exhibited <50% inhibition to both carbendazim and thiophanate methyl and nine isolates showed <50% inhibition to all three fungicides. Results indicated that there is a potential to develop cross resistance and hence farmers should be prudent in selecting the fungicide regime for cabbage cultivation. Molecular basis of the resistance is yet to be elucidated.