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

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A laboratory study on the effects of fertilizer addition on mobilization, percolation and leaching of calcium ions in soils of Anuradhapura district
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Ranaweera, Y.; Silva, R. C. L. De
This study aims to investigate the effect of fertilizer addition to limestone soils around Thirappane, in Anuradhapura District. Groundwater is the primary source of freshwater in this area. There is evidence that the degree of hardness of groundwater in the area has increased over the years, probably as a result of long-term and large-scale application of chemical fertilizer. Our results show that the exchangeable and total calcium ion concentrations in the soil of non- agricultural increases with depth of the soil profile, indicating the existence of calcium deposits beneath the soil profile. Columns (Dimensions ~ 4.00 cm2 x 100 cm) were filled with soil (up to 60 cm height in each column) from the study area and 0.5% (w/w) of nitrogen fertilizers (Ammonium sulfate and urea) were introduced to the columns to study the effects of fertilizers on properties of soil. Deionized water (100.0 mL) was added by using a dropper from the top of each column and it was allowed to pass through the soil at a rate of 1 mL/minute. The highest effect on the calcareous soil was shown by fertilizer containing ammonium sulfate. After running the columns for 30 days, it was observed that the pH of the leachate in the column introduced with urea, had gradually declined while the calcium ion concentration had gradually increased, whereas the pH of the leachate, in the column introduced with ammonium sulfate fertilizer, showed a rapid decrease and the calcium concentration was very high, compared to the control. Total calcium ion concentration had decreased down the soil sample columns while exchangeable calcium ion concentration increased. The pH value had also decreased down the soil profile. This indicates the dissolution of calcium carbonate in the soil due to the increment of acidity. This highlights that mobilization, percolation, and leaching of calcium ions in the soil change with nitrogen fertilizer application, potentially contributing to increased groundwater hardness
Surface modification of Leucaena leucocephala wood biochar using coconut vinegar
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Udawatta, M.; Silva, R. C. L. De; Silva, D. S. M. De
Over the last few decades biochar has emerged as a popular low cost adsorbent for water treatment due to its abundance and cost-effectiveness. Number of studies have reported the efficiency of strong acids such as nitric, sulfuric, hydrogen peroxide, etc. in activating biochar. However, as these chemicals are expensive, corrosive and difficult to be handled by unskilled personnel, use of these chemicals is limited to industrial activation processes. To provide a user friendly economical activation process, this study focused to evaluate the ability of natural coconut vinegar, in activating Leucaena leucocephala wood biochar. Coconut vinegar, a common food additive, is a 4 % acetic acid solution in water (4 g acetic acid/ 100 mL vinegar, pH 2.5). Leucaena leucocephala is a common, fast-growing tree with light wood and soft foliage. It is widely used for fuelwood. In this study, air dried Leucaena leucocephala wood pieces were allowed to burn in a domestic kiln (300 ºC, 2 hours) to produce biochar. The activation of biochar was done by soaking it in coconut vinegar for 24 hours followed by oven drying (120 ºC, 3 hours). After cooling it was washed with de-ionized water and further dried in oven at 80 ºC overnight. Fourier transform infrared spectra exhibited hydration of the C-O-C bridges of the biochar surface introducing new -OH groups and the possible introduction of carbonyl/ester/carboxylic functional groups to the biochar surface after the vinegar treatment. Recently, a positive correlation has been cited among the number of Chronic Kidney Disease of Unknown Etiology patients and the levels of ground-water hardness, in Sri Lanka. Hence, the efficiency of coconut vinegar activated Leucaena leucocephala biochar in reducing calcium ions from potable water was tested. Adsorption and desorption studies carried out using column tests showed a 1.7 fold increase of calcium ion adsorption capacity and a 7 fold increase of calcium ion retaining capacity after the vinegar treatment, with compared to the non-activated biochar. Calcium content in solutions was measured using flame photometry. Calcium adsorption capacities of non-activated biochar and activated biochar determined by column tests ranged from 3.10-3.82 mg/g and 5.27-6.68 mg/g respectively while calcium retaining capacities ranged from 0.16-0.22 mg/g and 1.28-1.4 mg/g respectively. Batch studies matched with both Langmuir (R2 = 0.9761) and Freundlich (R2 = 0.9785) isotherm models. Maximum adsorption, qm was calculated as 23.8 mg/g using Langmuir equation. This study concludes that Leucaena leucocephala biochar can be activated using coconut vinegar to be used as a safe and cost-effective adsorbent for calcium ion removal from potable water.