Browsing by Author "Ranaweera, S. A."

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Efficient dye removal from wastewater by using expired rice grain derived biochar: A sustainable solution for water purification
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Ranaweera, D. M. S. U.; Vithanage, M.; Ranaweera, S. A.
The accumulation of waste dyes in aquatic systems poses significant risks to human and animal health due to their hazardous and carcinogenic nature. Dyes also interfere with photosynthesis by reducing sunlight penetration in deep water. Although various methods have been developed to remove color contaminants from aqueous systems, there remains a need for cost-effective, environmentally friendly, and efficient adsorbents. Over 350,000 kg of expired rice is disposed of annually from warehouses in Sri Lanka. Because of the rich composition of nutrients in rice, they can be used as raw material to produce biochar. In this study, the remediation of Methylene Blue (MB) from simulated wastewater using biochar produced by pyrolysis of expired rice grains was investigated. Two types of biochar were prepared: non-modified (NMRG) and modified (MRG) through KOH activation. The efficiency of MB removal by these variants was evaluated. FT-IR spectra confirmed the modification of the rice biochar surface with various functional groups through alkali treatment, and Scanning Electron Microscopy (SEM) micrographs showed the opening of meso and macropores in the biochar due to KOH activation. Batch adsorption studies were conducted to determine the effects of MB concentration, pH, temperature, and contact time on MB removal. The optimum pH was found to be pH 4 for both NMRG and MRG, with an optimum contact time of 2 hours. The maximum MB adsorption was observed for a 2000 ppm MB solution at an optimum temperature of 30 °C. Experimental results indicated that MRG exhibited the highest adsorption capacity of approximately 169.93 mg/g with an 84.97% removal rate, while NMRG showed an adsorption capacity of 41.75 mg/g with a 20.88% removal rate. Thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and Gibb’s free energy (ΔG) were evaluated for both adsorbates. The ΔS and ΔH values for NMRG were 0.01 kJ mol⁻¹ K⁻¹ and 5.25 kJ mol⁻¹, respectively, whereas, for MRG, these values were 0.13 kJ mol⁻¹ K⁻¹ and 8.55 kJ mol⁻¹, indicating an increase in randomness during adsorption. The enthalpy values revealed the endothermic nature of the process, with MB uptake enthalpy for NMRG and MRG at 5.25 kJ mol⁻¹ and 8.55 kJ mol⁻¹, respectively. The Gibbs free energy for MRG was a large negative value (-30.45 kJ mol⁻¹), while for NMRG, it was a small positive value (8.89 kJ mol⁻¹), suggesting that adsorption was mainly governed by chemisorption. The Intra-Particle Diffusion model indicated that adsorption occurred through both intra- and inter-particle diffusion. The Toth isotherm and the Redlich-Peterson models were identified as the best-fit models for NMRG and MRG, with R² values of 0.99.
Removal of Ciprofloxacin from aquatic environments using Pristine and KOH activated waste rice biochar
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Vishwani, L. L. D.; Ranaweera, S. A.; Vithanage, M.
Ciprofloxacin (CPX) is an antibiotic used to treat many bacterial infections and is considered as a water pollutant, which induces antibiotic resistance. This study aimed to remove CPX from water using pristine (WRBC-P) and KOH-activated (WRBC-A) waste rice biochar derived at 500 ˚C. WRBC-P was prepared by pyrolysis of expired rice grains at a 5 ˚C/min heating rate. KOH activation was carried out using WRBC-P to obtain WRBC-A. Both biochar samples were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM). The data indicates that the activation improves the pore structure and the surface area of biochar. Removal of CPX by both biochar variants was studied in batch experiments. The edge experiments were conducted by varying the pH from pH 3 to 10, kinetics experiments at different time intervals up to 24 h and the isotherm studies at different initial CPX concentrations (2-25 mg/L) in the presence of 1 g/L dosage of biochar at 25 ˚C. Variations in CPX concentrations before and after adsorption studies were determined using UV-visible spectroscopy measuring absorbance at 277 nm λmax using a Quartz cuvette. The maximum adsorption capacity of CPX was observed at pH 7.3 for both WRBC-P and WRBC-A. After 12 hours of equilibrium time, the maximum adsorption capacities were 1.45 mg/g and 6.15 mg/g for WRBC-P and WRBC-A respectively. The fractional power model was the best-fitted model for the kinetic data obtained for both WRBC-P and WRBC-A. This explains that the rate of the adsorption of CPX on biochar depends on the concentration of CPX to non-integral power. This reflects that the CPX adsorption takes place via a complex mechanism with intermediate formation. Isotherm data confirms that the adsorption of CPX is a two-way process for both WRBC-P and WRBC-A. Hill isotherm model was fitted with cooperative binding between CPX and biochar showing a monolayer formation for the first part of the data set. After that, the Freundlich model was equipped with the multilayer adsorption of CPX on the biochar surface. Overall, experimental data suggested that the incorporation of CPX onto both WRBC-P and WRBC-A is mainly driven by both chemical and physical forces. CPX adsorption was a favorable process at room temperature and in the 7-8 pH range after 12 hours of contact time. WRBC-A demonstrated four times higher CPX removal capacity than that of WRBC-P indicating KOH activation as an efficient route to improve the adsorption capacity of biochar for the removal of CPX.