Efficient dye removal from wastewater by using expired rice grain derived biochar: A sustainable solution for water purification

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2024

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Faculty of Science, University of Kelaniya Sri Lanka

Abstract

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.

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Keywords

Adsorption, Biochar, Kinetic, Methylene Blue, Pyrolysis

Citation

Ranaweera D. M. S. U.; Vithanage M.; Ranaweera S. A. (2024), Efficient dye removal from wastewater by using expired rice grain derived biochar: A sustainable solution for water purification, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2024-Kelaniya) Volume 4, Faculty of Science, University of Kelaniya Sri Lanka. Page 160

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