Removal of Methylene Blue Using Agricultural Waste Biomass: A Comparative Study of Corncob, Rice Husk, and Walnut Shell

Industrial dye effluents have been identified as a substantial contributor to water contamination. In order to achieve the efficient removal of methylene blue (MB) using accessible and low-cost sorbents, a comparison was made of the removal performance of agricultural-waste biomass, including corncob, rice husk, and walnut shell. Without pretreatment, batch adsorption experiments were conducted for reaction times of 1-80 min at dosages of 2.5-7.5g/L with an initial MB concentration of 100mg/L. The suspensions were subjected to agitation with a jar tester at a frequency of 150 rpm, followed by a centrifugation step at 4,000 rpm for 10 min. The concentration of MB was subsequently quantified at a wavelength of 664 nm utilizing an ultraviolet-visible spectrophotometer. The maximum removal efficiencies were 99.2±0.04% with corncob, 97.4±0.61% with rice husk, and 94.1±1.48% with walnut shell at 80 min and 7.5g/L. Isotherm analysis revealed higher coefficient of determination (R2) for the Langmuir model (0.98-0.99) in comparison to the Freundlich model (0.94-0.96), suggesting that MB adsorption is more accurately represented by monolayer coverage on homogeneous sites. The findings of the kinetic analysis demonstrated that the pseudo-second-order kinetic model (R2 = 0.9985-1.0000) yielded a superior fit to all biomass in comparison to the pseudo-first-order kinetic model (R2 =0.003-0.932). This finding indicates that the pseudo-second-order kinetic model provides a superior description of the adsorption rates of the tested biomass. The Fourier-transform infrared analysis revealed the presence of characteristic functional groups of lignocellulosic biomass, including cellulose, hemicellulose, and lignin, across all sorbents. The overall peak intensities followed the order corncob>rice husk>walnut shell, which is consistent with the observed relative MB adsorption performance. Consequently, corncob, rice husk, and walnut shell biomass, in that order, were the most effective for MB removal in this study.