Efficient Removal of Methylene Blue Dye from Aqueous Solutions Using Raw Rice Straw as a Sustainable Biosorbent

Abstract

The contamination of water bodies by synthetic dyes from textile industries represents a major environmental challenge worldwide. This study investigates the utilization of raw rice straw (RS), an abundant agricultural waste, as a low-cost and eco-friendly biosorbent for removing methylene blue (MB) dye from aqueous solutions. The biosorption performance was evaluated through batch experiments under varying conditions of pH, contact time, initial dye concentration, and biosorbent dosage. Results demonstrated that raw rice straw exhibited remarkable adsorption capabilities, achieving up to 99% MB removal under optimal conditions at pH 4. The adsorption process reached equilibrium within 120 minutes and followed pseudo-second-order kinetics, indicating chemisorption as the dominant mechanism. Equilibrium data were best described by the Langmuir isotherm model, suggesting monolayer adsorption on a homogeneous surface. The maximum adsorption capacity increased with biosorbent dosage, with optimal performance achieved at 3.0 g L⁻¹. Characterization through SEM, FTIR, and XRD analyses revealed that the presence of porous structures, oxygen-containing functional groups, and amorphous regions in raw rice straw contributed significantly to its adsorption efficiency. The study concludes that raw rice straw, without any chemical modification or pyrolysis, serves as an effective, sustainable, and economically viable biosorbent for treating dye-contaminated wastewater, while simultaneously addressing agricultural waste management challenges.