Design and Application of a Sawdust–Alginate Biocomposite for Sustainable Cationic Dyes Removal from Aqueous Solutions

This study investigates a novel biocomposite material developed by immobilizing sawdust within a calcium alginate matrix (SDA 5%) for the removal of dyes from aqueous solutions. The material was synthesized and comprehensively characterized using FTIR, SEM, and EDS analyses and the pHpzc drift method. Laboratory-scale experiments were performed to evaluate its performance in removing Malachite Green (MG) under varying operational conditions, including initial dye concentration (10–50 mg/L), pH (3–6), and biosorbent dosage (1–6 g/L). At pH 6 and a biosorbent dose of 3 g/L, under constant agitation (130 rpm), SDA 5% achieved removal efficiencies exceeding 95% across all tested MG concentrations. Furthermore, the biosorption capacity increased with increasing initial dye concentration, reaching a maximum value of 15.93 mg/g at an initial MG concentration of 50 mg/L. Nonlinear kinetic modelling revealed that the pseudo-second-order model best described the biosorption process, while equilibrium analysis showed that the Hill and Sips nonlinear isotherm models, followed by Temkin, provided the most accurate fit to the experimental data. These results demonstrate the high biosorption capacity and favorable interaction between MG molecules and the biocomposite surface. Overall, the study highlights sawdust-alginate biocomposites as sustainable, low-cost, and environmentally friendly biosorbents with significant potential for practical wastewater treatment applications.