Comparative Optimization of Methyl Red Dye Removal from Aqueous Solution Using KOH-Modified Orange Peel and Moringa Leaf Biomass

Abstract

The discharge of dye-containing wastewater from industrial activities poses significant environmental challenges due to the persistence, visibility, and potential toxicity of synthetic dyes. This study compared the adsorption of methyl red from aqueous media using potassium hydroxide (KOH)-modified orange peels and Moringa oleifera leaves as low-cost biosorbents. The effects of initial dye concentration (2–10 mg L⁻¹), adsorbent dosage (0.1–0.5 g), solution pH (3–9), contact time (10–1440 min), and temperature (40–50 °C) on adsorption performance were investigated. The point of zero charge (pH_pzc) was determined to be approximately 5.1 for orange peels and 6.6 for moringa leaves, indicating differences in surface charge characteristics. Adsorption performance was evaluated using adsorption capacity (q_e) and percentage removal (%R). Orange peels consistently exhibited superior adsorption performance across most operational conditions. Maximum adsorption capacities of 2.386 mg g⁻¹ and 2.214 mg g⁻¹ were obtained for orange peels and moringa leaves while maximum removal efficiencies reached 95.43% and 88.57%, respectively. Adsorption was favored under acidic conditions, increased with contact time up to equilibrium, and generally improved with increasing temperature. The enhanced performance of orange peels was attributed to their lignocellulosic composition, abundance of surface functional groups, and improved accessibility of adsorption sites following alkali modification. The findings demonstrate that both biosorbents are effective and sustainable materials for methyl red removal; however, KOH-modified orange peels showed greater adsorption capacity and operational stability. These results highlight the potential of agricultural wastes as affordable alternatives for dye-contaminated wastewater treatment.