Biosorption of Methylene Blue onto Fuji Apple Peel Biosorbent: Effects of Agitation Speeds and Contact Time

Abstract

Methylene blue (MB) is a cationic dye found in industrial wastewater that requires effective and environmentally sustainable treatment. This study investigated Fuji apple peel (Malus domestica ‘Fuji’) as a low-cost, renewable biosorbent for MB removal, focusing on contact time and agitation speed. Batch experiments used 0.2 g of biosorbent in 25 mL of MB solution at a constant initial concentration of 1100 mg/L. Contact times ranged from 30 to 150 min, and agitation speeds ranged from 100 to 300 rpm. Residual MB concentrations were measured using UV–Vis spectrophotometry at 665 nm, and adsorption capacities were calculated from concentration differences. Adsorption kinetics were evaluated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Adsorption capacity increased with contact time to 120.369 mg/g at 60 min, followed by a slight decline at longer durations. Increasing agitation speed enhanced MB uptake up to 250 rpm, yielding the highest observed capacity of 125.119 mg/g, whereas capacity decreased at 300 rpm. These findings identify 60 min and 250 rpm as the most favorable contact time and agitation speed within the investigated ranges. Fuji apple peel therefore shows potential as an inexpensive, renewable biosorbent for MB removal, supporting the use of fruit peel biomass in wastewater treatment development.