Performance and mechanism of methylene blue biosorption on orange peel.

Biosorption of Methylene Blue (MB) from aqueous solution using orange peel biosorbent was experimentally investigated. The effects of dye concentration, solution pH, salt concentration and contact time were investigated in a batch model. The results showed that adsorption equilibrium was reached within one hour at two initial MB concentrations (200 and 1000 mg 1(-1)). The uptake of MB was significantly affected by the pH of dye solution. As the pH decreased, the uptake of MB decreased and was zero at pH 2. The Langmuir isotherm model fitted the experimental data well, and the maximum adsorption capacities of the orange peel were 246.8 +/- 10.6 and 370.3 +/- 31.0 mg g(-1) at pH 7 and pH 10, respectively. The uptake of MB was significantly affected by the high concentration of salts. Adsorption of MB onto orange peel was reversible, and the sorption/desorption efficiencies remained almost 100% even up to seven reuse cycles when the biosorbent loss was taken into consideration. The binding sites were identified to be primary carboxyl groups present in orange peel. The main mechanism of MB adsorption is considered to be electrostatic interaction.