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In this work, non-living red seaweed (Kappaphycus alvarezii) biomass was investigated as a new biosorbent of methylene blue from aqueous solution. The effect of operational parameters such as equilibrium pH, agitation time, initial dye concentrations, and biosorbent dosage on the biosorption capacity of Kappaphycus alvarezii was studied. The equilibrium solution pH was found to profoundly affect methylene blue sorption capacity of Kappaphycus alvarezii with pH 8 found to be optimum. Evidence from Fourier-transform infrared spectroscopy and scanning electron microscopy pictures confirmed the dye biosorption mechanism as electrostatic interaction between the negatively charged seaweed surface and positively charged methylene blue. Biosorption isotherms indicated that Kappaphycus alvarezii exhibited methylene blue uptake of 74.4 mg/g, according to the Langmuir model. The equilibrium isotherm data were evaluated using the Freundlich, Langmuir, Redlich-Peterson, and Toth models. Kinetic studies revealed that methylene blue uptake was fast with 97% or more of the uptake occurred within 60 min of contact time. The pseudo first and second order models were applied to describe kinetic data, of which the pseudo-first order described experimental data better with high correlation coefficient and low percentage of error values. � , Copyright � Taylor & Francis Group, LLC.

This study addresses removal of a basic dye, methylene blue, from aqueous Solutions by using dried Ulothrix sp. biomass as biosorbent. The effects of the initial dye concentration, contact time. temperature, solution equilibrium pH, biosorbent dosage, and mixing rate on biosorption of the dye have been investigated. It was found that 30 min is sufficient in order to reach adsorption equilibrium. The amount of methylene blue adsorbed onto Ulothrix sp. increased with increasing equilibrium pH and mixing rate, in contrary, it decreased with increasing temperature and sorbent dosage. The process followed the pseudo-second-order kinetic model. The isosteric enthalpy and entropy values were calculated as -11.8 kJ/mol and 37.5 J/(mol K). respectively. In addition, the results suggest that the physical interactions between sorbent particles and sorbate ions play an important role for the adsorption of methylene blue onto the biosorbent. (C) 2009 Elsevier B.V. All rights reserved.