Methylene blue biosorption from aqueous solutions by yellow passion fruit waste.

The yellow passion fruit (Passiflora edulis Sims. f. flavicarpa Degener) (YPFW) a powdered solid waste, was tested as biosorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solutions. Adsorption of MB onto this low-cost natural adsorbent was studied by batch adsorption at 25 degrees C. The effects of shaking time, biosorbent dosage and pH on adsorption capacity were studied. In alkaline pH region the adsorption of MB was favorable. The contact time required to obtain the maximum adsorption was 48 h at 25 degrees C. Four kinetic models were tested, being the adsorption kinetics better fitted to pseudo-first order and ion exchange kinetic models. The ion exchange and pseudo-first order constant rates were 0.05594 and 0.05455 h(-1), respectively. The equilibrium data were fitted to Langmuir, Freundlich, Sips and Redlich-Peterson isotherm models. Taking into account the analysis of the normal distribution of the residuals (difference of q(measured)-q(model)), the data were best fitted to Sips isotherm model. The maximum amount of MB adsorbed on YPFW biosorbent was 44.70 mg g(-1).