Effect of salinity on metal-complex dye biosorption by Rhizopus arrhizus

In this study the biosorption of Yellow RL, a metal-complex anionic dye, by dried Rhizopus arrhizus, a filamentous fungus, was investigated as a function of initial solution pH, initial dye concentration and initial salt (sodium chloride) concentration. The fungus exhibited the maximal dye uptake at pH 2 in the absence and in the presence of salt. Dye uptake increased with the dye concentration up to 1000 mgl(-1) and diminished considerably in the presence of increasing concentrations of salt up to 50 g l(-1). The fungus biosorbed 85.4 mg dye g(-1) dried biomass at 100 mg l(-1) initial dye concentration in the absence of salt. When 50 g l(-1) salt was added to the biosorption medium, this value dropped to 60.8 mg g(-1) resulting in 28.8% reduction in biosorption capacity. The Redlich-Peterson and Langmuir-Freundlich were the most suitable adsorption models for describing the biosorption equilibrium data of the dye both individually and in salt containing medium. The pseudo-second-order and saturation type kinetic models depicted the biosorption kinetics accurately for all cases studied. Equilibrium and kinetic constants varied with the level of salt were expressed as a function of salt concentration. (C) 2010 Elsevier Ltd. All rights reserved.