Biosorption of Direct Red-31 and Direct Orange-26 dyes by rice husk: Application of factorial design analysis

The present work describes the biosorption potential of low cost and easily available rice husk for the adsorptive removal of Direct Red-31 and Direct Orange-26 textile dyes. In the present investigation a 53 full factorial design analysis experiment was employed to optimize the process parameters for enhanced adsorptive removal of Direct Red-31 and Direct Orange-26 textile dyes from aqueous solution. Factorial experiments with three factors initial dye concentration, biosorbent dose and pH at five levels were conducted in duplicate. The biosorbent efficiency for the dyes was determined after 3 h of treatment at 30 °C using suitable size of biosorbent (0.255 mm). Analysis of variance (ANOVA), F-test and p-values were used to study the main, two ways and three ways interaction effects. The values of regression coefficients (R2 = 0.999) for both dyes confirmed the good fitness of model. A maximum biosorption capacity of 57.88 and 36.14 mg/g was observed at pH 2 and 3 for Direct Red-31 and Direct Orange-26, respectively, with 125 mg/L dyes concentration. The most significant variable was found to be dyes initial concentration. Moreover, the decolorization of both direct dyes was also affected by salts, heavy metal ions and surfactants.

► Biosorption potential of rice husk for the removal of direct dyes was investigated.
► A 53 full factorial design analysis was employed to optimize the process parameters.
► Analysis of variance, F-test and p-values were used to study the interaction effects.
► The most significant variable was found to be dyes initial concentration.