UTILIZATION OF CITRUS WASTE BIOMASS FOR SORPTION OF REACTIVE DYES FROM AQUEOUS SOLUTIONS

Abstract

The objective of study was to establish the potential of inexpensive and locally available biomaterial i.e. lignocellulosic waste of Citrus fruits as biosorbent to remove reactive dyes from aqueous solution. The Citrus waste biomasses i.e. Citrus reticulata, Citrus sinensis, Citrus limetta and Citrus paradisi were analyzed and screened having optimum sorption capacity for reactive dyes. Citrus sinensis biosorbent was selected and its sorption potential for Reactive yellow 42, Reactive red 45, Reactive blue 19 and Reactive blue 49 was investigated with variation in the parameters such as pH, biosorbent dose, initial dye concentration and temperature. Biosorbent was chemically treated by organic and inorganic reagents of which acetic acid enhanced the sorption capacities for Reactive yellow 42, Reactive blue 19 and Reactive blue 49; and acetonitrile for Reactive red 45 attaining equilibrium in 60 minutes. While immobilization of biosorbent into calcium alginate beads decreased the sorption capacity and prolonged the time to achieve equilibrium upto 120 minutes in case of all reactive dyes. Experimental data showed good fit with the Freundlich adsorption isotherm. Pseudo second order rate law described best the sorption mechanism with a high coefficient of determination (R 2 =0.99). The mechanism of sorption was found to be physiosorption. FT-IR analysis of biosorbent revealed the presence of C=O, C−O, NH and OH groups on the surface of biosorbent. SEM imaging of biosorbent surface before and after biosorption visualized fibrous texture of biosorbent. Desorption experiments were also performed to regenerate the biosorbent making the process more economical and environment friendly. The interactive effect of pH, biosorbent dose and dye concentration on the sorption capacity of Citrus sinensis biosorbent was investigated using central composite design matrix and response surface methodology. The probability values less than 0.0001 designated the good fit of sorption data by the model. High values of coefficient of determination (R 2 0.987, 0.998, 0.988 & 0.999 for Reactive yellow 42, Reactive red 45, Reactive blue 19 and Reactive blue 49, respectively) indicated evaluation of biosorption data by second order polynomial equations very well. The interactive effect of pH, biosorbent dose and dye concentration was found significant and sorption capacity was optimum at acidic pH range, smaller biosorbent dose and higher dye concentrations. The results proved Citrus sinensis to be a favorable biosorbent to be applied on industrial scale.