Application of Kinetic Models and Response Surface Methodology to Decolorization of Congo Red Dye with Biopolymer B6

Abstract

Biopolymer B6 produced by Bacillus sp. B6 was investigated regarding its decolorization of the azo dye Congo Red. Chemical analysis showed that biopolymer B6 with a weight-average molecular mass (Mw) of 11 kDa, was mainly composed of 60.6% polysaccharide and 11.8% protein. Fourier transform infrared (FTIR) spectroscopic analysis revealed the presence of carboxyl, hydroxyl and amino groups. Kinetic studies showed that decolorization of Congo Red was a gradual process, equilibrium was reached in 500 min. Pseudo-second order equation was able to provide a realistic description of decolorization kinetic. Kinetic studies indicated that the process for decolorization of Congo Red was mainly controlled by chemical bonding or biosorption, the cause of adsorption could involve valency forces through sharing or exchange of electrons between Congo Red and biopolymer B6. Response surface methodology was employed to optimize the decolorizing conditions. A Plackett–Burman experimental design was used to aid in the first step of optimization. Temperature, biopolymer B6 dosage and CaCl2 dosage were found to be significant factors affecting decolorization of Congo Red. A Box-Behnken statistical design was employed to determine the optimal value of each significant variable. The concentration of Congo Red was 10 mg/L, the optimum conditions were obtained as follows: biopolymer B6 19.3 mg/L; CaCl2 594 mg/L; T = 15.5°C, with the corresponding decolorization capacity of 288 mg/g, which was in close agreement with the predicted value of 290 mg/g. These results demonstrated that biopolymer B6 was a large, acidic proteoglycan complex of 11 kDa, had strong ability for decolorizing the azo dye Congo Red. In addition, biopolymer B6 could have a potential application in domestic wastewater treatment.