Removal of textile dye Reactive Black 5 from aqueous solution by adsorption on laccase-modified silica fume

Textile wastewater with the dye is released in various ways into the environment and it causes significant environmental problems. Due to the stability of modern dyes, conventional biological treatment methods for industrial wastewater are ineffective, resulting in an intensively colored discharge from the treatment facilities. Thus, there is a need for developing more effective treatment methods to eliminate dyes from the waste stream at its source. The most effective methods of dye removal from wastewater are adsorption and the use of enzymes. In this study, the removal of Reactive Black 5 (RB5) from aqueous solutions has been studied using silica fume (SF) waste material after its modification with laccase from Russulaceae (Lactarius volemus). Laccase was purified by using saturated precipitate (NH4)2SO4, DEAE-cellulose and immobilized on SF. Batch adsorption experiments have been performed as a function of pH, contact time, temperature, and adsorbent dosage. The optimum results were obtained at pH 9, contact time of 60 min, temperature of 30°C, and an adsorbent dosage of 1 mg/mL. The isotherm studies showed that the adsorption experimental data were fitted well by Langmuir isotherm model. The adsorption capacity was found to be 322.58 mg/g. Thermodynamic parameters including the Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes indicated that the adsorption of RB5 onto laccase-modified SF was feasible, spontaneous, and endothermic. ΔH and ΔS were 1,185 kJ/mol and 4.104 J/mol K, respectively. These parameters indicated that the adsorption of RB5 onto laccase-modified SF was feasible, spontaneous, and endothermic. The results show that the laccase-modified SF can be used for the treatment of aqueous solutions as an alternative low-cost adsorbent.