Immobilization of Aspergillus nidulans SU04 cellulase on modified activated carbon

Abstract

The present study deals with the immobilization of Aspergillus nidulans SU04 cellulase onto modified activated carbon (MAC). The effect of contact time, cellulase concentration, MAC dosage, and temperature for maximum immobilization percentage and immobilization capacity is investigated. The equilibrium nature of immobilization is described by Langmuir and Freundlich isotherms. The kinetic data were tested using the pseudo first order. The activation energy of immobilization was evaluated to be 11.78 J mol⁻¹. Results of the thermodynamic investigation indicate the spontaneity (∆G <0), slightly endothermic (∆H >0), and irreversible (∆S >0) nature of the sorption process. Entropy and enthalpy were found to be 41.32 J mol⁻¹ mg⁻¹ and 10.99 kJ mol⁻¹, respectively. The Gibbs free energy was found to be −22.79 kJ mol⁻¹. At 80 rpm, 323 K, 2 h, 5 mg of MAC, immobilization capacity was 4.935 mg cellulase per mg of MAC from an initial cellulase concentration of 16 mg ml⁻¹ with retention of 70% of native cellulase activity up to 10 cycles of batch hydrolysis experiments. The diffusion studies that were carried out revealed the reaction rate as μmol min⁻¹. At optimized conditions, immobilized cellulase had a higher Michaelis–Menten constant, K _m of 1.52 mmol and a lower reaction rate, V _max of 42.2 μmol min⁻¹, compared with the free cellulase, the K _m and V _max values of which were 0.52 mmol and 18.9 μmol min⁻¹, respectively, indicating the affinity of cellulase for MAC matrix.