Adsorption of urea nitrogen onto chitosan coated dialdehyde cellulose under biocatalysis of immobilized urease: Equilibrium and kinetic

Abstract

Chitosan coated dialdehyde cellulose (CDAC) and immobilized urease in gelatin membrane (IE) were prepared. The adsorption of urea nitrogen onto CDAC under biocatalysis of IE was studied in batch system. The equilibrium isotherm of urea nitrogen adsorption onto CDAC with different degrees of oxidation (DO) and the kinetics of adsorption with respect to the DO of CDAC (53, 78 and 95%), CDAC/IE weight ratio (50:4, 50:5 and 50:6), the initial urea nitrogen concentration (395.2, 648.8 and 767.3 mg/L) and temperature (37, 42 and 47 °C) were investigated. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Langmuir model in the entire saturation concentration range (128.2–708.2 mg/L). The maximum monolayer adsorption capacities obtained from Langmuir model are 70.18, 79.56 and 90.42 mg/g for the CDACs with DO 53, 78 and 95%, respectively, at CDAC/IE weight ratio 10:1 and 37 °C. The pseudo first-order and pseudo second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The results showed that adsorption process of urea nitrogen onto CDAC followed the pseudo second-order kinetic model. The DO of CDAC, CDAC/IE weight ratio, initial urea nitrogen concentration and temperature significantly affected the adsorption capacity. The apparent activation energy is 8.934 kJ mol −1 for the adsorption of the urea nitrogen onto CDAC under catalysis of IE at DO 95% of CDAC, CDAC/IE weight ratio 10:1 and initial urea nitrogen concentration 648.8 mg/L.