Urease was covalently immobilized onto porous chitosan beads via primary amine groups connected to the backbone via a six-carbon linear alkyl spacer. The optimum conditions for enzyme immobilization are activating the beads with 1%(w/w) glutaraldehyde, reacting the activated beads in pH 7 buffer with the enzyme, using an enzyme to bead weight ratio of 25, and without lyophilization. Chitosan-bound urease was found to fully retain its speci®c activity. Properties of the immobilized urease were characterized under batch and¯ow conditions. Increased optimum reaction temperature, enhanced thermal stability and storage stability, and excellent reusability were found after enzyme immobilization. Continuous hydrolysis of urea solution was studied in a column packed with the enzyme-containing beads for its possible application in regenerating dialysate solution during hemodialysis.

We developed biodegradable nanofibrous polylactide/chitosan membranes for the filtration of heavy metal ions. Polylactide and chitosan were first separately dissolved in trifluoroacetic acid. The solutions were then mixed and electrospun into nanofibrous membranes via an electrospinning process. The morphology of the spun nanofibers was examined using scanning electron microscopy. The average diameter of the electrospun nanofibers ranged from 419 to 695 nm. The metal removal capability of nanofibrous polylactide/chitosan membranes was measured and compared with that of bulk chitosan. The influence of various process conditions on metal removal capability was also examined. The experimental results suggested that the electrospun nanofibrous polylactide/chitosan membranes exhibit good heavy metal ion uptake capabilities. The metal removal capability of nanofibrous membranes increased with the initial metal ion concentrations and the pH value, while it decreased with the temperature and the filtering rate of the solutions. Furthermore, the electrospun membrane could be reused after the recovery process. The empirical results in this study suggested that electrospun nanofibrous polylactide/chitosan membranes can be good candidates for the removal of heavy metal ions.