A biosorbent was prepared by immobilizing and culturing Zoogloea ramigera cells in calcium alginate capsules to high density. The biosorbent (the cell and its exopolysaccharide "Zooglan") along with the [calcium] alginate is known to be responsible for cadmium rem ova I. The dry weight of the biosorbent reached 107 g/L after 3 days of cultivation and 220 g/L after 5 days based on the core volume of a 2.0-mm diameter capsule used. The biosorbents were completely contained in the core of the capsule where the cells grew preferentially near the shell of the capsules while the polymer distributed homogeneously in the core. The specific cadmium uptake by the capsule biosorbent was 1.9 mg/g adsorbent at an initial cadmium concentration of 3 mg/L. This is 1.24 times more than the specific cadmium uptake by the 1.8-mm beads prepared under a comparable condition. The capsules crosslinked with 1% triethylene tetramine and 1% glutamic dialdehyde solutions were superior to the uncrosslinked capsules in mechanical strength. The crosslinked capsules maintained their mechanical strength and adsorption/desorption capacity even after 30 cycles of repeated use. (C) 1999 John Wiley & Sons, Inc.