Preparation of Immobilized cells. P. putida CH11 grown in 100 mL of plate count broth was harvested by centrifugation (7500g, 10 min) and then washed with sterile distilled water three times. The organisms (105 cells/mL) were immersed in a sterile 4% Na alginate solution, and then the Na alginate solution containing the cells was dropped into a 4% CaCl2 solution by syringe to immediately form 3 mm diameter immobilized beads. These gel beads were activated by flushing with sterile
distilled water for 5 h. The activated beads exhibited excellent mechanical strength in the continuous experiments.