Activation of accumulated nitrite reduction by immobilized Pseudomonas stutzeri T13 during aerobic denitrification

The excellent removal efficiency of nitrate by the aerobic denitrifier, Pseudomonas stutzeri T13, was achieved in free cells system. However, poor nitrite reduction prevents efficient aerobic denitrification because of the nitrite accumulation. This problem could be conquered by immobilizing the cells on supports. In this study, strain T13 was immobilized by mycelial pellets (MPs), polyurethane foam cubes (PFCs) and sodium alginate beads (SABs). Higher removal percentages of TN in MP (43.78%), PFC (42.31%) and SAB (57.25%) systems were achieved compared with the free cell system (29.7%). Furthermore, the optimal condition for immobilized cell systems was as follows: 30 °C, 100 rpm shaking speed and pH 7. The shock-resistance of SAB system was relatively poor, which could collapse under either alkaline (pH = 9) or high rotating (200 rpm) conditions. The recycling experiments demonstrated that the high steady TN removal rate could be maintained for seven cycles in both MP and PFC systems.