A macro-porous cellulose carrier (AQUACEL(TM)) was used for immobilization of denitrifying bacteria to develop a practical, high-performance nitrogen removal system. When the immobilized cells were used for denitrification at a high nitrogen loading rate, flotation of carriers caused by the evolution of nitrogen gas occurred. For countering the problem of carrier flotation, new reactors in which hydrodynamic jet flow and centrifugal force are used. In these new reactors the floating carriers were distributed homogeneously and complete denitrification was achieved even at high loading rate of 20 kg-N/m(3)-carrier/d. This AQUACEL system was used for efficient denitrification of wastewater discharged from an electroplating factory.