A model of microbioL process occurring in biofilm immobilized on nonporous fine carrier grains and in liq. phase was presented. An impact assessment of a vol. fraction of the solid particles in the liq. phase and conditions for the existence of biofilm on conversion degree of the C substrate was performed. The simulations were performed for aerobic glucose biodegrdn. by Pseudomonas aeruginosa. Obtained results justified the immobilization of biofilm on fine particles from process safety point of view and improved the bioreactor capacity for removing C compds. The results were compared with the stationary properties of a 2 phase airlift reactor of the same design. A higher conversion degree of the carbonaceous substrate in title reactor was achieved than in the airlift one. The loss of bioreactor prodn. capacity due to leaching from the liq. phase was eliminated.