A novel outside cycle anaerobic reactor was developed based on the characteristics of expanded granular sludge bed (EGSB) and other anaerobic reactors. It was demonstrated that the sludge wash-off at high liquid upflow velocities could be controlled efficiently and good performance was achieved during municipal wastewater treatment. In order to achieve accurate prediction and effective control of sludge settling property in the reactor developed

a dispersion model was established on the basis of mass balance and free settling theory of granular sludge

taking consideration of the relevance between sludge settling velocity and sludge concentration. The simulation results of sludge distribution was in good agreement with the measured results at different liquid upflow velocities. In addition

the concentration of suspended solids (SS) in the effluent was simulated by introducing the separation efficiency of three-phase separator. The standard deviation of the simulated data was less than 6%. Based on the relative concentration of the liquid-sludge mixture

the sludge blanket height could be calculated by quadratic interpolation. The sludge blanket heights were basically identical at various upflow velocities

while the sludge concentrations at the same height differed.