THE STABILITY OF ACTIVATED-SLUDGE REACTORS WITH SUBSTRATE-INHIBITION KINETICS AND SOLIDS RECYCLE

The steady-state simulation of activated sludge reactors with settler and recycle of the concentrated biomass was considered for the case of substrate inhibition kinetics. Analytical relationships were developed for the continuous stirred tank reactor; numerical simulation was performed for other reactors. Occurrence of multiple solutions and hysteresis behavior are examined as a function of space time θ, recycle ratio R, recycle solids concentration XR and sludge age θc. The sensitivity of the outlet substrate conversion with respect to the degree of substrate inhibition and of hydraulic mixing is discussed; criteria are suggested in order to operate such bioreactors and to prevent washout occurrence. All results are presented in dimensionless form. © 1990.