PERIODIC AND NONPERIODIC OSCILLATORY BEHAVIOR IN A MODEL FOR ACTIVATED-SLUDGE REACTORS

A dynamic model for an activated sludge process is proposed to investi gate the stability and bifurcation characteristics of this industriall y important unit. The model is structured upon two processes: an inter mediate particulate product formation and active biomass synthesis pro cesses. The growth kinetics expressions are based on substrate inhibit ion and noncompetitive inhibition of the intermediate product. The bif urcation analysis of the process model shows static as well as periodi c behavior over a wide range of model parameters. The model also exhib its other interesting stability characteristics, including bistability and transition from periodic to nonperiodic behavior through period d oubling and torus bifurcations. For some range of the reader residence time the model exhibits chaotic behavior as well. Practical criteria are also derived for the effects of feed conditions and purge fraction on the dynamic characteristics of the bioreactor model.