A. Ajbar et G. Ibrahim, PERIODIC AND NONPERIODIC OSCILLATORY BEHAVIOR IN A MODEL FOR ACTIVATED-SLUDGE REACTORS, Mathematical and computer modelling, 25(10), 1997, pp. 9-27
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.