Modeling the Dynamics of an Activated Sludge Process Using Yield and Growth Functions

Abstract

Transient or dynamic responses often occur in continuous aerobic systems like the activated sludge process when environmental variables change. The system’s response to a dynamic load change has yet to be successfully modeled. In this paper we examine previously collected experimental data of the system’s response to a step change. The real time profile of the growth rate μ and the cell/substrate yield, Y, are studied via parametric manipulation. It was observed that both variables, μ and Y, experience an initial step drop and then a hysteresis response to a new steady-state level, following a sudden step change in the feed flow rate. A modified Monod equation is proposed here to qualitatively model the hysteresis dynamic response of a sudden dilution rate change to an open, continuous microbial growth system.