A model of the settler coupled to the biological reactor

A dynamic simulation model of the entire activated sludge process is presented. For the biological reactor the standard model by IAWQ, the Activated Sludge Model No. 1, is used, and for the continuous sedimentation in the secondary clarifier a new one-dimensional model based on the theory of non-linear partial differential equations is presented. What is new with the settler model is that the numerical algorithm is derived only from the conservation law and the constitutive batch settling flux assumption by Kynch (1952), without using any further ad hoc assumption (heuristics). The model includes the prediction of the concentrations of all biological components of the particulate and soluble material within and at the outlets of the settler. Effects such as hydrodynamics, biological activity and compression in the settler are not taken into account. It is shown how the analytical formulae for a steady-state solution in the settler can be used to obtain a steady-state solution for the entire system. The main aim of the paper is to present how mathematical solutions within the solids flux theory can be implemented.