A new model for wastewater treatment plant clarifier simulation

Our-dimensional models of clarifiers have been studied. In these models cla rifiers are considered as a set of layers exchanging matter from one to ano ther following two ways: convection and sedimentation. The sedimentation fl ux is deduced from the sedimentation velocity. This velocity can be stated as a function of the suspended solids' concentration only. This hypothesis induces a strong underestimation of the sludge blanket level. This underest imation is explained because the sedimentation velocity does not take into account all the physics and hydraulics of the clarifier. A complementary hy pothesis has thus been added to the model: the sum of convection Aux and se dimentation flux remains constant through all the depth of the clarifier. T his hypothesis is modeled as a null derivative of the flux over the depth. This differential equation leads to a new expression of the sedimentation v elocity. Two real cases have then been simulated using this new sedimentati on velocity. The simulated sludge blanket evolution fitted the experimental data. The suspended solids residence time in the clarifier correlated well with an empirical relation given by the bibliography. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.