A new model for wastewater treatment plant clarifier simulation

One-dimensional models of clarifiers have been studied. In these models clarifiers are considered as a set of layers exchanging matter from one to another following two ways: convection and sedimentation. The sedimentation flux is deduced from the sedimentation velocity. This velocity can be stated as a function of the suspended solidsʹ concentration only. This hypothesis induces a strong underestimation of the sludge blanket level. This underestimation is explained because the sedimentation velocity does not take into account all the physics and hydraulics of the clarifier. A complementary hypothesis has thus been added to the model: the sum of convection flux and sedimentation flux remains constant through all the depth of the clarifier. This hypothesis is modeled as a null derivative of the flux over the depth. This differential equation leads to a new expression of the sedimentation velocity. Two real cases have then been simulated using this new sedimentation 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.