Design Aspects of Gravity Settlers

The presence of the suspended solids is the most easily visible impurity in the liquid streams in several processes or the urban and industrial wastewater. These suspended particles may be either organic or inorganic in nature and can create problems in the process. The separation of the suspended solids using gravity settling to produce clarified overflow and thickened solids underflow has been used in the wastewater industry. The terms sedimentation or clarification are used to describe the process of gravity separation, depending on if the process focus is on the clarified water or the thickened solids, respectively.

The standard gravity settler design often fails to achieve the desired separation efficiency due to deviation from the normal operation conditions. This happens due to changes in the upstream i.e., feed to the gravity settler. In this situation, the behavior of the flow and particles in the top region of the tank is of particular interest since the particles remain in the supernatant and are carried to the effluent reducing the separation efficiency of the gravity settlers.

The separation of the particles in the gravity settler depends on several factors. One of the most important factors is the recirculation zones in the gravity settlers. The prediction of these recirculation zones is important in order to modify the design of the gravity settler for enhancing the separation efficiency.