PERFORMANCE OPTIMIZATION OF RECTANGULAR SETTLING TANKS IN SMALL WATER TREATMENT PLANTS BY NUMERICAL APPROACH

ABSTRACT Separation of suspended and colloidal materials from water and wastewater by settlement is one of the most widely used process in water and wastewater treatment. Hydraulic retention time is a main parameter for design and optimization of any water treatment tank or reactor. Determination of the retention time distribution at all different locations within the tank gives information about the possibility of presence of dead zones or and short circuits. The presence of dead zones decrease the effective volume of the tanks that may almost result in a short circuit between the inlet and outlet of the tank. some part of the flow exits the tank without spending the retention time required for settling. On the other hand, it also induces high turbulence intensity in other regions, which not only decreases the possibility of particle aggregation and deposition, but may also causes solids re-stabilization. A uniform flow field is essential to increase the efficient performance of settling tank. This enables particles to settle at a constant velocity and in less time. Serious design and selection of a suitable inlet baffle configuration for settling tanks is one method to decrease the regions and size of the dead zones which shall improve the process performance. The objective of this paper is to study the performance of diffusion drums inlet baffle for settling tanks. In this paper, a computational model has been mapped to the commercial FLUENT® solver and applied to simulate the flow within a 3D rectangular water tank. Finally, numerical results shall demonstrate the optimum hydraulic diameter ratios range for diffusion drums sizing