Abstract. Nowadays, a settling tank's removal efficiency is one of the most crucial matters for all water or wastewater treatment plants (WTPs or WWTPs). The unit can affect WWTP performance and improve the provided effluent quality. In this paper, the geometrical aspects of a settling tank were numerically analyzed via tracer curves, the finite-volume method, and ANSYS CFX software in which the baffle depth and diameter of a settling tank were assessed. Firstly, a previous study was similarly remodeled to verify simulation results. The impact of tank depth variation was numerically assessed where the outcomes showed that a deeper tank could raise discharge time or the hydraulic retention time (HRT). Thus, extensive discharge time may result in less polluted effluent, degrading more solids. However, the tank should not be too deeply based on costs. Moreover, the differential effect of baffle height was analyzed and indicated that lower height is more useful for boosting the HRT. An investigation of tank diameter changes also revealed that wider diameters bring about a broader HRT.

<p><strong>Abstract.</strong> Nowadays, settling tank's removal efficiency is one of the most crucial matter in all Water or Wastewater Treatment Plants (WTPs or WWTPs). The unit can affect a WWTP performance and improve effluent quality provided. In this paper, geometrical aspects of a settling tank were numerically analyzed via tracer curves, finite volume method and Ansys-cfx software in which, baffle depth and diameter of a settling tank were assessed. Firstly, a previous study was similarly remodeled to verify the simulation results. The impact of tank depth variation has been numerically assessed where the outcomes showed that deeper tank could raise discharge time or Hydraulic Retention Time (HRT). Thus, extensive discharge time may result in less polluted effluent degrading more solids. However, the tank should not be considered too deep regarding economic issues. Moreover, the differential effect of baffle height was analyzed and indicated that lower height is more useful to boost HRT. Investigation of tank diameter changes also revealed that wider diameters bring broader HRT.</p>