Among many factors affecting processes of the suspension removal in settling tanks an important role play turbulent mixing and resuspension of sediment deposited on the bottom of tank. For the purposes of removal process analysis the mathematical model of suspended sediment transport has been established. The model has been used for prediction of removal efficiency of laboratory-scale rectangular settling tank. For evaluation of parameters characterizing flow patterns and sediment falling velocity the radiotracer method has been used. The application of the model has been verified in laboratory conditions with satisfactory results. That gives base for planned study of industrial full scale rectangular settling tanks.