Study On Optimum Design Of Rectangular Settling Tanks

Settling tanks are usually used in water treatment for the removal of suspended solids (SS) by gravitational settling. Although there are all kinds of settling tanks, the basic elements of suspended particles removal are the same. Due to its simple structures, convenient management, low operating costs and strong adaptabilities to the changeable water quality, the rectangular settling tanks are still widely used in kinds of water and wastewater treatment.The empirical methods are usually adopted in the design of settling tanks, rarely considering the relationship between the suspended solids removal efficiency and the areas of the settling tanks. In order to overcome the questions and realize the fast, highly effective settling tanks design, a design method which is based on the column-settling tests is proposed in this paper. The importance of the column-settling tests to the design of settling tanks is analyzed, and the relationship between discrete particle settling and flocculent settling is discussed. It is proved that the same method namely the cumulative distribution curve can be used to calculate the total precipitation efficiency.In this paper, computer-aided data processing in the column-settling experiment is studied. The programming language of MATLAB is used to design a program for the data processing, and the interpolation and integral is carried on to process the precipitation data. The relation curve among the settling efficiency, the settling velocity of particles, and the retention time can be drawn precisely.According to the required settling efficiency, the appropriate settling velocity (namely the surface overflow rate of the settling tanks) and the appropriate retention time can be chosen to design the settling tanks. As compared with the settling tanks which are designed according to the conventional methods, the settling tanks that are designed by the method in this paper may save area 20%~30%. Obviously, the design parameters of the settling tanks which are obtained by the method in this paper are more precise and economic.