In this study, the first purpose is to make an appropriate computational fluid dynamics(CFD) model of clearwell in water treatment plant(WTP) which is verified by the pilot tests. The second one is to study how the shape and flow rate of clearwell have the effects on the $T_{10}$ value. The last one is to provide design criteria for clearwell in WTP to improve $T_{10}$ by using this CFD model.
Disinfection is a basic and effective microorganism inactivation method and has historically contributed to decrease waterborne diseases. But it has the proplem of producing disinfectant by-products(DBPs) like THMs. because of this problem. CT value concept is used. Flow pattern is an important thing that affects the $T_{10}$ value. This is affected by length/width(LW) ratio, showing how the baffing configuration is, is one of importnat factors. From the previous research, only LW ratio used to calculate the CT value. However the configuration, water height , and flow rate of clearwell have effects on CT value. Thus these factors must be considered to evaluate the CT value. It's difficult to modify the real clearrwell and to perform the tracer test. Therefore, CFD is used to simulate the actual condition in clearwell, and this CFD model is verified by the pilot test and paper data. By modifying this CFD model, the effects of shape and flow rate of clearwell are studied.
In the effect of shape factor, the width(X-direction)" length(y-direction) ratio of bottom area corresponding to the types are Type I-1:2, Type II-1:1 and Type III-2:1. Beacuse of the difference in the shapes of clearwell, the T10/T value attains the maximum difference of 0.15 with the same LW ratio. The region where maximum difference occurs is in a region where LW ratio is 25~30. This result can cause the serious problem beacause in designing the clearwell the LW ratio is in that region.
In the simulation by changing the flow rate, the trend is that with increasing the flow rate $T_{10}/T$ value in same LW ratio decreases. This phenomena is not related with the shape of clearwell, even though the decrease is differenct.
the conclusiton is that
1) If the flow rate of clearwell increases. the efficiency of clearwell decreases. This result occurs in any shape of clearwell(Type I, II and III).
2) In designing the clearwell, it's wrong to consider the LW ratio only, to calculate the $T_{10}/T$. The CFD simulation results indicate that the shapes of clearwell and flow rate are also considered as importantly as the $T_{10}/T$.
