WIMS can be used to calculate a WAS Flow rate to maintain a given Solids Retention Time (SRT).  There are several approaches to calculate a WAS, in this example we will use the following equation:

WAS Flow{MGD} = (Estimated Pounds Under Aeration - (Estimated Flow * Estimated TSS * 8.34 * Target SRT)) / (RAS Conc * Target SRT * 8.34)

In order to estimate values, we will use a 7 day moving aveage (MOV7 function)

1. Create a new variable called Target SRT.  We will enter our desired SRT in this variable. 

2. Create a calculated variable as shown:

3. Create a Monthly Data Entry form with Target WAS Flow, Target SRT.  Open form and test calculation:

See Also: Solids Wastage Report in Modeling.