Note: Example SWMM 5 Model for Activated Sludge
Here is one example of how to model an activated sludge tank. The image is Wikipedia (http://en.wikipedia.org/wiki/Activated_sludge) and is the watermark background in the SWMM 5 GUI. There is 100 lps inflow, 20 percent recycle and 10 percent sludge drawoff. You can adjust the amount of recycle and sludge altering the pump type 2 flows or if you want to increase the inflows – add more flow in the RawWater inflow node.