At times we need to use polymer to lower the TSS in the effluent of our activated sludge plant. Sometimes when we discontinue use, the turbidity goes up, and sometimes not. It seems that final clarifiers must normally serve as a selector for bacteria that coagulate/flocculate well, and that extended use of artificial polymer might deselect for such bacteria. I wonder whether any studies have dealt with this issue and might have come up with a way of predicting which way things will go when you discontinue polymer use.