The Poop

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.

I believe that your problems with turbidity in the clarifier discharge are more likely to be the result of conditions in the influent or the aeration tank because the turbidity doesn't always increase when you stop the polymer feed. For example, an increase in flow rate could cause the the TSS in the clarifier discharge to increase. Do you change any other operating parameters besides adding polymer to the discharge to the clarifier. If the waste load increases or WAS is increased, an increase in young sludge may not settle well and result in a small percentage of dispersed bacteria that increase the turbidity temporarily.

I forgot one possibility; too much polymer may act as a dispersant increasing the turbidity.

 

grrunyan