I never saw of a plant working with polymer addition in or before aeration basin if not for a temporary particular problem of bulking sludge cause by filamentous bacteria. But looking on internet I found a plant using polymer:
The polymer is added after the aeration as the biosolids are entering the final clarifier. The polymer ties the solids together and they sink. The clear water leaves the top of the clarifier, the solids with the polymer are pumped from the bottom back to the aeration basin. The polymer is consumed by the bacteria and the bacteria disperses. The bacteria consume the contaminants then once again polymer is added as they re-enter the clarifier. Settling doesn't occur in the aeration basin, air keeps everything mixed for good contact between the pollutants and bacteria.