Are Filamentous bacteria ...
Published by Ing.Tiziano Zampollo, Employee at Water Engineers & Consultants - WEnCo
Are Filamentous bacteria leading to poor settleability (e.g. bad SVI)? We have seen many ETPs with macroscopic bulking still producing excellent water, tho.
In event of bulking or foaming You may mechanically scrape the foam away (and carefully dispose the scum away) and/or chlorinate the return line to ox tank.
To fully address Your problem You should know more about its cause (lack or misbalance of nutrients, lack of substrate, toxics in feedwater, inhibitory compounds, low aeration efficiency, oversized ETP...are just my first guesses)
HTH