Reducing O2 in last AS stirring tank

Hi!

I am using ASM 1; every last ASU tank in each AS line is just a stirring tank (always non aerated) in order to reduce the oxygen content before NO recycle to avoid affecting the denitrification. The oxygen content in the model is around 1.1-1.2 mg/l, is it possible to lower it? How?

Thank you in advance,

Marco

My first guess would be to either use a longer tank (~ plug-flow) or have a higher MLSS.
You may try and use a 2-, 3-, .. tank ASU: see if the DO gets reduced significantly.
Or recirculate the RAS (or a portion) to this last tank.