I know that this is a little late based on the date of your post, but, you might find this interesting. I work with an extended air plant and we recently changed out the blowers and changed to fine bubble diffusers. The plant operates at approximately 40 to 45% of capacity (based on flow) and has average BOD's (<250 mg/l). When we brought the new equipment on line, the blowers could not be turned down low enough, so, the DO was too high (over 6.0), the sludge would not settle, there was excessive foam and the pH was running too low. The engineers who designed plant upgrades sized the blower to provide for a minimum mixing flow rate.
We were able to develop a control system that allowed the blowers to shut down for 15 min intervals. We had aeration/no aeration cycles. After some experimentation, the operators settled on 1/2 hr on, 1/2 hour off through most of the day with 15 min intervals during normally high flow levels. The foam disappeared. The pH came up. The D.O. floated around 2.0 during aeration cycles. The sludge began to settle better and the hypochlorite use dropped. The BOD removal rates remained above 90%. There is no significant accumulation of solids in the aeration basins.
The high efficiency blowers were already reducing the energy bill and this dropped the energy use by about 35% more.
You didn't say what type of blower system you are using, but, if they could handle on/off cycles, you might look into this type of control.