reactor air requirements?

[sjohns4]

I'm getting conflicting air requirements from two different modeling programs. The aeration basin has three zones with design DO levels of: 0,1,and 2 mg/l, respectively. There is a recycle flow from the third to the first zone for denitrification.
One program says the second and third zone need nearly the same volume of oxygen. The other is saying the second zone requires approximately 70% of the oxygen demand.

The second seems to go along with EPA "purple book" guidelines, but I dont believe those were based on a de-nitrification plant.

Any thoughts?

Thanks,

Mike

 

[bimr]

Do your programs address the energy required for mixing? If the air flow is less than the minimum flow required for mixing, then a mechanical mixers should be used.

 

[sjohns4]

I dont believe the programs do, but we have thought of that. By my calcs during the lower flow and loading conditions we need a lot more air for mixing then the bugs in the basin do. Currently they have no mixers in the aerobic cells. The DO control system we're installing will have operator set minimium air flow set points reguardless of DO. If in actuallity we find we're spending time running at min. air flow with high DO levels we'll quickly be installing some mixers.

 

[bimr]

If you do not put at least 20 SCFM/1000 cu. ft of air into the basin, the solids will settle on the basin floor.