I am afraid your info is ...
Published by Martin P. Pelle, Water Technology Advisor, Engineering & Built Project Utility Team EMEA at Cargill
I am afraid your info is still lacking a lot of essential input to have a full massbalance. NOrmally: first denitrification tank with very low (like Paolo suggested) O2 0.2-0.5ppm, then the nitrification 1,5-2,5 mg/l (why you need 5-6 mg/l? TO me that is a HUGE unnecessary destruction of electricity with that kind of heavy aeration).
BUT you need a large recirculation of the ML (mixed liquor) of the second tank back to the first, to bring back NO3 (with healthy sludge you do not have elevated levels of NO2) to the first tank for denitrification. This could be anything between 50% (compared to the feedflow) up to 300 or even 500% recirculation....but not sure if your system has been designed hydraulically for that (overflows, pumps etc). To know what the denitrification recirculation rate shoudl be you need to make the massbalance of N and C, using the usual stoechiometric reactions of nitrification/denitrificationMind: .
Denitrification recirculation is something else than sludge recycle (that is typically 100%) that brings back sludge from the secondary clarifier to your (preselector?) mixtank before the first 12h denitrification tank.
What puzzles me is that to me it seems you have just enough (even a bit of shortage) of Nkj versus COD, (easy circumstances C:N = 100/15 tough: 100:5) so most, if not all, would be needed to built enough biomass....taking away the need for denitrification. And with 80% COD removal, and such fluctuatiing N numbers in your effluent it sounds to me your system shoudl be able to perform more stable, no NO2, no NH3, and only couple of mg/l of NO3.
If you nonetheless still need nitri/denitrifucation, why don;t you get advice from organisations like COlsen (which incorporates annamox bacteria (red coloured) into your normal activated sludge saving hugely on your oxygen electrical consumption) or RHDHV (Royal Haskoning DHV) that have the NEREDA, granular aerobic sludge (cancelling your secondary clarifier, and potentially one of your activated sludge tanks).
Good luck!
1 Comment
the process for COD remove is all right, but the NH3-N reduction rate is not stable.in our plant, we add the other sludge to this system, and the NH3-N reduction rate will be promoted rapidly(about 7~14 days), but the NH3-N will change to NO2-N,until we add the other sludge to this system the same ,but we lower the DO, and the NH3-N change to NO3-N. now we will look on the NH3-N reduction rate will be stable,in the lack of NO2-N in our aerotion tank, or we add the other sludge to this system normality,to keep the NH3-N reduction rate .
Published by Lin JYH-YAN, advanced engineer at FORMOSA PETROCHEMICAL CORPORATION