Activated-Sludge Oxygen and Blower Air Demand
The oxygen the aeration system must supply and the blower air to deliver it.
Example
You enter
- BOD removed (lb/day) 2000
- Oxygen factor (lb O2 / lb BOD, 0.9-1.5) 1.1
- Ammonia-N nitrified (lb/day, 0 to skip) 200
- SOTE (%, ~10-35 diffused) 20
You get
- O2 demand (lb/day) 3120
- Blower air demand 1,895 scfm
Checked against published worked examples from: WEF aeration design.
Details, formula, and sources
ScopeO2 = factor x BOD_removed + 4.6 x NH3_nitrified, SOR = O2 / [alpha F 1.024^(T-20) (beta Cs,T - C) / Cs,20], air_scfm = SOR / (0.075 x 0.232 x SOTE x 1440). Nitrification adds 4.6 lb O2 per lb ammonia-N (easy to forget); diffused-aeration SOTE is only ~10-35%, so the air demand dwarfs the oxygen pounds. The largest energy cost at a plant.
Formula or tableO2_demand (AOR) = oxygen_factor x BOD_removed + 4.6 x NH3_nitrified; SOR = AOR / [alpha F 1.024^(T-20) (beta Cs,T - C) / Cs,20]; air_scfm = SOR / (0.075 x 0.232 x (SOTE/100) x 1440).
Source and editionActivated-sludge oxygen and air demand (WEF aeration design), by name.
Free accessThe oxygen-demand and air-from-SOTE relations are public wastewater-design results; the aeration equipment and the field transfer efficiency govern.
What governsEstimate. AHJ and licensed professional govern.
API field namesbod_removed_lb_day, oxygen_factor, nh3_nitrified_lb_day, sote_pct, o2_demand_lb_day, air_scfm
- Nitrification term 4.6 lb O2 per lb ammonia-N nitrified, added to the carbonaceous oxygen demandWEF aeration design
- Air from SOTE air_scfm = SOR / (0.075 lb/ft^3 x 0.232 O2 fraction x SOTE x 1440), SOR = AOR / [alpha F 1.024^(T-20) (beta Cs,T - C) / Cs,20]; diffused SOTE ~10-35%WEF aeration design