How do I calculate Oxygen requirement in an aerobic waste water pond?
you can actually calculate the theoretical oxygen requirement using the following formula:
O2 req (kgO2/d) = [Q * (S0-S) / (BOD5/BODL)]/ 1000
Where:
Q= flowrate m3/day
S0= infulent BOD/COD concentration (mg/L)
S= efulent BOD/COD concentration (mg/L)

FYI Successful decreasing of BOD and COD can be obtain by using high volume Oxygen Generator such as Submersible Aeration