Objective Question & Answer

First Stage BOD (Carbonaceous Demand): Represents the oxygen consumed by

heterotrophic bacteria to oxidize organic carbon compounds. This usually occurs over the first

5 to 8 days.

Second Stage BOD (Nitrogenous Demand): Represents the oxygen consumed by autotrophic nitrifying bacteria (Nitrosomonas and Nitrobacter) to convert ammonia and organic nitrogen into nitrites and nitrates. This nitrification process usually begins after about 5 to 10 days, once the carbonaceous organic matter is significantly reduced.