The characteristics of the single-sludge nitrification-denitrification process were investigated using influent organics as the carbon source and nitrate as an electron acceptor to see if any oxygen savings could be obtained. The key research tools used were mathematical modeling, computer simulation, the library, and discussions with experienced operating engineers. A mathematical model was obtained from the literature for the nitrification process. The summary of simulations using the model was that complete nitrification can be achieved at a temperature of 20\sp∘C, with a dissolved oxygen concentration of 2 mg/l and a sludge age of 4-5 days. A mathematical model was developed for the single-sludge nitrification-denitrification process and the influence of denitrification on oxygen requirements was studied by simulation. The conclusion was that, depending on the COD/NH\sb4\sp+ ratio, savings in oxygen, by the use of nitrate as an electron acceptor are in the range of 3 to 8 percent.