Determination of optimal COD/nitrate ratio for biological denitrification

This study utilized a new biochemical nitrogen potential (BNP) test to investigate the optimal carbon-to-nitrogen ratio for a conversion of nitrate to N2 in a biological denitrification process. The original Bernet model was modified in this study for calculating the optimal COD/NO3−-N (C/N) ratio to cover the influent nitrate concentrations <50 mg/l. The optimal C/N ratio results were also calculated using other methods based on the residual dissolved organic carbon (DOC) and the residual nitrate as well as the biogas production. Measurements of the N2O and N2 distribution were carried out to verify the validity of the calculated optimal C/N ratio. Conversely, if the C/N ratio was higher than the optimal value, quantities of the organic matter measured as BOD or COD in the treated effluent increased. Thus, the proposed BNP test and the calculation methods are reliable to predict a valid optimal C/N ratio for a maximum conversion of nitrate to N2 in the biological denitrification process.