Confirming the nitrate-to-oxygen conversion factor for denitrification

A number of studies have identified the possible phenomenon of COD "loss" in nutrient removal activated sludge systems incorporating unaerated zones. One potential cause for the calculated "loss" is in the mathematical assumption made with regards to nitrate reduction in denitrification. In the COD balance calculation a factor is used to convert the amount of nitrate used as a terminal electron acceptor to an equivalent amount of oxygen. The theoretical conversion factor of 2.86 gO(2) per gNO(3)-N denitrified is derived from oxidation/reduction half-reactions. Data from twelve 1 L dentrification batch tests in a closed reactor system were used to confirm this Factor. A value of 2.96 was observed but could not be distinguished statistically from the theoretical value. Interpretation of the data also revealed that no COD was "lost" in these dominant denitrifier experiments with a simple soluble substrate. (C) 1998 Elsevier Science Ltd. All rights reserved.