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 gO2 per gNO3-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.