Effect of influent chemical oxygen demand to nitrogen ratio on a partial nitrification complete denitrification process

A novel single-sludge process for achieving partial nitrification and complete denitrification (the PN/CD process) was tested at the bench-scale over a range of influent ratios of chemical oxygen demand (GOD) to total Kjeldahl nitrogen (TKN). Mean ammonia nitrogen concentrations in PN/CD process effluent varied from 6.5 to 8.4 mg/liter at influent COD/TKN ratios varying from 3.7 to 9.8. Ammonia nitrogen concentrations in the influent wastewater had little effect on effluent ammonia levels. Bleed-through of COD to the effluent was not observed at influent filterable COD/ammonia-N ratios between 2 and 11. Denitrification was nearly complete (mean effluent nitrate plus nitrite N less than or equal to 1.4 mg/liter) at influent COD/TKN ratios of 5.3 or greater, whereas nitrate and nitrite accumulation occurred at ratios less than 5.1. The denitrification performance of the pre-anoxic reactor of the PN/CD process was consistent with that of other pre-denitrification processes when compared in terms of relative input rates of COD and oxidized nitrogen. (C) 1998 Elsevier Science Ltd. All rights reserved.