Biofilm samples from a carbonaceous trickling filter were evaluated in bench scale reactors to determine their maximum potential dentrification rates. The samples were collected as intact, undisturbed biofilms by inserting clean microscope slides into the trickling filter at various locations, leaving them in place for 28 days, and then removing them and bringing them back to the laboratory. In the laboratory, they were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent that had been spiked with nitrate to a final concentration of 16-18 mg/L as N. Dissolved oxygen (D.O.) concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase to simulate conditions within the full-scale system. Nitrate loss from the reactors was monitored over a five hour period. Denitrification rates of 3.09 to 5.55 g-N/m2.d) either between (a) experimental runs or (b) sampling locaitons over the TF. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, recycle flows may be used to remove nitrate in their existing upstream TFs that currently nitrify downstream, recycle flows may be used to remove nitrate in their existing upstream TFs. This approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification.