The premise of this paper is that, even if influent carbon is insufficient to meet effluent nutrient limit requirements, it will be cost effective to make as much use of it as possible, before supplemental carbon is added. Many North American designs include primary anoxic zones that are too small to use the full denitrification potential of the secondary influent carbon. For the MLE process, nitrogen removal progressively increased up to primary anoxic volumes that are 45% the total reactor volume, and up to 400% IMLR flow. The limit to performance with increasing anoxic volume or IMLR flow is the point where NOx-N is reduced to zero in the anoxic zone. The required anoxic volume to maximize performance, and the associated IMLR flow depends on the secondary influent carbon/nitrogen ratio. In this study performance improved in the MLE process until the BOD5/ammonia-N reached 5.7, beyond which no further improvement occurred. Of the configurations evaluated for nitrogen removal, the Four-Stage Bardenpho process produced the lowest effluent TN. For combined phosphorus and nitrogen removal, the MUCT process produced the lowest effluent TP, but the highest TN.