The Metropolitan Council Environmental Services (MCES) in St. Paul, Minnesota has recently converted one-quarter of its existing 950,000 m3/d (250-mgd) Metropolitan Wastewater Treatment Plant (Metro Plant) from a nitrifying activated sludge (NAS) step feed secondary treatment system to a biological phosphorus (Bio-P) removal process. This modification is the first phase of a series of upgrades that will convert the entire Metro Plant to a Bio-P system and enable the plant to achieve a treated effluent total phosphorus limit of 1.0 mg/L annual average, coupled with a seasonal nitrification requirement. To accommodate these effluent requirements, previous planning efforts suggested that either additional tankage would be required, or that a significant capacity derating (17-percent or more) of the plant was necessary. This paper presents the significant findings and conclusions of the recent investigations at the Metro Plant, which have included wastewater characterization and bench scale testing, process modeling, a one-year full-scale process proving program, and capacity rating activities associated with this Bio-P program.