The Blue Plains AWTP is the largest advanced wastewater treatment facility of its type in the United States with a rated annual average day capacity if 370 million gallons per day and a peak wet weather capacity of 1.076 billion gallons per day. While other metropolitan areas have facilities with larger capacities, none of these provide the high level of treatment that Blue Plains does with its nitrification/denitrification and filtration process.
Sanitation 
Specifically, this is the Blue Plains Advanced Wastewater Treatment Plant.
From http://www.dcwasa.com/about/facilities.cfm:
The Blue Plains AWTP is the largest advanced wastewater treatment facility of its type in the United States with a rated annual average day capacity if 370 million gallons per day and a peak wet weather capacity of 1.076 billion gallons per day. While other metropolitan areas have facilities with larger capacities, none of these provide the high level of treatment that Blue Plains does with its nitrification/denitrification and filtration process.