Design and Operational Insights of the World's Largest Integrated Fixed Film Activated Sludge (IFAS) Process for Low Nitrogen Limits

The Narragansett Bay Commission (NBC) is in the initial stages of startup of integrated fixed film activated sludge (IFAS) process to achieve a monthly seasonal 5 mg/l total nitrogen effluent permit limit for their 291 MLD (77 mgd) Field's Point Wastewater Treatment Plant. The upgrades included new fine screens, supplemental alkalinity addition, supplemental carbon addition and conversion of the complete mix activated sludge reactors into plug flow IFAS reactors. Six (6) of the ten (10) reactors are currently converted for IFAS operation. The design was completed in 2008 following a comprehensive procurement process which included a system guarantee from the IFAS system supplier. When completed in 2014, it is expected to be the largest IFAS facility in the world. The initial results of the nitrogen removal performance prior to any system optimization or supplemental alkalinity and carbon addition indicated that effluent total nitrogen ranged from 8 to 12 mg/l total nitrogen (TN). Additionally the sludge volume index (SVI) at the 95 percent occurrence level has been reduced from 300 ml/g pre-IFAS condition to 150 ml/g post-IFAS condition. This paper will present a summary of the system procurement, design and nitrogen performance and operational insight of the new facility.