The Narragansett Bay Commission has significant initiatives related to nitrogen removal at both the Field’s Point and Bucklin Point Wastewater Treatment Facilities. These projects are required by Consent Agreements with the Rhode Island Department of Environmental management (RIDEM). The Consent Agreements require NBC to provide nitrogen removal at both Treatment Facilities in order to meet a seasonal (May to October) nitrogen limit of 5 mg/l.
The Biological Nitrogen Removal (BNR) facilities at Field’s Point include modifications to the ten existing aeration tanks, storage tanks and pumps for chemicals to adjust pH and to provide additional carbon, new energy efficient blowers to provide more air to the aeration tanks, new influent pumps to the aeration tanks, instrumentation to control the BNR process and upgrades to the computer control system. The modifications to the aeration tanks include subdividing each tank into a series of aerated and non-aerated (anoxic) zones to provide nitrification and denitrification. Nitrification will occur in the aerated portion of the tank using an innovative method known as the Integrated Fixed Film Activated Sludge (IFAS) process. In this process, small engineered plastic media are suspended in the wastewater to provide a site for a biofilm to grow on and within the structure of the media. The bacteria in the biofilm convert ammonia to nitrate which is then converted to nitrogen gas in the anoxic zone. The new facilities will be on line in December 2013.
Other improvements to be constructed under the BNR contract include replacement of the scum concentrator, modifications to the grit washers, new drive mechanisms for the primary and final clarifiers and a new Administration Building.
Prior to entering into the Consent Agreement with RIDEM for BNR at Bucklin Point, the NBC designed and constructed new nitrogen removal facilities at Bucklin Point to achieve a total nitrogen limit of 8 mg/l. Although the NBC has worked diligently to maximize nitrogen removal at Bucklin Point and has achieved significant reductions in nitrogen loading, NBC has determined that additional modifications are required to achieve compliance with the nitrogen limit of 5 mg/l.
In order to achieve the 5 mg/l limit, the NBC will further modify its four existing aeration tanks to provide additional anoxic and aeration zones, additional mixers and instrumentation, and new chemical storage tanks and pumps to provide additional carbon. Plastic media will not have to be added to the aeration zone as there is sufficient capacity in the aeration zone without the media. The new facilities will be on line in March 2014.