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The project was undertaken at the 20.6 MGD Mamaroneck Wastewater Treatment Plant (WWTP), one of four facilities operated by the Westchester County Department of Environmental Facilities that discharge to Long Island Sound. The County plants are subject to stringent total nitrogen (TN) discharges under a Total Maximum Daily Load (TMDL). Under this project, two (2) separate and distinct treatment trains, each consisting of one aeration tank and two final clarifiers, were separated from the balance of the plant. These two demonstration treatment trains were designed identically with one exception: only one train incorporated flexible strand fixed film media in order to study the ability of this media to enhance TN removals. Approximately 100,000 sq. ft of media was placed in zones B, D and F the aerobic zones, which constituted an aerobic fraction of 66 percent of the aeration tank.

The process train without fixed film media achieved higher TN removals on a full-scale basis. The IFAS system was subject to the growth of red worms that inhibited the nitrification process and process control steps (RAS chlorination and operation under low DO conditions) were undertaken to eliminate these organisms. Laboratory tests confirmed very low nitrification rates for the IFAS media compared to the suspended growth, and higher denitrification rates for the IFAS media relative to the mixed liquor. The originally hypothesized mechanism for the IFAS media to enhance overall TN removal was thought to be by enhancing nitrification. However, the results of the laboratory analysis indicated a benefit of increased denitrification. This data will benefit the understanding of mechanisms and rates of nitrogen removal in these types of BNR systems. Detailed data on total dissolved gas measurements will be presented to provide another tool in controlling floating sludge problems in the unique application of deep aeration for BNR and a presentation of full-scale tank profile work is also included.

Document Type: Research Article


Publication date: January 1, 2004

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