Water Environment Federation (WEF)

Plot testing of mbbr and ifas treatment processes for nitrification and denitrification at the mamaroneck wwtp



The Mamaroneck WWTP is one of four WWTPs in Westchester County that the New York State Department of Environmental Conservation (NYSDEC), through its State Pollution Discharge Elimination System (SPDES), imposed Waste Load Allocation (WLA) limits for nitrogen because of its discharge into the Long Island Sound. The focus of this Pilot Study was intended to test the ability of both Moving Bed Biofilm Reactor (MBBR) process and Integrated Fixedfilm Activated Sludge (IFAS) process for meeting future low effluent total nitrogen limits of approximately 4 mg/L. These two processes are worthwhile for this site because (1) a very high level of treatment can be achieved within a small area which is attractive since space is quite limited at the WWTP site and (2) the processes are well-suited for retrofit installation into the existing aeration tanks. The MBBR option required a tertiary denitrification stage, whereas the IFAS option required to achieve complete nitrification and denitrification in the existing pilot tankage with a total hydraulic retention time of only three hours. In order to provide adequate denitrification in such a limited volume, IFAS media was added to the post-denitrification stage with the thought that it would facilitate the growth of slower growing methanolotrophic (methanol-loving) bacteria on the media, enhancing denitrification and preventing their washout. This approach proved successful, effectively doubling the denitrification rate from 14 to 28 mg/L/hr. Nitrification rates and biomass growth on the media were measured through the test period. The loading to the pilot was pushed to its maximum during the coldest winter temperature enabling the two processes to be assessed under the most stressed conditions. Results from the pilot testing confirmed that either IFAS or the MBBR would be capable of achieving the target total nitrogen concentration.

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