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In an effort to enhance the reliability of the step-feed Biological Nitrogen Removal process and ensure that Total Nitrogen removal objectives are met in the future, the New York City Department of Environmental Protection (NYCDEP) continues to evaluate process operational modes that enhance nitrification and denitrification. This is particularly important for eight of the fourteen Water Pollution Control Plants (WPCPs) that operate centralized sludge dewatering facilities, where the nitrogen load contributed by the dewatering of anaerobically digested sludges can account for up to 30% of the total nitrogen load on the secondary system.

Opportunities to enhance the performance of the integrated side-stream centrate treatment system currently operated in four of the treatment facilities (“AT-3” process) are currently underway at the NYCDEP Applied Research Facility. Specifically, the advantages of enhancing the removal of the centrate nitrogen load through either nitritation/denitritation or nitrification/denitrification using methanol in the sides stream centrate treatment process was evaluated. Also, the impact of constantly seeding the main plant with nitrifying and methanol-degrading organisms grown in the AT-3 tank is being assessed.

The operation of the AT-3 side stream centrate treatment process with methanol addition proved to successfully reduce the nitrogen load in the centrate and to beneficially enhance the performance of the step-feed BNR process through bioaugmentation, particularly during the critical winter operating period. Operation of the AT-3 process in a nitritation/denitritation mode was feasible using high pH and free ammonia to inhibit the growth and development of the nitrite oxidizing bacteria. Control of the AT-3 process in the nitrification/denitrification mode was also stable and seemed to operate at higher kinetic rates than the nitritation/denitritation mode, thereby requiring a smaller side stream facility (2.6 day nominal HRT vs. a 4 day nominal HRT facility). The use of methanol in the AT-3 process provides substantial reduction in the external alkalinity demand required for sustaining nitrification. In addition, the heat generated by denitrification can assist in sustaining the AT-3 operations during the winter months, the most critical operating period for the NYCDEP facilities.
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Document Type: Research Article

Publication date: 01 January 2007

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