Optimization of an Intermittently Aerated BNR Pilot for Higher N Removal and Improved Settling

Authors:

  • Dana Fredericks - Hazen and Sawyer
  • Pusker Regmi - Brown and Caldwell
  • Mark W. Miller - Civil and Environment Engineering Department, Virginia Tech
  • Charles B. Bott - Hampton Roads Sanitation District

Water resource reclamation facilities (WRRFs) that discharge into the Chesapeake Bay are required to meet increasingly stringent total nitrogen (TN) and total phosphorus (TP) effluent limits in an attempt to reduce eutrophication. To accomplish nitrogen removal, many WRRFs have traditionally relied on performing nitrification followed by denitrification. Performing nitrogen removal requires 4.57 lb O2/lb N nitrified and approximately 5 lb COD/lb NO3-N denitrified.

In an effort to reduce the costs associated with biological nitrogen removal, recent research has focused on achieving nitrite-shunt (also known as nitritation). During nitrite-shunt, ammonia is oxidized to nitrite which is then denitrified to nitrogen gas. This process bypasses the production of nitrate and reduces the theoretical oxygen demand and supplemental carbon for N removal by 25% and 40%, respectively.

Another advance that is being studied is the implementation of the deammonification process. During deammonification, half of the influent ammonia is converted to nitrite. This nitrite is then combined with the remaining ammonia and converted directly to nitrogen gas by anaerobic ammonia oxidizing bacteria (anammox). These anammox bacteria do not require oxygen or supplemental carbon and therefore, the deammonification process is even less resource intensive than the nitrite shunt process.

In this work, results from a pilot study at the Chesapeake-Elizabeth WRRF is presented. This work focused on using a two sludge process in which the A stage is primarily COD removal and the B stage is primarily nitrogen removal. The B-stage, which is the focus of this research, consists of four completely stirred tank reactors (CSTR) in series that aim to promote the growth of ammonia oxidizing bacteria (AOB) over nitrite oxidizing bacteria (NOB) for short-cut nitrogen removal and subsequent downstream anammox polishing. The B-stage Ammonia versus NOx (AVN) aeration control strategy is a novel aeration scheme which assesses the concentration of ammonia (NH4+) and NOx (NO2-+NO3-) and adjusts duration of aerobic and anoxic duration with goal of maintaining an effluent NOx-N/NH4-N ratio of 1. This strategy has been proven effective in a single CSTR to achieve NOB out-selection treating domestic wastewater at 25 ᵒC.

For more information, please contact the author at dfredericks@hazenandsawyer.com.

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