Optimization of BNR Pilot for Higher N Removal Efficiency and Improved Settling


  • Dana Fredericks - Hazen and Sawyer
  • Pusker Regmi - Old Dominion University
  • Mark W. Miller - Virginia Tech
  • Charles B. Bott - HRSD

The pilot study at the Chesapeake-Elizabeth WWTP is a two sludge process in which the A stage is primarily COD removal and the B stage is primarily nitrogen removal. The B-stage 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 anaerobic ammonia oxidation (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 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 ?C.

In this study, optimization of B-stage process for higher N removal efficiencies is aimed by implementing various BNR configurations. Nitrogen removal efficiencies is being evaluated by operating B-stage in 1) MLE mode (1st tank anoxic rest intermittently aerated by AVN control) with different ratio of internal mixed liquor ratio (IMLR) 2) Full intermittently aeration under AVN control 3) Anaerobic selector (1st tank anaerobic without IMLR). Moreover, lower temperature performance will be evaluated by controlling wastewater temperature (25 ?C to 14 ?C). The settling performance of the B-stage will be evaluated extensively throughout the study. The process is monitored and controlled by a programmable logic controller (PLC) and various probes measuring DO, pH, MLSS, TSS, NH4+-N, NO2—N, NO3—N, and COD. Activity tests are performed once a week using bench scale 4L reactors to reveal to what degree NOB are being suppressed within the system.

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

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