Comparison of Aeration Strategies for Optimization of Nitrogen Removal in an A/B Process: DO, ABAC, and AvN Control

The AvN control strategy operates to regulate the effluent ratio of ammonia-N:NOx-N to a designated setpoint through variation of the aerobic fraction. This study compared operation of the AvN controller in the following configurations: 1) a fully intermittent strategy where all tanks are exposed to aerobic and anoxic periods and 2) an intermittent strategy in an MLE configuration where the first tank in series is designated as an anoxic selector. AvN in these configurations was compared to DO Setpoint Control (CAC) and Ammonia Based Aeration Control (ABAC) in MLE configurations. The study looked at operation of each aeration strategy with two different feed types: A-Stage effluent and primary clarifier effluent. The strategies were compared on the basis of nitrogen removal performance, COD/TIN Removal, and alkalinity consumption. AvN in an MLE configuration with PCE provided the best nitrogen removal performance and also the lowest consumption of alkalinity. AvN operation at high influent C/N resulted in a high degree of nitrogen removal (77.5% ± 6.1) but also the highest effluent nitrite concentrations (1.41 ± 0.38 mg-N/L). Particulate COD correlated strongly to NAR and TIN removal within the AvN strategy. AVN operation at low influent C/N resulted in poor TIN removal. Compared to A-Stage effluent, PCE was shown to significantly increase sCOD loading to the B-Stage increasing heterotrophic competition resulting in lower nitrifier activity rates.