Model study on real-time aeration based on nitrite for effective operation of single-stage anammox
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Anaerobic ammonia oxidation (Anammox) is an innovative technology for cost-efficient nitrogen removal without intensive aeration. However, effective control of the competition between nitrite oxidizing bacteria (XNOB) and Anammox bacteria (XANA) for nitrite is a key challenge for broad applications of single-stage Anammox processes in real wastewater treatment. Therefore, a real-time aeration scheme was proposed to determine dissolved oxygen (DO) based on nitrite concentration for effective control of XNOB growth while maintaining the XANA activity in a single-stage Anammox process. In this study, a non-steady state mathematical model was developed and calibrated using previously reported lab-scale Anammox results to investigate the efficiency of the proposed real-time aeration scheme in enhancing the Anammox process. Based on the calibrated model simulation results, DO of about 0.10 mg-O2/L was found to be ideal for maintaining effective nitrite creation by ammonia oxidizing bacteria (XAOB) while slowing down the growth of XNOB. If DO is too low (e.g., 0.01 mg-O2/L or lower), the overall rate of the ammonia removal is limited due to slow growth of XAOB. On the other hand, high DO (e.g., 1.0 mg-O2/L or higher) inhibits the growth of XANA, resulting in dominancy of XAOB and XNOB. According to the simulation results, nitrite concentration was found to be a rate-limiting parameter on effective nitrogen removal in single-stage Anammox processes. We also found that nitrite concentration can be used as a real-time switch for aeration in a single-stage Anammox process. A schematic aeration method based on real-time nitrite concentration was proposed and examined to control the competition between XANA and XNOB. In the model simulation, the XANA activity was successfully maintained because the schematic aeration prevented an outgrowth of XNOB, allowing energy-efficient nitrogen removal using single-stage Anammox processes.
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