Comparison of sensor driven aeration control strategies for improved understanding of simultaneous nitrification/denitrification.

A pilot scale process was operated with A-stage effluent (ASE) and primary clarifier effluent (PCE) in MLE, all tanks aerated, A/O, and A2O configurations. Continuous DO control at high DO (2 mg/L), low DO (0.1-0.3 mg/L), ammonia-based aeration control (ABAC), and ammonia versus NOx (AvN) control (both continuous and intermittent operation) were compared on the basis of total inorganic nitrogen (TIN) removal, and simultaneous nitrification-denitrification (SND). The highly loaded adsorption/bio-oxidation (A/B) process configuration (4 hr HRT) with intermittent aeration was capable of achieving a maximum TIN removal of 80%, while the A2O process with PCE feed, an 11 hr HRT, and 0.2-0.3 mg/L DO continuous aeration achieved a maximum of 88% TIN removal. ABAC and AvN control did not always result in DO setpoints low enough to achieve SND, and even if setpoints were low enough to achieve SND that did not always result in increased overall TIN removal over continuous DO control of 2 mg/L. While there are other benefits to transitioning to sensor driven aeration control strategies such as ABAC and AvN, increased TIN removal during continuous aeration is not guaranteed. Results suggest that although low DO is a prerequisite for SND, carbon availability for denitrification in the aerobic zone is more likely to be the limiting factor once low DO conditions are met. PRACTITIONER POINTS: Intermittent aeration control results in higher TIN removal than continuous aeration at the same total SRT Continuous aeration AvN control is not likely to result in more TIN removal than continuous aeration ABAC for a given COD and nitrogen load Configurations that are designed to maximize predenitrification (e.g., MLE and A2O) are less likely to achieve increased SND in the aerobic zone from low DO operation than configurations that are not (e.g., A/O).