Optimization of the Aeration Strategies in a Deammonification Sequencing Batch Reactor for Efficient Nitrogen Removal and Mitigation of N2O Production

In deammonification systems, nitrite-oxidizing bacteria (NOB) suppression and nitrous oxide (N 2 O) mitigation are two important operational objectives. To carry out this multivariable analysis of response, a comprehensive model for the N cycle was developed and evaluated against experimental data from a laboratory-scale deammonification granular sludge sequencing batch reactor. Different aeration strategies were tested, and the manipulated variables comprised the dissolved oxygen (DO) set point in the aerated phase, aeration on/off frequency (F), and the ratio (R) between the non-aerated and aerated phase durations. Experimental results showed that a high ammonium utilization rate (AUR) in relation to the low nitrate production rate (NPR) (NPR/AUR = 0.07–0.08) and limited N 2 O emissions ( E N 2 O < 2%) could be achieved at the DO set point = 0.7 mg O 2 /L, R ratio = 2, and F frequency = 6–7 h –1 . Under specific operational conditions (biomass concentration, NH 4 + -N loading rate, and temperature), simulation results confirmed the feasible aeration strategies for the trade-offs between the NOB suppression and N 2 O emission. The intermittent aeration regimes led to frequent shifts in the predominating N 2 O production pathways, that is, hydroxylamine (NH 2 OH) oxidation (aerated phase) versus autotrophic denitrification (non-aerated phase). The inclusion of the extracellular polymeric substance mechanism in the model explained the observed activity of heterotrophs, especially Anaerolineae, and granule formation.