Impacts of intermittent and continuous aeration modes on performance, substrate dynamics, and microbial ecology of mainstream nitrification processes

Intermittent and continuous aeration strategies in combination with solids retention time (SRT) were investigated in terms of their impact on the performance and ecology of mainstream nitrification. Two lab-scale reactors (R1 and R2) were seeded with the same inoculum and subjected to intermittent aeration and continuous low aeration, respectively at statistically similar air-supply rates. For both reactors, SRT was progressively decreased from 8 d during Phase I to 4 and 2.5 d during Phases II and III, respectively. Compared to R2 (93 +/- 4.8 %), R1 achieved more stable and higher ammonia oxidation (99 +/- 0.13 %) averaged across SRTs. In R1, Nitrosospira were the dominant AOB, while in R2, AOB were a combination of Nitrosospira and Nitrosomonas. Among NOB, Nitrospira were more abundant than Nitrobacter for both R1 and R2 across SRTs. Intermittent aeration in R1 supported higher relative abundance of Comammox Nitrospira than R2. Notably, the enrichment patterns for nitrifying bacteria in the two reactors reflected distinct drivers (beyond microbial kinetics), including inoculum composition, extant oxygen or nitrogen concentrations or both. Overall, intermittent aeration strategies are integral to the design of biological nitrogen removal processes, although other considerations such as operational feasibility and process emissions might ultimately influence operating strategies.