Ammonia-based feedback aeration control could avoid an unnecessary air supply and, therefore, save energy. However, this control method could be impacted by many factors such as solids retention time (SRT), nitrite oxidation rate, dissolved oxygen (DO) variation, influent load, temperature, and regular low DO operation. This study indicated that, with an unlimited DO (DO ≥ 2 mg/L), the minimal SRT required to achieve complete nitrification was between 5 and 10 days. If the SRT was ≤ 20 days, reducing the DO could result in accumulation of nitrite. Nitrite could also accumulate under a peak ammonia load with a SRT of less than 15 days. In contrast, ammonia-based feedback control resulted in regular low DO operation. Because low DO enriches nitrifiers and selects nitrite-oxidizing bacteria (NOB) with a greater oxygen affinity, the required SRT to avoid the accumulation of nitrite can be substantially reduced. The authors recommend using a minimal SRT of 20 days to start a system. When the system reaches a stable condition, the minimal SRT can be reduced to 15 days, if needed. A pilot-scale field experiment indicated that the adverse effect of a low temperature can be overcome by extending the SRT.