Mature aerobic granular sludge (AGS) was inoculated in a continuous-flow reactor to treat low ammonia sewage, and the feasibility of achieving partial nitritation in a continuous-flow aerobic sludge system and the demand for R value (the ratio of dissolved oxygen and ammonia nitrogen) when partial nitritation is achieved at different temperatures (30, 20, and 10℃) were investigated. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and ammonia nitrogen (NH4+-N). The results revealed that stable nitritation in a continuous-flow aerobic sludge reactor could be achieved via ratio control, and the value of R were 0.50 (±0.05), 0.35 (±0.03), and 0.20 (±0.02) at the temperatures 30, 20, and 10℃, respectively, from which it can be concluded that stronger oxygen-limiting conditions were required when the temperature was lower. The experiment of fluorescence in situ hybridization (FISH) revealed that ammonia oxidizing bacteria (AOB) have a certain concentration, and the relative number of nitrite oxidizing bacteria (NOB) gradually reduced through the ratio control strategy. Based on the ratio control strategy and the characteristics of wastewater quality, full nitritation of high ammonia wastewater may be allowed; however, for low ammonia wastewater, only partial nitritation is recommended.
Keywords: aerobic granular sludge; continuous-flow; low temperature; partial nitritation; ratio control.