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.　©　2018,　Science　Press.　All　right　reserved.