Partial　nitrification　to　nitrite　has　been　frequently　obtained　at　high　temperatures,　but　has　proved　difficult　to　achieve　at　low　temperatures　when　treating　low　strength　domestic　wastewater.　In　this　study,　the　long-term　effects　of　temperature　on　partial　nitrification　were　investigated　by　operating　a　sequencing　bath　reactor　with　the　use　of　aeration　duration　control.　The　specific　ammonia　oxidation　rate　decreased　by　1.5　times　with　the　temperature　decreasing　from　25　to　15　degrees　C.　However,　low　temperature　did　not　deteriorate　the　stable　partial　nitrification　performance.　Nitrite　accumulation　ratio　was　always　above　90%,　even　slightly　higher　(above　95%)　at　low　temperatures.　The　nitrifying　sludge　accumulated　with　ammonia-oxidizing　bacteria　(AOB),　but　washout　of　nitrite-oxidizing　bacteria　(NOB)　was　used　to　determine　the　short-term　effects　of　temperature　on　ammonia　oxidation　process.　The　ammonia　oxidation　rate　depended　more　sensitively　on　lower　temperatures;　correspondingly　the　temperature　coefficient　theta　was　1.172　from　5　to　20　degrees　C,　while　theta　was　1.062　from　20　to　35　degrees　C.　Moreover,　the　larger　activation　energy　(111.5　kJ　mol(-1))　was　found　at　lower　temperatures　of　5-20　degrees　C,　whereas　the　smaller　value　(42.0　kJ　mo1(-1))　was　observed　at　higher　temperatures　of　20-35　degrees　C.　These　findings　might　be　contributed　to　extend　the　applicability　of　the　partial　nitrification　process　in　wastewater　treatment　plants　operated　under　cold　weather　conditions.　It　is　suggested　that　the　selective　enrichment　of　AOB　as　well　as　the　washout　of　NOB　be　obtained　by　process　control　before　making　the　biomass　slowly　adapt　to　low　temperatures　for　achieving　partial　nitrification　to　nitrite　at　low　temperatures.　Crown　Copyright　(C)　2010　Published　by　Elsevier　B.V.　All　rights　reserved.