Abstract：Low temperature will inhibit the growth and metabolism of denitrifying bacteria, resulting in poor nitrogen removal efficiency and substandard effluent quality in winter sewage treatment plants. The key measure to solve the problem is to screen the heterotrophic nitrifying and aerobic denitrification strains with high denitrification ability at low temperature. In this study, the low-temperature denitrifier strain was isolated from the activated sludge of a chemical plant in Inner Mongolia, and the strains was identified. Nitrogen removal characteristics were studied by using ammonia nitrogen, nitrate nitrogen and nitrite nitrogen as the only nitrogen sources. The effects of different single factors (carbon source, C/N, pH, rotational speed, temperature) on nitrogen removal performance were studied. The response surface method was used to optimize the key factors of nitrogen removal efficiency in order to determine the optimal nitrogen removal conditions. Finally, the isolated strain was applied to 2 different types of sewage in order to test its nitrogen removal effect. The results showed that the low-temperature resistant bacteria screened from sludge were identified as Enterobacter cloacae, and named N2 (GenBank No. OQ834747). The removal efficiency of strain N2 on ammonia nitrogen (304 mg/L), nitrate nitrogen (37 mg/L) and nitrite nitrogen (30 mg/L) reached 100% at 8 ℃. The strain N2 showed excellent removal ability of 300 mg/L ammonia nitrogen when carbon source of sucrose, carbon-to-nitrogen ratio (C/N) of 8~20, pH of 7~9, and rotation speed of 150~180 r/min, the optimal nitrogen removal conditions of strain N2 were as follows: carbon source of sucrose, C/N of 8.97, pH of 6.62, under these conditions, the removal rate of total nitrogen reached the highest (83.2%). Under the condition of low temperature of 8 ℃, the ammonia nitrogen removal rate of chemical plant sewage and coking plant sewage reached 100% and 91%, and the total nitrogen removal rate reached 99% and 80%, respectively. Therefore, N2 strain has excellent growth and nitrogen removal performance at low temperature and could be applied to wastewater nitrogen removal in cold areas.
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