Abstract:The heat-shock method was used to treat immobilized activated sludge, and NO₂^--N accumulation was successfully achieved. The investigation of the temperature and processing time of the heat shock revealed that nitrite oxidizing bacteria (Nitrite oxidizing bacteria, NOB) was completely deactivated when heated at 60 ℃for 10 min, while ammonia oxidizing bacteria (Ammonia oxidizing bacteria, AOB) still exhibited some activity. PCR-DGGE revealed that NOB residue after heat shock were Candidatus Nitrospira defluvii, which only when the biomass reach a certain value to appear nitrification performance. Two different temperatures were used to heat shock the immobilized granules, after which continuous-flow experiments were conducted. It was discovered that all two groups of heat shocked immobilized granules could remain stably nitritation, but the higher the temperature the longer the time was required for start stable nitritation. However,NO₃^--N accumulation occurred in the reactor after stably nitritation for 65 d. Therefore, the immobilized granules were heat-shocked again, and nitrite nitrogen accumulation recurred in the reactor.