Continuous experiments were performed in a membrane bioreactor (MBR) system. Under the tested conditions, 49.4 to 90.6% of total nitrogen (TN) was found to be removed. The COD/TN ratio as well as the dissolved oxygen (DO) concentration was the key factor influencing the TN removal efficiency. A heterotrophic nitrifier, named Bacillus sp. LY, was newly isolated from the system. Batch experiments show that Bacillus sp. LY could utilize the organic carbon as the source of assimilation when it grew on glucose and ammonium chloride medium accompanying the formation of oxidized-nitrogen. It also could denitrify nitrate while nitrification. After 24 days incubation, the removal efficiencies of the COD and TN by Bacillus sp. LY were 71.7% and 61.2%, respectively. The phylogenetic analysis of Bacillus sp. LY was performed and the phylogenetic tree of Bacillus sp. LY and the neighboring nitrifiers was given.

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