Heterotrophic nitrification in MBR: isolation and characterization of heterotrophic nitrifying bacteria

The method of isolating the heterotrophic nitrifiers and the characterization of the heterotrophic nitrification were studied in this paper. Continuous tests via a membrane bioreactor (MBR) were operated under the controlled conditions to proliferate the nitrifiers. Two heterotrophic nitrifiers, named Bacillus sp. ILY and Brevibacillus sp. LY, were newly isolated from a MBR in which the efficiency of TN removal was up to 80 %. Since no autotrophic ammonia oxidizers and nitrite oxidizers could be detected by fluorescence in situ hybridization (FISH), oxidized-N production was unlikely to be catalyzed by autotrophic nitrifiers during the heterotrophic nitrifiers' isolation in this study. The batch test results indicate that Bacillus sp. LY and Brevibacillus sp. LY could utilize the organic carbon as the source of assimilation when grew on glucose and ammonium chloride medium companying the formation of oxidized-nitrogen. They also could denitrify nitrate while nitrification. After 21 days incubation, the removal efficiencies of the COD by Bacillus sp. LY and Brevibacillus sp. LY were 71.7 % and 52.6 %, respectively. The removal efficiencies of TN by the two isolates were 69.2 % and 35.6 %. The phylogenetic analysis of the two isolates and the neighbouring nitrifiers was performed and the phylogenetic tree was given. Bacillus sp. ILY and Brevibacillus sp. LY could become the new bacterial resources for heterotrophic nitrification and might play a bioremediation role for nutrient removal.