Abstract: High nitrogen concentration is one of the important causes of water eutrophication. Biological nitrogen removal is an effective way to remove nitrogen from water. A strain of bacteria, coded as WS-2, was isolated from landfill soil and identified as Agrobacterium sp. based on 16S rDNA gene sequencing. The strain could remove 95.8% of the ammonia in the water within 42 h, producing mainly N₂, nitrate and intracellular nitrogen, which accounted for 42.4%, 23.8% and 19.4% of the initial nitrogen, respectively. Meanwhile the bacteria could remove 80.5% of the nitrate and 97.1% of the nitrite in the water within 84h, producing N₂ and intracellular nitrogen, which accounted for 50.2%-51.0% and 17.0%-17.8% of the initial nitrogen, respectively. It is, therefore, obvious that Strain SW2 bacteria are capable of performing simultaneous heterotrophic nitrification and aerobic denitrification, and during the processes, they turn most ammonia, nitrate and nitrite into gaseous nitrogen and little into intracellular nitrogen. Further experiments of using the bacteria to treat eutrophied water reveal that the bacteria, fixed on polyurethane foams and then subjected to aeration, are capable of removing 84.3%, 71.3%, 94.7% and 55.8%, respectively of COD_cr, total nitrogen, ammonia and total phosphorus, which demonstrates that its strain of bacteria has a high application potential in remedying eutrophied water bodies.

Key words: Agrobacterium sp., heterotrophic nitrification, aerobic denitrification, biological nitrogen removal