The Nitrogen Removal Characteristics Of Heterotrophic Nitrification-aerobic Denitrification Strain XH02 And The Changes Of Community Structure During Enhancing Nitrogen Removal

With the rapidly development of the agriculture and industry, nitrogen pollution in water has an increased trend, which has serious latent danger to our human health and organisms. Thus the environmental problem caused by the nitrogen contamination has aroused people’s attention increasingly.The study of nitrogen removal in water has become an important issue. The novel heterotrophic nitrification-aerobic denitrification bacteria have been reported for the past few years, and have become one of the hotspots in the field of biological nitrogen removal from wastewater. A heterotrophic nitrification-aerobic denitrification strain XH02 was screened from aerobic activated sludge through domestication, which was identified as Ochrobactrum anthropi with molecular biology, physiology and phylogenetic analysis. The characteristics of nitrogen removal, the influence of XH02 to strengthen the nitrogen removal and the community of bacteria of the reactor were studied. The conclusions are as follows:(1) The optimal nitrifying conditions and denitrifying conditions of XH02 by single factor process were carbon source citrate sodium, temperature 35℃, speed 120r/min, C/N 8, pH 7.0 and 9.0 respectively. Under the optimal conditions,average removal rate was 88.8%, 100.0% and 94.8% at 48 h for ammonium, nitrate and nitrite. The environmental factors of heterotrophic nitrification were optimized with response surface methodology, the results indicated that its optimal nitrifying conditions were temperature 34℃,speed 125 r/min,C/N 7.5 and pH 7.5. Under such nitrifying conditions,the average removal rate was 82.2% at 24 h for ammonium. The removal rate of ammonia nitrogen has been improved 14.9% of single factor design under the optimized with response surface methodology.(2) In the mixed system of ammonia-nitrate or ammonia-nitrite, there was a competitive relationship between nitrification and denitrification. When the ratio of ammonia-nitrate or ammonia-nitrite was less than 5:1, the ammonia could promote the removal of nitrate and nitrite. When the ratio of ammonia-nitrate or ammonia-nitrite was 5:1, the ammonia removal rate could improve, and didn’t have significant effects on the removal rate of nitrate and nitrite.(3) HAO, NAP and NIR were the key enzymes in nitrogen removal. We speculated the nitrification pathways was XH02 converted ammonia to hydroxylamine followed by part of hydroxylamine to nitrite, then denitrified the nitrite to gaseous nitrogen, and part of hydroxylamine was converted to nitrogenous gases directly; And the strain could effectively utilize nitrate and nitrite nitrogen, the denitrification pathway was XH02 converted nitrate to nitrite, then denitrified the nitrite nitrogenous gases, but the concent of nitrite was lower throughout the entire process.(4) The adding of XH02 strengthened the nitrogen removal in the reactor, the diversity, community structure were obvious changed in the reactor. Shannon-winner index firstly decreased and then increased, and finally inclined to stable value. The relative content of XH02 exhibited an increased trend, and finally reached the stable status. There were original species significantly reduce, such as Acinetobacter, Aquabacterium, Myxococcus, Lactococcus and so on. And there were species diversity of microorganism obviously increased, such as Treponema, Fontibacter and Arenimonas.