| Recently, nitrogen removal which plays an important role in controlling water pollution has received more and more attention. Due to the disadvantage of traditional technologies for biological nitrogen removal, the research on novel technology which focuses on enhancing the efficiency and stabilization of biological nitrogen removal, as well as saving the consumption of construction and operation become an urgent need. With the development of aerobic denitrification and magnetic strengthening, in this paper, the aerobic denitrifier which having high potential of denitrification was isolated, the performance of magnetic strengthening on the denitrification characteristics of function microbe and the efficiency of biological nitrogen removal system was further investigated, meanwhile, under the magnetic condition, the microbial community structure in the system was detected, and the relationship and dynamic variation of nitrobacteria and denitrifying bacteria was analyzed.A high efficient aerobic denitrifying bacterium belonging to Pseudomonas sp. was isolated from activated sludge, named T13, having the excellent removal efficiency of nitrate and total nitrogen which achieved 97.75 % and 89.74 % respectively. The optimal temperature for the growth and denitrification of T13 ranged from 25 to 35℃, and a nitrogen removal ability of T13 could be found even at a lower temperature such as 15℃. The optimal pH was neutral and low alkali, and the optimal C/N was 3-12. Such a strain could utilize nitrate and nitrite as electron acceptors for nitrate respiration, achieving high-efficiency removal of nitrate and nitrite which were higher than 90 %.Both the intensity and modes of magnetic interaction had great effects upon the physiological characteristics of function microbe regarding aerobic denitrification. Strain T13 showed better performance at the magnetic intensity of 150 mT, the nitrate removal efficiency and dehydrogenase activity increased 7.2 % and 2.38 folders respectively compared to the control condition without magnetic interaction. And the removal of nitrate caused by T13 could reach 100 % when adding magnetic powder into the system. Further, the remarkable improvement of nitrate and COD removal by magnetic interaction was also found in SBR system incubated strain T13. It was presumed that magnetic field had a particular biological effect on the micro activity in order to regulate the reaction of biological nitrogen removal. Considered with the tendency of COD and nitrogen removal, the optimal range of magnetic field was 60-90 mT. Magnetic treatment could reduce the zeta potential of sludge particle and increase the sludge sedimentation rate correspondingly.Magnetic strengthening biological nitrogen removal based on aerobic denitrifiers was investigated at low temperature. It was found that magnetic field was beneficial for the operation of simultaneous nitrification and denitrification (SND) system including shortening the HRT, improving the stabilization and efficiency, enhancing the tolerance to pH and achieving the contamination removal with high standard. Under low temperature, the MSBR-SND (Magnetic-SBR-SND) fed with 377 mg/L of COD and 67 mg/L of ammoniac nitrogen showed a high degree of contamination removal, the average removal of ammoniac nitrogen, total nitrogen and COD was 95.76 %, 60 % and around 82 % respectively.Based on the PCR-DGGE (denaturing gradient gel electrophoresis of polymerase chain reaction) protocol, together with the cluster analysis and Shannon divergence, it was clear that magnetic interaction could induce to a better micro activity of bacterium which adapting the magnetic field and help for forming the stable community structure in the ecosystem rapidly. Under different HRT and DO, the total community structure was stable, while it changed much more intensely with the changed pH, but the effect of these operational parameters on microbial community diversity in the magnetic-added system of biological nitrogen removal was uniformly low. The community structure and microbial diversity of nitrification bacteria and denitrifiers were also affected by the above parameters, but the function microbe T13 which became the dominance strain in this ecosystem presented perfect tolerance to the variation in these conditions, indicating the stabilization of the magnetic-added system for nitrogen removal.Through the systemic research on performance and mechanism on magnetic strengthening biological nitrogen removal based on aerobic denitrifiers, it can be determined that magnetic effect could promote the growth and metabolism of aerobic denitrifiers and help for keeping their dominance state in ecosystem of nitrogen removal, and the technology of magnetic strengthening composite biological nitrogen removal have obvious advantages on improving treatment capable and efficiency of biological nitrogen removal system,especially under low temperature conditions. Therefore this investigation provides a new approach to novel technology of biological nitrogen removal and feasible application in the cold regions of north china.
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