Nitrogen removal and microbial communities in a three-stage system simulating a riparian environment

The riparian zone is an active interface for nitrogen removal, in which nitrogen transformations by microorganisms have not been valued. In this study, a three-stage system was constructed to simulate the riparian zone environments, and nitrogen removal as well as the microbial community was investigated in this ‘engineered riparian system’. The results demonstrated that stage 1 of this system accounted for 41–51 % of total nitrogen removal. Initial ammonium loading and redox potential significantly impacted the nitrogen removal performances. Stages 1 and 2 were both composed of an anoxic/oxic (A/O) zone and an anaerobic column. The A/O zone removed most of the ammonium load (6.8 g/m²/day), while the anaerobic column showed a significant nitrate removal rate (11.1 g/m²/day). Molecular biological analysis demonstrated that bacterial diversity was high in the A/O zones, where ammonium-oxidizing bacteria and nitrite-oxidizing bacteria accounted for 8.42 and 3.32 % of the bacterial population, respectively. The denitrifying bacteria Acidovorax sp. and the nitrifying bacteria Nitrosospira/Nitrosomonas were the predominant microorganisms in this engineered riparian system. This three-stage system was established to achieve favorable nitrogen removal and the microbial community in the system was also retained. This investigation should deepen our understanding of biological nitrogen removal in engineered riparian zones.