[Transformation of Ammonia in Wetland Sediments for Treatment of Mining Wastewater]

Nitrogen elements play an important role in the biogeochemical cycle of artificial wetlands. In this study, we investigated the anaerobic transformation of ammonia nitrogen and its main pathways in sediment in an artificial wetland. Results showed that the anaerobic ammonia oxidation (ANAMMOX) process and iron reduction occurred in wetland sediment, coupled with anaerobic ammonia oxidation (Feammox). Feammox used Fe(Ⅲ) to oxidize ammonia nitrogen to produce nitrogen; intermediate products were nitrate, nitrite, and N₂O. Addition of ferrihydrite promoted the Feammox process and ammonia nitrogen loss caused by Feammox was enhanced from 1.69 to 2.72 mg·(kg·d)^-1. When ferrihydrite was added, a loss of 28% of total nitrogen (TN) in the wetland occurred, associated with Feammox, increasing to 42%. Anaerobic ammonia oxidation was significantly inhibited with addition of ferrihydrite and TN loss in the system decreased by about 25%. Results showed that the formation of goethite by mineralization of ferrihydrite inhibited the ANAMMOX process, promoting Feammox to lead to competing electronic donors for the S-ANAMMOX process, causing inhibition of the S-ANAMMOX process. This achieves the purpose of reducing TN loss in the wetland system. In addition, this may have some significance for further understanding the interaction between iron reduction and the nitrogen cycle in the wetland.