Nitrogen removal characteristics of anammox biofilm and analyses of the dynamic network structure of functional microbes under gradient nitrogen stress

The universal porous gel/vertical fixed bed-anaerobic ammonia oxidation (UPG/VFB-A) is a complex efficient denitrification symbiotic system of microorganisms for leachate. However, the different gradient nitrogen loading lead to dynamic correlation and difference in biofilm formation remain unclear. Therefore, the UPG/VFB-A was operated for 300 days under gradient total nitrogen loading rate (TNLR) conditions, and its biofilm biomass characteristics, bacterial population succession and functional denitrification gene dynamic network were investigated to achieve strong impact resistance and recovery of the reactor for landfill leachate. The results showed that the total nitrogen removal efficiency (TNRE) was 92.4 ± 2.7% and the nitrogen removal (NR) up to 487.0 ± 20.5 mg/L. The system was highly resistant and resilient to high concentrations of FA (11.68 mg/L) and FNA (0.0467 mg/L) with total nitrogen removal rate (TNRR) up to 1.12 kg/m3/d. Candidatus Kuenenia (from 0.09% to 17.2%) with high tolerance to FA and FNA was superior to Candidatus Brocadia (from 9.7% to 4.7%) as the main AnAOB. Meanwhile, the gradient nitrogen had a significant effect on the abundance of genes related to nitrogen conversion, and the relative abundance of typical anammox genes hzs and hdh was highest at a feedwater load of 1.34 kg/m3/d, reaching 20.7% and 16.5%, respectively. This study can provide guidance for anammox treatment of landfill leachate in practical engineering.