Nitrogen management in landfill leachate using single-stage anammox process-illustrating key nitrogen pathways under an ecogenomics framework.

Simultaneous functional gene expressions using mRNA, rate measurements, and biochemical analysis proved the consistent contribution of ammonia oxidizers, heterotrophic denitrifiers, and anammox bacteria in a single-stage attached growth partial nitritation/anammox system for nitrogen management in landfill leachate. Average removal efficiencies of ammonia-nitrogen, total inorganic nitrogen, and COD were 94%, 88%, and 26%, respectively, in the reactor. Off-gas NO fluxes increased at relatively higher dissolved oxygen. Batch activity tests revealed the occurrence of significant anammox activity even in the presence of high concentrations of organic carbon in the influent. mRNA based functional expressions of nitrite reductase (nirK and nirS) and hydrazine synthase (hzsA) suggested simultaneous active heterotrophic denitrification and anammox, respectively. 16S rRNA amplicon sequencing revealed Proteobacteria (36-56%), Planctomycetes (10-31%), and Bacteroidetes (6-39%) as dominant phyla in the reactor. Candidatus brocadia was observed as the most abundant genus representing anammox community.