Simultaneous partial nitrification, anammox and denitrification (SNAD) process for nitrogen and refractory organic compounds removal from mature landfill leachate: Performance and metagenome-based microbial ecology

In this study, a simultaneous partial nitrification, Anammox and denitrification (SNAD) bioreactor was constructed for mature landfill leachate treatment, which exhibited favorable NH₄⁺-N (98.9-99.9%), TN (90.7-94.9%) and bio-refractory organic compounds (46.2-67.7%) removal efficiencies. Stoichiometric analysis demonstrated that the synergy of ammonium-oxidizing bacteria and Anammox bacteria dominated TN removal (96.1-97.2%). NO₃^--N produced in Anammox could be further reduced through (partial) denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The results highlighted that humic-like and their intermediates might serve as the electron donor for these (partial) denitrifiers and DNRA bacteria to remove NO₃^--N, and could be effectively removed from mature landfill leachate in SNAD bioreactor. Metagenomic characterization further demonstrated that phyla Chloroflexi, Chlorobi and genera Nitrosomonas, Ignavibacterium and Aminiphilus might be responsible for such humic-like degradation. Overall, this work offers new insights into the metagenome-based bioinformatic roles for the previously understudied microorganisms in SNAD bioreactor for mature landfill leachate treatment.