Integrated fixed-film activated sludge partial nitritation-anammox (IFAS-PN/A) for landfill leachate treatment rapidly established through the thermal inactivation of nitrite oxidoreductase.

Partial nitritation-anammox (PN/A) is a promising process for treating landfill leachate. Nevertheless, its application was hindered by challenges such as long start-up times for partial nitritation and instability in nitrite supply. In this study, an integrated fixed-film activated sludge (IFAS) PN/A system, which was rapidly built-up (2 days) through thermal treatment, was adopted to treat mature landfill leachate. The system operated for 240 days with a long sludge retention time (30-35 days) under 22-28 °C conditions, achieving a nitrogen removal rate of 0.683 kg N/(m·d) and a total inorganic nitrogen removal efficiency of 96.89 %. Nitrite-Oxidizing Bacteria (NOB) were rapidly washed out from the reactor due to the synergistic effects of thermal treatment, biological toxicity, and microbial antagonism. Anaerobic Ammonium-Oxidizing Bacteria (AnAOB) were enriched in the biofilm (17.83 %), with the dominant genus shifted from Candidatus Brocadia to Candidatus Kuenenia, accounting for 17.12 % (day 231). Ammonia-Oxidizing Bacteria (AOB) in the flocs were the primary contributor (83.74 ± 3.34 %) to nitritation and were effectively retained. High concentration of activated sludge ensured a sufficient nitrite supply to AnAOB and enhanced the synergy among functional microbes. These results demonstrated that the IFAS-PN/A system, rapidly established via the thermal treatment, is a highly effective and feasible nitrogen removal process for landfill leachate.