Biological nitrogen removal via combined processes of denitrification, highly efficient partial nitritation and Anammox from mature landfill leachate

The combined processes of pre-denitrification, highly efficient partial nitritation and Anammox were developed to treat mature landfill leachate. In the partial nitritation stage, an outstanding nitrite production rate (NPR) of approximately 1.506 kg·(m3 day)−1 of mature landfill leachate was achieved in a zeolite biological aerated filter (ZBAF) due to the inhibition of nitrite-oxidizing bacteria (NOB) by free ammonia (FA) and free nitrous acid (FNA). With respect to the nitrogen removal performance of the combined process, remarkable nitrogen removal efficiencies (NRE) and nitrogen removal rates (NRR), which exceeded 90.0% and 0.490 kg·(m3 day)−1, respectively, were detected based on the stable and efficient partial nitritation performance and reasonable control of effluent nitrite to ammonium ratios (at approximately 1.2) in the ZBAF. High-throughput sequencing analysis further revealed that the dominant bacteria genera Paracoccus and Comamonas in the denitrification reactor, Nitrosomonas in the ZBAF and Candidatus Kuenenia and Candidatus Anammoxoglobus in the Anammox reactor were demonstrated to be responsible for denitrification, partial nitritation and Anammox process, respectively.