LAUSR

Abstract In situ aeration combined with leachate recirculation is an effective method of treating carbon and nitrogen pollutants in landfills. In this work, we investigated the effects of in situ treatment of aged landfill leachate in aerobic–anaerobic recirculation-simulated landfill (AARL) and the feasibility of hydroxylamine addition to promote total nitrogen (TN) removal. Results showed that the hydroxylamine-treatment group had high TN removal and simultaneous nitrification and denitrification efficiency. High-throughput sequencing showed that hydroxylamine addition promoted the abundance of Nitrosomonas (ammonia-oxidising bacteria (AOB)) in the aerobic zone. However, nitrite did not accumulate because the nitrite oxidation efficiency of nitrite-oxidising bacteria was higher than the ammonia oxidation efficiency of AOB. Moreover, Methylocaldum was the dominant bacteria in AARL. This study contributed to the development of AARLs for the in situ remediation treatment of mature landfill leachate.