Effect of ammonium concentration on methane oxidation and CO ₂ removal in an anaerobic biotrickling filter treating synthetic landfill gas and leachate

BACKGROUND Landfill gas (LFG) and leachate are commonly treated separately through energy‐intensive processes. This study evaluated the integration of both streams in an anaerobic biotrickling filter (BTF) to achieve simultaneous methane (CH 4 ) and carbon dioxide (CO 2 ) removal coupled with ammonium (NH 4 + ) transformation, and how the microbial community mediates these processes. RESULTS The BTF was fed with synthetic landfill gas (CH 4 /CO 2 /N 2 , 50:35:15% v/v) and operated under two NH 4 + levels (500 and 3700 mg L −1 ) in the presence of sulfate (SO 4 2− , 200 mg L −1 ). At 500 mg NH 4 + L −1 (Stage I), simultaneous CH 4 oxidation (16 615.7 ± 5266.2 nmol CH 4 cm −3 d −1 ) and CO 2 removal (5481.6 ± 5000.2 nmol CO 2 cm −3 d −1 ) were achieved, reaching a mean CH 4 and CO 2 removal efficiencies (RE) of 43.9% and 19.9%, respectively, with 37.6% NH 4 + removal. At 3700 mg NH 4 + L −1 (Stage II), CH 4 elimination capacity (EC) notably dropped (0.5% RE), while CO 2 EC persisted at lower levels (7.5% RE), achieving a value of 2101.7 ± 2433.1 nmol CO 2 cm −3 d −1 and 65% NH 4 + removal. Microbial analysis revealed a consortium in which Methanosarcina and Methanobacterium potentially mediated reverse methanogenesis. The coexistence of denitrifiers ( Caenispirillum , Aquabacterium ) and sulfur‐cycling bacteria (Desulfobacterota) suggests that C 1 transformations were supported by syntrophic interactions. CONCLUSION This study demonstrates the feasibility of simultaneously treating LFG and leachate in a BTF reactor. NH 4 + concentration acted as key driver of reactor performance and metabolic activity, indicating that NH 4 + load can be used as a strategic control variable to drive the system functionality, offering an alternative for LFG mitigation.