Integration of methane oxidation with anammox for enhancing nitrogen removal: Performance, mechanisms, and machine learning analysis

Anaerobic ammonia oxidation (anammox) is a promising process for nitrogen removal, yet nitrate accumulation limits its application. This study developed a methane (CH₄)-driven system integrating denitrification and anammox for efficient nitrogen removal with CH₄ recycling. In a long-term operation of a CH₄-fed up-flow anaerobic sludge blanket reactor (UASB), a total nitrogen removal efficiency of 93 % was achieved under the operational condition of a hydraulic retention time (HRT) of 6 h and an influent nitrogen concentration of 450 mg N L⁻¹. CH₄ enhanced nitrogen removal by irritating the growth of denitrifying bacteria (the abundance of Pseudomonas increased to 8 %) without requiring anaerobic methanotrophic (ANME) archaea or denitrifying anaerobic methane oxidation (DAMO) bacteria. Futhermore, the abundance of anaerobic oxidizing bacteria (AnAOB) rose from 0.5 % to 18.6 %. Random Forest modeling identified AnAOB activity, effluent NH₄⁺ and NO₃⁻ as key factors governing removal efficiency. This study demonstrates that CH₄-driven denitrification coupled with anammox significantly enhances wastewater nitrogen removal efficiency, providing a novel strategy for CH₄ utilization in bioremediation.