Magnetite modulates bacterial cooperation during cathodic nitrogen removal in bioelectrochemical systems under trace...

Nitrate and ammonium co-contamination poses a major challenge for sustainable nitrogen removal, especially under microoxic conditions. This study investigated the effect of magnetite on microbial nitrogen metabolism and nitrite accumulation in biocathodes of bioelectrochemical systems under 0.25 mg/L dissolved oxygen. Magnetite improved total nitrogen removal by 22.8 %, reduced peak nitrite levels by 22.6 %, and lowered residual ammonium by 49.2 %. Magnetite promoted interspecies cooperation, driving modular specialization in nitrite reduction while suppressing dissimilatory nitrate reduction to ammonium. Concurrently, it stimulated ammonia-oxidizing bacteria activity, accelerating ammonium conversion and mitigating nitrite accumulation through enhanced denitrification. A cooperative microbial pattern emerged, with dominant species such as Hanamia sp. and Moheibacter sp. carrying out nitrite reduction, while less abundant species performed single nitrogen metabolic processes. This study highlights the role of magnetite in integrating aerobic and anaerobic nitrogen pathways, offering a sustainable strategy for controlling complex nitrogen pollution.