Enhancing anammox nitrogen removal by static magnetic field exposure: Performance, microbial community and symbiotic relationship analysis

Anammox batch reactors were operated with different static magnetic field (SMF) intensities (0 mT, 40 mT, and 100 mT). The impacts of SMF and the influent nitrogen concentration on nitrogen removal were analyzed. Sludge characteristics, microbial community structure, and metabolism pathways were explored. The results show that a high nitrogen load greatly decreased the nitrogen removal efficiency. Still, applying SMF with appropriate intensity enhanced the nitrogen removal performance, especially under high nitrogen loading conditions. Systems with 40 mT SMF at normal nitrogen loading conditions had the highest total nitrogen removal efficiency. In contrast, a higher SMF intensity was conducive to the anammox process with a high nitrogen load. Candidatus Kuenenia was fast enriched under high nitrogen loading conditions in the control systems. However, Candidatus Brocadia was more abundant than Ca. Kuenenia in the systems with SMF application. SMF was the main factor affecting the microbial metabolism, enhancing the metabolic pathways related to bacterial growth and resistance to environmental stress. The metabolic interactions between the anammox bacteria and other bacteria were enhanced by applying SMF to the anammox process, especially for the cross-feeding of cofactors and vitamins in the anammox consortia.