Effects of tourmaline on anaerobic ammonia oxidation process: Mechanistic Understanding and performance evaluation

The anaerobic ammonium oxidation (Anammox) process has emerged as a pivotal technology in wastewater nitrogen removal due to its advantages of eliminating the need for external carbon sources, low sludge yield, and reduced energy consumption. Tourmaline, a naturally polarized mineral characterized by spontaneous polarization and trace element release, has been validated as an effective functional amendment for regulating microbial microenvironments in recent years. This study established 6 sets of Tourmaline Anaerobic Ammonium Oxidation-Upflow Anaerobic Sludge Bed (TmAna-UASB) reactors with tourmaline dosages of 0, 2, 4, 6, 8, and 10 g L^-1, the nitrogen removal performance of Anammox was systematically monitored and evaluated. Variations in extracellular polymeric substances (EPS) content and morphological evolution of granular sludge were analyzed via scanning electron microscopy (SEM). Structural transformations of flocculent sludge and granular sludge were elucidated, and 16S rRNA high-throughput sequencing coupled with PICRUSt2 functional prediction were employed to decipher dynamic shifts in functional microbial consortia and underlying regulatory mechanisms. This work firstly identifies a dose threshold effect (8 g L^-1) of unmodified tourmaline directly enhancing Anammox activity. Mechanistically, tourmaline facilitates an electron transport pathway characterized by “NH₄⁺-N → tourmaline → EPS (humic substances) → NO₂^–-N” synergy, alongside quorum sensing (QS) −induced flocculent sludge granulation and microbial community restructuring. These findings provide a theoretical foundation for the direct application of tourmaline in Anammox systems, advancing breakthroughs in high-efficiency biological nitrogen removal technologies under carbon neutrality objectives.