Electric field-biochar integrated anammox system for high-efficiency nitrogen and phosphorus removal under elevated nitrogen concentration shock

Slow anammox bacteria (AnAOB) proliferation ability, without phosphorus removal function, and nitrogen removal capacity deteriorates to high nitrogen concentration shock are main technical bottlenecks in anammox process. In this work, an electric field-biochar integrated anammox system, which uses carbon felt (R1) and iron mesh (R2) as electrode, respectively, was developed to simultaneously remove nitrogen and phosphorus. Due to the advantages of vivianite precipitation formation and iron intensified AnAOB enrichment in R2, the nitrogen and phosphorus removal efficiency reached 89.41 % and 78.54 % in R2 (200 mg/L NH₄⁺-N and 260 mg/L NO₂₋-N), higher than startup stage (69.64–73.10 % and 37.93–39.04 %) to R1 (88.81 % and 41.68 %). Particularly, the integrated system has a higher performance to high nitrogen concentration shock (400 mg/L NH₄⁺-N and 530 mg/L NO₂₋-N), with higher nitrogen and phosphorus removal efficiency (83.72 % and 79.02 %). Furthermore, molecular spectroscopy and rheological tool revealed that the developed anammox system increased sludge granulation ability and mechanical strength, preventing biomass loss and maintaining metabolic homeostasis. Importantly, R2 was more conducive to enriching AnAOB (43.17 % of Candidatus Kuenenia and 1.30 % of Candidatus Brocadia), enhancing the nitrogen metabolic gene activity and diversifying nitrogen removal pathway. This work would shed the light on the strategy development of integrating electric field and biochar with anammox system for simultaneously nitrogen and phosphorus removal at high nitrogen load shock.