Acclimatization of Candidatus Brocadia to high nitrogen and salinity loads in a sequencing batch reactor: performance and operational insights

ABSTRACT This study investigated the acclimatization of Candidatus Brocadia, a freshwater anaerobic ammonium oxidation (Anammox) species, to high nitrogen (up to 1.39 gN/L) and salinity (up to 14.3 gNaCl/L) loads in a semicontinuous sequencing batch reactor. Over one year of operation, the reactor achieved stable nitrogen removal performance, with nitrite removal efficiency exceeding 99% at nitrogen loading rates and salinity concentrations up to 0.72 gN/L/d and 14.29 gNaCl/L, respectively. These results rank among the highest reported for Candidatus Brocadia under similar conditions, demonstrating the feasibility of applying this freshwater species to high-strength, saline effluents such as those from agricultural systems. Batch experiments were conducted to further explore the impact of salinity and the monovalent-to-divalent cation ratio on Anammox activity. The results suggest that while salinity is the primary inhibitory factor, the presence of divalent cations such as Ca2+ and Mg2+, which likely mitigate salinity, may explain the high performance achieved in this study. Additionally, a novel method for real-time determination of nitrite consumption kinetics via pH monitoring was validated, offering a reliable tool for Anammox activity assessment.