Decryption for nitrogen removal in Anammox-based coupled systems: Nitrite-induced mechanisms

Abstract

This study investigated the effects of NO2- on synergetic interactions between Anammox bacteria (AnAOB) and sulfur-oxidizing bacteria (SOB) in an autotrophic denitrification-Anammox system. The presence of NO2- (0–75 mg-N/L) was shown to significantly enhance NH4+ and NO3- conversion rates, achieving intensified synergy between AnAOB and SOB. However, once NO2- exceed a threshold concentration (100 mg-N/L), both NH4+ and NO3- conversion rates decreased with increased NO2- consumption via autotrophic denitrification. The cooperation between AnAOB and SOB was decoupled due to the NO2- inhibition. Improved system reliability and nitrogen removal performance was achieved in a long-term reactor operation with NO2- in the influent; reverse transcription-quantitative polymerase chain reaction analysis showed elevated hydrazine synthase gene transcription levels (5.00-fold), comparing to these in the reactor without NO2-. This study elucidated the mechanism of NO2- induced synergetic interactions between AnAOB and SOB, providing theoretical guidance for engineering applications of Anammox-based coupled systems.