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

This study investigated the effects of NO-2 on synergetic interactions between Anammox bacteria (AnAOB) and sulfur-oxidizing bacteria (SOB) in an autotrophic denitrification-Anammox system. The presence of NO-2 (0-75 mg-N/L) was shown to significantly enhance NH+4 and NO-3 conversion rates, achieving intensified synergy between AnAOB and SOB. However, once NO-2 exceed a threshold concentration (100 mg-N/L), both NH+4 and NO-3 conversion rates decreased with increased NO-2 consumption via autotrophic denitrification. The cooperation between AnAOB and SOB was decoupled due to the NO-2 inhibition. Improved system reliability and nitrogen removal performance was achieved in a long-term reactor operation with NO-2 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 NO-2. This study elucidated the mechanism of NO-2 induced synergetic interactions between AnAOB and SOB, providing theoretical guidance for engineering applications of Anammox-based coupled systems.

Automated summary

This study investigated the effects of NO-2 on the synergistic interactions between Anammox bacteria (AnAOB) and sulfur-oxidizing bacteria (SOB) in an autotrophic denitrification-Anammox system. The presence of NO-2 was shown to enhance NH+4 and NO-3 conversion rates, intensifying the synergy between AnAOB and SOB. However, excessive NO-2 inhibited the cooperation between AnAOB and SOB, leading to decreased conversion rates.