Decryption for Nitrogen Removal in Anammox-Based Coupled Systems: Nitrite-Induced Mechanisms

Abstract

This study investigated the effects of nitrite 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 nitrite-induced synergetic interactions between AnAOB and SOB, providing theoretical guidance for engineering applications of Anammox-based coupled systems.

Keywords: Anammox, autotrophic denitrification, nitrite-induced, Nitrogen removal