Robust partial nitrification and anammox under low-strength nitrogen condition by regulating organic-induced symbiosis of denitrifiers and anammox bacteria

Low-strength nitrogen usually limits the efficiency of partial nitrification and anaerobic ammonium oxidation (anammox). To address this challenge, an organic-induced regulation strategy based on microbial interaction characteristics was proposed. Short-range addition of acetate for bio-screening is essential for achieving this regulation. After bio-screening, enhanced partial nitrification and anammox performance were achieved within 47 days. In the start-up phase, denitrifiers outcompeted nitrite oxidizing bacteria (NOB) for nitrite utilization, thereby enhancing the inhibition of NOB. The relative abundance of anammox bacteria (AnAOB) was maintained at approximately 8.6 % due to an increase in extracellular proteins, which was conducive to material exchange and symbiosis between denitrifiers and AnAOB. Transcriptomic analysis revealed that bio-screening induced mixotrophic metabolism of AnAOB, characterized by up-regulating the expression of genes involved in organic carbon and energy metabolism, thereby improving the stability of the anammox process. This study provides valuable insights for enhancing anammox performance under low-strength nitrogen conditions.