Novel single-stage autotrophic nitrogen removal via co-immobilizing partial nitrifying and anammox biomass

•A novel single-stage autotrophic nitrogen removal system was developed.•The max. NRR reached 1.69 kg N/m3/d in our system with removal efficiency of 77%.•Partial nitrifying biomass prove to form a thick layer around anammox biomass.

In this study, we developed an effective strategy to achieve single-stage autotrophic nitrogen removal by co-immobilizing partial nitrifying and anaerobic ammonia oxidation (anammox) biomass. Batch experiments were carried out to determine the optimum dissolved oxygen concentration of 1.5 mg/L, and the optimum biomass ratio of partial nitrifying biomass versus anammox biomass of 1:2. In continuous experiment, the total nitrogen removal rate reached 1.69 g N/L/d (nitrogen loading rate up to 2.2 g N/L/d). At the stable running stage, the TN average removal efficiency reached 77%. Scanning electron microscopy observations showed microorganisms greatly increased after 80 days cultivating. FISH analysis indicated that most anammox cells agglomerated in groups and ammonia oxidizing bacteria formed a thick layer around anammox cells.