Nitrogen removal enhancement reinforced by nitritation/anammox in an anaerobic/oxic/anoxic system with integrated fixed biofilm activated sludge.

The enhancement of nitrogen removal was reinforced by nitritation/anammox in an anaerobic/oxic/anoxic (AOA) system of integrated fixed biofilm activated sludge. Nitritation was first attained by the method of free nitrous acid (FNA) inhibition with ammonia residues, and anaerobic ammonia oxidizing bacteria (AnAOB) were then added into the system, which enabled the occurrence of nitritation coupled with anaerobic ammonia oxidation (anammox). The results indicated that nitrogen removal was enhanced by the nitritation/anammox pathway with an efficiency of 88.9%. A microbial analysis showed that the ammonia oxidizing bacterium (AOB) Nitrosomonas was enriched on the biofilm (5.98%) and in the activated sludge (2.40%), and the AnAOB Candidatus Brocadia was detected on the biofilm with a proportion of 0.27%. Nitritation/anammox was attained and maintained due to the accumulation of functional bacteria.