Enhancing sewage nitrogen removal via anammox and endogenous denitrification: Significance of anaerobic/oxic/anoxic operation mode.

Efficient nitrogen removal from domestic sewage was obtained in a sequencing batch biofilm reactor (SBBR) operated in alternate anaerobic/oxic/anoxic (A/O/A) mode. For the influent total nitrogen (TN) ranging from 30.0 to 63.3 mg N·L-1, the average nitrogen removal efficiency was 90.3 ± 2.9% with removal rate of 42.3-76.2 mg N·L-1·d-1. According to the high-throughput sequencing analysis, anammox bacteria (0.40-0.61%) were enriched, and some genera that could carry out endogenous denitrification, including Comamonadaceae and Dechloromonas, were observed, indicating that the special conditions in the SBBR might combine autotrophs with heterotrophs for enhanced nitrogen removal. The nitrogen removal mechanism was analyzed based on stoichiometry and continuous and cyclic tests. Results indicate that partial nitrification-anammox was the primary nitrogen removal pathway, accounting for 60.4% of the TN removed. Endogenous denitrification accounted for 25.7% of the TN removed. Overall, the A/O/A mode could combine autotrophic nitrogen removal with endogenous denitrification, enhancing sewage nitrogen removal.