Achieving Mainstream Nitrogen Removal through Coupling Anammox with Denitratation.

Achieving maintream anammox is critical for energy-neutral sewage treatment. This study presents a new way to achieve mainstream anammox, which couples anammox with denitratation (nitrate reduction to nitrite) instead of nitritation (ammonium oxidation to nitrite). An anoxic/oxic (A/O) biofilm system treating systhetic domestic wastewater was used to demonstrate this concept for over 400 days. This A/O biofilm system achieved a total nitrogen (TN) removal efficiency of 80 ± 4% from the influent with a low C/N ratio of 2.6 and a TN concentration of 60.5 mg/L. Nitrogen removal via anammox was found to account for 70% of dinitrogen production in the anoxic reactor. Batch tests confirmed that the anoxic biofilm could oxidize ammonium using nitrite as electron acceptor, and that it had a higher nitrate reduction rate than the nitrite reduction rate, thus producing nitrite for the anammox reaction. Metagenomic analysis showed that Candidatus Jettenia caeni and Candidatus Kuenenia stuttgartiensis were the top two dominant species in anoxic biofilm. Genes involved in the metabolism of the anammox process were detected in anoxic biofilm. The abundance of nitrate reductase (73360 hits) was much higher than nitrite reductase (13114 hits) in anoxic biofilm. This system can be easily integrated with the high-rate activated sludge technology, which produces an effluent with a low C/N ratio. While this new design consumes 21% more oxygen in comparison to the currently studied nitritation/anammox process, the nitrite-producing process appears to be more stable.