Start-up of the Simultaneous Nitrification, Anammox, and Denitrification (SNAD) Reactor and Efficacy of a Small Amount of Organic Carbon

In perspective of the issue of how to begin simultaneous nitrification, anammox, and denitrification (SNAD) rapidly, the sequencing batch biofilm reactor (SBBR) was adopted to enrich ammonia-oxidizing bacteria (AOB) and anammox bacteria (AnAOB) rapidly and to inhibit nitrite-oxidizing bacteria (NOB) after three phases (67 days) of culture, and the impacts of different low carbon-nitrogen ratios (COD/N) on denitrification performance of the process were investigated. The results showed that preventing the accumulation of nitrite (NO2--N) was the key to start SNAD successfully. The removal efficiencies of ammonia nitrogen (NH4+-N) and total nitrogen (TN) in the system can reach more than 99% and 90%, respectively. Corresponding to COD/N = 0, 1 and 2, removal efficiencies of NH4+-N were 99.6%, 99.5%, and 98.5% respectively and removal efficiencies of TN were 93.8%, 97.2%, and 98.1%, respectively; the total nitrogen removal rate (TNRR) was greater than 0.29 kg N m(-3) day(-1). It indicates that the presence of a small amount of COD is beneficial to the denitrification of NO3--N without affecting the effect of simultaneous nitrification and anaerobic ammonium oxidation, which further improves the efficiency of nitrogen removal. High-throughput sequencing analysis showed that the ratios of AOB, AnAOB, and denitrifying bacteria were 7.3%, 20.1%, and 7.66%, respectively. Candidatus Kuenenia was the only genus of the SNAD reactor with anaerobic ammonium oxidation. AOB, Anammox, and heterotrophic denitrifying bacteria were present in the system, while ammonia oxidation and anaerobic ammonium oxidation played a dominant role in the denitrification process.