Nitrogen removal by simultaneous partial nitrification, anammox and denitrification (SNAD) in a structured-bed reactor treating animal feed processing wastewater: Inhibitory effects and bacterial community

The aim of this study was to investigate the post-treatment of UASB effluent by treating animal feed production wastewater using simultaneous partial nitrification, anammox and denitrification (SNAD) in a structured-bed reactor subjected to low aeration and recirculation. The average nitrogen loads applied were 0.307, 0.249 and 0.149 kgN m−3d−1, correlated to COD/N ratios of 0.28, 0.41 and 0.26 (Phases 1, 2 and 3, respectively). The best mean values for removal efficiencies of total-N and COD were obtained in Phase 1 with 48 ± 24% and 63 ± 20%, respectively, reaching a maximum total-N removal efficiency of 79%. The anammox process was the main pathway of nitrogen removal, as pointed out in the nitrogen mass balance. High free ammonia (FA) concentrations in Phases 2 and 3, associated to the limitation of oxygen supply, caused inhibition of nitrite oxidizing bacteria (NOB) activity, leading to NO2 accumulation, having an impact on the denitrifying activity. At the end of the operational period, sequencing analysis detected sequences related to heterotrophic denitrifiers (22.5%), anammox bacteria, Candidatus Anammoximicrobium (2%) and ammonia oxidizing bacteria (AOB) belonging to Nitrosomonadales and Nitrosomonas (0.6%). These results demonstrated that nitritation, denitrification and anammox were likely in the processes involved in nitrogen removal in this reactor.