Two-step partial nitritation/Anammox process in granulation reactors: Start-up operation and microbial characterization.

ABSTRACT

A two-stage Partial Nitritation (PN)/Anammox process was carried out at lab-scale conditions to treat reject water from a municipal WWTP. PN was achieved in a granular SBR obtaining an effluent with a NH4(+)-N/NO2(-)-N molar ratio around 1.0. The microbial characterization of this reactor revealed a predominance of Betaproteobacteria, with a member of Nitrosomonas as the main autotrophic ammonium oxidizing bacterium (AOB). Nitrite oxidizing bacteria (NOB) were under the detection limit of 16S rRNA gene pyrosequencing, indicating their effective inhibition. The effluent of the PN reactor was fed to an Anammox SBR where stable operation was achieved with a NH4(+)-NNO2(-)-NNO3(-)-N stoichiometry of 11.250.14. The deviation to the theoretical stoichiometry could be attributed to the presence of heterotrophic biomass in the Anammox reactor (mainly members of Chlorobi and Chloroflexi). Planctomycetes accounted for 7% of the global community, being members of Brocadia (1.4% of the total abundance) the main anaerobic ammonium oxidizer detected.