Abstract: In this study, the nitrogen removal performance of PDA process was investigated by using UASB reactor. High TN removal efficiency (91.97%) was achieved at influent nitrogen loading rate of 0.64 kg/m3d. Anammox bacteria did execute the function of converting nitrate to nitrite in PDA system according to 15N isotope labeling experiments and the contribution was approximately 36.3%. Candidatus_Brocadia, Candidatus_Kuenenia and Thauera were functional strains for anammox and denitrification process, respectively. Thauera and Candidatus_Brocadia were more important for TN removal at high loading rates (0.64 kg/m3d). This result provides a theoretical and technical foundation for the application of denitrifying ammonium oxidation process.