Advanced nitrogen removal from municipal wastewater via two-stage partial nitrification-simultaneous anammox and denitrification (PN-SAD) process

A modified two-stage anammox process was constructed and achieved advanced nitrogen removal from municipal wastewater. The first stage was Partial Nitrification (PN), in which nitrite accumulation rate was over 95% by controlling dissolved oxygen concentration (< 1 mg/L) and aeration time (90-120 min). The second stage was simultaneous anammox and denitrification (SAD), in which the reactor was fed with the effluent of the first stage and a part of raw wastewater. The effluent total inorganic nitrogen (NH4+-N, NO2--N and NO3--N) was only 1.6 +/- 0.8 mg N/L and the nitrogen removal efficiency reached 97.1%. The proportion of anammox in nitrogen removal was up to 73-82% and Candidates Brocadia was the main anammox genus accounted for 8.0-2.2%. And partial denitrification occurred with the appearance of Thauera (0-1.0%). The PN-SAD process is an energy-saving treatment for municipal wastewater with a total hydraulic retention time of 6 h.