Mainstream anammox driven by micro-oxygen nitrification and partial denitrification using step-feed for advanced nitrogen removal from municipal wastewater

This study developed a novel integrated nitrification, partial denitrification (PD), and anammox (INPDA) process in micro-aerobic sequencing batch reactor using step-feed strategy treating municipal wastewater. The results showed that the INPDA could achieve a 94.5 ± 1.1% total inorganic nitrogen (TIN) removal efficiency with effluent TIN concentration as low as 2.3 mg/L. The micro-aerobic with low dissolved oxygen concentration of 0.36 ± 0.01 mg/L allowed complete ammonium oxidation to nitrate. The applied step-feed by optimizing influent distribution ratio to 5:3 provided sufficient organics for nitrate reduction to nitrite. According to mass balance analysis, anammox was the dominant nitrogen removal pathway (87.9%). Microbial analysis indicated that aerobic nitrifiers Nitrosomonas (1.2%) and Nitrospira (0.9%) ensured full nitrification, while PD bacteria Thauera (27.1%) conducted labor metabolism coordination with anammox bacteria Candidatus Brocadia (1.3%) for nitrogen removal. These findings demonstrate that the INPDA has a good prospect for energy-efficient municipal wastewater treatment.