Achieving partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) by the inhibition of sulfide to accomplish stabilized nitrogen removal.

The simultaneous partial nitrification, anammox, and denitrification (SNAD) process is widely applied for treating high-ammonia wastewater, but its application to low-ammonia organic wastewater has been scarcely explored. In this study, a partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) system was established to treat organic wastewater with low ammonia concentration. Experimental results revealed that sulfide at 5 mg/L selectively inhibited nitrite-oxidizing bacteria (NOB) but had little effect on ammonium-oxidizing bacteria (AOB). Finally, NOB was suppressed in PND system by intermittently adding sulfide to the PND system. The PND system provided nitrite and activated sludge enriched with AOB to the SNAD system during stable operation. The SNAD system demonstrated chemical oxygen demand (COD) and nitrogen removal efficiencies of 89.86 % and 86.45 %. Candidatus Brocadia and Nitrosomonas were the main ammonium oxidizing bacteria (AnAOB) and AOB. The contribution of AOB and denitrifying bacteria (DNB) to nitrogen transformation was 67.15 % and 25.33 % in the PND system. In the SNAD system, the contributions of AnAOB, AOB, and DNB were 34.40 %, 33.59 %, and 27.56 %, respectively. Overall, this study provided a new sustainable strategy for treating organic wastewater with low ammonia concentration.