Cooperative mechanism of ultrafast nitrogen removal between partial denitrification and anammox on metagenomics and metabolomics

This study innovatively demonstrates the feasibility of coupling PD with anammox (PD/A) using nitrifying sludge from wastewater treatment plants (WWTPs) as the sole inoculum, achieving simultaneous anammox bacteria enrichment and ultra-high-rate nitrogen removal. Rapid establishment of stable PD within 40 days, achieving an 84.6 % nitrate-to-nitrite transformation ratio (NTR). Anammox bacteria enrichment without external anammox inoculum, culminating in a nitrogen removal rate (NRR) of 1.11 kg N/(m3 d) and 95.0 % total nitrogen removal efficiency (NRE) after 190 days, the nitrogen removal performance surpassing most conventional systems. Metabolomic profiling revealed significant upregulation in three core metabolic networks: Enhanced heme synthesis can promote cytochrome c production for electron transport chain optimization in anammox reactions. Upregulation of aspartate metabolism facilitated carbon skeleton supply for anammox bacteria (AnAOB) growth and energy supply, upregulation of nucleotide metabolism boosted transcriptional activity of AnAOB and denitrifying bacteria (DNB). These mechanistic insights elucidate the metabolic synergy driving PD/A systems, advancing their scalability for energy-efficient mainstream wastewater treatment applications.