Multivalent manganese-mediated synergistic aerobic denitrification boost nitrogen removal in oligotrophic aquatic systems: Insight into microbial functional and metabolic complementarity

Efficient nitrogen removal from oligotrophic lakes and reservoirs necessitates the development of innovative, eco-friendly strategies to mitigate the limitation of organic electron donors. We engineered four multivalent manganese (Mn) composite-functionalized bioreactors for oligotrophic water remediation, which demonstrated a sustained total nitrogen removal efficiency exceeding 97.66% over five operational cycles. Manganese powder-doped activated carbon achieved the highest nitrate removal rate, ranging from 0.29956 to 0.39831 mg/L/d. Immobilization with sodium alginate has mitigated manganese oxidative corrosion, thereby resulting in more sustained long-term reactive performance. Furthermore, denitrifying bacteria synergistically promote the enrichment of phosphorus-accumulating microorganisms and manganese-oxidizing bacteria (Burkholderiaceae, Methylophilaceae, and Azospirillaceae), which play pivotal roles in denitrification and manganese cycling, within Mn addition (MNA) reactors. Correlation analyses revealed stronger co-occurrence patterns between denitrification genes and manganese-oxidizing genes in the MNA reactors compared to the control. The abundance of ATP-binding cassette transporter genes, particularly encoding lipopolysaccharide transport (wzt) and lipoprotein release (lolD), increased by 1.37–1.90-fold and 1.31–1.80-fold, respectively, in the MNA reactors relative to the control reactor. Furthermore, the metabolic complementarity network suggested that MNA not only promoted community metabolic competition and complementarity effects but also enhanced higher energy production and respiratory activity. These findings establish a manganese-driven microbial enhancement strategy for sustainable nitrogen removal from polluted surface waters, offering new opportunities for eco-engineered water treatment.