Novel HN-AD bacterium G11: Deciphering the denitrification mechanism and nanoFe₃O₄ enhancement research

Aiming at the issues of complex process and low nitrogen removal efficiency of traditional biological denitrification treatment of nitrogenous wastewater, in this study, a highly efficient strain Acinetobacter sp.G11 was screened from aerobic denitrifying sludge enriched by SBR reactor, which was identified by 16S rDNA as Acinetobacter sp. Under the optimal conditions, the nitrogen removal rates of the strain were 5.27,4.49 and 6.14 mg/(L‧h) for the single nitrogen sources (NH₄⁺-N, NO₃^--N, NO₂^--N) and mixed nitrogen sources, and the total nitrogen removal rates reached 6.59 mg/(L‧h). Genome-wide and nitrogen balance analyses confirmed two possible ways of nitrogen removal in G11:nitrogen assimilation and heterotrophic nitrification aerobic denitrification (HN-AD). The key genes encoding HAO (hao), NAP (nap), NIR (nirk/nirs), and NOS (nosZ) are not present in the G11 genome, indicating that it achieves nitrogen removal through a distinct denitrification mechanism. The study found that the addition of 0.5 g/L nanoFe₃O₄ enhanced the total nitrogen (TN) removal efficiency from 92.04 % to 98.2 %, increased the nitrate nitrogen removal rate from 3.84 mg/(L·h) to 5.45 mg/(L·h), enhanced the activities of nitrate reductase (NAR) and nitrite reductase (NIR) by 4.22 and 4.81 fold, and upregulated the expression of key genes norW, nrtP, nasA, and nasD by 5.16-fold, 3.71-fold, 3.43-fold, and 4.80-fold, respectively. The present study provides excellent bacterial resources and regulatory strategies for aerobic denitrification enhanced by nanometallic materials, which has important potentials for application in the field of wastewater treatment.