Enhanced Nitrate Removal by Paracoccus denitrificans with Biocharsupported Nano Zero-Valent Iron in Batch Experiments: A Metabolomic Perspective
Chengju Sun, Bian Yao, Hongfei Zhang, Longfei WangIntroduction:
Biological denitrification is a crucial strategy for remediating nitratepolluted water bodies. However, its efficiency is often constrained by two factors: insufficient electron donors and limited denitrification rates. Nano Zero-Valent Iron (nZVI) can act as a potential electron donor but faces challenges such as agglomeration, whereas Biochar-supported nZVI (BC/ZVI) can improve its stability. However, the mechanism by which BC/ZVI enhances microbial nitrate reduction, particularly its effects on isolated denitrifying strains and its metabolomic impacts, remains poorly understood.
Methods:
In this study, one representative denitrifying strain, Paracoccus denitrificans, was employed in variable-batch experiments, and the effects of supplementing BC, ZVI, and BC/ZVI on denitrification efficiency were explored, particularly from a metabolomic perspective.
Results:
The results showed that supplementation with BC/ZVI could inhibit ZVI agglomeration and increase the abundance of surface oxygen-containing functional groups, e.g., C-O-C. The highest denitrification rate constant was observed in the BC/ZVI treatment (0.3 g·L-1), reaching 0.350 h-1. This value was approximately 6.5-, 5.3-, and 4.0-fold higher than those in the Control, BCsupplemented (0.066 h-1), and ZVI-supplemented (0.088 h-1) groups, respectively. 100% nitrate removal was achieved within 24 hours in the treatment. The addition of BC/ZVI could increase the electron transport system activity by up to 204.6%. Metabolomics identified 89 differential metabolites in the BC/ZVI-supplemented treatment, of which 82 were upregulated, thereby activating key pathways, e.g., the TCA cycle, nitrogen assimilation, amino acid synthesis, and nucleic acid precursor synthesis.
Discussion:
This study used BC/nZVI with a single denitrifying strain instead of mixed microbes. Metabolomics uncovered how BC/nZVI regulates the strain’s metabolism, and the correlation between ETSA and metabolic shifts was quantified. The results explain the mechanism of enhanced denitrification by the composite.
Conclusion:
Three innovations are highlighted: (1) BC/nZVI was combined with pure denitrifiers for the first time; (2) metabolomics clarified its regulation on single-strain metabolism; (3) the link between ETSA and metabolic changes was quantified. This work supports the application of BC/nZVImicrobe nitrate removal systems.