Nano zero-valent iron (nZVI) induces the shift from denitrification to ammonification in microbial nitrate respiration for treatment of low C/N wastewater

The biological reduction of nitrate is a green and cost-effective route for nitrogen recovery. However, in view of the low conversion efficiency and limited information on the contribution of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) under low carbon to nitrogen (C/N) ratio conditions, nano zero-valent iron (nZVI) was used as a supplementary electron donor to modulate the nitrate reduction process of denitrifying system. In this study, under different C/N ratios and nZVI dosages, batch experiments combined with 15N isotope tracing and microbial metagenomic analysis were conducted to explore the regulatory mechanisms for nitrogen removal. However, excessive dosage of nZVI might cause cellular damage, even leading to acute toxicity. 15N isotope tracing and microbial metagenomic analysis further confirmed that nZVI preferred to promote the DNRA pathway rather than the denitrification pathway. This work is advantageous for increasing efficiency of DNRA and provides new insights for the efficient recovery of ammonium from low C/N wastewater.