Understanding Zerovalent Iron Exposure on Biological\nNitrogen Removal: From Impacts to Potential Mechanisms

Microorganism-dominated nitrogen\nconversion in wastewater treatment\nis of great significance to the nitrogen cycle. Until now, Fe<sup>0</sup> has been widely used in sludge dewaterability, sulfide control,\nand bioenergy recovery. However, there is limited information about\nthe comprehensive assessment of Fe<sup>0</sup> on multiple biological\nnitrogen removal processes. Here, the impact of Fe<sup>0</sup> dosage\non the activity of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria,\nanammox bacteria, and denitrifiers was evaluated. The results revealed\nthat anammox has a more sensitive response to iron dosages (5.34 mM),\nand improved intracellular iron (216%) is the key to stimulating microbial\nmetabolism by accelerating electron transfer, enzymatic activity,\nand ATP biosynthesis. Moreover, the long-term operation confirmed\nthat additional Fe<sup>0</sup> increased the relative abundance of\nammonia-oxidizing bacteria, anammox bacteria, and denitrifiers, and\nthe enriched nitrogen removal pathways further improved the nitrogen\nremoval to 93.3% from 79.2% in an oxygen-limited system. This study\nhelps us deeply understand the underlying mechanism of microbial activity\nstimulated by iron.