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

Microorganism-dominated nitrogen conversion in wastewater treatment is of great significance to the nitrogen cycle. Until now, Fe0 has been widely used in sludge dewaterability, sulfide control, and bioenergy recovery. However, there is limited information about the comprehensive assessment of Fe0 on multiple biological nitrogen removal processes. Here, the impact of Fe0 dosage on the activity of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, anammox bacteria, and denitrifiers was evaluated. The results revealed that anammox has a more sensitive response to iron dosages (5.34 mM), and improved intracellular iron (216%) is the key to stimulating microbial metabolism by accelerating electron transfer, enzymatic activity, and ATP biosynthesis. Moreover, the long-term operation confirmed that additional Fe0 increased the relative abundance of ammonia-oxidizing bacteria, anammox bacteria, and denitrifiers, and the enriched nitrogen removal pathways further improved the nitrogen removal to 93.3% from 79.2% in an oxygen-limited system. This study helps us deeply understand the underlying mechanism of microbial activity stimulated by iron.