Effect of Zero-Valent Iron (ZVI) on nitrogen and Fe(II) metabolism in Anammox-Hydroxyapatite (HAP) system under low-temperature stress

Low temperatures were a critical factor that inhibited anaerobic ammonium oxidizing bacteria (AnAOB) activity. This study demonstrated the effect of exogenous zero-valent iron (ZVI) on Anammox-hydroxyapatite (HAP) system at 17°C. The results showed that long-term addition of ZVI increased the system nitrogen removal efficiency by 8.59% and alleviated the inhibition of AnAOB by low temperature. After addition of ZVI, the activity of AnAOB and the heme c content increased by 58.20% and 4.83%, respectively. Moreover, the functional enzyme activities of NIR, HZS, and HZO increased by 94.12%, 36.36%, and 16.67%, respectively. The concentrations of quorum sensing molecules, i.e., C 6 -HSL and C 8 -HSL, increased by 191.17% and 41.54%, respectively, after ZVI addition. Metagenomic analysis revealed that the addition of 5   g/L ZVI stimulated the relative abundance relative abundance of Fe(II) metabolism-related genes in AnAOB at 17 °C, thereby contributing to the uptake, transport, utilization, and storage of Fe(II). The addition of ZVI could improve the nitrogen removal performance of the anammox-HAP system at the low temperature.