Long-term performance and mechanism of in-situ biogenetic sulfidated zero-valent iron for enhanced nitrate reduction

The biogenetic sulfidation of zero-valent iron (BS-ZVI) by sulfate-reducing bacteria (SRB) has been demonstrated to enhance the reactivity of ZVI. However, long-term performance of BS-ZVI and related mechanism were still unknown. Therefore, columns containing sponge iron and SRB are built to prepare BS-ZVI in-situ and study its long-term performance. Over 80 % of NO₃‾ was reduced to NH₄⁺ by in-situ BS-ZVI within 140 days, which was higher than the sole ZVI treatment (40 %-60 %). The bonding of ZVI and FeS_x was in-situ firstly and finally loaded on ZVI. The reduction of Fe(III) by S(-II) and SRB contributed to the formation of FeS_x, which improved the electrons transfer. Moreover, BS-ZVI enhanced the enzymes activity of SRB, thus accelerating the metabolic transformation of lactic acid to acetic acid. The accumulation of acetic acid enhanced the removal efficiency of NO₃‾ through the dissolution of passivation layer. Overall, this study demonstrated a reactivity enhancement of ZVI through biogenetic sulfidation, which provided a new alternative method for the remediation of groundwater.