Effect of low temperature on abiotic and biotic nitrate reduction by zero-valent Iron

The effect of low temperatures on abiolic and biotic nitrate (NO3-) reduction by zeto-valent iron (ZVI) were examined at temperatures below 25 degrees C. The extent and rate of nitrate removal in batch ZVI reactors were determined in the presence and absence of microorganisms at 3.5, 10, 17, and 25 degrees C. Under anoxic conditions, NO3- reduction rates in both ZVI-only and ZVI-cell reactors declined as temperature decreased. In ZVI-only reactor, 62% and 17%, of initial nitrate concentration were reduced 1116 days at 25 and 3.5 degrees C, respectively. The reduced nitrate was completely recovered as ammonium ions (NH4+) at both temperatures. The temperature dependent abiotic reduction rates enabled us to calculate the activation energy (Ea) using the Arrhenius relationship, which was 50 kl/mol. Nitrate in ZVI-cell reactors was completely removed within 1-2 days at 25 and 10 degrees C, and 67 of reduction was achieved at 3.5 degrees C. Only 18-25% of the reduced nitrate was recovered as NH4+ in the ZVI-cell reactors. Soluble iron concentrations (Fe2+ and 1431) in the ZVI reactors were also measured as the indicators of anaerobic corrosion. In the ZVI-cell reactors, soluble iron concentrations were 17 times higher than that in ZVI-only reactors at 25 degrees C, suggesting that the enhanced nitrate reduction in the ZVI-cell reactors may be partly due to increased redox activity (i.e., corrosion) on iron surfaces. Anaerobic corrosion of ZVI was also temperature dependent as substantially lower concentrations of corrosion product were detected at lower incubation temperatures; however, microbially induced corrosion (MIC) of ZVI was much less impacted at lower temperatures than abiotic ZVI corrosion. This study demonstrated that ZVI-supported microbial denitrification is not only more sustainable at lower temperatures, but it becomes more dominant reaction for nitrate removal in microbial-ZVI systems at low temperatures. (C) 2020 Elsevier B.V. All tights reserved.

Automated summary

The study found that ZVI-supported microbial denitrification is more sustainable at lower temperatures, and it becomes a more dominant reaction for nitrate removal in microbial-ZVI systems at low temperatures.