Effects of anions on bio-chemical degradation of nitrate in groundwater

Combining denitrifying bacteria with sodium oleate-nanoscale zero-valent iron (SONZVI) has been proven to be effective for aqueous phase nitrate remediation. However, the effects of coexistent ions on nitrate reduction in a groundwater environment, which is at low temperature and under anoxic, light-excluded conditions, remain elusive. In this study, nitrate reduction by microbial-NZVI was evaluated via batch tests in the presence of common anions (SO4 (2-), PO4 (3-) and Cl-) in two different environments: groundwater environment and room environment. The results showed that nitrate was largely reduced within 10 days in an SONZVI + cell reactor in the groundwater environment, while only 79 % of the nitrate was reduced over 10 days in the room environment. In the groundwater environment, the removal efficiency could be accelerated by chloride or phosphate, but inhibited by sulfate. There were mainly two reaction stages, which were chemical reduction degradation and denitrifying degradation. Pseudo-first-order kinetics was used to describe the two reaction stages. In the first stage, the existence of the anions inhibited nitrate degradation. The synergistic effects of these anions on nitrate removal followed the order of Cl-, SO4 (2-), and PO4 (3-). The results implied that using microbial-NZVI is a potential approach for in situ remediation of groundwater with nitrate contamination.