Bisulfite boosts the reduction activity of zero-valent iron towards p-nitrophenol under anoxic conditions

Zero-valent iron (ZVI) is widely used in the field of wastewater treatment and groundwater remediation, but it suffers from low reactivity due to the surface passivation layer. In the present work, bisulfite was used as an additive to enhance the reduction activity of ZVI under anoxic conditions. It was found that the reaction kinetic constant of p-nitrophenol reduction in ZVI/bisulfite process was approximately 132 times higher than that by ZVI alone. Bisulfite could dissolve and reduce some iron oxide on the ZVI surface, resulting in the exposure of more active sites like Fe0 and Fe(II) for p-nitrophenol reduction through direct electron transfer. Common substances in water had no effects on p-nitrophenol degradation by ZVI/bisulfite process, but phosphate suppressed ZVI corrosion seriously. This work provides a simple, cost-effective and environmental-friendly method to improve the reducing activity of ZVI under anoxic conditions.