Effect of aged nanoscale zero-valent iron amendment and capping on phosphorus mobilization in sediment

Abstract

Nanoscale zero-valent iron (nZVI) has been extensively investigated as remediation materials. Understanding the influence of nZVI on sedimentary phosphorus mobilization is vital to its application in sediment remediation. In this study, the effects of aged nZVI (A-nZVI) amendment and capping on the mobilization of phosphorus from sediment to overlying water (O-water) were studied. The results showed that under high A-nZVI dosage condition, A-nZVI addition effectively reduced the efflux of dissolved reactive phosphorus (DRP) from sediment to O-water under oxygen deficit condition, and induced the transformation of reductant-soluble phosphorus (BD-P) to metal oxide-bound inorganic phosphorus (NaOH-IP) and residual phosphorus (Res-P) in sediment, making the inorganic phosphorus more stable than the control. Under low A-nZVI dosage condition, A-nZVI amendment still had the ability to diminish the risk of DRP released from sediment into O-water. Furthermore, A-nZVI capping effectively hindered DRP release from sediment into O-water, and its controlling efficiency was higher than A-nZVI amendment under oxygen deficit condition. Under anoxic condition, the A-nZVI amendment and capping both can decrease the concentrations of DGT (diffusive gradient in thin-films)-measured labile phosphorus (PDGT) in the profile of O-water and uppermost sediment, but they both had ineffective reduction efficiencies of PDGT in the lower sediment profile. The A-nZVI amendment and capping increased the microbial diversity and richness of surface sediment and stimulated the growth of some Fe-reducing bacteria in the surface sediment. The uptake of DRP by the A-nZVI capping layer located on the sediment–water interface was an important reason for intercepting DRP diffusion from sediment into O-water by the A-nZVI capping. Overall, A-nZVI can be used as an in-situ active capping material for controlling DRP release from sediment to O-water.