Enhanced in-situ sediment remediation by calcium peroxide coupled with zero-valent iron: Simultaneous nitrogen...

As the potential causes of eutrophication, nitrogen (N) and phosphorus (P) in sediments have received wide attention. However, few of the in-situ sediment remediation methods can achieve simultaneous N removal and P stabilization in sediments. In this study, different impacts on N, P and organic matter (OM) properties of sediments and overlying water with different proportions of calcium peroxide (CaO₂) coupling with zero-valent iron (ZVI) were explored through incubation experiments. Compared with CaO₂ or ZVI alone, the total nitrogen (TN) removal ratios in the whole system at 0.6 g/kg CaO₂ coupled with 40 g/kg ZVI increased by 167.91% and 152.04%, respectively. Due to the enhancement of oxidation, the removal efficiency of OM from sediments increased by 118.51%. Meanwhile, the genera related to denitrification (e.g., Anaerobacillus, Haloplasma, and Clostridium_sensu_stricto_8) were also enriched in this coupling group, which was due to the enhanced decomposition of OM and the electron donation of ZVI. In addition, CaO₂ coupled with ZVI stabilized P through chemical precipitation, which converted organic phosphorus (Org-P) into more stable calcium bounded P (Ca-P) in sediments. Hence the coupling effectively increased total P (TP) content in sediments and reduced P concentration in water.