CaO2 coupled with ZVI to achieve nitrogen removal and phosphorus fixation simultaneously

In this study, different effects on N, P and OM properties of sediments and overlying water with different proportion of CaO2 and ZVI coupling were explored through incubation experiments. Compared with CaO2 alone, the removal efficiency of OM in sediment and total N in the system at 0.6 g/kg CaO2 coupled with 40 g/kg ZVI was increased by 7.58% and 2.15%, respectively. Meanwhile, the genera related to denitrification (e.g., Bacillus, Haloplasma and Clostridium_sensu_stricto_8) were also enriched in this coupling ratio. The action of these microorganisms promoted by ZVI helped to reduce TN (17.78%), NO3--N (21.11%) and COD (23.50%) in overlying water. This meant that the addition of ZVI avoided the increase of pollutant in overlying water caused by the oxidation of CaO2. In addition, CaO2 coupled with ZVI fixed phosphorus through chemical precipitation, effectively increasing TP content in sediments and reducing P concentration in water. Considering comprehensive effect, 0.6 g/kg CaO2 and 40 g/kg ZVI were recommended for sediment remediation.