Sedimentary phosphorus immobilization with the addition of amended calcium peroxide material

The immobilization of sedimentary phosphorus (P) by capping sediments with amended calcium peroxide material (ACPM) and CaO 2 was investigated, the sediments and overlying water from a black-odor river. Under the capping with ACPM and CaO 2 , the pH and dissolved oxygen (DO) in the overlying water were higher than in the control. This contributed to the more loss of external P under the ACPM (the phosphate sorption was fitted well by the Langmuir equation, the maximum P sorption capacity up to 29.28 mg P g −1 ). Additionally, ACPM improves the decrease of the reduction materials (e.g., NH 4 + -N, Fe 2+ ) in the pore water compared to that associated with CaO 2 , resulting in a less obvious dissolved inorganic P (DIP) in the pore water, but the accumulation of DIP in the pore water with CaO 2 suggested an explosive release once the micro-environment conditions encounters adverse conditions. The sharp reduction of Fe/Al-P and Res-P contributes to the increase of DIP in the pore water, with a release of up to 390.60 mg P kg −1 DW (dry weight), whereas the value is only 62.55 mg P kg −1 DW when capped with ACPM. Correspondingly, the percentage of the bioavailable P to Tot-P decreases rapidly from 17.27% (control, 0–2 cm) to 7.21% (ACPM, 0–2 cm) and 10.57% (CaO 2 , 0–2 cm), indicating the obvious P immobilization. The implication is that the application of CaO 2 is not suitable for direct use, while the combination with other materials (e.g., WPS) is a better choice.