Positive remediation on sedimentary P by combination of capping with calcium hydroxide and oxidation with perhydrol.

The capping is called passive remediation because the sedimentary P was released and then immobilized by the capping materials. However, the release depends on the environmental conditions. Therefore, a hypothesis was proposed that the oxidant was used to accelerate sedimentary P release and the capping material was used to capture those released P. It is positive remediation to reduce sedimentary P amount. The results show that soluble reactive phosphorus (SRP) concentration in the overlying water and pore water increased and then decreased gradually under the combination of sodium percarbonate (SPC) and Ca(OH), similar as that under the capping with single Ca(OH). The sedimentary P amount was reduced considerably and P concentration in the capping layer increased obviously after 60 days, compared with the capping with single Ca(OH). All these indicated that oxidation improved the sedimentary P release and the released P was captured and immobilized by the capping material of Ca(OH). However, the acceleration of sedimentary P release due to the oxidation is obviously different from the traditional mechanism that the oxic condition in the sediment is favor of the immobilization on sedimentary P. It is attributed to the oxidizability of ·OH from SPC. The reduction of mobile-P and the increase of Ca-P under the combined use are observed. This is similar as traditional mechanism of oxic condition. It is sure that positive remediation reduced sedimentary P amount, resulting in the decrease of P release risk in a long time.