硝酸钙缓释颗粒原位修复黑臭底泥的作用机制及其应用

为解决水体中沉积底泥的内源污染释放问题，亟需高效底泥修复技术。硝酸盐为底泥微生物的电子受体，可通过反硝化作用氧化底泥的黑臭物质，是极具潜力的底泥修复剂。为探明硝酸盐在实际工程中的修复效果和潜在问题，结合实验室模拟和实际修复工程，分析了投加硝酸钙颗粒对黑臭底泥原位修复的环境过程。结果表明，投加硝酸钙缓释颗粒产品能显著提高底泥氧化还原势能（以Fe(II)/Fe(III)表征），促进黑臭物质转化，实际硫化物氧化率达85.2%，使得底泥由黑转黄，最终实现修复目标。同时，硝酸钙修复底泥的过程不受上覆水水质影响，且因修复过程消耗了大量底泥耗氧物质（硫化物和易降解有机质），使水体整体复氧能力提高。另一方面，钙离子的加入使磷素以较为稳定的钙磷形态转化，能改变水相总磷的归趋（TP_SedCaN < TP_CK，p < 0.01）。然而，由于反硝化产气增加了底泥孔隙，增加了泥水界面表面积和污染物扩散通量，故在修复初期存在底泥污染物和硝酸盐向其浓度较低的水相扩散，产生了一定风险，而实际上这也有利于泥相污染物的加速释放。因此，建议在可控工程段，联合覆盖法阻断污染物扩散或联合曝气加速水相污染物氧化，以确保在控制风险的前提下达到最优的底泥修复效果。

Mechanism and application of in situ remediation of black and smelly sediment by calcium nitrate sustained-release particles

In order to solve the problem of endogenous pollution release of sediment in water body, the efficient sediment remediation technology is urgently needed. Nitrate is the electron acceptor of sediment microorganisms, which can oxidize the black-odor substance through denitrification process, therefore it is a potential agent for sediment remediation. In order to explore the remediation effects and potential problems of nitrate in practical engineering, this study conducted laboratory and field experiments to explored the environmental processes in in-situ sediment remediating by adding calcium nitrate pellets (SedCaN pellets). The results showed that the addition of calcium nitrate could significantly increase the redox potential in sediment (characterized by Fe(II)/Fe(III)) and promote the transformation of black-odor substances, meanwhile the color of sediment turned from black to yellow, which indicated that the remediation target was achieved. The actual sulfide oxidation rate was up to 85.2%. At the same time, the remediation was not affected by the quality of overlying water. A large number of oxygen-consuming substances (sulfide and easily degradable organic matter) were consumed in the process of repairing sediment, which improved the overall reoxygenation capacity of water body. The addition of calcium ions could stabilize the phosphorus as the form of Ca-P, which decreased the release of phosphorus from sediment to water phase (TPCaN < TPCK, p < 0.01). However, the gaseous nitrogen produced by denitrification increased the sediment porosity, which increased the diffusion flux of pollutants from sediment-water interface surface. At the initial stage of remediation, there was a certain risk due to the diffusion of sediment pollutants and nitrates, but in fact, it was also conducive to the accelerate the pollution release out of the sediment. Therefore, it was suggested to block the diffusion of pollutants by combining covering method or to accelerate the oxidation of water phase pollutants by combining aeration approaches in the controllable engineering section, so as to achieve the best sediment remediation effect on the premise of controlling the risk.