The Inhibition Of Phosphorus Release By Sediments-Capping

In recent years, the eutrophication of water bodies is becoming serious. The discharge of excessive concentration of nitrogen and phosphorus (especially phosphorus) into the receiving water could be the major factor of eutrophication, consequently restoration of eutrophic water bodies should effectively be managed by reducing internal contamination and concentrations of nutrient.Caohai is a severely eutrophic lake, and contains 1318 t of phosphorus in the surface 10 cm of sediments, which could release into the water column in specific condition, thus sediment is one of the most important sources of phosphorus in the water column, therefore, the success of eutrophic water bodies restoration often depends on the phosphorus release from sediment. This study simulated the condition of Caohai sediment, and investigated the release of phosphorus, then several materials were compared with regard to their capacity of preventing phosphorus and nitrogen release from sediments, and filtrated capping materials reducing internal contamination, and then integrated the technology of in-situ capping with vegetation restoration, and studied inhibition of controlling phosphorus release from sediments. The specific contents and results are as follows:1) Investigate the release of phosphorus at Caohai sediment. The results showed that the concentrations of phosphorus release from sediments were much higher under the anoxic condition than those under the aerobic condition, and the time of distribution equilibrium of phosphorus exchange across sediment-water interface were evidently longer under the anoxic condition (29 days) than those under the aerobic condition (10 days).2) Filtrate capping materials. Through adsorption experiment, filtrated capping materials to prevent phosphorus release from sediments, and optimized the proportion of capping materials. The results showed that while the initial concentration of phosphorus was 2 mg/L, at equilibrium the amounts of adsorption phosphate by admixture of red soil, gypsum and calcium oxide, admixture of gypsum and calcium oxide, ironic chloride modification of kaolin, red soil and sand respectively were 4.72 mg/g,4.01 mg/g,1.70 mg/g,1.08 mg/g and 0.369 mg/g, therefore the order of adsorption capacity of phosphorus was as follows, admixture of gypsum and calcium oxide> admixture of red soil, gypsum and calcium oxide> modified kaolin by ferric chloride> red soil> river sand, while the initial concentrations of phosphorus was 2 mg/L.3) The above five materials cap sediments of Caohai, then different capping materials were compared with regard to the effect of preventing phosphorus release, and further studied the release process of phosphorus after sediments-capping through layered test. The results of statistical analysis showed that the order of phosphorus retention in sediments was that admixture of red soil, gypsum and calcium oxide> red soil> admixture of gypsum and calcium oxide> river sand.4) Red soil and admixture of red soil, gypsum and calcium oxide cap sediment, then studied the impact of capping materials covered on the upper of sediments on the growth of submerged plants, and understood the effect of sediments-capping and planting submerged plants on preventing phosphorus release. The results showed that red soil and admixture of red soil, gypsum and calcium oxide covered on the upper of sediments had no obvious impact on the growth of submerged plants, and the integrated process of sediments-capping and submerged plants could effectively prevent phosphorus release from the sediment.