The Effects Of Thermally-Treated Calcium-rich Attapulgite On The Inactivation Of P In Lake Sediment And The Influencing Factors

Plenty of studies discovered that lake eutrophication still can presist for several dacades even though the external phosphorus was effectively controlled. This is due to the fact that internal-P can continuously release into overlying water from lake sediment. Hence, lake sediment remediation was deemed as the main method to control lake eutrophication. Moreover, the main method is to add or cap some reactive materials into the surface of lake sediment. In this study, the previously selected low-cost thermally-treated calcium-rich attapulgite was used as P-inactivation agent, and it was added into lake sediment with different doses. P sorption capacity on the material amended sediment and its supply ability as well as the ecological safety of the material addition were studied. A self-developed Y-shape apparatus was adopted to study the effects of resuspension on the stability of surface material amended sediment and phosphorus control efficiency.Batch study indicated that the P sorption capacity and sorption rate can be greatly enhanced with the addition of the thermally-treated calcium-rich attapulgite. Specifically, the P sorption capacity can be increased 1.5 to 2.0 times and the P sorption rate can be increased 1.7 to 3.7 times with addition of 5% to 20% of the thermally-treated calcium-rich attapulgite. Furthermore, P sorption on the amended lake sediment was less influenced by pH, NO3- and HCO3- than by SO4- to a moderate degree and by SiO32- to a much larger degree. The results of diffusive gradients in thin films (DGT) measurement indicated the ability of P supply from lake sediment was largely inhibited by material addition. P fraction indicated that material addition can transform mobile P to calcium bound phosphorus and increase the percentage of inert P in lake sediment, therefore lower the risk of P release from lake sediment into overlying water. The chronic toxicity test showed that material addition can increase the pH value of lake sediment. However, it was still safe when the percentage of material addition was in the range of the reasonable scope.The sediment resuspension experiment showed that the addition of phoslock and thermally-treated calcium-rich attapulgite all can enhance the anti-wave capacity of surface sediment and can greatly reduce the concentration of SRP in overlying water. Results indicated that the erosion depth and the concentration of SRP were positively correlated with the magnitude of wind. Mini-Peeper analysis indicated that material addition can reduce the SRP concentration in porewater. The indication of P supply ability of R (the ratio of DGT-P to P in porewater) was 29% to 79% of the control and which indicated that material addition can lower the P supply ability from sediment to porewater. The two materials all can transform sediment mobile P and Al-P to Ca-P and increase the percentage of inert phosphorus in lake sediment under the disturbance of wind.All of the results indicated that the thermally-treated calcium-rich has the characteristic of excellent P control efficiency, low-cost and easily handling and has the potential to be used as P-inactivation agent and can be applied widely in eutrophic lake management.