Phosphorus sorption and supply from eutrophic lake sediment amended with thermally-treated calcium-rich attapulgite and a safety evaluation

Modified clays are being increasingly used as P-inactivation agents for lake eutrophic control. However, the interaction of P with these material amended sediments still remain unclear. This study investigates the P sorption and supply from the thermally treated calcium-rich attapulgite amended eutrophic lake sediments as well as the ecological safety of material addition. The results indicated that P sorption on material amended sediment can be well fitted by a modified Langmuir model. Material addition can greatly enhance the P sorption capacity of lake sediment and lower the zero equilibrium P concentration (EPC0), which can turn lake sediment from a source to a pool. P sorption on raw and material amended sediment generally decreases with an increase of the water pH value. But material amended sediment still can adsorb a large amount of P even in very alkaline conditions resulting from algal blooms. Furthermore, P sorption on amended lake sediment was less influenced by NO3− and HCO3− than by SO42− to a moderate degree and by SiO3− 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. This was due to sediment mobile P had been transformed into stable Ca-P. A toxicity study indicated that material additions can increase pH value in lake sediment and can cause a toxic effect on benthic organisms when a large addition of material is involved, but this would be greatly attenuated in the field. The results of this study indicated that thermally treated calcium-rich attapulgite has the potential to be used as a P-inactivation agent for lake eutrophication control.