Reduction of sediment internal P-loading from eutrophic lakes using thermally modified calcium-rich attapulgite-based thin-layer cap

We conducted a laboratory evaluation of a low-cost P-capping agent-700°C-heated natural calcium-rich attapulgite (NCAP700)-in terms of its ability to reduce internal P-loading in lake sediments. Batch studies indicated that NCAP700 could effectively reduce sediment mobile P (Pmobile) in various types of lake sediment, and the dosage equation required to immobilize Pmobile was developed accordingly. The equation was then applied to a laboratory incubation study on intact sediment cores. The results indicated that the NCAP700-based thin-layer cap can enhance the redox potential (Eh), pH and dissolved oxygen (DO) in surface sediment. However, this enhancing effect was decreased with increasing time. P fluxes and the concentration of P in overlying water and pore water from sediment could be effectively inhibited under anaerobic conditions. P fractionation analysis indicated that 34.5% of Pmobile was bound in the upper 2 cm sediment layer during a 40-day remediation period, but this only exerted a minor influence on the Pmobile in the 2-4 cm sediment layer. P immobilization by NCAP700 was mainly achieved through transformation of Pmobile to stable Ca-P. These results indicate that NCAP700 can be used for lake eutrophication control by means of thin-layer capping.