First attempt for in situ capping with lanthanum modified bentonite (LMB) on the immobilization and transformation of organic phosphorus at the sediment-water interface

Abstract

LMB is a widely utilized material for the management of sediment-derived phosphorus (P) in eutrophic lakes. However, the properties of organic P at the sediment-water interface and the effect of LMB on organic P fractions in sediments are still unclear. The batch studies reported here indicate that LMB has good adsorption properties toward organic P (Glucose-6-phosphate), and the tentative adsorption mechanism relies on chemisorption. Laboratory microcosmic experiments were conducted to study the immobilization effect of LMB on the organic P in water and sediments. The results indicated that the concentration of total P, labile P and organic P in overlying water and pore water could be effectively reduced by LMB capping of sediments. After treatment, the optimal immobilization effects appeared on the 7th day and until the 60th day. However, the fractions of organic P change during the capping time. Active organic P eluted with NaHCO3 transforms into moderately labile or non-labile P through the physical and chemical processes, as well as microbial action. Microbial community analysis showed that the addition of LMB had inhibitory effect on the phosphorus-solubilizing bacteria, which also affected the transformation between various forms of organic P. This study provided new insights of LMB in situ capping of organic P and the mechanisms of the migration and cycling of internal organic P, which is beneficial for the management of eutrophic lakes.