Phosphate inactivation and remediation with different reagents in in-situ treatment on contaminated sediment of lakes

In this paper, we studied the solidification/stabilization technology by using different immobilization reagents to reduce the potential of releasing of phosphorous from the lake sediment to the surrounding environment. Phosphorous is often bound to iron, aluminum and calcium compounds or to clay mineral surfaces in different inorganic forms. The organic P is found in a more labile form or in a refractory form Which is difficult to release during mineralization and thus, permanently buried in the sediment. Aluminum sulphate (Alum) is an effective reagent used to bind and precipitate P in hardwater lakes. It was found that the frequency and severity of phytoplankton blooms decreased with alum-induced reductions in hypolimnetic P where the effectiveness of treatment can last up to 14 years. Iron salts are also effective in hindering P releases. Fe (III) was found to be more effective in binding and stabilizing P in the sediment than Fe (II). However, vivianite (ferrous phosphate) is more prevalent in many lake bottoms due to the redox conditions. This leads to a simple technique where aeration can be applied simultaneously during the immobilization process with iron addition to increase hypolimnetic DO concentrations and decrease sediment P release. Lime is also one of best reagents in the immobilization of P for economical purpose in hard water lakes. Adding Lime into the lake can cause over saturation of Ca2+ in the water column and make P precipitate into the sediment as hydroxyapatite. The hydroxyapatite in sediments will continue to adsorb P and prevent the release of phosphate into the upper layer water. Internal release may occur by the potentially mobilization of particularly loosely sorbed organic and inorganic fractions, as well as the iron-bound and redox-sensitive sorption of P.