Use of Reactive Materials to Bind Phosphorus.

Phosphorus (P) losses from agricultural soils have caused surface water quality impairment in The Netherlands. The generic Dutch fertilizer and manure policy, which strives towards equilibrium fertilization in 2015, will not be sufficient to reach the surface water quality standards of the European Water Framework Directive in 2015, due to the large amounts of P accumulated in Dutch soils. Accordingly, additional measures have to be considered to further reduce P enrichment of surface waters. At present, innovative remediation practices are developed using reactive barriers placed along ditches or retention filters at the end of tile drains to remove P from soil waters. Other practices include the use of amendments blended with land-applied P sources (e.g., manure) to reduce P solubility or P-rich topsoil to decrease P release by the soil solid phase. For these practices, many different reactive materials have been proposed, which can be categorized as natural materials, industrial byproducts, and man-made products. Before field application, the phosphorus binding capacity (PBC) of these materials, which is strongly related to their chemical composition (i.e., Fe, Al, and Ca), should be known as a criterion for material selection and in order to be able to estimate the amount of material needed to control P solubility at the desired level. In addition to the PBC, the reactive materials should have a good hydraulic conductivity to minimize the risk of system clogging. Also, their concentration of inorganic contaminants has to be evaluated, because especially industrial byproducts may contain elevated levels of heavy metals. We will present results of a laboratory study during which physical and chemical properties of two reactive materials (iron sludge and iron-coated sand) and their PBC's (batch and column experiments) were measured. These materials are produced as byproducts during the purification of deep groundwater for drinking water.