Journal of Water Resource and Protection, 2011, 3, 235-244 doi:10.4236/jwarp.2011.34030 Published Online April 2011 (http://www.scirp.org/journal/jwarp) Copyright © 2011 SciRes. JWARP Predicting Phosphorus Sorption onto Steel Slag Using a Flow-through Approach with Application to a Pilot Scale System Chad J. Penn, Joshua M. McGrath Oklahoma State University, Oklahoma, USA E-mail: chad.penn@okstate.edu; mcgrathj@umd.edu Received February 11, 2011; revised March 11, 2011; accepted March 31, 2011 Abstract Reducing phosphorus (P) loads from soils to surface waters is necessary for solving the problem of eutrophication. Many industrial by-products have been shown to sorb appreciable amounts of dissolved P from solution and it has been proposed to use P sorption materials (PSMs) such as steel slag in landscape scale “filters” for trapping dissolved P in runoff. The objective of this study was to model the effect of retention time (RT) and P concentration on P sorption by steel slag and a surface modified slag in a flow- through system. Sorption of P onto steel slag and rejuvenated-modified steel slag was measured using a traditional batch isotherm and a flow-through setting at several RTs and P concentrations. Flow-through data were used to produce a model that estimated P sorption based on RT and P concentration. The model was tested on a pilot-scale pond filter consisting of the same slag materials. For both the materials, flow-through tests indicated an increase in RT increased P removal efficiency but decreased the total amount of P removed at saturation. The Langmuir model developed from batch isotherms overestimated and underestimated P sorption in normal and rejuvenated slag respectively, relative to flow-through. Normal and rejuvenated slag removed 38 and 36% of P in the pilot-scale pond filter after 2 weeks of pumping. The Langmuir equation poorly predicted P sorption in the pond filter while the flow-through model produced reasonable estimates. Results suggest that flow-through methodology is necessary for estimating P sorption in the context of landscape P filters. Keywords: Phosphorus, By-Products, Phosphorus Removal Structure 1. Introduction Input of phosphorus (P) to surface waters can contribute to eutrophication of receiving water bodies. Potential sources of P to surface waters include waste-water treatment plants, horticultural operations, and runoff from agricultural and urban/suburban land (including golf courses). In regard to runoff, dissolved P is the most difficult form to control since particulate losses are typically controlled by maintaining sufficient soil cover and reducing erosion [1]. Dissolved P loads in runoff are greatest from soils that are high in soil test P and soils with recent surface applications (not incorporated) of P [2-3]. Previous research has shown that application of P sorbing materials (PSMs) directly to high P soils or to animal manures prior to land application can reduce losses of dissolved in runoff during rainfall events [4-5]. However, such reductions in P runoff concentrations may be temporary since P is not truly removed from the system [6-7]. As an alternative, it has been suggested that PSMs could be used in a “P removal structure” or a constructed, isolated structure for treating P rich runoff prior to reaching surface bodies of water [8]. Penn et al. [7] constructed a P removal structure in a surface water drainage ditch located on the Eastern Shore of Maryland, U.S. This structure contained an iron rich by- product that possessed a high P sorption capacity. In a single rainfall event that lasted nearly 18 h, the structure removed 99% of the dissolved P that entered it. One disadvantage of this material was that it had low hydraulic conductivity; therefore the amount of water that could be treated was limited. A by-product from the steel industry that has potential for use in P removal structures is steel slag.