Developing a remediation strategy for phosphorus immobilization: effect of co-blending, al-residual and ca-mg amendments in a manure impacted spodosol

Abstract

A remediation strategy called “co-blending” was developed for rapid phosphorus (P) immobilization. Immobilization was achieved through the combination of an Al-based water treatment residual (Al-WTR) with Ca-Mg-based materials (Slag and magnesium oxide) for use in incubation and leaching experiments. Al-WTR was co-blended with Slag and MgO as “Al-WTR+Slag” and “Al-WTR+MgO,” respectively. Sequential extraction was used to delineate P species into operationally defined fractions: soluble or exchangeable, Al-Fe, and Ca-Mg-bound pools. Results from soils used in the incubation experiment showed that Al-amended material tended to sequester P bound (∼26%) to the Al-Fe pool. On the other hand, Ca-Mg-based materials tended to sorb (∼70%) of P greatly associated to the Ca-Mg pool. Amendments were applied at 2% or 20 g kg-1 as Al-WTR, MgO, and Slag and at 1%+1% or 10 g kg-1+10 g kg-1 as co-blended Al-WTR+MgO and Al-WTR+Slag, respectively, on mass basis. Results from leaching data suggest that treatment effects on pH are significant at (p < 0.0001) and also significant (p < 0.01) with weeks of leaching. A similar significant (p < 0.0001) trend was observed for effects of treatment on redox potential (Eh). However, treatment effects on weeks of leaching were not significant. Cumulative soluble P (mg) of leachate showed linear reduction (96%) from the control (without amendments) using a regression model. Potential co-blended material selected was Al-WTR+Slag (1%+1%) due to less P in leachates, moderate effect on pH, and fewer amounts of Al-WTR and Slag used compared with 2% Al-WTR and Slag, respectively. In addition, the RMSE of Al-WTR+Slag data fitted to a regression model was the least. Results suggested that the metal cations Al, Ca, and Mg tended to bind different forms of total P at any given pH. Through co-blending, less soluble P may be lost to the environment than using sorption materials independentl