Aluminum water treatment residuals as permeable reactive barrier sorbents to reduce phosphorus losses

Two aluminum water treatment residuals (Al-WTRs) from water treatment plants in Manatee County, FL and Punta Gorda, FL were evaluated as potential permeable reactive barrier (PRB) media to reduce groundwater phosphorus (P) losses. Short-term (<24 h) P sorption kinetics and long-term P sorption capacity were determined using batch equilibration studies. Phosphorus desorption was characterized following P loadings of 10, 20, 30, 40 and >70 g kg−1. Sorption and desorption studies were conducted on the <2.0 mm material and three size fractions within the <2.0 mm material. The effect of dissolved organic carbon (DOC) on P retention was determined by reacting Al-WTRs with P-spiked groundwater samples of varying initial DOC concentrations. Phosphorus sorption kinetics were rapid for all size fractions of both Al-WTRs (>98% P sorption effectiveness at shaking times ⩾2 h). The effect of DOC was minimal at <150 mg DOC L−1, but modest reductions (<22%) in P sorption effectiveness occurred at 587 mg DOC L−1. The P sorption capacities of the Manatee and Punta Gorda Al-WTRs (<2.0 mm) are ∼44 g kg−1 and >75 g kg−1, respectively, and the lifespan of an Al-WTR PRB is likely many decades. Desorption was minimal (<2% of the P sorbed) for cumulative P loadings <40 g kg-l, but increased (<9% of the P sorbed) at cumulative P loads >70 g kg−1. The <2.0 mm Manatee and Punta Gorda Al-WTRs are regarded as ideal PRB media for P remediation.

Research highlights
► Two aluminum water treatment residuals assessed as permeable reactive barriers to reduce P loss.
► Determined P sorption kinetics, long-term P sorption capacity, and the stability of sorbed-P.
► Observed rapid P sorption kinetics and high sorption capacity for both residuals.
► Residuals can likely irreversibly bind P for decades at expected field conditions.