Parametric evaluation of batch equilibria for storm-water phosphorus adsorption on aluminum oxide media

Elevated and variable aqueous and granulometric concentrations of phosphate species (P) are commonly observed in urban rainfall runoff. Though physical operations such as sedimentation can potentially separate particulate P, aqueous P requires a unit process approach such as adsorption. Therefore, adsorption of aqueous P on aluminum oxide coated media (AOCM), a porous soil-type substrate coated with aluminum oxide, is investigated. Parameters studied include media size, phosphate concentration as total dissolved phosphorus (0-25 mg/L), pH (5-9), ionic strength (0.000 5-0.2 M as KCl), and the presence of coexisting ions such as [Ca.sup.2+], S[O.sup.2-.sub.4]]-, and N[O.sup.1-.sub.3]. Results indicate that adsorption (mg/g) increased with decreasing AOCM size and decreasing pH. [Ca.sup.2+] enhanced P adsorption by forming ternary complexes; S[O.sup.2-.sub.4] inhibited P adsorption by competing for available adsorption sites. Ionic strength and N[O.sup.1-.sub.3] had minor to negligible effects on adsorption equilibrium, respectively. Chemical adsorption between P and AOCM resulted in low desorption potential. Adsorption data were modeled with Freundlich isotherms. After batch adsorption by AOCM, results indicate that P could be significantly reduced, meeting most surface water discharge requirements. DOI: 10.1061/(ASCE)EE.1943-7870.0000041 CE Database subject headings: Stormwater management; Best Management Practice; Adsorption; Phosphate; Aluminum; Equilibrium; Clays.